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+Project Gutenberg (https://www.gutenberg.org) public repository for
+eBook #67314 (https://www.gutenberg.org/ebooks/67314)
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-The Project Gutenberg eBook of Water Reptiles of the Past and
-Present, by Samuel Wendell Williston
-
-This eBook is for the use of anyone anywhere in the United States and
-most other parts of the world at no cost and with almost no restrictions
-whatsoever. You may copy it, give it away or re-use it under the terms
-of the Project Gutenberg License included with this eBook or online at
-www.gutenberg.org. If you are not located in the United States, you
-will have to check the laws of the country where you are located before
-using this eBook.
-
-Title: Water Reptiles of the Past and Present
-
-Author: Samuel Wendell Williston
-
-Release Date: February 3, 2022 [eBook #67314]
-
-Language: English
-
-Produced by: Peter Becker and the Online Distributed Proofreading Team
-             at https://www.pgdp.net (This file was produced from images
-             generously made available by The Internet Archive)
-
-*** START OF THE PROJECT GUTENBERG EBOOK WATER REPTILES OF THE PAST
-AND PRESENT ***
-
-
-
-
-
-Transcriber’s Notes:
-
-  Underscores “_” before and after a word or phrase indicate _italics_
-    in the original text.
-  Equal signs “=” before and after a word or phrase indicate =bold=
-    in the original text.
-  Small capitals have been converted to SOLID capitals.
-  Illustrations have been moved so they do not break up paragraphs.
-  Typographical and punctuation errors have been silently corrected.
-
-
-                    THE UNIVERSITY OF CHICAGO PRESS
-                           CHICAGO, ILLINOIS
-
-                               _Agents_
-                    THE CAMBRIDGE UNIVERSITY PRESS
-                         LONDON AND EDINBURGH
-                     THE MARUZEN-KABUSHIKI-KAISHA
-                          TOKYO, OSAKA, KYOTO
-                          KARL W. HIERSEMANN
-                                LEIPZIG
-                      THE BAKER & TAYLOR COMPANY
-                               NEW YORK
-
-
-
-
-                WATER REPTILES OF THE PAST AND PRESENT
-
-                      BY SAMUEL WENDELL WILLISTON
-                   _Professor of Paleontology in the
-                        University of Chicago_
-
-                            [Illustration]
-
-                    THE UNIVERSITY OF CHICAGO PRESS
-                           CHICAGO, ILLINOIS
-
-                           COPYRIGHT 1914 BY
-                       THE UNIVERSITY OF CHICAGO
-
-                          All Rights Reserved
-                        Published October 1914
-
-                        Composed and Printed By
-                    The University of Chicago Press
-                       Chicago, Illinois, U.S.A.
-
-
-
-
-PREFACE
-
-
-It was just forty years ago that the writer of these lines, then an
-assistant of his beloved teacher, the late Professor B. F. Mudge,
-dug from the chalk rocks of the Great Plains his first specimens of
-water reptiles, mosasaurs and plesiosaurs. To the youthful collector,
-whose first glimpse of ancient vertebrate life had been the result of
-accident, these specimens opened up a new world and diverted the course
-of his life. They were rudely collected, after the way of those times,
-for modern methods were impracticable with the rifle in one hand and
-the pick in the other. Nor was much known in those days of these or
-other ancient creatures, for the science of vertebrate paleontology was
-yet very young. There were few students of fossil vertebrates—Leidy,
-Cope, and Marsh were the only ones in the United States—and but few
-collectors, of whom the writer alone survives.
-
-Those broken and incomplete specimens, now preserved in the museum of
-Yale University, will best explain why this little book was written.
-The author offers it, so far as lies within him, as an authoritative
-and accurate account of some of the creatures of earlier ages which
-sought new opportunities by going down from the land into the water.
-So far as possible he has endeavored to make the text understandable,
-and, he hopes, of interest also, to the non-scientific reader. He will
-not apologize for such scientific terms as remain, since only by their
-use can precision be attained: there are no common English equivalents
-for them. The reader will find their explanations in the chapter on the
-skeleton of reptiles, and especially in the illustrations.
-
-The author has had the opportunity during recent years of critically
-studying nearly all the reptiles described in the following pages,
-but, if that were the only source of his information, the accounts of
-many would have been meager. He has endeavored, briefly at least, to
-mention the names of all those to whom we are chiefly indebted for our
-knowledge, but in such a work as this it is manifestly impracticable to
-give due credit to every one.
-
-To the friends who have been of assistance in various ways he tenders
-his sincere thanks: to Professor E. Fraas for photographs and the kind
-permission to reproduce some of his excellent illustrations; to Dr.
-Dreverman, of the Senckenberg Museum, for several excellent photographs
-for reproduction or restoration; to Dr. Hauff, of Holzmaden, for an
-excellent photograph of an ichthyosaur; to Dr. H. F. Osborn, of the
-American Museum, for permission to reproduce the spirited restoration
-of ichthyosaurs drawn by Mr. Knight; to Professors Schuchert and Lull,
-and Dr. Wieland, of Yale University; to Dr. Hay and Mr. Gilmore, of the
-National Museum, to Mr. Barnum Brown and Dr. McGregor, of the American
-Museum, and to Professor Merriam, of the University of California, for
-photographs and other favors.
-
-                                        SAMUEL W. WILLISTON
-    UNIVERSITY OF CHICAGO
-           July, 1914
-
-
-
-
-CONTENTS
-
-
-    CHAPTER                                                   PAGE
-         I. INTRODUCTION                                        1
-
-        II. CLASSIFICATION OF REPTILES                         13
-
-       III. THE SKELETON OF REPTILES                           19
-
-        IV. THE AGE OF REPTILES                                44
-
-         V. ADAPTATION OF LAND REPTILES TO LIFE IN THE WATER   59
-
-        VI. ORDER SAUROPTERYGIA                                73
-                    Plesiosauria.
-                    Nothosauria.
-
-       VII. ORDER ANOMODONTIA                                 102
-                    Lystrosaurus.
-
-      VIII. ORDER ICHTHYOSAURIA
-                             107
-        IX. ORDER PROGANOSAURIA                               126
-                    Mesosaurus.
-
-         X. ORDER PROTOROSAURIA                               132
-                    Protorosaurus.
-                    Pleurosaurus.
-
-        XI. ORDER SQUAMATA                                    138
-                    Lizards.
-                    Mosasaurs.
-                    Snakes.
-
-       XII. ORDER THALATTOSAURIA
-                            171
-      XIII. ORDER RHYNCHOCEPHALIA                             176
-                    Choristodera.
-
-       XIV. ORDER PARASUCHIA                                  184
-                    Phytosauria.
-
-        XV. ORDER CROCODILIA                                  194
-                    Eusuchia.
-                    Mesosuchia.
-                    Thalattosuchia.
-
-       XVI. ORDER CHELONIA                                    216
-                    Side-necked Turtles.
-                    Snapping Turtles.
-                    Fresh-water or Marsh Tortoises.
-                    Land Tortoises.
-                    Sea-Turtles.
-                    Ancient Sea-Turtles.
-                    Leather-back Marine Turtles.
-                    River Turtles.
-
-
-
-
-CHAPTER I
-
-INTRODUCTION
-
-
-In most persons the word reptile incites only feelings of disgust and
-abhorrence; to many it means a serpent, a cold, gliding, treacherous,
-and venomous creature shunning sunlight and always ready to poison. Our
-repugnance to serpents is so much a part of our instincts, or at least
-of our early education, that we are prone to impute to all crawling
-creatures those evil propensities which in reality only a very few
-possess. Were there no venomous serpents—and there are but two other
-venomous reptiles known—we should doubtless see much to admire in those
-animals now so commonly despised; because a few dozen kinds, like the
-rattlesnakes, copperheads, and cobras, protect themselves in ways not
-unlike those used by man to protect himself, we unjustly abhor the
-thousands of other kinds, most of which are not only innocent of all
-offense toward man, but are often useful to him.
-
-There are now living upon the earth more than four thousand kinds or
-species of cold-blooded animals which we call reptiles, all of which
-are easily distinguishable into four principal groups: the serpents
-and lizards, the crocodiles, the turtles, and the tuatera. Their
-habits and forms are very diverse, but they all possess in common
-certain structural characters which sharply distinguish them from
-all other living creatures. A reptile may be tersely defined as a
-cold-blooded, backboned animal which breathes air throughout life.
-And yet, it is not quite certain that this definition is strictly
-correct when applied to all the reptiles of the past, since it has
-been believed that certain extinct ones may have been warm-blooded.
-By this definition, short as it is, we at once exclude a large number
-of cold-blooded, air-breathing, backboned animals which were formerly
-included by scientific men among the true reptiles, and even yet are
-popularly often so included—the amphibians or batrachians. These
-animals, now almost wholly represented by the despised toads, frogs,
-and salamanders, were, very long ago, among the rulers of the land,
-of great size and extraordinary forms. But they have dwindled away,
-both in size and in numbers, till only a comparatively few of their
-descendants are left, none of them more than two or three feet in
-length, and all of them sluggish in disposition and of inoffensive
-habits. While we may speak of the amphibians as air-breathing, they
-are, with few exceptions, water-breathers during the earlier part of
-their existence. Some may pass their whole lives as water-breathers,
-while a few begin to breathe air as soon as hatched from the egg; but
-these are the marked exceptions.
-
-In many respects the internal structure of the amphibians of the
-present time is widely different from that of reptiles, though there
-can be no doubt that the early amphibian ancestors of the modern
-toads, frogs, and salamanders were also the ancestors of all living
-and extinct reptiles, and it is a fact that the living amphibians
-differ more from some of the ancient ones than those early amphibians
-did from their contemporary reptiles. Discoveries in recent years have
-bridged over nearly all the essential differences between the two
-classes so completely that many forms cannot be classified unless one
-has their nearly complete skeletons. We know that some of the oldest
-amphibians, belonging to the great division called Stegocephalia,
-were really water-breathers during a part of their lives, because
-distinct impressions of their branchiae, or water-breathing organs,
-have been discovered in the rocks with their skeletal remains, but we
-are not at all sure that some of the more highly developed kinds were
-not air-breathers from the time they left the egg; indeed, we rather
-suspect that such was the case.
-
-We are also now quite certain that, from some of the early extinct
-reptiles—the immediate forbears probably of the great dinosaurs—the
-class of birds arose, since the structural relationships between
-birds and reptiles are almost as close as those between reptiles and
-amphibians.
-
-Huxley believed that the great class of mammals arose directly from
-the amphibians, and there are some zoölogists even yet who think that
-he was right. But paleontologists are now quite sure that they were
-evolved from a group of primitive reptiles, known chiefly from Africa,
-called the Theriodontia; quite sure because nearly all the connecting
-links between the two classes have already been discovered—to such an
-extent, indeed, that really nothing distinctive of either class is left
-save the presence or absence of the peculiar bone called the quadrate,
-the bone with which the lower jaw articulates in birds and reptiles;
-and certain elemental parts of the lower jaw itself. And even these
-bones, in certain mammal-like reptiles, had become mere vestiges.
-Even the double condyle of the mammal skull, with which the vertebrae
-articulate, so like those of the amphibian skull that Huxley based his
-belief of the amphibian origin of the mammals chiefly upon it, has now
-been found in certain reptiles. Warm-bloodedness, one of the diagnostic
-characters of birds and mammals, is not really very important, since
-it must have arisen in these two classes independently, and we may
-easily conceive that the earliest mammals were cold-blooded or that the
-immediate ancestors of the mammals were warm-blooded.
-
-It is an interesting fact in the history of the vertebrates, as of
-all other groups of animals and plants, that the chief divisions
-arose early in geological history. Every known order of amphibians
-and reptiles, unless it be that including the blind-worms, was
-differentiated by the close of the Triassic period. The frogs are now
-known from the Jurassic. The mammals and birds also quite surely date
-their birth from the Triassic. And this early differentiation of the
-chief groups is doubtless due to the fact that the potentialities of
-diverse evolution are limited by specialization. It is apparently a law
-that evolution is irreversible, that it never goes from the special to
-the general, that an organism or an organ once extinct or functionally
-lost never reappears. And it is also a law in evolution that the parts
-in an organism tend toward reduction in number, with the fewer parts
-greatly specialized in function, just as the most perfect human machine
-is that which has the fewest parts, and each part most highly adapted
-to the special function it has to subserve. And these laws explain why
-it is that no highly specialized organism can be ancestral to others
-differing widely from it. The more radically distinct an organism
-is from its allies, the earlier it must have branched off from the
-genealogical tree.
-
-The many new discoveries of extinct forms so often intermediate, not
-only between the larger groups, but between many of the lesser ones as
-well, are making the classification of the vertebrates increasingly
-difficult. At one time it was sufficient to define a reptile as a
-cold-blooded animal with a single occipital condyle, that is, with
-a single articular surface between the skull and the first vertebra
-of the neck; a mammal as a warm-blooded animal with two articular
-surfaces; but these definitions are no longer strictly correct.
-Connecting links do not break down classification, as one might think,
-but they do often spoil our fine systems and compel our classifiers to
-take a wider view of nature than their own narrow province affords.
-
-We can never hope that most, or even the greater part, of all the
-animals which have lived in the past will ever become known to us,
-even imperfectly. Doubtless the species of the past geological ages
-outnumbered many times, perhaps hundreds of times, all those now
-living, since many of these latter are merely the remnants of far
-more varied and extensive faunas. At times the conditions for the
-preservation of the remains of animal life have been more favorable
-than at others, and, under such favorable conditions, a fairly good
-glimpse is sometimes given us of the fauna of some isolated epoch
-and locality in the earth’s history. Those animals which lived in
-and about the water have been preserved in greater numbers and more
-perfectly than the strictly land animals, since fossils are due to
-the preserving action of water, with few exceptions. Of those animals
-which lived upon the land or in the air only the rarest of accidents
-carried the skeletons into the lakes, seas, and oceans. And, even when
-they had been covered by sediments at the bottoms of lakes and seas
-and hidden away from adverse agencies, it has often happened that the
-great erosions of later ages have carried away and destroyed the rocks
-in which they were inclosed. The records of long intervals of time
-have thus been lost in all parts of the world. That we are able to
-obtain even an imperfectly continuous history is due to the fact that
-the intervals thus lost are not everywhere contemporaneous, that the
-missing records of one place may be filled out in part elsewhere. But
-this substitution of records from a distance can never make the history
-complete. If, in human history, we had only the records for one century
-in China, for another in England, and for yet another in South America,
-how imperfect indeed would be our knowledge of human progress. Animals
-and plants are never quite alike in remote regions, and they never have
-been. The living reptiles of North and South America are today almost
-entirely different, and, were their fossil remains to be discovered a
-million years hence, it would be very difficult to decide that they had
-once lived contemporaneously; difficult, though perhaps not impossible,
-since some are so nearly alike that their relationships or possible
-identity would probably be established after long search. This will
-serve to make clear how very difficult it is, for the most part, to
-correlate exactly the geological formations in remote regions of the
-earth, or even sometimes in adjacent regions where the fossils are
-scanty, or the conditions under which the animals had lived were very
-different.
-
-There are long periods of time, millions of years at a stretch perhaps,
-throughout which our knowledge amounts to little or nothing concerning
-many land reptiles which we are sure must have existed abundantly. No
-better example of our oftentimes scanty knowledge can be cited than
-the following. Until within the past fifteen years it was thought that
-true land lizards, of which there are about eighteen hundred species
-now living, dated back in their history no farther than about the
-close of the great Secondary Period, or the Age of Reptiles. But a
-single skull of a true land lizard has been discovered in the Triassic
-deposits of South Africa, a skull of a form so nearly like that of the
-modern iguana of America that its discoverer, Dr. Broom, has called
-it _Paliguana_. The lizards must have been in existence, probably
-many thousand species of them, during all the great interval of time
-between the Middle Triassic and the close of the Cretaceous, since it
-is a law which can have no exception, that a type of life once extinct
-never reappears. The “ancient iguanas” of the Trias must have been the
-forbears of many, if not all, of the lizards of later times, though
-nothing is known of their descendants through a period of time which
-can be measured only by millions of years.
-
-However, notwithstanding these imperfections of our geological records,
-we know very much more about extinct reptiles than we do about living
-ones, so far at least as those parts capable of preservation in the
-rocks are concerned. Were our knowledge of reptiles confined to the
-forms now living upon the earth it would be relatively very incomplete
-since, aside from the lizards and snakes, they are merely the remnants
-of what was once a mighty class of vertebrates.
-
-Not only do we learn from the remains preserved in the rocks the
-precise shape and structure of the bones of the skeleton and their
-precise articulations, but we are often able to determine not a little
-regarding the forms which the living animals had by the impressions
-made by the dead bodies in the soft sediment which inclosed them
-before decomposition of the softer parts had ensued, sediments which
-afterward solidified into hard rock. But these impressions are, with
-rare exceptions, only those of profiles or of flattened membranes.
-The rounded bodies of life do not retain their shape long enough for
-the sediment to harden; in most cases the flesh has decomposed before
-being entirely covered by sediment. Sometimes the integument and
-scales in a carbonized condition are actually preserved, retaining
-some of the actual structure of the organized material. The carbon
-pigment of the skin has sometimes been preserved in patterns indicating
-the color-markings in some of these ancient reptiles; and even the
-microscopic structure has been detected in carbonized remains of
-organs. Fossil stomach contents, the bony remains of unhatched young,
-as well as the delicate impressions of skin and membrane, all add to
-our knowledge of the structure and habits of the animals which lived so
-long ago. Many other things also may be learned, or at least inferred,
-concerning the living animals and their habits from the positions in
-which the skeletons are found, from the nature of the rocks which
-inclose them, or from the character and abundance of other fossils
-found with them. The frequent discovery of bones which had been injured
-and mended during life, or the living amputation of members, often
-tell of the characteristics of the creatures. So, too, the climatic
-conditions under which the animals lived may often be inferred with
-tolerable certainty; the presence of “stomach-stones” reveals something
-of the food habits, and even of the structure of the alimentary canal,
-etc.
-
-All this information is gained slowly, often very slowly, and with
-much labor and pains. Rarely or never is it the case that all the
-information obtainable concerning any one kind of an extinct animal
-is furnished by a single specimen. Skeletons are very seldom, perhaps
-never, found quite complete, with all their parts in their natural
-positions; and the nature of the matrix inclosing them usually prevents
-a study of all parts of any specimen. If a newly discovered fossil
-is widely different from the corresponding parts of any creature
-previously known, whether living or extinct, we cannot infer very much
-from a few bones as to what the remainder of the skeleton is like.
-Such inferences or guesses in the past have often resulted in grievous
-error, and self-respecting paleontologists are now very reluctant to
-speculate much concerning extinct animals from fragments of a skeleton,
-no matter what those fragments or bones may be; future discoveries are
-sure to reveal errors. It is, therefore, only by the accumulation of
-much material, and by the careful study and comparison of all known
-related animals, that reliable conclusions can be reached. Often it
-requires scores of specimens to determine the exact structure of a
-single kind of animal, and, as the collection and preparation of
-fossil skeletons are tedious and expensive, our knowledge sometimes
-increases very slowly. In recent years, however, there have been many
-more students of extinct backboned animals than formerly, and there are
-now many museums and universities which spend annually large sums of
-money in the collection and preparation of such fossils. This greater
-activity of the last twenty years is bringing to light many new and
-strange forms, as well as completing our knowledge of those previously
-imperfectly known.
-
-It is commonly, but erroneously, believed that the bones of extinct
-animals are usually found in excavations made for the purpose. It
-is true that not a few specimens of fossils have been discovered
-in excavations made for other purposes, such as railway cuttings,
-quarries, wells, etc., but if no others were found our knowledge of the
-animals of the past would be very meager indeed. Fossils are, for the
-most part, found by deliberate search over the denuded rocks in which
-they occur. Methods of search and collection will best be understood by
-the following description of the noted fossil-bearing rocks of western
-Kansas.
-
-[Illustration: FIG. 1.—A characteristic chalk exposure in western
-Kansas, a hundred acres or more in extent.]
-
-About the middle of Cretaceous times, there extended from the Gulf of
-Mexico on the south to or nearly to the Arctic Ocean on the north a
-narrow inland ocean or sea, a few hundred miles in width, covering what
-is now the western part of Kansas and the eastern part of Colorado,
-and separating the North American continent into two distinct bodies
-of land. This ocean, because of its location, bordered on both sides
-by low-lying lands—the Rocky Mountains had not then been pushed
-up—doubtless was comparatively calm and placid, free from violent
-storms and high tides. That the climate, in the region of Kansas at
-least, was warm or even subtropical is fairly certain, since plants
-allied to those now living in warm, temperate, or subtropical regions
-were then living much farther to the north; and since the animals
-which then lived in this sea were only such as would be expected
-in waters of warm temperature. Its tributary rivers could have been
-neither large nor swift-flowing, since the sediment at its bottom was
-free, or nearly free, from in-brought material. This was at least the
-case not very far from its shores. Its slowly falling sediment was
-composed, almost exclusively, of microscopic shells of animals and
-plants, foraminifera and coccoliths. The deposits thus made are almost
-identical with those now forming in various parts of the world in clear
-but not deep waters, away from the immediate coasts of the continents,
-almost pure chalk. Animals dying in this inland sea fell slowly to
-the bottom during or after decomposition of their softer parts, and
-the slowly increasing sediments covered up and buried the preservable
-parts. The many predaceous fishes and other scavengers with which the
-waters abounded often tore the decomposing bodies apart, separating
-and displacing the bones of the skeleton; and the currents of the
-shallow waters washed others apart. Often the teeth of fishes and other
-carnivorous animals are found imbedded in the bones, and many are the
-scars and toothmarks observed in the fossil bones.
-
-After the ocean had dried up and the bottom had been raised far above
-the present level of the oceans, other deposits made in lakes and by
-the winds covered deeply the consolidating sediments, burying them for
-millions of years with all that they contained. Long-continued erosion
-by winds and rains has again laid bare many parts of the old ocean
-bottom, and has washed them out into ravines and gullies. Many hundreds
-of square miles of this chalk are now laid bare in western Kansas, upon
-which the growth of vegetation has been prevented by the arid climate.
-Here and there may now be discovered protruding from the sloping or
-precipitous surfaces of this exposed chalk bones or parts of bones of
-the old animals buried so long ago in the soft sediment of the ancient
-ocean bottom.
-
-The sharp-eyed searcher after fossils detects these protruding, often
-broken and weather-worn, petrified bones, which themselves betray the
-presence often of other parts of their skeletons still concealed in the
-chalky hillside. Fortunate is he if he has discovered a specimen soon
-after it appeared at the surface, before the rains have washed away
-and destroyed most of the remains that had been there preserved. Still
-more fortunate is he if all or nearly all of the original skeleton has
-been preserved together in its natural relations. After days, perhaps
-weeks, of labor, the specimen is secured and shipped to the laboratory.
-Those parts which have been washed out of the chalky rock before the
-discovery of the specimen are always more or less injured and for the
-most part lost, their fragments strewn down the hillside, for erosion
-is always slow and many years may have elapsed since first the specimen
-had appeared at the surface. More frequently, perhaps, a few strokes
-of the pick and shovel disclose but one, two, or three bones remaining
-in the rocks. The specimen, if large, or composed of many bones, is
-carefully uncovered sufficiently to show its extent, and then, so far
-as possible, removed in large blocks of the rock. The bones themselves,
-notwithstanding their petrifaction, are usually soft and easily broken,
-and their separate removal from the matrix may require weeks or even
-months of labor, work which cannot be done prudently in the field.
-
-Of many specimens the rock matrix is so hard that the task of removing
-it from the bones is slow and difficult, indeed well-nigh impossible,
-for the bones are usually softer than their surrounding matrix. On the
-other hand, the matrix may be so soft and friable that it cannot be
-quarried out in blocks. In such cases the separate divisions, as large
-as they can be excavated and safely handled, are carefully covered with
-thick bandages of burlap and plaster-of-paris, often strengthened with
-rods of iron or boards. The skeleton of a single animal treated in this
-way may require weeks and even months to collect, prepare, and mount in
-the museum.
-
-From what has been said the reader will understand how it is possible
-to make an approximately accurate picture of extinct animals as they
-appeared in life—approximately accurate, never absolutely so. The
-flesh and other soft parts of an animal are never petrified, though
-it is a common belief that they may be. Petrified men and women are
-still occasionally shown in cheap museums, but they are always frauds.
-Many times has the writer been called upon to express an opinion as
-to the nature of some concretion which the discoverer was sure was a
-petrified snake, turtle, or even some part of the human body, because
-of fancied resemblances in shape and size. Not too emphatically can it
-be said that anything dug from the earth having the shape of a living
-animal and alleged to be petrified is either an accidental resemblance
-or a deliberate humbug—if we except such extraordinary casts as those
-of Pompeii. The Cardiff Giant and the Muldoon are still fresh in the
-memory of some of us. There have been a few instances where flesh has
-been preserved in the North, frozen for thousands of years, but frozen
-fossils are very different from petrified fossils. Flesh decays before
-it possibly can be petrified, and only rarely is the residue of flesh,
-tendons, and skin, that is, the carbon and mineral matters, preserved.
-
-[Illustration: FIG. 2.—Removing a specimen of fish in a block from the
-chalk of western Kansas.]
-
-One may sometimes restore extinct animals as in life, knowing fully
-the shape and structure of the skeleton, and still be far from the
-real truth. All elephants of the present time have a bare or nearly
-bare skin. If all that we knew of the extinct mammoth were derived
-from the skeleton we should never have suspected that the creature
-was clothed during life with long and abundant hair, such as has been
-found with the frozen bodies in Siberia. Nor should we suspect that
-the dromedary and Bactrian camels of today have large masses of fat
-on their backs, if we knew only their skeletons. It must therefore be
-remembered that all restorations of extinct animals, representing them
-as in life, are merely the sum of our knowledge concerning them, as
-close approximations to the real truth as it is possible to make. Or,
-rather, they should be such approximations; unfortunately many such
-restorations have been made by artists wholly unacquainted with the
-anatomy of the creatures they attempt to represent, often adorned with
-appendages drawn from a too vivid imagination.
-
-
-
-
-CHAPTER II
-
-CLASSIFICATION OF REPTILES
-
-
-There is very much doubt, very much uncertainty, among paleontologists
-about the classification of reptiles. No two writers agree on the
-number of orders, or the rank of many forms. Some recognize twenty or
-more orders, others but eight or nine. And this doubt and uncertainty
-are due chiefly to the many discoveries of early forms that have been
-made during the past twenty years. The many strange and unclassifiable
-types which have come to light in North America, South Africa, and
-Europe have thrown doubt on all previous classificatory schemes,
-have weakened our faith in all attempts to trace out the genealogies
-of the reptilian orders; and classification is merely genealogy.
-It is only the paleontologist who is competent to express opinions
-concerning the larger principles of classification of organisms,
-and especially of the classification of reptiles. The neozoölogist,
-ignorant of extinct forms, can only hazard guesses and conjectures
-as to the relationships of the larger groups, for he has only the
-specialized or decadent remnants of past faunas upon which to base
-his opinions. About some things we can be quite confident; about some
-groups opinions have crystallized, and we all agree, except perhaps on
-trifles. The dinosaurs, the pterodactyls, the crocodiles, for instance,
-offer only minor problems to perplex the systematist, but the origin
-and the relations, not only of these, but also of nearly all the
-others, are still involved in obscurity. The question, whence came the
-ichthyosaurs, the plesiosaurs, the turtles, etc., seems almost as far
-from solution as it did fifty years ago. With every problem solved a
-dozen more intrude themselves upon us. Hence, classification simply
-represents the present condition of our knowledge, our present opinions
-as to genealogies. It was the fashion a dozen years ago to draw all
-sorts of genealogical trees on the slightest pretext, to trace in
-beautifully clear lines the precise descent of all kinds of animals;
-and very few have been worth the paper on which they were printed.
-When facts are numerous enough, conclusions are patent even to the
-novice; when facts are few and obscure, one can guess about as well as
-another. In general, it may be said that the older a group of animals
-is the more abstruse are the problems presented; first, because of the
-lack of abundant material; second, because the forms speak to us in an
-unfamiliar language that we cannot easily interpret. The classification
-of the mammals approaches more nearly the ultimate truth than does that
-of any other group of organisms, because we know more about the extinct
-forms than we do of any other class, and also because we know more
-about the living forms than we do about any other living animals.
-
-Species of reptiles are, for the most part, vague quantities in
-paleontology; they can be determined with assurance only by the
-comparison of abundant material. Adult characters in mammals are
-apparent in the ossification of the skeleton, and size can be used
-within moderate limits in the determination of species; but size in
-reptiles means but little; no one could possibly say that the skeleton
-of an alligator six feet in length is not that of an adult animal if
-he knew nothing else about the Crocodilia. So also the compression and
-malformations of bones from the processes of fossilization obliterate
-specific characters in great part. Nor are specific characters easily
-distinguishable in the skeletons of living reptiles. The genus,
-therefore, among fossil reptiles is practically the unit, and we may
-be sure that for every well-defined genus we discover there existed
-numerous minor variations, which, had we the living animals to study,
-we should call species. We classify the living Crocodilia into two
-families, about four well-defined genera—perhaps even five or six—and
-about twenty-five species. Of the living lizards there are about
-eighteen hundred species, twenty families, and four larger groups
-or suborders. In all probability the lizards have never been more
-abundant and more varied than they are at the present time. Possibly
-these proportions of species, genera, families, and suborders may
-represent approximately the proportions that have existed at some time
-or other in most of the other groups which we call orders—approximately
-only, for we can never be quite sure that we evaluate the structural
-characters of different groups of organisms quite equally. The absence
-of a molar tooth in a mammal would ordinarily indicate a genus, the
-absence of a tooth in a reptile might not indicate even a variety or
-a race. Whence it follows that classification of organisms is not
-and never will be an exact science. The value of characters used in
-classification is very unequal, as we have seen. No two persons see
-these characters from the same viewpoints, and in consequence no
-two persons whose opinions are worth while ever wholly agree as to
-classification.
-
-The following scheme differs only in minor details from the more
-conservative of the generally accepted views, and those differences
-are, for the most part, the writer’s own opinions, to be taken for
-what they are worth. It may be said decisively that no classification
-of the reptiles into major groups, into super-families or subclasses
-that has so far been proposed is worthy of acceptance; there is no
-such subclass as the Diapsida or Synapsida, for instance. And we have
-very much more to learn about the early reptiles before any general
-classification of the reptiles can be securely founded. It is very
-probable that the primary radiation of the reptiles into the various
-lines of descent, into its main branches, occurred much earlier than
-we have been disposed to believe; that before the close of Paleozoic
-time, perhaps before the close of the Carboniferous, all the great
-groups of reptiles had gone off from the main stem, and that since then
-only smaller and smaller branches have appeared. There have been no new
-orders of reptiles in all probability since Triassic times, and perhaps
-none since Permian.
-
-Taxonomists are often disposed to cut the Gordian knots of
-relationships by raising the ranks of the animals they study to
-independent positions. More than thirty independent orders of reptiles
-have been proposed by different students, and quite as many of mammals
-and of birds; possibly after more forms have been discovered there will
-be as many proposed for the amphibians. Sometimes, indeed, it is better
-to make such independent groups than to unite lesser ones on doubtful
-evidence. But the writer, for one, believes that it is more worthy of
-the thoughtful scientific student to seek for relationships than for
-differences. It is far easier to destroy than to construct, to make
-new genera, families, and orders than to unite those already proposed.
-To raise every proposed suborder of reptiles to an order, as has been
-proposed by various writers, and the orders to subclasses, only leaves
-classification where it was; nothing has been added to taxonomy save a
-lot of new names to perplex and annoy the student.
-
-In the following scheme of classification three groups provisionally
-called orders are prefixed by an asterisk.
-
-
-CLASS REPTILIA
-
-    Order =COTYLOSAURIA=
-        Primitive reptiles with notochordal vertebrae, imperforate
-        temporal region, persistent intercentra; two coracoids;
-        plate-like pelvis, with all or most of the amphibian skull
-        elements; short legs and short neck; phalangeal formula
-        primarily 2, 3, 4, 5, 3(4).
-        Suborder =Diadectosauria=  Permocarboniferous, North America.
-                 =Pantylosauria=   Permocarboniferous, North America.
-                 =Labidosauria=    Lower Permian, North America.
-                 =Pareiasauria=    Upper Permian, Europe, Africa.
-                 =Procolophonia=   Triassic, Europe, Africa.
-
-    Order =CHELONIA=
-        Temporal region imperforate. Head and limbs more or less
-        retractile within a box formed chiefly by the exoskeleton.
-        Suborder =Pleurodira=     Triassic to recent.
-                 =Cryptodira=     Jurassic to recent.
-                 =Trionychoidea=  Cretaceous to recent.
-
-    Order =THEROMORPHA=
-        Primitive reptiles with notochordal vertebrae, perforate
-        temporal region, persistent intercentra; two coracoids;
-        plate-like pelvis with median vacuity; no free
-        dermosupraoccipitals in skull; longer legs and neck;
-        phalangeal formula 2, 3, 4, 5, 3(4).
-        Suborder =Pelycosauria= (_sens. lat._) Permocarboniferous,
-                                                  North America, Europe.
-                  =Dromasauria=                 Upper Permian, Africa.
-                  =Dinocephalia=                Middle and Upper
-                                                      Permian, Africa.
-
-    Order =THERAPSIDA=
-        Reptiles with a single temporal perforation on each side;
-        vertebrae not notochordal; intercentra not persistent;
-        pelvis with vacuity; skull bones reduced; teeth heterodont;
-        phalangeal formula, 2, 3, 3, 3, 3.
-        Suborder =Anomodontia=    Permo-Trias, Africa, North America.
-                 =Therocephalia=  Upper Permian, Africa.
-                 =Theriodontia=   Trias, Africa.
-
-    Order =SAUROPTERYGIA=
-        Aquatic reptiles with a single temporal vacuity; no
-        supratemporal bone, or quadratojugal; ribs single-headed,
-        diapophysial; coracoids large, meeting in middle line,
-        single; neck long, tail short.
-        Suborder =Nothosauria=   Triassic, Europe.
-                 =Plesiosauria=  Triassic to close of Cretaceous,
-                                                      cosmopolitan.
-
-    ⃰Order =PROGANOSAURIA=
-        Primitive aquatic reptiles; single (? upper) temporal
-        perforation; neck elongate; nares posterior; vertebrae
-        notochordal; intercentra persistent; pelvis plate-like;
-        phalangeal formula 2, 3, 4, 5, 4(6). Permocarboniferous,
-        Africa, South America.
-
-    Order =ICHTHYOSAURIA=
-        Reptiles with all aquatic adaptations; a single, upper
-        temporal perforation; both supratemporal and squamosal
-        present; a single coracoid. Middle Triassic to Benton
-        Cretaceous, cosmopolitan.
-
-    ⃰Order =PROTOROSAURIA=
-        A single, upper temporal vacuity, quadrate fixed (neck
-        vertebrae elongate); bones hollow; cervical ribs
-        single-headed, articulating with centrum; pelvis plate-like.
-        Permian, North America, Europe.
-
-    Order =SQUAMATA=
-        A single, upper temporal vacuity, or, secondarily none;
-        quadrate loosely articulated with cranium; teeth on palate;
-        intercentra more or less persistent; a single coracoid; ribs
-        single-headed, central.
-        Suborder =Lacertilia=  Trias to recent.
-                 =Mosasauria=  Upper Cretaceous, cosmopolitan.
-                 =Ophidia=     Upper Cretaceous to recent.
-
-    ⃰Order =THALATTOSAURIA=
-        Aquatic reptiles; two (?) temporal vacuities; ribs
-        single-headed, attached to centrum; single coracoid; no
-        intercentra. Trias, California.
-
-    Order =RHYNCHOCEPHALIA=
-        Two temporal vacuities on each side; palate with teeth;
-        intercentra persistent; a single coracoid; teeth acrodont;
-        ribs articulating with centrum and arch.
-        Suborder =Rhynchosauria= Triassic, Europe.
-                 =Sphenodontia=  Triassic to recent.
-                 =Choristodera=  Uppermost Cretaceous, lowermost
-                                        Eocene, North America, Europe.
-
-    Order =PARASUCHIA=
-        Subaquatic reptiles, with two temporal vacuities; an
-        antorbital vacuity; no false palate; pubis entering
-        acetabulum; ribs double-headed, diapophysial.
-        Suborder =Phytosauria=  Upper Trias, cosmopolitan.
-                 =Pelycosimia=  Trias, Africa.
-                 =Pseudosuchia= Trias, Europe, North America.
-
-    Order =CROCODILIA=
-        Two temporal vacuities; teeth thecodont; a false palate;
-        pubis excluded from acetabulum; single coracoid; ribs
-        double-headed, diapophysial; subaquatic or aquatic.
-        Suborder =Eusuchia=       Jurassic to recent.
-                 =Thalattosuchia= Upper Jurassic, Europe.
-
-    Order =DINOSAURIA=
-        Ambulatory reptiles, with two temporal vacuities; no false
-        palate; pubis entering acetabulum; ribs double-headed,
-        diapophysial.
-        Suborder =Theropoda=  Upper Trias to close of Cretaceous,
-                                                      cosmopolitan.
-                 =Orthopoda=  Close of Trias to close of Cretaceous,
-                                                      cosmopolitan.
-                 =Sauropoda=  Upper Jurassic, Lower Cretaceous,
-                                                      cosmopolitan.
-
-    Order =PTEROSAURIA=
-        Volant reptiles; fourth finger greatly elongated to support
-        patagium; neck vertebrae elongated; bones hollow; ribs
-        double-headed, diapophysial; a single coracoid; no clavicles
-        or interclavicle; two temporal vacuities.
-        Suborder =Pterodermata=    Jurassic, Europe.
-                 =Pterodactyloidea= Upper Jurassic to Upper Cretaceous,
-                                              Europe, North America.
-
-
-
-
-CHAPTER III
-
-THE SKELETON OF REPTILES
-
-
-The bony framework, or skeleton, that which gives form and stature
-to the body, and which serves for the support of the soft parts and
-the attachment of muscles, is, with rare exceptions, all that is ever
-preserved of fossil animals. Because, therefore, students of extinct
-animals must rely so much, if not exclusively, upon the skeleton
-much attention has been given to the study of comparative osteology,
-the science of bones. Not only are most of the bones of the skeleton
-characteristic of the genus to which they belong, but the more
-general plan of the skeleton, or parts of the skeleton, is likewise
-characteristic of the larger groups. The paleontologist may become so
-expert in deciphering the characters of single bones, or even parts
-of bones—often all that are known of animals new to science—that he
-is able to hazard guesses as to the general structure of the skeleton
-to which they belong. But such guesses usually will approximate the
-real truth only in the degree that the bones upon which they are based
-approximate like bones of other animals that are better known. Not all
-parts of the skeleton are equally characteristic of the type of animal
-which possessed them. A tooth of a mammal may positively determine the
-species to which it belongs, while the toe bone of the same animal
-might not enable one to guess at its family, even. As a rule one can
-seldom be quite sure of the species of a reptile unless the larger part
-of the skeleton, or at least the skull, is available, although almost
-any bone of the skeleton, if one is expert, will permit a decision as
-to the family, if not the genus.
-
-One must often depend upon the positions and relations of the bones,
-as found in the rocky matrix, for the final determination of many
-characters. One can, for instance, never be sure of the number of
-bones in the neck, trunk, tail, or feet of a reptile, until specimens
-have been found with all such bones in position. It is for this reason
-that much care is exercised in the collection of specimens of fossil
-animals, and especially of fossil reptiles, to preserve all parts of
-the skeleton, so far as possible, in the relations they occupied in the
-rocks until they can be studied in the laboratory. Many grievous errors
-have been made in the past by hasty inferences from fragmentary and
-poorly collected specimens.
-
-[Illustration: FIG. 3.—_Limnoscelis_, a subaquatic cotylosaur, from the
-Permocarboniferous of New Mexico.]
-
-Because of the reliance which must be placed upon the skeleton it
-will be necessary to speak somewhat in detail of its structure in
-the reptiles, and to use not a few terms in its description that are
-unfamiliar to the general reader. So far as possible technical terms
-will be avoided, though some must be used, as there are no equivalents
-in the English language for them. The reader may use this chapter as a
-sort of explanatory index or glossary for the better elucidation of the
-necessary details of the following chapters.
-
-It is needless to say that the skeleton of a reptile is arranged on
-essentially the same plan as that of our own; the bones have the
-same names that they have in our own skeleton, but there are more of
-them, and the individual bones, as a general rule, are less highly
-specialized, that is, are not so well adapted for special functions.
-In a word, the skeleton of a reptile for the most part is generalized,
-though particular parts may be highly specialized for particular uses.
-As a rule, if not as a law, the course of evolution has been to reduce
-the number of parts and to adapt those which remain more closely to
-their special uses, either by increase in size, or by modifications of
-their shape and structure.
-
-
-SKULL AND TEETH
-
-The skull of reptiles is much more primitive or generalized in
-structure than is that of mammals, to such an extent, indeed, that
-there is yet much doubt as to the precise homologies of some of the
-bones composing it; and, inasmuch as the names were originally given,
-for the most part, to the bones of the human skull, there is still
-some confusion among students as to the proper names in all cases, a
-confusion that doubtless will not be wholly dissipated until we know
-much more about the early or more primitive reptiles than we do at
-present.
-
-[Illustration: Fig. 4 Fig. 5]
-
-[Illustration: FIG. 4.—_Seymouria_, a primitive cotylosaurian.
-Skull, from above: _pm_, premaxilla; _n_, nasal; _l_, lacrimal; _p_,
-prefrontal; _f_, frontal; _pf_, postfrontal; _it_, intertemporal;
-_st_, supratemporal; _sq_, squamosal; _ds_, dermosupraoccipital; _t_,
-tabulare; _j_, jugal; _po_, postorbital; _m_, maxilla; _s_, surangular;
-_ang_, angular; _pa_, parietal.
-
-FIG. 5.—_Seymouria_, skull from the side. Explanations as in fig. 4.]
-
-As in other parts of the skeleton, there has been a reduction in the
-number of parts of the reptile skull from that of the more primitive
-forms, and a better adaptation of those which remain for the special
-uses they subserve. This reduction in number has been caused in part
-by the actual loss of bones, in part by the fusion of contiguous ones.
-The most primitive reptiles had no less than seventy-two separate bones
-in the skull;[1] the human skull has but twenty-eight inclusive of the
-ear bones. There is but little variation, either in the number or in
-the relations of bones, in the mammalian skull. If one knows the human
-skull thoroughly he can easily understand the structure of the skull
-of any mammal. The same cannot be said of the skulls of reptiles; one
-would be greatly puzzled in the comparison of the skulls of turtles
-and crocodiles, if he knew nothing about other forms. And it is safe
-to formulate another general law in evolution here: Characters which
-have been longest inherited are least liable to change. The earliest
-reptiles had at least four pairs of bones which have disappeared
-in all later reptiles; and they had some bones in pairs which have
-fused in later reptiles, either with their mates or with contiguous
-bones. The crocodile has at least two pairs of bones which have
-disappeared in turtles. On the other hand, the turtle has at least one
-pair of free bones which have been fused with adjacent bones in the
-crocodiles, and one pair that is fused which is free in the latter.
-The lizard has one pair of bones that has been wholly wanting in other
-reptiles for millions of years, while on the other hand it has lost
-some bones that are present in all other modern reptiles. The four
-parts of the occipital bone of mammals, basioccipital, exoccipitals,
-and supraoccipital, are almost invariably free and there is a single
-occipital condyle, except in the Theriodontia.
-
-[1] Paired maxillae, premaxillae, nasals, prefrontals, lacrimals,
-frontals, parietals, dermosupraoccipitals, tabularia, supratemporals,
-intertemporals, squamosals, jugals, quadratojugals, postorbitals,
-postfrontals, quadrates, exoccipitals, paroccipitals, vomers,
-palatines, pterygoids, sphenomaxillae, stapes, transverse, alisphenoids
-or orbitosphenoids, epipterygoids, articulars, prearticulars, angulars,
-surangulars, coronoids, splenials, dentaries, one supraoccipital, one
-basioccipital, one basisphenoid, one ethmoid.
-
-[Illustration: FIG. 6.—_Labidosaurus_, a cotylosaur. Skull from above:
-_pm_, premaxilla; _n_, nasal; _m_, maxilla; _l_, lacrimal; _p_,
-prefrontal; _fr_, frontal; _pf_, postfrontal; _po_, postorbital; _j_,
-jugal; _pa_, parietal; _sq_, squamosal; _ds_, dermosupraoccipital;
-_pf_, parietal foramen.]
-
-In this reduction or fusion of parts, or in addition thereto, there has
-been a general lightening-up of the whole skull-structure in reptiles
-from the rather massive and protected form of the older to the lighter,
-less protected, and more fragile type of the later ones, since speed,
-greater agility, better sense organs, and doubtless greater brain power
-have rendered unnecessary or useless the older kinds, just as modern
-methods and modern arms have rendered useless the coat of mail of the
-Middle Ages.
-
-[Illustration: FIG. 7.—_Edaphosaurus_, a theromorph reptile from the
-Permian of Texas. Skull with single temporal vacuity.]
-
-The old reptiles had a continuous covering or roof for the skull,
-pierced only by the openings for the nostrils in front—the nares—the
-orbits for the eyes near the middle, and a smaller median opening
-back of them for the so-called “pineal eye.” The temporal region,
-that is, the region back of the orbits on each side, was completely
-roofed over by bone for the support and protection of the jaw muscles.
-In later reptiles this region has been lightened, either by holes
-that pierce it or by the emargination of its free borders, as in the
-turtles. The openings have occurred in different ways, and with the
-loss of different bones in various lines of descent. In one large
-group of reptiles, comprising the pterodactyls, dinosaurs, phytosaurs,
-crocodiles, and rhynchocephalians, there are two openings on each side,
-called the supratemporal and lateral temporal vacuities. In another
-still larger group there is a single vacuity on each side, all members
-of which it has been thought were markedly related to each other.
-Some of these, the lizards, snakes, and mosasaurs, the ichthyosaurs,
-and probably the proganosaurs, have the single opening high up on
-the side, corresponding apparently to the supra temporal vacuity of
-the double-arched forms, as those with two openings are called. Many
-others, however, like the whole order Therapsida and the Theromorpha,
-have the single opening lower down and bounded differently; their
-relationships are doubtful, since it is very much of a question how the
-single opening has arisen. There have been many theories to account for
-the origin of the temporal vacuities, but all are yet speculations.
-Notwithstanding these doubts, which more recent discoveries have
-intensified, there can be none that the structure of this region of the
-skull offers important and reliable characters for the classification
-of the reptiles into the larger groups, but, unfortunately, we are
-very uncertain yet as to what this classification should be. We are
-confident that all those reptiles having two temporal vacuities on each
-side are related to each other; we are yet very much in doubt as to the
-classification of all other reptiles, or at least all others having
-only a single temporal vacuity on each side.
-
-[Illustration: FIG. 8.—_Sphenodon_ (tuatera). Skull from side and
-above: _pm_, premaxilla; _n_, nasal; _prf_, prefrontal; _f_, frontal;
-_pf_, postfrontal; _p_, parietal; _po_, postorbital; _sq_, squamosal;
-_m_, maxilla; _j_, jugal; _qj_, quadratojugal; _q_, quadrate; _c_,
-coronoid; _sa_, surangular; _art_, articular; _pa_, prearticular; _d_,
-dentary; _an_, angular.]
-
-Better evidences of relationships, or the absence of relationships, are
-offered by the presence of certain bones in the skulls in some orders
-that are lost in others, since it may be accepted as an axiom that new
-bones have not appeared in the skulls of reptiles, birds, or mammals;
-and that no bone which has once disappeared has ever been functionally
-regained by the descendants of those that lost it. The presence,
-then, of an extra bone in the temporal region of the lizards or the
-ichthyosaurs is proof that they have had a long and independent descent
-from reptiles which possessed it.
-
-The mandible of the earliest reptiles was composed of not less than
-seven separate and distinct bones, as shown in the accompanying
-figures. The mandible of no modern reptile has more than six, and some
-have fewer. The mandible of mammals is composed of a single bone,
-the dentary; those reptiles, the Theriodontia, which doubtless were
-ancestral to the mammals in Triassic times, have all the bones, except
-the dentary, much reduced, or even vestigial. The prearticular bone, as
-shown, so far as known, has been absent in all reptiles since Triassic
-times, except the ichthyosaurs, plesiosaurs, _Sphenodon_, and turtles,
-all reptiles of ancient origin. The coronoid bone primitively extended
-the whole length of the teeth on the inner side; in all reptiles,
-except the plesiosaurs, since Triassic times it is either reduced to
-a small bone back of the teeth or is absent. So also the splenial has
-been greatly reduced in size in all later reptiles and may be wanting
-as in _Sphenodon_ and modern turtles. The articular of reptiles, it is
-now generally believed, is represented in mammals by one of the ear
-bones, the quadrate by another.
-
-[Illustration: FIG. 9.—Mandible of _Trimerorhachis_, a stegocephalian
-amphibian, ancestrally related to the reptiles: _A_ from within;
-_B_ from without. The coronoid is composed of three bones, the true
-coronoid (_cor_), the intercoronoid (_icor_), and the precoronoid
-(_pc_). The splenial is composed of two, the true splenial (_sp_) and
-the postsplenial (_psp_). The prearticular (_pa_) is broad, the dentary
-(_d_) is small; and the angular (_an_) is only slightly visible on the
-inner side.]
-
-[Illustration: FIG. 10.—Mandible of _Labidosaurus_, a cotylosaur
-reptile: _A_ from within; _B_ from without. The coronoid (_cor_) is a
-single bone, but extends far forward. The splenial (_sp_) is also a
-single bone, replacing the two of the amphibians. The _prearticular_
-(_pa_) is narrower, and the angular (_ang_) appears broadly on the
-inner side. The dentary (_d_) is much larger and the surangular (_sa_)
-is distinct. The articular (_art_) is small.]
-
-[Illustration: FIG. 11.—Mandible of _Alligator_, a modern, highly
-specialized reptile, from within. The coronoid (_cor_) is small and
-is situated far back; the splenial (_sp_) does not extend to the
-symphysis; the prearticular (_pa_) has disappeared, or has fused with
-the angular (_an_) or articular (_art_). The dentary (_d_) has become
-the chief bone of the mandible.]
-
-The teeth of reptiles are of much less importance, as a rule, in the
-determination of relationships than are the teeth of mammals. Rarely
-are their shapes of specific, and often not of generic, importance,
-though their number and relative sizes may be. The teeth of mammals,
-as a rule, are forty-four or less in number, and they are always
-inserted in distinct sockets in the jaw bones. Among reptiles they
-are indefinite in number, and may be attached to any of the bones
-of the palate and sometimes also to the coronoid of the mandibles.
-Furthermore, except in those reptiles related to the immediate
-ancestors of the mammals, they are alike or nearly alike in the
-jaws, that is, homodont, not distinguishable into incisors, canines,
-and molars. They may be inserted in separate sockets (thecodont),
-in grooves, or simply be co-ossified to the surface of the bone
-(acrodont). And they are usually reproduced indefinitely by new teeth
-growing at the side of the base or below them. More usually they are
-pointed and curved; sometimes they are flattened, with sharp cutting
-edges in front and behind in the more strictly carnivorous reptiles;
-in those of herbivorous habits they are more dilated and roughened on
-the crown, not pointed; in not a few they are low, broad, and flat
-and are used only for crushing the hard shells of invertebrates. With
-the very few exceptions among certain dinosaurs, they never have more
-than one root for attachment. The evolutional tendency for reptiles,
-as for the mammals, is to loose teeth, especially those of the palate.
-Among living reptiles it is only the most primitive types, such as
-the lizards, snakes, and the tuatera, which have teeth on the palatal
-bones, and in none are there teeth on the vomers, as was the rule in
-the ancient reptiles. The lizards may have them on pterygoids and
-palatines, and the tuatera has them on the palatines only. There may be
-as many as eighty on each jaw, above and below, and hundreds of smaller
-ones on the palate, or they may be reduced in number to five or six,
-or even to a single one; some reptiles, like the turtles and later
-pterodactyls, have none. The teeth of reptiles are composed of the same
-kinds of tissues as are the teeth of mammals, that is, of dentine and
-enamel, but the enamel is always thin, perhaps because the teeth are
-so easily replaced that a thicker protective covering is not needed.
-The arrangement of the dentine in primitive reptiles is complicated,
-that is, plicated or folded in labyrinthine figures, like that of
-many stegocephalian amphibians, the Labyrinthodontia, especially.
-This labyrinthine structure of the dentine persisted longest in the
-ichthyosaurs.
-
-
-VERTEBRAE AND RIBS
-
-The spinal column or backbone of reptiles, as in all air-breathing
-vertebrates, is made up of a variable number of separate segments
-called vertebrae, permitting flexibility. Each vertebra is composed of
-a body, or centrum, and an arch on the dorsal side for the protection
-of the spinal cord. Various projections from the vertebra, called
-processes, serve for the attachment of ligaments or muscles, for
-articular union with adjacent vertebrae, or for the support of ribs,
-and these processes have characteristic differences in different
-reptiles. The pair in front and behind, for articulation with the
-adjoining vertebrae, may become obsolete or even lost in swimming
-reptiles, as we shall see; they are called zygapophyses. In not a few
-reptiles there is an additional pair for zygapophysial articulation
-in front and behind, called zygosphene and zygantrum, for the greater
-strengthening of the column; they are especially characteristic of
-snakes and certain lizards. In certain other reptiles, especially the
-long-necked dinosaurs, there is an additional pair arranged differently
-from the zygophene, that have received the names hyposphene and
-hypantrum.
-
-[Illustration: FIG. 12.—Procoelous vertebra of snake: _za_, zygantrum;
-_zs_, zygosphene; _ps_, posterior zygapophysis.]
-
-On the top of the arch is the spine or spinous process, which may vary
-enormously in size and length; sometimes it is flattened or dilated
-above for the support of an exoskeleton, or it may be heavy and massive
-for the attachment of strong muscles and ligaments. In the modern
-basilisk lizards and in the ancient _Dimetrodon_ and _Edaphosaurus_
-from the Permian rocks of Texas these spines are of enormous length,
-some of them nearly four feet long in reptiles not twice that length.
-Slender crawling reptiles usually have no spines, or only vestigial
-ones. On the sides of the arch there may be a distinct transverse
-process for the articulation of the rib.
-
-In all early reptiles the ends of the body or centrum are concave,
-as they are in nearly all fishes. Such a conformation, called
-amphicoelous, gives great flexibility to the spinal column, but only
-moderate strength, since the intervening spaces are filled with
-cartilage in life. In all living reptiles, with few exceptions, the
-body is concave, like a saucer, in front and correspondingly convex
-behind, and the intervening cartilage has largely disappeared. Such a
-mode of union, called procoelous, adds greatly to the strength of the
-backbone, enabling it to receive greater shocks or greater pressure
-without dislocation; or to sustain the greater strain of muscles used
-in running swiftly or in climbing. Among living reptiles, only the
-gecko lizards and the tuatera have biconcave vertebrae. Some extinct
-reptiles, such as some of the dinosaurs, animals that walked erect upon
-their legs, had their vertebrae convex in front and concave behind
-(opisthocoelous). Birds, though walking erect, have a very different
-and more complicated articulation of the cervical vertebrae, and
-certain reptiles, like the turtles, have very complicated cervical
-vertebrae.
-
-In the embryos of all vertebrate animals there appears first an
-elongated fibrous rod, called the notochord, in the place of the future
-spinal column. This rod may persist through life, never ossifying, as
-was the case with all the earliest fishes, and is the condition in some
-living ones. As the embryo grows, however, the separate segments, or
-vertebrae, ossify about this rod in all reptiles, forming bony rings,
-perforate at first in the middle for the more or less constricted
-notochord. This stage was the permanent condition in all the earliest
-reptiles and in some later ones. Such animals are said to have
-notochordal vertebrae, the notochord more or less continuous, like a
-string of beads, the beads representing the enlargements between the
-contiguous vertebrae.
-
-[Illustration: FIG. 13.—Notochordal cervical vertebrae, with
-intercentra, of _Ophiacodon_, a primitive theromorph reptile from the
-Permocarboniferous of New Mexico: _pa_, proatlas; _an_, arch of atlas;
-_o_, odontoid; _ax_, axis.]
-
-In many early amphibians, and probably in all the earliest ones, as
-well as in the fishes from which they were derived, the vertebra
-is more complicated in that it is composed of at least three pairs
-of separate bones, two of which united with each other, the third
-finally disappearing in modern animals, or at the most represented
-by a mere vestige called the intercentrum. The dorsal pair of these
-bones, called the neurocentra, forms the arch of the vertebra. The
-ventral posterior pair, called the pleurocentra, increases in size and
-unites to form the centrum or body of the vertebra; while the ventral
-anterior pair, early united with each other, is called the hypocentrum
-or intercentrum, persistent in all early reptiles as a vestige between
-the centra on the ventral side. This divided condition of the vertebra
-is persistent in the first vertebra, the atlas of all higher animals,
-in which the so-called body is the hypocentrum or intercentrum, the
-arch is the neurocentrum, while the pleurocentra have fused more or
-less with the anterior part of the next vertebra, the axis, to form the
-so-called odontoid. That this is the real explanation of the structure
-of the atlas is proved by the various stages of its evolution in the
-reptiles, from the earliest (Fig. 15) in which it scarcely differs
-from rhachitomous—as this structure is called—vertebrae of an early
-amphibian, to the modern in which the structure is nearly like that of
-mammals.
-
-[Illustration: FIG. 14.—Rhachitomous dorsal vertebra of _Eryops_:
-_n_, neurocentrum or arch; _pl_, pleurocentrum; _i_, intercentrum or
-hypocentrum; _az_, anterior zygapophysis; _pz_, posterior zygapophysis;
-_d_, diapophysis, for tubercle of rib; _p_, parapophysis, for head of
-rib.]
-
-In front of the atlas, that is, between it and the skull, there was, in
-all early reptiles, as well as in some later ones, like the crocodiles
-and tuatera, the remnant of what is believed to have been another
-vertebra, of which only the arch remains, and which is called the
-proatlas. In its earliest condition it articulated with the skull in
-front and the arch of the atlas behind.
-
-As in mammals, the vertebrae of the different regions have received
-distinctive names, cervical, dorsal, lumbar, sacral, and caudal. The
-numbers of each region are far more variable than they are among
-mammals, the total number of vertebrae in the column varying from
-about thirty to more than five hundred, in certain snakes. Nor are the
-different regions always easily distinguishable, especially those in
-front of the sacrum. In the earliest reptiles there was practically
-no neck, and only two vertebrae, the atlas and axis, that properly
-can be called cervical. Very soon, however, the reptiles developed a
-longer neck with seven vertebrae, a number that has remained singularly
-constant in higher animals, especially in the mammals. In most modern
-reptiles there are from seven to nine; in a few lizards, five. But the
-number was much more inconstant among the older reptiles; some of the
-plesiosaurs had as many as seventy-six cervical vertebrae; some of the
-older lizards even had as many as eighteen.
-
-Ordinarily the cervical vertebrae differ from those behind them only
-in the small size or fusion of their ribs; sometimes, however, as in
-the Protorosauria and Pterosauria, the vertebrae may be much elongated.
-The dorsal vertebrae of reptiles vary in number from ten in turtles
-and some dinosaurs to forty-three in _Pleurosaurus_; and under the
-name dorsal we include the so-called lumbar, as there is seldom any
-real distinction between the two series, save the smaller size or the
-co-ossification of the ribs of the latter.
-
-[Illustration: FIG. 15.—_Ophiacodon_, a primitive theromorph reptile:
-proatlas, atlas, and axis, with ribs.]
-
-[Illustration: FIG. 16.—Sacrum of _Chelone_.]
-
-The sacrum in reptiles primitively consisted of a single vertebra,
-which bore a large rib on each side for the support of the pelvis. Very
-early, however, a second or even a third vertebra was added to it from
-behind. The number two is the rule among reptiles, both ancient and
-modern; among crawling reptiles the number never exceeds three, but
-among ambulatory and flying reptiles the number may be as great as in
-any mammal.
-
-The number of caudal vertebrae in reptiles is exceedingly variable,
-from a dozen or fifteen up to a hundred and fifty or more. In snakes
-but two regions are distinguishable, the caudal and precaudal, and the
-number altogether may reach nearly five hundred. With the exception
-of the first few basal caudal vertebrae (pygals) and the minute ones
-at the extreme tip, all caudal vertebrae of reptiles bear a slender,
-usually =Y=-shaped bone below in the interval between the centra,
-for the protection of the vessels and nerves. Because of their shape
-they have been called chevrons, and are really outgrowths from the
-intercentra.
-
-The ribs of reptiles are of more importance in classification than
-one would suppose. The primitive rib was a slender, curved bone,
-with the vertebral end dilated to articulate continuously with the
-intercentral space—that between the centra and the anterior part of
-the arch. And this is the condition still remaining in the tuatera.
-Very soon, however, the lower end of the articular surface (capitulum)
-became separated from the upper (tubercle) by a notch, and the ribs
-became distinctly double-headed. And this mode of articulation is
-the rule among mammals. Among later reptiles, however, there were
-many modifications. In nearly all the head migrated a little backward
-on the centrum. By the loss of the tubercle in lizards, the head
-became truly single-headed, and attached solely to the body; and this
-condition is characteristic of the order Squamata. In another large
-group the head of the rib gradually migrated up on the arch and on
-the transverse process (diapophysis), so that both head and tubercle
-are attached to the diapophysis; and this condition is equally
-characteristic of the orders of reptiles known collectively as the
-Archosauria—the crocodiles, pterodactyls, dinosaurs, and phytosaurs.
-In the Sauropterygia, the ribs are single-headed and attached to the
-end of the diapophysis. Finally in most ichthyosaurs the capitulum and
-tubercle both articulate with the body of the vertebra.
-
-[Illustration: FIG. 17.—_Ostodolepis_, a primitive theromorph reptile.
-Vertebrae from in front and side, with primitive double-headed rib and
-intercentrum.]
-
-Ribs primitively were probably attached to all the vertebrae to the end
-of the tail. In the earliest reptiles that we know they are present on
-all vertebrae as far back as the tenth or twelfth caudal only, those of
-the caudal for the most part co-ossified with the centra. The ribs of
-the neck vertebrae more quickly disappeared, or became fused with the
-vertebrae, and only in the crocodiles among living reptiles are there
-ribs on the atlas. The sacral ribs, on the other hand, became much
-larger and stouter and developed an articulation at their outer ends
-for the support of the ilium (Fig. 16).
-
-The so-called ventral ribs are slender ossifications in the connective
-tissue under the skin, on the under side of the body, and are
-characteristic of most reptiles. The anterior ones doubtless fused
-together more or less to form the sternum or breast bone, which was
-otherwise absent in the early reptiles.
-
-
-PECTORAL OR SHOULDER GIRDLE
-
-Those bones which form the framework for the support of the anterior
-extremity in vertebrate animals are known collectively as the pectoral
-girdle. In our own skeleton there are but two on each side, or four in
-all, the scapula or shoulder-blade, and the clavicle or collar-bone. A
-third bone, however, is represented in all mammals by a mere vestige
-which early unites with the scapula and is called the coracoid
-process. In the lowest forms of mammals, the Monotremata, of which the
-_Ornithorhynchus_ and _Echidna_ are the only examples, not only is
-this coracoid bone largely developed, articulating with the sternum
-or breast bone, but there is an additional coracoid bone in front of
-this; and there is also an interclavicle. Indeed, the pectoral girdle
-in these mammals is more primitive or generalized in structure than it
-is in any living reptiles, composed of scapula, coracoid, metacoracoid,
-and clavicle on each side and an interclavicle in the middle. No living
-reptiles have the metacoracoid, and, as is the case with many mammals,
-some reptiles have no clavicles.
-
-Primitively, that is, in all the old reptiles, the girdle is composed
-of scapula, coracoid, metacoracoid, clavicles, and interclavicle,
-while in some of the very oldest there is yet another bone, more or
-less of a vestige, derived from the ancestral amphibians and called
-the cleithrum or supraclavicle. The scapula is more or less elongated
-in crawling and climbing reptiles; more slender and bird-like in those
-which walked erect after the manner of birds and mammals; shorter and
-more fan-shaped in the swimming reptiles, as we shall see. In some
-pterodactyls, unlike all other known animals, the scapula articulated
-at its upper end with the backbone, giving a much firmer support
-for the anterior extremities. Only in those reptiles allied to the
-ancestors of the mammals has the scapula ever had a spine or projection
-on its dorsal side.
-
-[Illustration: FIG. 18.—_Cacops_, a Permian stegocephalian, ancestrally
-allied to the primitive reptiles, with rhachitomous vertebrae and large
-cleithrum above the scapula.]
-
-Of the two coracoid bones in the original pectoral girdle the posterior
-one began to disappear early and is entirely lost in all reptiles that
-lived later than Triassic times, though it still persists in the lowest
-mammals, as we have seen. In most later reptiles the remaining coracoid
-has become less firmly attached to the scapula than it was in the older
-reptiles. It usually has a small foramen piercing it near the middle of
-the upper border or end, the supracoracoid foramen. The clavicle, while
-more constant among reptiles than among mammals, has been lost in some,
-the Crocodilia, for instance, as also the dinosaurs and pterodactyls.
-The interclavicle is more constant in reptiles, a more or less
-=T=-shaped bone underlying the coracoids where they join, or the breast
-bone; but there were some reptiles that lost it, the dinosaurs and
-pterodactyls, for instance. In the turtles both the clavicles and the
-interclavicle form a part of the under shell or plastron.
-
-[Illustration: FIG. 19.—Scapula (_sc_), coracoid (_cor_), and
-metacoracoid (_mcor_) of _Dimetrodon_]
-
-The cleithrum is known in only a few of the old reptiles; it is a
-more or less slender bone which lies along the upper front margin of
-the scapula, articulating at its lower end with the upper end of the
-clavicle on each side.
-
-The breast bone or sternum, while not properly a part of the pectoral
-girdle, may be mentioned here. In reptiles it is rarely well developed
-or even ossified, the flying reptiles known as the pterodactyls being
-the most notable exceptions. It was a comparatively late development in
-this class, the earliest ones not possessing it even in a cartilaginous
-condition. It was doubtless evolved from the more or less numerous and
-slender ossifications on the under side of the body called ventral
-or abdominal ribs, after the coracoids had become reduced and more
-slender. Whenever it is present the coracoid articulates with it
-on each side in front. In most lizards it remains as a cartilage
-throughout life.
-
-[Illustration: FIG. 20.—Clavicles and interclavicle of _Ophiacodon_, a
-theromorph reptile from the Permocarboniferous of New Mexico.]
-
-
-ANTERIOR EXTREMITY
-
-The upper arm bone, or humerus, like most other bones of the
-extremities, has been greatly modified by the habits of the different
-reptiles. In running and climbing reptiles it is always slender, while
-in burrowing reptiles it is short and stout and much expanded at the
-extremities, like the humerus of the mole among mammals. And we shall
-also see how greatly modified it was among the swimming reptiles.
-The humerus of flying reptiles has an enormous process on the side,
-corresponding to the attachment of the deltoid muscle. The head of the
-humerus, for articulation with the glenoid cavity of the scapula, is
-rounded in all reptiles, except the pterodactyls, and the articulation
-is always at the extremity. At the lower extremity the protuberance
-at the outer or radial side is called the ectocondyle; that on the
-inner or ulnar side, the entocondyle. Between the two at the end are
-the articular surfaces for the radius and ulna, the capitellum and
-trochlea. A little above each of these condyles there is usually, on
-one side or the other or on both, a foramen or hole for the passage of
-arteries or nerves. That on the inner side, which is characteristic of
-all early reptiles and of many mammals, is called the entepicondylar
-foramen; that on the outer side, the ectepicondylar foramen; the latter
-is present in the lizards, and both are found in the tuatera and some
-of the early reptiles.
-
-[Illustration: FIG. 21.—Anterior extremity of _Ophiacodon_.]
-
-The radius and ulna are always distinct bones in reptiles, and always
-freely movable on each other; they are usually shorter than the
-humerus, but in some springing and climbing reptiles they are quite as
-long.
-
-The carpus or wrist of reptiles consists primitively of eleven
-distinct, irregularly shaped bones, which articulate more or less
-closely with each other in three rows. Those of the first row, all true
-carpals, are known usually as the radiale, intermedium, ulnare, and
-pisiform, corresponding quite with the bones of the human wrist known
-as the scaphoid, lunar, cuneiform, and pisiform. The second row has
-but two bones, on the radial side, known as the centralia; while the
-third row has a bone to correspond to each of the metacarpals, five
-in number, and collectively known as the carpalia. Some or indeed all
-of these bones may be either absent or unossified, that is, remaining
-through life as nodules of cartilage. Seldom, however, are there less
-than nine bones in the carpus of reptiles.
-
-The metacarpals, like the digits, primitively were five in number, and
-seldom are there less, though the fifth is sometimes lost, and rarely
-also the first. They are more or less elongate bones, increasing in
-length from the first to the fourth, with the fifth usually shorter.
-The first and the fifth are usually more freely movable on the wrist
-than are the other three.
-
-The number of joints or phalanges in the fingers of all primitive
-reptiles is that of the modern lizards and the tuatera, that is, two
-on the first finger or thumb, three on the second, four on the third,
-five on the fourth, and three on the fifth. The crocodiles have one
-less phalange on the fourth digit; the turtles have usually two less
-on the fourth and one less on the third, that is, with precisely the
-same arrangement that is found in our own fingers and that of mammals
-in general, two on the thumb and three on each of the other fingers.
-As exceptions the river turtles have four bones in the fourth digit.
-And this mammal-like and turtle-like arrangement of the phalanges was
-that of those early reptiles, the Theriodontia, from which the mammals
-arose. The last or ungual phalange of reptiles is usually claw-like,
-that is, sharp, curved, and pointed, but sometimes it is more nail-or
-hoof-like.
-
-
-PELVIC OR HIP GIRDLE
-
-The pelvic girdle or pelvis in reptiles and higher animals consists
-of three bones on each side, often closely fused in adult reptiles
-and together known as the innominate bone. The upper or dorsal one of
-these three bones—that to which the sacrum is attached—is the ilium;
-the one on the lower or ventral side in front is the pubis; and that on
-the ventral side behind is the ischium. On the outer side, where these
-three bones meet, is a cup-like depression, sometimes a hole, called
-the acetabulum, for the articulation of the head of the thigh bone,
-homologous with the glenoid articulation of the pectoral girdle, which,
-as we have seen, was originally formed by three bones, the scapula,
-coracoid, and metacoracoid, the two latter bones, like the pubis and
-ischium, meeting in the middle line below. In all the primitive and
-early reptiles the pubis and ischium form a continuous plate of bone
-without holes in it, except a small one just below the acetabulum in
-the pubis, called the obturator foramen, and corresponding to the
-supracoracoid foramen of the coracoid. One may almost always recognize
-these two bones by the presence of the foramen. This “plate-like”
-condition of the pelvis has been lost in all late and modern reptiles
-by the appearance of a larger or smaller vacuity between the pubis
-and ischium, either paired, when it corresponds quite with the
-so-called obturator opening of mammals, or singly in the middle. This
-old-fashioned character, like the old-fashioned type of pectoral
-girdle, disappeared entirely about the close of the Mesozoic period,
-the Choristodera, described in the following pages, being the last of
-the kind.
-
-[Illustration]
-
-[Illustration: FIG. 22.—Pelvis of _Ophiacodon_: _A_ from side; _B_ from
-above; _pu_, pubis; _il_, ilium; _is_, ischium.]
-
-The ilium in reptiles usually has a more or less prolonged process
-or projection turned backward by the side of the anterior caudal
-vertebrae, but in those animals which walked erect on the hind legs,
-the dinosaurs and pterodactyls, as also some of the more erect-walking
-reptiles ancestral to the mammals, this process was directed forward,
-as in birds and mammals. The crocodilia, unlike all other known
-reptiles, have the pubes excluded from the acetabulum, and they do not
-meet in a median symphysis. This character alone will distinguish any
-crocodilian from all other reptiles. But there is some doubt as to the
-homology of the bones usually called pubes in the crocodiles. Some of
-the bipedal dinosaurs have the pubis forked, the anterior part directed
-downward and forward, and not meeting its mate in a symphysis, the
-posterior process long and slender, lying below the long ischium, as
-in birds. Indeed, when this peculiarity of the dinosaurian pubis was
-first discovered, it was thought to be an evidence of the immediate
-relationship of birds; its structure is now interpreted differently.
-
-
-POSTERIOR EXTREMITY
-
-The thigh bone or femur in reptiles, like the humerus, is variable
-in size and shape. Only in those reptiles that walked erect is the
-articulation of the head set off from the shaft of the bone by a
-distinct neck. In others the articulation is at the extreme top of
-the bone, since the thigh bones are habitually turned more or less
-directly outward from the acetabulum and the long axis of the body.
-The more or less pronounced rugosities at the upper end of the femur,
-for the attachment of muscles, called trochanters, are not easily
-distinguishable into the greater and lesser, as in mammals. Sometimes,
-as in the erect-walking dinosaurs, there is a more or less pronounced
-process on the shaft lower down, called the fourth trochanter, for the
-attachment of caudal muscles. On the back part of the shaft there is a
-ridge or line for the attachment of muscles, corresponding to the linea
-aspera of the mammalian femur. The projections at the lower end on the
-sides are called condyles.
-
-The two bones of the leg, or shin, are usually shorter than the thigh
-bones, though in running and leaping animals they may be quite as long
-or even longer. That on the inner or big toe side is called the tibia,
-and articulates with the distal end of the femur, but chiefly with its
-inner condyle. It has a more or less well-developed crest in front
-above for the attachment of the extensor muscles directly, since there
-never is a patella in reptiles, and only rarely sesamoid bones of any
-kind. The fibula, at the little-toe side of the leg, is usually more
-slender than the tibia, though it may be larger in swimming reptiles
-and even in some running forms. It disappeared in some of the later
-pterodactyls. Its upper articulation has a more gliding and somewhat
-rotary motion on the outer condyle of the femur, turning the foot
-outward in extension of the leg.
-
-[Illustration: FIG. 23.—Right hind foot of _Ophiacodon_: _a_,
-astragalus; _c_, calcaneum; _c1_, _c2_, centralia; 1, 2, 3, 4, 5,
-tarsalia.]
-
-The tarsus of reptiles differs from that of mammals, in that the
-chief movements of extension and flexion of the foot upon the leg
-occur within the tarsus rather than between the tarsus and leg bones.
-Primitively the tarsus of reptiles consisted of nine bones, two in
-the first row, two in the second, and five in the third, but in all
-modern reptiles the bones of the middle row and the fifth one in the
-third row have disappeared; in some lizards and turtles the two of
-the first row are fused. The two bones of the proximal row correspond
-quite to the astragalus and calcaneum, the astragalus articulating with
-both tibia and fibula proximally, the calcaneum with the latter only.
-The oldest known tarsus of any vertebrated animal, one from the Coal
-Measures of Ohio, has this structure, while in all the early amphibians
-there were three bones, the tibiale, intermedium, and fibulare. Some
-of the later swimming reptiles, like the ichthyosaurs and plesiosaurs,
-have apparently this amphibian structure, with three bones that are
-usually called tibiale, intermedium, and fibulare, but it is very
-doubtful indeed whether they are homologically the same. In the middle
-row two centralia are known in one or two very ancient reptiles, but
-for the most part there is only a single centrale, and even that is
-usually lost in later reptiles. The third row, like the third row of
-the carpus, had a distinct bone for each digit originally, but the
-fifth one was very soon lost and has never reappeared. The structure
-of the digits and number of bones are quite like those of the hands,
-except that the fifth toe has four bones instead of three, that is,
-the phalangeal formula was 2, 3, 4, 5, 4. As a rule in terrestrial
-reptiles, as in terrestrial mammals, the hind foot is more specialized
-than the front ones.
-
-Most reptiles have an external covering or exoskeleton of horny plates
-or scales or bony scutes. Horny scales are of course not preservable
-as petrifactions, though in many instances their actual carbonized
-remains or their impressions have been detected. Such information comes
-only rarely, though doubtless in the course of time we shall obtain
-it for most extinct reptiles. In the mosasaurs, for instance, very
-perfect impressions showing the detailed structure of the scales have
-been frequently found. Similar impressions were long since observed
-by Lortet in _Pleurosaurus_, and in not a few dinosaurs impressions
-of most wonderful perfection have been found. It is only in the water
-reptiles, probably, that all external coverings tended to disappear.
-
-Bony dermal plates or scutes are less common among reptiles, though by
-no means rare. The turtles, as is well known, are almost completely
-inclosed in such an exoskeleton, bones which have coalesced more or
-less to form a box or carapace within which the head and limbs may be
-withdrawn for protection. In the modern crocodilians also the body is
-more or less protected by small bone plates forming rows on the back
-and sometimes on the under side. The ancient phytosaurs had similar
-plates. Not a few of the dinosaurs were more or less covered with bony
-scutes and sometimes with large bony plates or spines. Some modern
-lizards have bony plates over the body instead of horny scales.
-
-
-
-
-CHAPTER IV
-
-THE AGE OF REPTILES
-
-
-Geologists divide the history of the earth, since life first appeared
-upon it, into four general eras, the Proterozoic, Paleozoic, Mesozoic,
-and Cenozoic, that is, into eras of first life, ancient life, middle
-life, and recent life. These divisions were made long ago by geologists
-when it was believed that extraordinary changes, great cataclysmic
-revolutions, marked their limits.
-
-With a fuller knowledge of the life of the past we know that evolution
-has been continuous and uninterrupted; possibly accelerated or retarded
-at times, but without break. Were the earth’s history to be written
-anew, with our present knowledge, and with an unbiased mind, it is
-very doubtful whether many of the time divisions would have the same
-limits that they have now—whether the Paleozoic would terminate with
-the Carboniferous, or the Permian, or the Trias, or whether indeed we
-should think it necessary to make any primary divisions whatsoever. In
-other words, our greater knowledge of living and extinct organisms,
-and of the rocks which contain fossils, has made the problems of
-classification much more complex than they seemed to be formerly.
-It is much easier to classify organisms or rocks, or anything else,
-when we know only a few isolated kinds—much easier to draw divisional
-lines. Geological history is like a volume in which pages, leaves, and
-even whole chapters either are missing or are printed in languages
-which we understand only imperfectly. Where the lost or unknown parts
-belong, the largest divisions may be made, and possibly such may have
-been epochs of unusual activity, of diastrophic changes which greatly
-accelerated organic evolution. No one can say just where the dividing
-line should be drawn between the rocks of Paleozoic and Mesozoic age,
-or between the Mesozoic and Cenozoic, for there is none; the most
-that we can hope for is to make the divisions everywhere in the world
-conform to those first made for local reasons.
-
-    ------------------------------------+----------------------------+----------------------------------------+-------
-            PALEOZOIC                   |         MESOZOIC           |               CENOZOIC                 |
-    ----------------------------+-------+--------+--------+----------+------+---------+-------+--------+------+-------
-           CARBONIFEROUS        |PERMIAN|TRIASSIC|JURASSIC|CRETACEOUS|EOCENE|OLIGOCENE|MIOCENE|PLIOCENE|PSTCNE| RECENT
-    ----------------------------+-------+--------+----+---+-----+----+------+---------+-------+--------+------+-------
-    PTEROSAURIA Pterodactyloidea|       |        |----|--████████████|      |         |       |        |      |
-                                |       |        |    |   |     |    |      |         |       |        |      |
-                Pterodermata····|       |        |███████ ?     |    |      |         |       |        |      |
-                                |       |        |    |   |     |    |      |         |       |        |      |
-    DINOSAURIA  Theropoda·······|       |   ███████████████████████████ ?   |         |       |        |      |
-                                |       |        |    |   |     |    |      |         |       |        |      |
-                Sauropoda·······|       |        |   █████████  |    |      |         |       |        |      |
-                                |       |        |    |   |     |    |      |         |       |        |      |
-                Orthopoda·······|       |        |? ███████████████████ ?   |         |       |        |      |
-                                |       |        |    |   |     |    |      |         |       |        |      |  Birds
-    BIRDS       ················|       |        |    | ██████████████████████████████████████████████████████████████
-                                |       |        |    |   |     |    |      |         |       |        |      |
-    CROCODILIA  Thalattosuchia··|       |        |    |███|     |    |      |         |       |        |    Crocodiles
-                                |       |        |    |   |     |    |      |         |       |        |      |
-                Eusuchia········|       |        | ███████████████████████████████████████████████████████████████████
-                                |       |        |    |   |     |    |      |         |       |        |      |
-    PARASUCHIA  Phytosauria·····|       |████████|    |   |     |    |      |         |       |        |      |
-                                |       |        |    |   |     |    |      |         |       |        |      |
-                Pseudosuchia····|       | ███████|    |   |     |    |      |         |       |        |      |
-                                |       |        |    |   |     |    |      |         |       |        |      |
-    RHYNCHO-    Rhynchosauria···|       |  ██████|    |   |     |    |      |         |       |        |     Sphenodon
-                                |       |        |    |   |     |    |      |         |       |        |      |
-      CEPHALIA  ················|       |    █████ █ █ █ █████::|::::|::::::|:::::::::|:::::::|::::::::|██████████████
-                Choristodera····|       |        |    |    |    |   ████    |         |       |        |      |
-                                |       |        |    |    |    |    |      |         |       |        |      |
-    THALATTOSAURIA··············|       |     ███|    |    |    |    |      |         |       |        |      |
-                                |       |        |    |    |    |    |      |         |       |        |      | Snakes
-                    Ophidia·····|       |        |    |    |    |   ██████████████████████████████████████████████████
-                                |       |        |    |    |    |    |      |         |       |        |      |
-    SQUAMATA        Lacertilia··|       |     ███|::::|::████?::|::███████████████████████████████████████████████████
-                                |       |        |    |    |    |    |      |         |       |        |      |
-                    Mosasauria··|       |        |    |    |    |██████     |         |       |        |      |Lizards
-                                |       |        |    |    |    |    |      |         |       |        |      |
-    PROTOROSAURIA···············|████████::::::::|::::|████|    |    |      |         |       |        |      |
-                                |       |        |    |    |    |    |      |         |       |        |      |
-    PROGANOSAURIA··············████     |        |    |    |    |    |      |         |       |        |      |
-                                |       |        |    |    |    |    |      |         |       |        |      |
-    ICHTHYOSAURIA···············|       |  ██████████████████████████|      |         |       |        |      |
-                                |       |        |    |    |     |   |      |         |       |        |      |
-    THEROMORPHA  Caseasauria····|███    |        |    |    |     |   |      |         |       |        |      |
-                                |       |        |    |    |     |   |      |         |       |        |      |
-                 Pelycosauria::███████████::::███|?   |    |     |   |      |         |       |        |      |
-                                |       |        |    |    |     |   |      |         |       |        |      |
-                 Diadectosauria█████    |        |    |    |     |   |      |         |       |        |      |
-                                |       |        |    |    |     |   |      |         |       |        |      |
-    COTYLOSAURIA Pantylosauria███       |        |    |    |     |   |      |         |       |        |      |
-                 Procolophonia··|█████████:::::::|::::|████|(Labidosauria)  |         |       |        |      |
-                                |       |        |    |    |     |   |      |         |       |        |      |
-                 Pareiasauria···|·██████|        |    |    |     |   |      |         |       |        |      |
-                 Microsauria    |       |        |    |    |     |   |      |         |       |        |      |
-                   ██████████████████   |        |    |    |     |   |      |         |       |        |      |
-    AMPHIBIANS                  |       |        |    |    |     |   |      |         |       |        |    Amphibians
-    ==================================================================================================================
-              Pleurodira········|       |     ████████████████████████████████████████████████████████████████████████
-                                |       |        |    |    |     |   |      |         |       |        |      |Turtles
-    CHELONIA  Cryptodira········|       |        |    |███████████████████████████████████████████████████████████████
-                                |       |        |    |    |     |   |      |         |       |        |      |
-              Trionychoidea·····|       |        |    |    |     |   █████████████████████████████████████████████████
-                                |       |        |    |    |     |   |      |         |       |        | River Turtles
-    SAUROPTERYGIA Nothosauria···|       |  █████ |    |    |     |   |      |         |       |        |      |
-                                |       |        |    |    |     |   |      |         |       |        |      |
-                  Plesiosauria··|       |  ██████████████████████████|      |         |       |        |      |
-                                |       |        |    |    |     |   |      |         |       |        |      |
-               Dromasauria      |  ████ |        |    |    |     |   |      |         |       |        |      |
-                                |       |        |    |    |     |   |      |         |       |        |      |
-               Dinocephalia     |  ████ |        |    |    |     |   |      |         |       |        |      |
-                                |       |        |    |    |     |   |      |         |       |        |      |
-    THERAPSIDA Anomodontia      |    ████████████|    |    |     |   |      |         |       |        |      |
-                                |       |        |    |    |     |   |      |         |       |        |      |
-               Therocephalia    |  ████ |        |    |    |     |   |      |         |       |        |      |
-               Theriodontia     |       |  █████ |    |    |     |   |      |         |       |        |      |
-                                |       |        |    |    |     |   |      |         |       |        |      |Mammals
-    MAMMALS·····················|·      |      ██|::::|:██████:::|:███████████████████████████████████████████████████
-    ----------------------------+-------+--------+----+----+-----+---+------+---------+-------+--------+------+-------
-              FIG. 23_a_.—Range of the Reptilia. Heavy lines indicate occurrence in North America.
-
-The periods of the Paleozoic era are the Cambrian, Ordovician,
-Silurian, Devonian, Carboniferous, and Permian, in the order as given;
-those of the Mesozoic era are the Triassic, Jurassic, and Cretaceous;
-those of the Cenozoic era, the Eocene, Oligocene, Miocene, Pliocene,
-Pleistocene, and Recent. As a relic of an old classification we still
-often divide the Cenozoic into two quite arbitrary divisions, the
-Tertiary and the Quaternary, the latter including the Pleistocene and
-Recent only. The same may be said regarding the limits of each of
-these periods as of the eras; the sole problem is to make each period
-contemporaneous throughout the world, an exceedingly difficult problem,
-because no faunas or floras have ever been the same over the whole
-earth. Indeed, with the exception of some of the lowliest and most
-generalized forms, or man himself, no species are the same throughout
-the earth today. Inasmuch as we must depend upon the fossils in the
-rocks for the determination of the ages, where none is quite the
-same in strata of remote localities the identification becomes very
-difficult or even impossible. Nor are the periods, as accepted, of
-equal or even approximately equal duration; the Cretaceous period, for
-instance, was longer than all the remainder of the Mesozoic, longer
-perhaps than all the time which has elapsed since its close.
-
-The earliest animals with a backbone, or rather the earliest that we
-call vertebrates—for some vertebrates have no vertebrae—began their
-existence, so far as we know, in late Ordovician times, as attested
-by fish bones in Ordovician rocks of Colorado and Utah. The first
-evidences of the existence of air-breathing vertebrates in geological
-history are footprints preserved in the uppermost Devonian rocks of
-Pennsylvania. We call them amphibian because they resemble footprints
-associated with amphibian skeletons in later formations, and because
-the foot itself is still the most important difference we know between
-fishes and the higher animals.
-
-[Illustration: FIG. 24.—Permocarboniferous landscape (adapted from
-Neumayr) with restoration of _Eryops_, a stegocephalian amphibian
-ancestrally allied to the reptiles; and _Limnoscalis_, a cotylosaur (in
-water).]
-
-In the rocks of the next great time division, the Mississippian, as we
-call it in America, corresponding more or less closely with the Lower
-or Subcarboniferous of other parts of the world, numerous footprints
-of amphibians have been discovered, but no fossil remains except a
-few from near its close in Scotland. From the Upper Carboniferous, or
-Pennsylvanian, however, not only numerous footprints but the actual
-skeletons, or impressions of skeletons, have long been known in Europe
-and America. Until recently all these footprints and skeletons were
-supposed to be exclusively amphibian. We are now almost sure that some
-of them belonged to reptiles of lowly type, the earliest coming from
-near the middle of the Pennsylvanian of Linton, Ohio. The amphibians of
-this period were, for the most part, salamander-like creatures of from
-a few inches to two or three feet in length. They all belong to the
-group collectively known as the Stegocephalia, except that very near
-the close of the period there appeared small, slender, small-legged
-aquatic forms which seem to be the ancient representatives of the real
-salamanders of modern times. Some of the Stegocephalians had become
-greatly specialized as legless, snake-like, or eel-like creatures.
-
-[Illustration: FIG. 25.—Restoration of _Seymouria_, the most primitive
-of known cotylosaur reptiles. From the Permian of Texas, about two feet
-long.]
-
-By the beginning of Permian times tremendous changes had taken place
-in the land life. The small amphibians of the Carboniferous types
-dwindled away, soon to disappear, and their places were taken by others
-of peculiar types, for the most part larger; and by many and diverse
-kinds of reptiles—water reptiles, marsh reptiles, land reptiles, and
-even climbing tree reptiles. From the uppermost Carboniferous and
-Lower Permian rocks of the United States more than fifty genera and
-twice that many species of amphibians and reptiles have been made known
-in recent years, and doubtless as many more will be discovered in the
-future. From other parts of the world the history of reptiles of the
-Lower Permian is yet scanty, two or three forms from South America, as
-many more from Africa, and a half-dozen or so from Europe are all; and
-of these very few are known at all well.
-
-[Illustration: FIG. 26.—_Captorhinus_, a cotylosaur reptile from Texas.]
-
-We classify all the known forms of reptiles from the Lower Permian
-under three or four orders, the Cotylosauria, Theromorpha or
-Pelycosauria, Proganosauria, and possibly the Protorosauria, but the
-classification is yet provisional, representing merely the present
-stage of our knowledge. The Proganosauria and Protorosauria, including
-distinctively aquatic reptiles, will be more fully described in
-the following pages. To give even a brief description of the more
-terrestrial reptiles of this, the earliest known reptilian fauna, would
-be beyond our purpose; the accompanying life restorations by the author
-of some of the more typical and better known forms, based upon nearly
-perfect skeletons, will suffice.
-
-From the reptiles and amphibians of the Lower Permian of Texas and New
-Mexico to the ichthyosaurs of the Middle Triassic of California there
-is a complete gap in the records of the land life of North America. We
-do not know what became of all the remarkable animals of the Permian.
-There are few traces of their descendants elsewhere known, unless it
-be in South Africa. From the Middle and Upper Permian of South Africa
-and Russia, a marvelous reptilian fauna has been made known in recent
-years. More than a hundred species of six or seven groups, and at least
-two orders have been described. Of these the Cotylosauria are the
-continuation of the American order, but include more specialized forms,
-the Pareiasauria and the Procolophonia, all of them, like the more
-primitive American forms, characterized by the imperforate temporal
-region. The Therapsida, likewise, seem to be the continuation of the
-American Theromorpha, so closely allied to them that it is difficult
-to draw a distinguishing line between them. On the other hand, these
-African reptiles merge through the Theriodontia into the mammals in the
-Triassic. They are all terrestrial, crawling reptiles, except a few
-which are described on a later page under the Anomodontia.
-
-[Illustration: FIG. 27.—Restoration of _Labidosaurus_, a cotylosaur
-reptile from Texas, about three feet long.]
-
-The records of the lower part of the Triassic period are scanty
-everywhere in the world, save perhaps in Africa. Before the close of
-the period, however, probably every important group of cold-blooded
-air-breathing animals had made its appearance in geological history,
-if we except the snakes; even the mammals had appeared, and possibly
-the birds. The Cotylosauria, Theromorpha, and Therapsida disappeared,
-the latter giving birth to the mammals; the nothosaurs and plesiosaurs,
-the ichthyosaurs, dinosaurs, crocodiles, phytosaurs, rhynchocephalians,
-lizards, and turtles have all left records of their existence in Upper
-Triassic rocks; and the pterodactyls had also, in all probability,
-begun their career, though none is surely known till the Jurassic.
-
-During Jurassic times all these orders of reptiles waxed prosperous
-and powerful, and branched out in many ways and in countless numbers;
-many new kinds of each appeared—the marine crocodiles, the quadrupedal
-dinosaurs, etc.—but no order or suborder, so far as we know,
-disappeared before its close. And this prosperity continued on into
-the Lower Cretaceous and for many even into the Upper Cretaceous. The
-largest dinosaurs disappeared in the Lower Cretaceous, so far as our
-knowledge goes, but the old-fashioned crocodiles continued on into
-the Upper, to give place to the new-fashioned kinds. The ichthyosaurs
-lingered on for a while on the western continent, but the mosasaurs
-appeared, and the plesiosaurs reached their highest evolution and
-continued to the end. The flying reptiles attained the zenith of
-their evolution, but disappeared before the close. The marine turtles
-attained the maximum of specialization and size. The upright-walking
-dinosaurs continued on unabated to the close of the period; and a new
-kind of dinosaurs appeared near the end.
-
-[Illustration: FIG. 28.—Restoration of _Dimetrodon_, a pelycosaur
-reptile from the Permian of Texas; about eight feet long.]
-
-With the opening of the next great era—the Cenozoic or Tertiary—the
-reptiles dwindled away to their present insignificant position, while
-the birds and mammals appeared in great numbers and varied forms. The
-Age of Reptiles was closed and the Age of Mammals had begun.
-
-The history of the reptiles during the Cenozoic is an uneventful one;
-they ceased their dominion upon land, in the water, and in the air.
-Their remains are scanty, for the most part, in the rocks of the
-Tertiary, and such as are known differ only in details from those now
-living. The land tortoises only, like the mammals of Oligocene and
-Miocene times, seized the opportunities of open prairies and prospered.
-A few of the late Mesozoic forms continued a short while into the
-Eocene. No new groups, perhaps few new families, came into existence
-during the greater part of this time; it was the age only of land
-tortoises and the poisonous snakes among reptiles.
-
-
-EXTINCT REPTILES OF NORTH AMERICA
-
-The oldest known fossil reptile of North America, or indeed of the
-world, is represented by a single specimen, lacking the skull, from
-black shales of Middle Pennsylvanian age overlying a coal seam at
-Linton, Ohio. The specimen was originally described as an amphibian,
-but was later recognized by Professor Cope as a true reptile. It was
-more fully described by the writer under the name _Eosauravus Copei_,
-who agreed with Cope as to its reptilian nature. Until the skull is
-discovered, however, the precise relationships of the animal must
-remain doubtful.
-
-The next later rocks that have yielded reptilian remains are those
-of Illinois and Texas formerly supposed to be of Permian age. Later
-evidence, furnished by invertebrates, however, seems to prove that
-the lowermost of the strata are of uppermost Carboniferous age. The
-Illinois deposits, so far as known, are of very limited extent,
-consisting practically of a single bone-bed in black shale in the
-immediate valley of the Kaskaskia River near Danville. The known
-fossils from this bone-bed—all isolated bones—are preserved in the
-museum of the University of Chicago, and include the types of several
-genera later recognized in the Texas deposits.
-
-The deposits of Texas, extending northward through Oklahoma to the
-south line of Kansas, are of considerable extent, for the most part
-lying along the Wichita River and its tributaries, north of Seymour,
-Texas. They are composed chiefly of red clays and sandstones of
-fresh-water or delta origin, perhaps eight hundred feet in total
-thickness. Beds of like character and yielding similar fossils are also
-known from northern New Mexico on the tributaries of the Chama River.
-Their chief characters, as well as restorations of some of the more
-noteworthy forms, have already been given.
-
-No vertebrate fossils are known in America from the Upper Permian and
-Lower Triassic. Marine limestones of Middle and Upper Triassic age
-of Nevada and northern California have yielded numerous remains of
-primitive ichthyosaurs, the only known remains of the thalattosaurs,
-and a few others of doubtful affinities, all of which have been
-described by Dr. Merriam. The Upper Triassic exposures, of considerable
-extent, occur between the Pitt River and Squaw Creek in Shasta County,
-California. Reptilian remains from the Middle Triassic are so far known
-only from the limestones of West Humboldt and New Pass regions of
-western and central Nevada.
-
-[Illustration: FIG. 29.—Restoration of _Varanops_, a theromorph reptile
-from the Permian of Texas; about four feet long.]
-
-Land reptiles of Middle and Upper Triassic age are known from many
-widely separated localities in the United States, but chiefly from
-the extensive “red beds” of the Rocky Mountain region. The fossils
-from these beds occur for the most part at least in the horizon called
-the Shinarump. Its age is usually considered to be Upper Triassic,
-but the character of the fossils seems to indicate possibly the
-Middle Triassic. Aside from the stereospondylian amphibians, the last
-of the Stegocephalia, the vertebrates from this horizon and these
-regions are chiefly Phytosauria. A few anomodonts, or what seem to be
-anomodonts—the only record of their occurrence outside of Africa—are
-known from Wyoming and Utah. And a single specimen from the Wind
-River red beds, described by the writer as _Dolichobrachium_, may
-represent reptiles allied to the dinosaurs. Phytosaur fossils of this
-horizon have been discovered in Utah, the Wind River Mountains, and
-near Laramie City in Wyoming; in southwestern Colorado; in western
-Texas; and in various places in New Mexico and Arizona. Doubtless when
-these fossiliferous beds are more thoroughly explored many new and
-interesting reptiles will be discovered.
-
-Phytosaur remains, probably of about the same age as the Rocky Mountain
-ones, have long been known from the Triassic of North Carolina.
-From somewhat more recent Triassic deposits in Connecticut and
-Massachusetts, several skeletons of small carnivorous dinosaurs, and
-various parasuchian remains have been described by Marsh, Lull, and
-Talbot. And these beds have long been famous in Massachusetts for their
-footprints, for the most part originally referred to birds, but now
-pretty well known to have been made by dinosaurs and amphibians.
-
-No vertebrate fossils of Lower or even Middle Jurassic age are known
-from North America. From the Baptanodon beds of Wyoming, limestones of
-about two hundred feet in thickness, four genera of plesiosaurs, the
-very peculiar ichthyosaur from which the beds take their name, and a
-few bones of an ancient crocodile are known.
-
-Immediately overlying the Baptanodon beds, the Morrison beds, of from
-two hundred to four hundred feet in thickness, probably of Uppermost
-Jurassic and Lowermost Cretaceous age, have yielded an exceedingly rich
-vertebrate fauna, consisting chiefly of dinosaurs. Discovered first in
-the vicinity of Morrison, Colorado, in 1877, hundreds of tons of bones
-have been collected from these beds for various museums. The dinosaurs
-include many genera of all three suborders, varying in size from that
-of a cat to some of the largest known land animals. Of other reptiles a
-very few jaws of a true rhynchocephalian, a fragment of a wing bone of
-a pterodactyl, numerous turtles, and crocodiles, only, are known. The
-beds are predominantly black-clay shales, intercalated with sandstones,
-and all are of fresh-water origin.
-
-From beds definitely known as Lower Cretaceous (Trinity) in Oklahoma,
-a few bones of a sauropod dinosaur are known, and from nearly
-corresponding rocks in southern Kansas, plesiosaurs, crocodiles,
-turtles, and carnivorous dinosaurs are known from sparse remains.
-Doubtless the Potomac beds of Virginia, which have yielded bones of
-various dinosaurs, are also of Lower Cretaceous age.
-
-[Illustration: FIG. 30.—Restoration of _Casea_, a theromorph reptile
-from the Permian of Texas, about four feet long.]
-
-With the exception of a single vertebra of doubtful affinities and
-the cast of a turtle-shell no vertebrate fossils have ever been
-discovered in the extensive sandstones of Dakota age, the lowermost
-of the Upper Cretaceous. From the next horizon above the Dakota, the
-Benton Cretaceous, chiefly marine limestones, at least three genera
-of plesiosaurs are known from Kansas, Texas, and Arkansas, with two or
-three more from the limestone shales of Wyoming. A few specimens of
-armored dinosaurs, two genera of ancient crocodiles, nearly the last of
-their kind, some marine turtles, and a few vertebrae of ichthyosaurs,
-the last of the order known anywhere in the world, are also known from
-the Benton Cretaceous of Wyoming.
-
-Continuous with the Benton limestones above in Kansas are the famous
-beds of Niobrara chalk; perhaps no fossil deposits in the world are
-more famous. Exposures covering hundreds of square miles in western
-Kansas, almost pure chalk, have furnished fossil-hunters during the
-past forty years literally thousands of specimens of mosasaurs,
-hundreds of pterodactyls, and scores of plesiosaurs and marine turtles,
-in addition to the famous birds with teeth and countless fishes of
-diverse kinds. Two or three specimens of spoon-billed dinosaurs have
-been found in these deposits, but no other reptiles of any kinds. Beds
-of like age in Colorado and New Mexico have furnished a few specimens
-of mosasaurs.
-
-From the marine beds of Fort Pierre age, next above the Niobrara in the
-west, have come some excellent specimens of two genera of mosasaurs,
-three or four forms of plesiosaurs, a few pterodactyls, the largest of
-all marine turtles, and still fewer specimens of dinosaurs, in Kansas,
-South Dakota, Wyoming, and Montana. From deposits of approximately like
-age in Mississippi, Alabama, and New Jersey, many incomplete specimens
-were found years ago of mosasaurs, plesiosaurs, and turtles, the last
-of the amphicoelian crocodiles, the first of the procoelian crocodiles,
-and the famous specimen of _Hadrosaurus_ which served for the Hawkins
-restoration, the first attempt of its kind.
-
-From the uppermost Cretaceous beds of America, the Lance, Judith
-River, or Belly River beds as they are variously called, have come
-the remains of a marvelous reptilian fauna. These beds may be grouped
-together though not all contemporaneous, and there is dispute about
-their age, some excellent paleontologists insisting that the uppermost
-are really of Eocene age. From Colorado east of Denver, from eastern
-Wyoming, from Montana, and especially from the vicinity of Edmonton
-in Canada, as also occasionally in western Texas and New Mexico,
-have come many marvelous specimens of dinosaurs, huge bipedal
-carnivorous dinosaurs, great spoon-billed aquatic dinosaurs, armored
-stegosaurian dinosaurs, and many kinds of the great horned dinosaurs,
-the Ceratopsia, so far known only from these beds. Here at the very
-close of the Age of Reptiles, at the close of the Age of Dinosaurs,
-are found the ultimate specializations of all the chief groups of
-dinosaurs except the long-necked quadrupedal dinosaurs which gave up
-the ghost in Lower Cretaceous times. Many were provided with horns and
-spines, some indeed seemed to have bristled with spines throughout,
-a sure sign that they were approaching the end of their career. The
-modern type of crocodiles had usurped the ancient forms of the early
-Cretaceous, and reached the largest size of their race perhaps, though
-but few specimens are known. Here also in these beds we find the
-first representatives of lizards and snakes in America, though snakes
-have been described from earlier strata, perhaps, in Brazil. Those
-archaic, old-fashioned rhynchocephalians described on a later page as
-the Choristodera appeared also for the first time in these beds, and
-persisted for a little while in the Eocene, in Europe and America. And
-with all these there has very recently been described the last of the
-plesiosaurs, whose race went out with the dinosaurs at the very close
-of the Mesozoic. It is needless to say that the turtles also occur,
-for, as a general rule, wherever vertebrate fossils are found, in rocks
-of the land or the sea, marine or fresh-water, there will be some bones
-of turtles among them.
-
-With the beginning of the Cenozoic the record of the reptiles
-becomes relatively scanty in America. In the warm waters of the old
-Eocene lakes and rivers of Wyoming lived countless crocodiles, true
-crocodiles of modern aspect and of large size. But, as the climate
-of North America grew progressively colder, the crocodiles retreated
-to the south, till, in the Oligocene, the scanty remains of the last
-crocodiles are found in the American Tertiary. On the other hand, as
-the open lands appeared toward the close of the Eocene, and in the
-Oligocene and Miocene, the land tortoises throve and grew greatly in
-size. In the Bad Lands of South Dakota one may see their remains in
-almost incredible numbers. And in equally great numbers are these land
-tortoises, in shape much like the common box tortoise of today, but
-vastly larger, found in the rocks of the late Miocene or early Pliocene
-age in western Kansas. And these are the last records of the big
-tortoises in North America; their descendants are perhaps yet living in
-the Galapagos Islands.
-
-The history of the lizards and snakes, the only other reptiles found
-in the Cenozoic rocks of America, is very brief. A few specimens from
-the Lower Eocene of Wyoming; a few skinks and amphisbaenas from the
-Oligocene Bad Lands of South Dakota, and some bones of a python-like
-snake in the early Eocene of Wyoming are about all that we know of the
-Squamata in the Tertiary. Doubtless snakes and lizards were just as
-abundant then as now, though but few were preserved, for they are and
-always have been distinctly terrestrial animals, that only by accident
-fell into places where they could be fossilized.
-
-The author has collected reptile bones from nearly all of the horizons
-here mentioned and believes that the list is complete.
-
-
-
-
-CHAPTER V
-
-ADAPTATION OF LAND REPTILES TO LIFE IN THE WATER
-
-
-In the never-ceasing struggle for existence all forms of life upon the
-earth, whether consciously or unconsciously, are continuously striving
-for improvement; striving to flee from adverse environments, or to
-adapt themselves better to those which must be endured; to escape
-their enemies, or to find means whereby they may withstand them; to
-find more or better food, or to prevent others from despoiling them
-of what they have. There is always more or less of unrest, more or
-less of discontent, if such terms may be used of the lower organisms.
-It sometimes happens with groups of organisms that by reason of
-unusual or extraordinary traits they become so perfectly adapted to
-their environments, to their surroundings, or so easily adaptable to
-changes in their environments, that they remain for long ages securely
-protected and little changed. But, as with man himself, improvement is
-usually the result of adversity—adversity which stimulates but does not
-destroy. And the word improvement, translated into biological language,
-means simply specialization, that specialization which adapts the
-organism better to its mode of life, which fits it the better to excel
-its less ambitious or less capable competitors. No animals or plants
-are perfect; if they were, there would be no advancement, no struggle.
-If all physical conditions stood still, or remained uniform, perhaps
-life would stand still, but conditions never have and never will stand
-still, and life must change to meet changed conditions.
-
-Thus it is that which makes life easier, which lessens the dangers
-of destruction, which insures the continued prosperity of the race,
-is seized upon and utilized by all plants and animals, so far as
-possible. As said long ago by Tennyson,[2] the first law of life is
-not the preservation of self, but the prosperity of the race. Whatever
-the causes may be whereby the offspring are better adapted to conquer
-in the struggle for existence, whatever may be the laws governing
-changes and specialization, whether heredity, Mendelism, mutation,
-natural selection, or Lamarckism, we call the process evolution.
-
-[2]    Are God and Nature then at strife,
-       That Nature lends such evil dreams?
-       So careful of the type she seems
-       So careless of the single life.—_In Memoriam_, lv.
-
-To escape from the severe competition of the overcrowding animals
-of the sea, some of those creatures we call fishes long ago became
-air-breathers and took possession of the unoccupied land. From among
-the myriads which were driven into unbreathable water, by accident or
-by their enemies, or led there in the search for more easily acquired
-or better food, some survived and found that the oxygen of the air was
-quite as breathable as that of the water. Steadily their progeny became
-better and better adapted to the unusual life until they ceased to be
-fishes and became amphibians, from which have arisen in like manner all
-the reptiles and birds and mammals that live or have lived upon the
-earth.
-
-With more and better powers, developed under better opportunities, not
-a few of these descendants have repeatedly sought safety from their
-newly acquired enemies of the overcrowded land, or a better supply of
-food in the sea; gradually, perhaps incidentally at first, as we shall
-see is the case with some lizards today, but later with increased
-adaptation to their new surroundings, they become truly sea or water
-animals, no longer able to live upon the land. In these changed
-conditions and with concomitantly changed habits they never reverted to
-the primitive condition of fishes, never became water-breathing animals
-again, for that would be actual retrogression, a seeming impossibility
-in evolution. Nor indeed does it seem possible that a land creature
-after its reversion to water life ever can return to the land again.
-
-A fish through long ages of evolution has become well adapted to its
-environments; its shape is the best for speed or varied evolutions in
-the water; its teeth and mouth-organs are best suited for the food it
-requires. Now it is evident that if animals of very different habits
-and form should go back to the water and seek to compete with creatures
-already well adapted to their surroundings, they must, so far as
-possible, acquire like forms and like habits. And any improvement on
-such forms and habits that their higher development permits them to
-attain will of course be of advantage in their competitive struggles.
-A fish makes most use of its tail fin for propulsion. It follows
-that a land animal seeking to compete with it under like conditions
-must acquire a tail fin or some other organ which subserves its
-purpose as fully. The body fins are of little use to a fish, save for
-equilibration, for preserving its position, for stopping quickly, or
-for changing the direction of its movements quickly—very different
-functions from those of the corresponding organs, the limbs, of higher
-vertebrates. There are few better examples of predaceous, fish-eating
-fishes than the common gar-pike of our rivers, fishes with a slender
-body covered with very smooth scales, a strong tail, a short neck, and
-long jaws armed with numerous slender and sharp teeth. Such a fish,
-darting into a school of smaller fishes, by quick, sudden changes of
-movement, actively opening and closing its jaws, is sure to seize some
-of its sought-for prey. In a direct trial of speed with its victims it
-would most likely be worsted.
-
-There have been many animals of high and low rank which in the
-past and present have gone back from a terrestrial existence to a
-life in the water, finding at last a congenial home away from the
-shores. Or, perhaps, like the monitor lizards of today, they have
-found temporary safety in the water when hard pressed by their land
-enemies, and finally found, not only protection, but an abundant
-supply of easily obtainable food therein. As in every vocation of
-life there have been many failures in such attempts, many partial
-successes only. But not a few have found abounding and enduring
-success and final prosperity—success that has led possibly to undue
-adaptation to surroundings, and to the acquirement of great size,
-for that has been the invariable end of water air-breathers of long
-duration—specializations which finally prevented them from meeting new
-exigencies. It seems to be a law of evolution that no large creatures
-can give rise to races of smaller creatures; and as we shall see, the
-largest sea-animals have been the final evolution of their respective
-races.
-
-There are no better examples of such success today, nor has there been
-in all the geological ages, so far as we know, more perfect examples
-of the adaptation of air-breathing animals to an aquatic life than the
-great whalebone whales. In Eocene times their ancestors were walking
-and running land animals; of that there can be not the slightest doubt,
-since we cannot conceive, as did the older naturalists, of their direct
-descent from the fishes while having all the essential structure of
-mammals, i.e., lungs, circulatory system, manner of breeding and
-rearing the young, etc. Of the living whales, or Cetacea, there are
-now in existence two very distinct types, so different from each other
-that some have supposed them to have been evolved from different
-types of land mammals. One of these is best exemplified by the great
-baleen whale, having a broad, short head and no teeth. It feeds upon
-crustaceans chiefly, which are strained from the water by the great
-fringe or net of “whalebone.” The other type is seen in the porpoise
-or dolphin. These cetaceans have numerous, pointed and recurved teeth,
-which they use as did many of the reptiles, hereinafter described, for
-the seizure and retention of fishes and other swimming animals. So
-great have been the changes in all these cetaceans, in the adaptation
-to an aquatic life, that we are almost at a loss to conjecture from
-what kinds of land animals they have descended. The great zeuglodont
-whales of early Tertiary times have long been thought to be a sort of
-connecting link between them and their land ancestors, and it is still
-probable that they were. The forms of zeuglodont whales that have been
-discovered in Africa within recent years bear so much resemblance
-in their skull and teeth to the contemporary carnivores, that many
-paleontologists think, with good reason, that they were descended from
-them, that is, from the ancestors of all our dogs, cats, weasels,
-bears, etc., of modern times. And we have much reason to believe that
-future discoveries will bring further and more decisive proof of their
-origin before many years have elapsed. The modern Sirenia, the dugongs
-and manatees, exclusively aquatic mammals, which feed upon seaweeds at
-the bottoms of shallow bays and harbors, or in the mouths of rivers,
-are now known, practically with certainty, to be the descendants in
-these same African regions of the earliest ancestors of our sheep,
-oxen, and horses, known so certainly that they are often classed with
-them, or at least with the elephants, which approach them in their
-ancestral line even more closely.
-
-A third type of living aquatic air-breathers is seen in the seals,
-sea-lions, etc. They are much less highly specialized, however, than
-the whales or sirenians, since they are still capable of considerable
-freedom upon land, which they recurrently seek for the breeding of
-their young. They still retain the primitive covering of hair, lost
-almost entirely by the cetaceans and sirenians and functionally
-replaced for the conservation of heat by a thick layer of blubber.
-Instead of losing the hind legs and developing the tail as a propelling
-organ like the whales, the seals encountered precisely the reverse
-experience. The hind legs have been developed into most efficient
-paddles or sculls, and the tail has been for the most part lost.
-They are fish-eaters, it is true, but they do not have the long jaws
-possessed by the porpoises and toothed whales.
-
-In the sea-otters, beavers, and even the muskrats, we have examples
-of less complete adaptation of land mammals to water life, the most
-of them showing the beginnings at least of structural adaptations
-similar to those of the seals. From an attentive examination of all
-these animals, living as well as extinct, which have attained partial
-or complete success as air-breathing water animals, we find certain
-laws existing, if we may call them such, which we may discuss a little
-in detail. As we have seen in the comparison of the whale with the
-seal, the methods of adaptation have not always been the same, and some
-recent writers have endeavored to classify aquatic animals under many
-groups, to which they have given learned technical names, most of which
-will not concern us here in dealing with the reptiles only.
-
-Beginning with the head, we find that all those reptiles and most of
-the mammals which have become aquatic fish-eaters have an elongated
-skull, or rather an elongated face. The jaws are long and slender, and
-the teeth are not only numerous but also sharp and slender, much like
-those of the gar-pike, indeed. It is remarkable, too, that in most
-such animals the external nostrils are situated, not at the extremity
-of the snout, as in all terrestrial mammals and reptiles, but far back
-near the eyes. In the whales this position of the nostril enables the
-animals to breathe without continuous muscular exertion while floating
-on the surface; that is, the nostrils are at the top of the head. In
-the sirenians, on the other hand, which live habitually at the bottom
-of shallow waters, coming to the surface to breathe only, the nostrils
-are situated so that they are the first to emerge, that is, they are
-near the front end. The crocodiles, with a more or less elongated face,
-as also the Choristodera, described farther on, are exceptions, since
-their nostrils are at the extremity of the snout. Both of these types,
-however, notwithstanding the elongation of the face, are only partly
-aquatic in habit, and in the crocodiles the breathing organs have
-undergone a strange modification in accordance with habits peculiarly
-their own, as will be explained later on. Whether this recession of the
-nostril toward the eyes can be explained in all cases by the peculiar
-breathing habits is, however, doubtful. Possibly in some cases, such as
-the phytosaurs, described later, the creatures used their long beaks
-to probe in the mud while breathing. Possibly the posterior position
-has been in some cases rather the result of the elongation of the face,
-leaving the nostrils behind in some forms, or carrying them forward in
-others. Nevertheless posterior nostrils always indicate more or less
-aquatic habits.
-
-In all the earliest reptiles, as we have seen, the neck was short,
-like that of their immediate progenitors, the ancient amphibians. The
-shoulders were close to the skull, with not more than two vertebrae
-that could be called cervical. It happens that most of the earliest
-reptiles, as we know them, were more or less amphibious in habit, and
-all of them were probably good swimmers; nevertheless in all likelihood
-reptiles began their career as a class with a very short neck. The
-earliest known distinctly terrestrial reptiles had a moderately long
-neck composed of six or seven cervical vertebrae. It may therefore be
-assumed with much probability that all later reptiles with a greater
-or less number of cervical vertebrae are specialized animals, so far
-as the neck is concerned. Most living reptiles have eight cervical
-vertebrae; a few have nine, and still fewer have but five. Birds may
-have as many as twenty-four, while all mammals, with two or three
-exceptions, have the primitive number seven. Among extinct reptiles,
-however, there were not a few with more numerous neck vertebrae, some
-having the enormous number of seventy-six.
-
-An ordinary fish has apparently no neck whatever, the trunk
-being seemingly attached to the head, nearly as in the primitive
-amphibians and primitive reptiles. It is evident that a movable neck
-of considerable length would not only be of no use to the swiftly
-swimming fish, but a positive disadvantage to it. The body is quickly
-and easily turned by the powerful tail fin, and a long neck could be
-of no use that the tail would not better subserve. It is therefore
-of interest to learn that, as a rule, aquatic animals of all kinds
-having a powerful propelling tail have also a short neck, acquired
-either by the loss of neck vertebrae, or, as in the mammals, by the
-shortening and coalescence of the normal number of seven. There are
-very few exceptions to this rule of a short neck and a long tail.
-Those strange little reptiles of Paleozoic times, the first that we
-know that returned to the water, the Proganosauria, have not only a
-long, flattened tail, but also an unduly elongated neck of from nine to
-twelve vertebrae.
-
-On the other hand, certain unrelated reptiles of the past, the
-dolichosaurs, nothosaurs, and plesiosaurs, with a short non-propelling
-tail, developed a long neck—sometimes an excessively long one in the
-plesiosaurs. The turtles, some of which have attained a high adaptation
-to water life, have invariably a short tail and a freely movable,
-relatively long neck, a neck which Dr. Hay tells us has increased
-in length from the beginning of their race by the simple elongation
-of the vertebrae, as in the giraffe, and never by the addition of
-vertebrae. We may then account it a rule that swimming animals with
-a long neck have a short tail, and those with a short tail have a
-long flexible neck. Even in the plesiosaurs there is some variation
-of the length of the tail in correlation with the neck. Short-tailed
-animals must necessarily propel themselves through the water by the aid
-of their legs, especially the hind legs. If one watches an actively
-swimming alligator he will observe that the front legs are folded or
-collapsed by the side of the body, while the hind legs, much bent,
-are used only slightly in propulsion. The animal swims by a marked
-sinuous or serpentine movement, like that of a snake upon land,
-extending throughout the tail and part of the body, at least. An animal
-propelling itself by its limbs could not move sinuously, and use its
-legs actively at the same time, and it is probable that the long neck
-has been evolved compensatorily.
-
-With this shortening of the neck and sinuosity of movement there is
-developed in every case a long trunk as well as a long tail. The trunk
-becomes more slender and cylindrical, more like that of a snake, with
-an actual increase of the bones composing it, reaching the great
-number of forty-three vertebrae in that most sinuous of all water
-reptiles with legs, _Pleurosaurus_ of the Protorosauria. And the tail,
-primitively having perhaps sixty or seventy vertebrae, may have as
-many as one hundred and fifty in the more typical aquatic forms. This
-elongation of trunk and tail must be of great advantage to the swimming
-reptile, just as the racing scull is a more perfect type of speedy
-craft than a flat-bottomed scow. Dr. Woodward has said that the fate of
-all fishes, if they continue their evolution long enough, is to become
-eel-like.
-
-Not only was the tail greatly elongated in swimming reptiles, but it
-was also more or less flattened. In the beginning of water adaptation
-the flattening was throughout the tail, as in the living alligators and
-crocodiles. As the adaptation to water life became more perfect, the
-flattening became more and more restricted to the extremity; that is,
-the flattening begins like that of a salamander and in the end becomes
-like that of a fish, a terminal fin. And some of the actual stages in
-the evolution of the fish-like fin have been observed by Dr. Merriam
-in the earlier and more primitive ichthyosaurs of California. In those
-animals swimming chiefly in a horizontal direction the tail fin has
-become like that of fishes, that is, vertical; but in those animals
-which use the tail chiefly for ascending and descending rapidly in the
-water the fin is developed in a horizontal position, examples of which
-are seen in the flukes of whales and sirenians.
-
-All animals living upon the land require firm articulations between the
-different bones of the skeleton, and especially between the vertebrae,
-for the support and control of the body. Among aquatic animals there
-is a strong tendency toward looseness of joints, with increasing
-flexibility. Fishes have the articular processes between the arches
-of the vertebrae feebly or not at all developed, and the centra or
-bodies of the vertebrae have thick pads of cartilage between them. Firm
-union between the vertebrae would restrict freedom of movement, and
-firmness is not required when the body is surrounded on all sides by
-water of nearly the same specific gravity as the body itself. And it is
-doubtless for the same reasons that the articulations of all strictly
-aquatic reptiles have for the most part become looser and less firm,
-especially those between the different vertebrae.
-
-The same looseness of articulation is also found in the ribs of
-aquatic animals. In most animals, and in all those which walk erect,
-like the mammals, each rib is firmly attached to the backbone by two
-distinct joints, the head and tubercle, with an interval between
-them. This double attachment prevents much in-and-out movement of the
-ribs and gives a firm support for the attachment of the muscles of
-respiration, as well as for those supporting the viscera. This firmness
-is unnecessary in animals living always in the water, and the ribs
-therefore in all aquatic animals tend to become single-headed and
-loose. The lower or capitular articulation has been lost in part, or
-almost wholly, in many cetaceans. It has been said that a whale cast up
-on land will die of suffocation, not for the lack of air, for it is an
-air-breathing animal like ourselves, but because it can no longer use
-its respiratory muscles attached to the loosely articulated ribs; it
-suffocates because the ribs collapse.
-
-As would be expected, the greatest modifications of structure in the
-adaptation of air-breathers to water life are found in the limbs. No
-other parts of the body have such different functions in water and on
-land as the limbs and fins. The limbs of a dog, or a cat, or a man
-are feeble organs for swimming in comparison with the fins of a fish,
-and if the land animal must compete with fishes to prey upon them for
-food it must acquire like swimming powers. As a matter of fact, the
-limbs of all typically aquatic air-breathing animals have lost nearly
-all external resemblance to the legs of walking and running animals,
-and have become more or less fin-like in function—fin-like in shape
-and function, but never fin-like in actual structure. No creature can
-go back and begin over again, any more than a man can again become a
-child with all its possibilities for improvement and development. If
-an animal cannot modify the organs it already possesses so as to adapt
-them to new and changed uses by the aid of evolutionary forces it must
-fail in the struggle. It can never acquire new material, never get new
-fingers and toes, new organs or parts of organs; all its possibilities
-lie in the improved and new uses it can make of the material which it
-received from its ancestors.
-
-The beginning of aquatic adaptation of the limbs lies in the membranous
-webs between the toes of frogs, salamanders, ducks, seal, otters, etc.,
-where the feet are used largely or entirely for propulsion through
-the water, in the absence of a propelling tail. And this membrane,
-in the majority of cases, is the extent of aquatic adaptation in
-air-breathing animals. In those animals, however, such as most of the
-reptiles described in the following pages, where the tail has developed
-as the propelling organ, the limbs lose to a greater or less extent
-their propelling function and become merely organs of equilibration
-and control. Of the two pairs of fins of fishes it is evident that
-the anterior ones have the more important equilibrational function;
-the hind ones have a much less important use as guiding organs; as
-a matter of fact, in not a few fishes the hind or pelvic fins have
-actually migrated forward to supplement the function of the pectoral
-fins. It is for these reasons that those animals best adapted of all
-for life in the water—the whales and sirenians—have lost the hind legs
-completely. In other tail-propelled air-breathers the hind legs have
-become progressively smaller and less powerful than the front ones. In
-all short-tailed water animals, however, where the legs, and especially
-the hind legs, have the important function of propulsion to subserve,
-they still retain the large size and firm connections with the body,
-examples of which will be seen in the seals, sea-otters, marine
-turtles, and plesiosaurs.
-
-Because the legs are no longer needed for the support or propulsion of
-the body in long-tailed air-breathers, their connection with the body
-becomes less and less firm, long before their entire disappearance. In
-animals using the legs for crawling or walking the bones of an arm and
-thigh are elongated, and the joints are always well formed, permitting
-varied, extensive, and firm movements. Just the reverse is the tendency
-in all those animals that propel themselves by the aid of the tail in
-the water, since here what is needed is broad, short limbs, not long
-and slender ones.
-
-Most reptiles have five digits on each hand or foot; the bones of the
-wrist and ankle are well formed, as in mammals, and the digits are
-elongate, with a very definite arrangement of the bones composing them,
-as already described, never exceeding five in any one finger or toe.
-
-In the paddles of water reptiles, as the limbs are usually called,
-the bones of the first segment, that is, the humerus and femur, are
-always greatly shortened in those having a propelling tail, and even
-in some with a short tail, such as the seals, and in a lesser degree
-in the sea-otters. On the other hand, in those animals which use the
-legs chiefly for direct propulsion these bones are elongated, as
-exemplified by the plesiosaurs and marine turtles. In all save the
-seals and their kind, and the otters, whose legs are used rather as
-sculls than as oars, the bones of the next segment, the radius and
-ulna of the front pair, the tibia and fibula of the hind pair, are
-always shortened, and one can tell the stage of aquatic adaptation, as
-exemplified, for instance, in the plesiosaurs and ichthyosaurs by the
-degree of shortening of these bones. Indeed, the first suggestion in
-any crawling animal of water habits is shown in the relative lengths of
-the epipodial bones, as these bones are called. Furthermore, cursorial
-or terrestrial habits are suggested by the relative size of the smaller
-bone of the leg, that on the little-toe side, the fibula. In birds,
-pterodactyls, and most running animals, it disappears in part or
-wholly. In swimming animals it tends to grow larger than the tibia, as
-will be conspicuously seen in the paddle of the mosasaurs.
-
-The bones of the wrist change in two ways: by becoming cartilaginous,
-as in whales and salamanders, or by becoming more firmly ossified
-and more closely united, as in the plesiosaurs. The digits always
-are elongated, often extraordinarily so, either by the elongation of
-individual bones or phalanges, or by the development of new bones.
-These new bones, when they occur, are new growths, not the reproduction
-of the old elements of fishes, and there may be as many as twenty
-such new elements or phalanges in a single digit. There is one marked
-exception among reptiles to this hyperphalangy, as the increased
-number of phalanges is called, and that is the turtles. As we have
-seen, in the elongation of the neck among turtles there never has
-been an actual increase in the number of vertebrae; so also in the
-elongation of the digits the normal number of three in each digit
-has never been exceeded, except among the river turtles, where there
-are four in the fourth digit—possibly a relic of original conditions
-rather than the beginning of hyperphalangy; but the individual bones
-have become greatly elongated. In living reptiles, birds and mammals
-of the land, the fifth toe is always shorter than the fourth. In the
-seals, the sea-otter, and to a less degree in the muskrat, the fifth
-toe has become elongated. And the elongation of this toe is the first
-and most decisive indication of a webbed foot of strong propelling
-power among the aquatic reptiles of the past, as exemplified especially
-by the proganosaurs. Finally, in one order of extinct reptiles, the
-ichthyosaurs, there has been an actual increase in the number of
-digits, in some to as many as nine in each paddle.
-
-In addition to all these modifications of the skeleton, the bones
-themselves tend to become softer and more spongy in aquatic animals.
-The bones of the whale, as is well known, are very spongy in texture,
-and those of the seals and sea-lions contain an unusually large amount
-of oily matter. So, too, the bones of the extinct water reptiles—of
-many of them at least—were more spongy than those of their land
-relatives; and this is due in part perhaps to their lessened use as
-muscular supports, in part perhaps to the necessity of a lessened
-specific gravity. As a rule sea-animals need to be of the same specific
-gravity as the water in which they live, or a little less. The bones
-of the living sirenians, the manatees and dugongs, so far from being
-light and porous, are unusually dense and solid. The sirenians live
-habitually at the bottom of shallow waters, feeding upon vegetable
-growths; and doubtless their bottom-feeding habits account for the
-solidity of the bones. A whale would float to the top, while a
-dugong would sink to the bottom, on the relaxation of all muscular
-movement. And we shall see that certain reptiles in the past had in all
-probability like bottom-feeding habits, because of the solidity of the
-bones of their skeletons.
-
-Many birds and fishes have a peculiar ossification of the usually
-tendinous outer covering of the eyeball, called the sclerotic
-membrane. These ossifications form a flattened or somewhat projecting
-conical bony ring about the pupil of the eye. The individual bones
-are flat and more or less imbricated plates, with some motion between
-them. Accommodation for vision in reptiles, birds, and fishes is not
-the simple process that it is in mammals, where it is controlled
-by simple ciliary muscles which compress the lens, causing it to
-assume a more spherical or a more flattened form, thus changing the
-focus. In reptiles accommodation is effected by the compression of
-the eyeball by means of external muscles, elongating it and causing
-its front part to expand or project. The imbricated sclerotic plates
-permit this expansion and contraction of the eyeball. Under great
-internal or external air pressure the cornea, the only unprotected
-part, must necessarily change its contour unless some compensatory
-force is brought to bear to counterbalance it; and this doubtless was
-the function of the sclerotic plates so commonly present in aquatic
-reptiles.
-
-Among terrestrial reptiles there are not a few examples of the
-ossification of such sclerotic plates, notably among the skink
-lizards. Every known form of extinct reptiles of aquatic habit had
-them, and even some of the subaquatic dinosaurs, like _Diplodocus_ and
-_Trachodon_. One may say with assurance that it is impossible for any
-reptile to become thoroughly adapted to aquatic life without acquiring
-large and strong sclerotic plates.
-
-Most land reptiles are or were covered by horny scales or bony plates;
-the pterodactyls are the only order of terrestrial reptiles with
-no such covering of which we have any evidence. Such coverings are
-wholly unneeded for animals living in the water. Not only are they
-unnecessary, but the increased resistance to the water would be more or
-less detrimental to rapid swimming. It is for these reasons doubtless
-that bony plates or horny scales disappeared for the most part from the
-skin of all truly aquatic reptiles and mammals.
-
-The foregoing are the chief acquired characteristics of aquatic
-air-breathing animals and especially aquatic reptiles in adaptation
-to their new mode of life. The resemblances, sometimes striking,
-thus brought about in animals of very different origin and remote
-relationships have often been mistaken for evidences of kinship,
-that is, direct inheritance from common ancestors. Such acquired
-resemblances in unrelated animals are known as parallel or convergent
-evolution. It has often been difficult to distinguish between
-convergent evolution and direct evolution, and difficulties still
-perplex and trouble the student of natural history in every branch
-of life. Not till all such problems are solved can we hope to attain
-the true classification of animals and plants. The whales a century
-ago were considered merely breathing fishes; the ichthyosaurs until a
-quarter of a century ago were supposed to be the direct descendants of
-fishes; lizards and crocodiles were grouped together in a single order;
-and salamanders were called reptiles not very long ago.
-
-Perhaps the reader will be able from the foregoing to understand
-and appreciate better some of the difficulties that confront the
-paleontologist in his attempts to solve the problems of past life; to
-understand why he sometimes makes mistakes, for he has by no means
-yet learned all the permutations of the skeleton in any class of
-vertebrates, and is not sure that the laws he accepts are not subject
-to modifications and exceptions. If he is truly scientific he hesitates
-long in prophesying or conjecturing.
-
-
-
-
-CHAPTER VI
-
-SAUROPTERYGIA
-
-
-Very scanty are the early human records of those strange reptiles
-known as the plesiosaurs. Were one to search through the many works
-published during the latter half of the seventeenth century and all
-of the eighteenth, devoted to “lapides petrifacti,” “figured stones,”
-“reliquia diluvii,” or by whatever other fanciful names fossils were
-known, here and there he would probably find descriptions and figures
-of bones of these reptiles. It would hardly seem that plesiosaurian
-bones could have been overlooked by the curious, so abundant are they
-in many places. But there is no such history of the early discovery
-of the plesiosaurs as there is of the ichthyosaurs and mosasaurs.
-Their birth into human history was very formal and proper, under
-the ministrations of a learned doctor of science, the renowned
-Conybeare, of whom we shall speak again. It was he, who with De la
-Bêche, late Director of the British Geological Survey, described for
-the first time, in 1823, one of these reptiles, to which he gave the
-name _Plesiosaurus_, meaning “like a lizard.” He distinguished the
-plesiosaurs from ichthyosaurs, with which it is possible that they had
-previously been confounded, and gave a good description of considerable
-material. Cuvier, a little later, gave a more complete description
-of the same remains which had served Conybeare and De la Bêche for
-their original description, and for the first time made it evident
-that fossil plesiosaurs were widely and abundantly distributed over
-the earth. The closing sentence of Cuvier’s chapter devoted to the
-discussion of these creatures in his _Ossemens Fossiles_ was really
-prophetic, not only of the many discoveries of the plesiosaurs yet to
-be made, but of all other extinct animals as well: “I doubt not that,
-in a few years it may be, I shall be compelled to say that the work
-which I have today finished, and to which I have given so much labor is
-but the first glimpse of the immense creations of ancient times.”
-
-[Illustration: FIG. 31.—Restoration of _Plesiosaurus guilelmi
-imperatoris_ (left figure) and _Thaumatosaurus victor_ (right figure),
-Liassic plesiosaurs. (From E. Fraas.)]
-
-In quick succession there followed many other discoveries of
-plesiosaurs, not only in England but elsewhere in Europe. The famous
-English anatomist and paleontologist, Sir Richard Owen, to whom we
-owe, perhaps, more than to anyone else our present knowledge of these
-animals, the eccentric Hawkins of England, the learned von Meyer of
-Germany, and, in later times, more especially Seeley and Andrews of
-England, Fraas of Germany, Bogalobou and Riabanin of Russia, as well
-as many others, have brought to light during the past century many and
-varied forms of those sea-reptiles. Blaineville in 1835 gave to the
-plesiosaurs an ordinal rank under the class Ichthyosauria, and even the
-astute Owen in 1839 united them with the ichthyosaurs as a suborder of
-his Enaliosauria, or “sea-saurians.” He called them Sauropterygia, or
-“reptile-finned,” and these terms, Enaliosauria, Ichthyopterygia, and
-Sauropterygia, have long persisted in works on natural history because
-of the prestige of Owen’s name. As we shall see later, the plesiosaurs
-are really of remote kinship to the ichthyosaurs, and there is no such
-natural group as the Enaliosauria. It often takes years to distinguish
-between apparent and real relationships among living organisms, and
-both of these groups of sea-saurians have had a sorry experience in the
-treatment they have received from nomenclators.
-
-Perhaps because of the writings of Dean Buckland in his famous
-_Bridgewater Treatise_, in large part a theological disquisition,
-though of real scientific merit, the ichthyosaurs and plesiosaurs
-early became widely and popularly known, and, even to this day, these
-reptiles, together with the dinosaurs, first made known by Rev. Dr.
-Mantell, are often supposed to be the most typical and horrid of
-monsters. Many and fabulous are the tales that have been told of
-them in literature both grave and gay. The preacher adduced them as
-evidences of the great world-catastrophe told in biblical history, and
-the German student sings of them to the tune of the “Lorelei”:
-
-    Es rauscht in Schachtelhalmen, verdächtig leuchtet das Meer;
-    Da schwimmt mit Thränen in Auge ein Ichthyosaurus einher.
-    Ihn jammert der Zeiten Verderbniss, denn ein sehr bedenklicher Ton
-    War neuerlich eingerissen in der Liasformation.
-    Der Plesiosaurus, der alte, der jubelt in Saus und Braus;
-    Der Pterodactylus selber flog jungst betrunken nach Haus.
-    Der Iguanodon, der Lümmel, wird frecher zu jeglicher Frist;
-    Schon hat er am hellen Tage die Ichthosaura geküsst.
-
-We now know that they were not the monsters of horrid mien that they
-were once supposed to be: the largest plesiosaurs, were they living
-today, would find unopposable foes in the vicious and cruel crocodiles.
-They were relatively stupid and slow, cruel enough to the smaller
-creatures, but of limited prowess. But in structure and habits they are
-among the most remarkable of all the animals of the past or present.
-
-Although their remains are among the most abundant and widely
-distributed of all fossil reptiles, the plesiosaurs as a whole are less
-perfectly known than either the ichthyosaurs or the mosasaurs, and it
-has been within a comparatively few years only that an approximately
-complete knowledge of any form has been obtained. This is partly due
-to the fact that the order comprises vastly more kinds, more species,
-genera, and families than does any other order of marine reptiles;
-partly because their remains, though widely distributed over the earth,
-and in rocks of many geological epochs, are seldom found completely
-preserved; usually specimens comprise only a few bones or single bones,
-and complete skeletons are rare. Were there but few kinds, the many
-specimens discovered would mutually supplement each other, finally
-completing our knowledge; but the fragments of many kinds only add to
-our confusion. Nevertheless, because the plesiosaurs lived so long in
-geological history, their remains are found in rocks of many different
-kinds, and since it is improbable that any of them had great specific
-longevity, it is very probable that all these described species, or
-most of them, often made known from single bones, will eventually be
-found to be distinct, and that many more will be added to them. It does
-not seem improbable that within the next forty or fifty years not less
-than a hundred species of plesiosaurs will have been discovered in
-North America alone. At the present time perhaps that many have been
-described from the whole world.
-
-When Blaineville gave the name Plesiosauria to the aquatic reptiles
-described by Conybeare, Cuvier, and others, he had no knowledge of
-others of an intermediate kind between them and land reptiles. His
-group-term then can be properly applied only to the truly aquatic
-forms, and Owen’s name Sauropterygia becomes available in a wider
-sense to include all the known types belonging to the order of which
-the plesiosaurs form a part. Of this order then there are two clearly
-marked divisions or suborders, the Plesiosauria and the Nothosauria,
-the former having a complete aquatic adaptation, the latter only
-a partial one. While the two suborders are evidently allied, some
-authors have suggested that their differences are only familial; others
-have thought that they are really orders. We shall see how close the
-relationships are.
-
-
-PLESIOSAURIA
-
-It was Dean Buckland who facetiously likened the plesiosaurs to a snake
-threaded through the shell of a turtle, and the simile was not an
-inapt one in his day. The vernacular designation of them—long-necked
-lizards—conveys the same impression of their chief peculiarity, but the
-name is less applicable than it once was, since recent discoveries have
-brought to light forms with a relatively short neck.
-
-Though the plesiosaurs are nearly perfectly adapted to an aquatic
-life, the adaptation was, in many respects, of a very different kind
-from that of the ichthyosaurs—so very different that we have not yet
-quite finished conjecturing as to the habits of the living animals. As
-already suggested in the popular name, the most striking characteristic
-of the typical plesiosaurs, the one which suggested to Buckland his
-frequently quoted simile, is the ofttimes enormously long neck,
-proportionately longer than that of any other known creatures of the
-past or present. In other truly aquatic animals the neck is actually
-shortened in the acquirement of a fish-like shape, and the number of
-bones composing it reduced. In the Sauropterygia the neck is usually
-longer than any truly land animals ever possessed, the longest-necked
-forms having as many as seventy-six vertebrae in the cervical region.
-The elongation of the neck among mammals is always due to an increase
-in the length of the individual bones, never to an increase in the
-number from seven, with but a single exception—a South American sloth
-which has nine cervical vertebrae. The long neck of birds is due both
-to an increase in the length of the individual vertebrae and to an
-increase in their number, to as many as twenty-one. But the elongation
-of the neck among plesiosaurs was very variable indeed; sometimes it
-was ten or twelve times the length of the head, at other times it was
-even shorter than the head. And the number of bones composing it was
-also extremely variable, scarcely any two species having the same,
-the known extremes being seventy-six and thirteen. In _Elasmosaurus
-platyurus_, for instance, the longest-necked plesiosaur known, the head
-was two feet in length, the neck twenty-three, the body nine, and the
-tail about seven; on the other hand, in the shortest-necked plesiosaur
-known, _Brachauchenius Lucasi_, the head was two and one-half feet
-in length, the neck less than two feet, and the body about five; the
-length of the tail is unknown.
-
-[Illustration: FIG. 32.—Skeleton of _Trinacromerum osborni_, a
-Cretaceous plesiosaur, as mounted in the University of Kansas Museum.]
-
-Not only was the number of vertebrae so extraordinarily increased in
-many plesiosaurs, but in the longest necks the vertebrae themselves, as
-in birds, were more or less elongated, especially the posterior ones,
-which may be six or seven times the length of the anterior ones. Not
-only was the neck of such great length in many plesiosaurs, but it also
-tapered very much toward the head.
-
-The vertebrae are always biconcave, but the cavities are shallow,
-saucer-like, sometimes almost flat at each end, and very different from
-the conical fish-like cavities of ichthyosaurian vertebrae.
-
-[Illustration: FIG. 33.—Restoration of _Elasmosaurus platyurus_, an
-Upper Cretaceous plesiosaur.]
-
-Often the vertebrae are short throughout the vertebral column;
-sometimes the posterior cervicals and the dorsals are elongated and
-very robust. The trunk or body proper was never much elongated in the
-plesiosaurs, having only from twenty-five to thirty vertebrae. The
-tail was always shorter than the trunk, and it tapered rapidly to the
-extremity; in some specimens it has been observed to turn up slightly
-near the extremity, as though for the support of a small terminal fin.
-
-[Illustration: FIG. 34.—Cervical vertebrae, from the side and behind,
-and dorsal vertebra from in front of _Polycotylus_, a Cretaceous
-plesiosaur: _az_, anterior zygapophysis; _pz_, posterior zygapophysis,
-_r_, _r_, _r_, cervical ribs; _d_, articulation of dorsal rib.]
-
-The ribs in the cervical region are short, but so locked together
-posteriorly as not to permit much lateral motion. They are sometimes
-double-headed in the neck, sometimes single-headed, but both heads
-when present articulate or are attached to the body of the vertebrae,
-distinguishing them at once from those of other animals, except the
-ichthyosaurs. In the dorsal region the ribs are attached high on the
-arch to the extremity of the stout transverse processes by a single
-head, very much as they are in some cetaceans, and quite unlike the
-condition in any other known reptile. They end freely below, having
-no attachment to a breast bone or other bony parts. Because of their
-shape and position as frequently found, the body in life must have been
-flattened from above downward, and broad; indeed, this shape is quite
-certain because of the very broad expanse of the coracoids, between the
-articulations of the front legs.
-
-[Illustration: FIG. 35.—Pectoral girdle of _Trinacromerum_ from above:
-_ic_, interclavicle; _cl_, clavicle; _sc_, scapula; _c_, coracoid.]
-
-The shoulder-girdle or pectoral arch is strangely unlike that of any
-other reptiles. There is no breast bone, since the breast bone is a
-comparatively late development in reptiles, not appearing, probably,
-until after the plesiosaurs had begun their existence. Taking the
-place of the sternum, the very large and broad coracoidsjoin each
-other in the middle, forming a sort of subdermal armor on the under
-side of the body in front. In some of the largest plesiosaurs these
-two bones measured together about six feet in length by four in
-width. Though so very large they are thick only in front between the
-articulations of the forelegs. The shoulder-blades are much reduced
-in size and are extraordinarily modified. The blade proper, that is,
-that part extending backward and upward, is narrow and small, affording
-but little surface for the attachment of muscles. On the inner side,
-extending toward the middle in front of the coracoids, there is another
-projection, often broad and large, to which was attached the clavicles
-when present, and often this projection met its mate of the opposite
-scapula in the middle in front of the coracoids in a broad union. The
-clavicles or collar-bones are small and thin, and sometimes absent;
-they also are united in the middle posteriorly with the coracoids when
-the scapula did not intervene. And the interclavicle also is sometimes
-wanting. Altogether the pectoral bones form a very large, broad, and
-concave trough inclosing the whole of the under side of the anterior
-part of the body. This extensive surface must have furnished attachment
-to stout and strong muscles controlling the downward and inward motion
-of the paddles.
-
-There is a well-developed sacrum of three vertebrae for the support
-of the pelvis or hip bones. The reason for its persistence in animals
-so thoroughly adapted for life in the water will be understood later.
-The ilium is slender; it was attached to the sides of the sacrum by
-ligaments, only, not forming a firm union, but strong nevertheless.
-The pubes and ischia, the other bones of the pelvis on the under side
-of the body, like the corresponding bones of the pectoral girdle, were
-enormously enlarged, forming great flat, bony plates.
-
-Besides these large bony plates of the shoulder and pelvic girdles,
-the short abdominal region was inclosed by numerous series of strong
-ventral ribs, that is, overlapping rod-like bones on each side,
-connected with a central piece. It will be seen that the whole under
-side of the body, from the base of the neck to the base of the tail,
-was well protected by bones, rigid and unyielding in front and behind,
-flexible for a short space below the abdomen; this surface, however,
-was not flat like the under shell of a turtle, but rounded from side to
-side.
-
-[Illustration: FIG. 36.—Pelvic girdle from above of _Trinacromerum
-osborni_, an Upper Cretaceous plesiosaur: _p_, pubis; _is_, ischium;
-_il_, ilium.]
-
-Many of the characteristics of the limbs of the plesiosaurs are
-peculiar to themselves; others they had in common with other aquatic
-reptiles and mammals. The paddles resemble those of the ichthyosaurs
-more nearly than those of any other reptile, and it was doubtless this
-superficial resemblance which so long deceived the early anatomists
-as to the affinities of the two orders. Unlike all other aquatic
-animals, however, the plesiosaurs have the hind limbs nearly or quite
-as large as the front ones, and they doubtless were equally effective
-in function. The humerus and femur are always elongate, though broad
-and massive. In no other aquatic animals, save the marine turtles,
-do we find these bones relatively so long and strong; they are very
-short in the cetaceans, the sirenians, the ichthyosaurs, mosasaurs,
-thalattosaurs, and the marine crocodiles, in front at least. The strong
-muscular rugosities of the plesiosaurian bones are very suggestive of
-powerful swimming muscles.
-
-[Illustration: FIG. 37.—Pelvic girdle of _Elasmosaurus_: _p_, pubis;
-_is_, ischium; _il_, ilium.]
-
-[Illustration: FIG. 38.—Paddles of Plesiosaurs: _A_, right hind
-paddle of _Thaumatosaurus_, after Fraas; _B_, right hind paddle of
-_Trinacromerum_; _C_, right front paddle of same individual; _f_,
-femur; _fb_, fibula; _t_, tibia; _h_, humerus; _r_, radius; _u_, ulna.]
-
-The bones of the forearms and legs, the wrists and ankles are all
-polygonal platelets of bones, closely articulating with each other.
-The finger and toe bones have a more elongated, hour-glass shape
-than those of the ichthyosaurs, resembling more nearly those of the
-mosasaurs, indicating a greater flexibility than the ichthyosaurs
-possessed. The ichthyosaur paddles must have been quite like the fins
-of fishes in function, while doubtless those of the plesiosaurs were
-capable of a more varied use, as indeed was required of them. Their
-articulation with the trunk was more of a ball-and-socket joint than in
-the other reptiles, showing possibility of considerable rotation on the
-long axis, and an antero-posterior propelling action. The paddles were
-certainly more powerful than those of any other aquatic air-breathing
-animals. There were no additional digits, all plesiosaurs having
-neither more nor less than five in each hand and foot. Hyperphalangy
-was sometimes carried to an excessive degree, some digits of some
-species having as many as twenty-four bones, a larger number than has
-been observed in any other air-breathing vertebrate.
-
-[Illustration: FIG. 39.—Pectoral girdle (in part) and front paddles
-of _Elasmosaurus_ (after Riggs): _sc_, scapula; _h_, humerus; _cor_,
-coracoid; _r_, radius; _u_, ulna.]
-
-In Fig. 38 on p. 85 are shown two paddles, the front and hind paddles
-of a single individual of a very specialized plesiosaur from the
-Upper Cretaceous of Kansas (_Trinacromerum_). The long arm and thigh
-bones are followed by remarkably short and broad bones in place of
-the elongated forearm and leg bones of the land reptiles. Not only
-are these bones much broader than they are long, but there have been
-developed additional bones back of them in the same row—new bones
-which have no counterpart in any terrestrial reptiles. In the first of
-the three figures is shown a hind paddle of one of the earliest known
-plesiosaurs, _Thaumatosaurus_, from the lower part of the Jurassic of
-Germany. It will be seen here that the tibia and fibula are much more
-elongated than in _Trinacromerum_, and much more like the leg bones
-of land reptiles. A still more primitive stage in the evolution of
-the swimming paddle of the plesiosaurs will be seen in Fig. 48 on p.
-99, the possibly ancestral, amphibious nothosaur. Here the tibia and
-fibula, while relatively very much shorter than in any land reptile,
-still have, together with all the other bones of the leg, a terrestrial
-or amphibious type. In Fig. 39 is seen the front paddles of the
-long-necked _Elasmosaurus_, which, though one of the latest of all
-plesiosaurs in geological history, has the structure of its paddles
-somewhat intermediate between that of the earlier _Plesiosaurus_ and
-the later _Trinacromerum_.
-
-[Illustration: FIG. 40.—Skull of _Elasmosaurus_ from the side: _pm_,
-premaxilla; _m_, maxilla; _po_, postorbital; _j_, jugal.]
-
-The skull of the long-necked plesiosaurs is surprisingly small in
-comparison with the remainder of the skeleton, often very snake-like
-in shape, though very un-snake-like in structure. The short-necked
-plesiosaurs had often a relatively larger skull, in _Pliosaurus_, for
-instance, more than five feet long, sometimes rather broad and short,
-sometimes remarkably long and slender. The external nostrils were
-situated far back, very near the eyes, and were very small. The eyes,
-of considerable size, though by no means so large as those of the
-ichthyosaurs, were directed laterally, and were provided with a ring of
-bony sclerotic plates—rather small and weak ones, however. The quadrate
-bones—bones peculiar to the reptiles and birds—to which the lower jaws
-are articulated, are, as in the ichthyosaurs and crocodiles, rigidly
-fixed and immovable. The lower jaws, always rather slender, are firmly
-united in front, sometimes for a long distance, as in the modern
-gavials. The teeth of the broad-headed plesiosaurs are long, slender,
-pointed, and recurved, of a murderously cruel shape; they are deeply
-implanted in sockets, and number from twenty to thirty on each jaw
-above and below. There are no teeth on the bones of the palate, such
-as the mosasaurs possessed. The slender-jawed, gavial-like plesiosaurs
-have more numerous, but smaller teeth. The surface of the skull on each
-side behind, for the attachment of the muscles closing the mandibles,
-is of great extent; in some this surface is increased by a high, thin
-crest in the middle, as in strongly carnivorous animals, all of which
-give conclusive evidence of the powerful muscles used in biting and
-seizing. There is but one temporal opening on each side, as in the
-ichthyosaurs and the mosasaurs, whereas the crocodiles, thalattosaurs,
-phytosaurs, etc., have two. The brain cavity of all plesiosaurs is
-small, though the cavities of the internal ears, the semicircular
-canals at least, are large. The semicircular canals in vertebrates have
-little or nothing to do with the function of hearing; they serve rather
-for equilibration, for the co-ordination of muscular movement; possibly
-we may infer from their large size in the plesiosaurs that they were
-not at all clumsy in their movements. There is a large opening for
-the pineal body, the so-called eye in the roof of the brain cavity,
-though its possession does not necessarily imply the possession of a
-functional organ.
-
-[Illustration: FIG. 41.—Skull of _Trinacromerum_ from the side: _ang_,
-angular; _d_, dentary; _pm_, premaxilla; _po_, postorbital; _j_, jugal;
-_sur_, surangular.]
-
-The Plesiosauria included some of the largest aquatic reptiles that
-have ever existed, equaled, perhaps, though not exceeded, by some of
-the extinct crocodiles. The largest known are probably those of the
-Kansas chalk, or the Jurassic of Wyoming, which probably reached a
-length of nearly or quite fifty feet, of which the neck formed about
-one-half. Some of them had paddles more than six feet in length. The
-head of the largest was about five feet in length, or about the size
-of that of the largest known ichthyosaurs and mosasaurs. The smallest
-known adult plesiosaurs were nearly ten feet in length. The teeth of
-the largest and most carnivorous plesiosaurs sometimes measure four
-inches in length.
-
-[Illustration: FIG. 42.—Restoration of _Trinacromerum_, a Cretaceous
-plesiosaur; length about ten feet.]
-
-As is the case with both the ichthyosaurs and mosasaurs, skeletons
-of plesiosaurs have been discovered with nearly all their bones in
-their relative positions, and with impressions of skin and outlines of
-body made before decomposition. Though our knowledge of the external
-appearance of the plesiosaurs when alive is perhaps not as full as we
-could wish, it is sufficient to give us a fairly good conception of
-what the animals really were. The skin was smooth and bare, without
-scales or plates of any kind, and Dames has described a terminal or
-nearly terminal fleshy dilatation of the tail, forming a sort of caudal
-fin, which may have aided as a steering apparatus. Mounted skeletons
-are preserved in a few museums, notably the British Museum, the
-American Museum of New York City, and the museum of the University of
-Kansas. Many nearly complete skeletons, however, preserved as they were
-found in the matrix, are shown in various museums.
-
-With these, principal facts regarding the structure, size, and external
-form of these animals we may venture to draw certain conclusions, or at
-least to offer certain conjectures as to their habits in life.
-
-Because of the rigid structure of the jaws, united in front and
-incapable of any lateral movement posteriorly, quite as are the jaws
-of crocodiles, we are sure that prey of any considerable size could
-not have been swallowed whole. The crocodiles tear away portions of
-the flesh of their victims by quick, powerful jerks, and it is very
-probable that the flat-headed plesiosaurs tore their food apart in
-the same manner. In these kinds the teeth are much larger and more
-irregular in size than are those of the long-snouted plesiosaurs, and
-their use was certainly as much for tearing as for seizing. There are
-the same differences between the size of the head and the size of the
-teeth among the various plesiosaurs that there are among the modern
-crocodiles and gavials. While the crocodiles seize and destroy even
-larger prey, drowning and tearing their victims to pieces, the gavials
-are more exclusively fish-eating, for which their small, sharp, and
-more numerous teeth especially fit them. Their food, of small size,
-is swallowed entire, and they are comparatively harmless, so far as
-animals of considerable size are concerned.
-
-The long neck, the thickset body, and short, stout tail are not at
-all what we should expect to find in quick-swimming animals. We may
-therefore assume that the motions of the plesiosaurs through the
-water were more turtle-like than fish-like. The tail, even though
-provided with a terminal, fin-like dilatation, was of little use in
-the propulsion of the body, since the range of its movements was
-restricted; it possibly served in a measure as a steering organ, a
-rudder. The large, freely movable paddles must have been effective
-organs of locomotion, and this function accounts for the relatively
-large size of the posterior pair, and the firm union of the pelvis with
-the vertebral column through the sacrum. With the hind limbs used as
-oar-like organs, a firmer union with the skeleton was required than
-the soft yielding flesh would permit. At the same time this union
-was ligamentous only, not bony and unyielding, since the limbs were
-never used to support the body upon the ground; and it is of interest
-to observe that the ilia are directed, not upward and forward, but
-upward and backward to the sternum, precisely the position that would
-be expected with the force or thrust coming from behind, and not
-below the yielding ligaments. Were the tail longer and more powerful,
-the hind limbs would have been smaller and weaker, of use chiefly in
-equilibration, involving the loss of any connection with the vertebral
-column and the disappearance of the sacrum. It is of interest, finally,
-to observe that many of the slender-jawed plesiosaurs had a relatively
-short neck; they were doubtless more distinctively fish-eating in
-habit, and possessed greater speed. That the limbs of plesiosaurs
-were powerful propelling organs is also conclusively proved by their
-structure. Quite unlike all those animals whose locomotion in the water
-is chiefly effected by the tail, the humeri and femora, the upper
-arm and thigh bones were elongated, and not shortened. They form the
-rigid and stout handles of oars whose blades are the thinner, flexible
-forearm, wrist, and fingers, or the corresponding foreleg, ankle,
-and toes. No other purely aquatic reptiles, save the turtles, which
-likewise are of the oar-propelled type, have elongated arm and thigh
-bones.
-
-Textbook illustrations of the plesiosaurs usually depict the necks,
-like those of the swans, freely curved, and a popular scientific
-article in one of our chief magazines a few years ago depicted one
-of them with the neck coiled like the body of a snake. One noted
-paleontologist, indeed, not many years ago described the plesiosaurs as
-resting on the bottom in shallow waters with the neck uplifted above
-the surface viewing the waterscape! And when we consider the fact that
-some species of the elasmosaurs had a neck not less than twenty feet in
-length, such a flexible use of it would not seem improbable. But the
-plesiosaurs did not and could not use the neck in such ways. They swam
-with the neck and head, however long, directed in front, and freedom
-of movement was restricted almost wholly to the anterior part. The
-posterior part of the neck was thick and heavy, and could not have been
-moved upward or downward to any considerable extent and not very much
-laterally. From all of which it seems evident that the plesiosaurs
-caught their prey by downward and lateral motions of their neck, rather
-than by quick swimming.
-
-[Illustration: FIG. 43.—Gastroliths and bones of an undetermined
-plesiosaur from the Lower Cretaceous of Kansas.]
-
-About thirty years ago, the late Professor Seeley, a well-known English
-paleontologist who devoted much attention to the study of these
-reptiles, found with the remains of a medium-sized plesiosaur nearly a
-peck of smoothly polished, rounded, and siliceous pebbles. He believed
-that their occurrence with the skeleton was not accidental, but that
-they had been intentionally swallowed by the animal when alive, and
-formed at its death a part of its stomach contents. Even earlier than
-this the same habit had been noticed. Nearly at the same time that
-Seeley mentioned the peculiar discovery he had made the present writer
-found several specimens of plesiosaurs in the chalk of western Kansas
-with which similar pebbles were associated, an account of which was
-given soon afterward by the late Professor Mudge. Since then numerous
-like discoveries have made it certain that the plesiosaurs usually,
-if not always, swallowed such pebbles in considerable quantities, for
-what purpose we do not yet feel sure; one can only hazard a guess. The
-small size of the pebbles, or gastroliths, as they have been called,
-a half-inch or less in diameter, found with skeletons of large size,
-indicate much more complete digestion of the hard parts of their food
-than is the case with many other reptiles; no solid substance of size
-could have passed out of the plesiosaur stomach, and such is the case
-with the modern crocodiles, which have a like habit of swallowing
-pebbles. That the plesiosaurs picked up these siliceous pebbles,
-sometimes weighing a half-pound, accidentally with their food is highly
-improbable; they surely had something to do with their food habits. It
-is not at all unreasonable to suppose that the plesiosaurs, because of
-their comparative sluggishness, fed upon anything of an animal nature,
-whether living or dead, which came in their way; that carrion, squids,
-crustaceans, and fishes were all equally acceptable; they were probably
-largely scavengers of the old oceans. Barnum Brown found among the
-stomach contents of a plesiosaur fragments of fish and pterodactyl
-bones, and cephalopod shells. Gallinaceous birds, most of which have
-the same pebble-swallowing habit, have a thick-walled muscular stomach
-or gizzard, in which the pebbles serve as an aid in the trituration of
-food. Modern crocodiles, with the same pebble-swallowing habit, have a
-thick-walled muscular stomach, gizzard-like, though of course not as
-large as in birds; and the same habit has been noted by Des Longchamps
-in the ancient teleosaur crocodiles.
-
-It is hardly possible yet to decide whether or not the plesiosaurs
-were denizens of the open oceans for the most part, far from land.
-That many of them were rovers is quite certain. With the skeleton of
-a large plesiosaur found some years ago in western Kansas, there were
-many siliceous pebbles which could have come only from the shores
-of the old Cretaceous seas about the Black Hills, hundreds of miles
-distant. Some of the pebbles are red quartzite, quite identical with
-that of the bowlders brought to Kansas millions of years later by the
-glacial drift from outcroppings near the northern line of Iowa. The
-bones of plesiosaurs are often found in deposits believed to be of
-deep-water origin. But they are also found in Kansas associated with
-the remains of small turtles, flying reptiles, and birds which could
-only have lived near the shores. Indeed, their remains have often
-been found with those of strictly fresh-water animals which had been
-brought down by the floods to the seas. Their wide but rather sparse
-distribution in all kinds of marine sediments would rather indicate
-that they were at home far out in the tempestuous ocean or near the
-shores in protected bays, though probably they preferred the shallow
-water littoral regions. One conclusion is quite justified: they were
-not gregarious, as were the ichthyosaurs.
-
-It is not certain that the plesiosaurs were viviparous, though there
-are good reasons for the belief that they were. Remains of two embryos
-were found years ago in England associated in such a way that it is
-reasonable to suppose they were unhatched young, though embryos have
-never yet been found associated with skeletons of adults, as have those
-of ichthyosaurs in numerous instances. Bones of young, often quite
-young, plesiosaurs, are frequently found in shallow water deposits, and
-if the young were actually born alive they must have swum freely in the
-open waters while yet of very tender age. Rather singularly, however,
-the remains of these young plesiosaurs always occur as isolated bones.
-
-In geological range the plesiosaurs were very persistent, extending
-through nearly all the Mesozoic. They began their career as fully
-evolved plesiosaurs, so far as we now know, near the close of the
-Triassic period, and reached their culmination in the Upper Cretaceous,
-but survived to the close of that period. In the beginning of their
-career they were associated with the marine crocodiles and the
-ichthyosaurs, but outlived them to find companions and probably
-enemies in the huge and voracious mosasaurs of the later Cretaceous
-times. At no time do they appear to have been especially numerous, nor
-does it seem probable that they were ever a dominant type of marine
-vertebrate life, though their remains occur everywhere that marine
-deposits of the Jura and Cretaceous are known. Indeed, it may be said
-with almost certainty that rocks of these ages and of that character
-everywhere in the world contain fossil plesiosaurs. Their bones have
-been made known from Europe, Asia, Africa, Australia, and North and
-South America. From North America thirty or more species have been
-described from New Jersey, Alabama, Mississippi, Texas, Arkansas,
-Kansas, Nebraska, Colorado, New Mexico, Wyoming, North and South
-Dakota, California, etc.
-
-The cause of their final extinction no one knows, nor can we
-conjecture much about it with assurance. That climatic conditions
-became unfavorable for them is highly improbable, considering
-their cosmopolitan habits; they were not discriminating in their
-environments. After successfully withstanding their fiercest foes, the
-ichthyosaurs, crocodiles, and mosasaurs, and large carnivorous fishes,
-it does not seem probable that they would succumb to lesser enemies,
-though it may be that they were finally attacked successfully, not
-in the fulness of their strength as adults, but while young, by more
-insidious enemies. More probably after their long life of millions of
-years they had grown old, as everything grows old, and had become so
-fixed and unplastic in their structure and habits that even slight
-causes were at last their undoing. When we shall have bridged over
-that still imperfectly known transition period between the great Age
-of Reptiles and the greater Age of Mammals we shall have learned
-more definitely some of the causes of the extraordinary revolution
-in vertebrate life that then occurred. The plesiosaurs went out
-with nearly all of their kind, the mosasaurs, the pterodactyls, the
-dinosaurs; and, so far as we now know, their places in the sea, land,
-and air were not immediately taken by any other creatures.
-
-[Illustration: FIG. 44.—_Nothosaurus_; restoration after E. Fraas;
-landscape by Dorothy Williston.]
-
-
-NOTHOSAURIA
-
-A few years after the discovery of the plesiosaurs by Conybeare, the
-remains of animals of allied kinds were found in the Triassic rocks of
-Bavaria. At first they were supposed to be those of true plesiosaurs,
-and even the astute Cuvier was not very clear about them. Cuvier was
-the first to call attention to them, expressing the opinion that
-some of the fossils were of previously unknown animals allied to the
-crocodiles, lizards, and plesiosaurs. It was von Meyer, however, who
-first introduced a nothosaur to the scientific world under the name
-_Conchiosaurus_. A year later Count George of Münster described other
-forms under the name _Nothosaurus_, meaning “false lizard.” Count von
-Münster was a most zealous collector of the fossils of the Triassic
-deposits of Bavaria, amassing, after thirty years of active and
-enthusiastic labor, a very large amount of material, which, at his
-death, was purchased by the King of Bavaria and placed in the hands of
-von Meyer for study. Von Meyer was to Germany what Owen was to England,
-a man of deep learning, having an extensive knowledge of comparative
-anatomy, and being thorough and critical in his work. His descriptions
-and illustrations of these rich collections made by von Münster are
-masterpieces of scientific thoroughness. He recognized in _Nothosaurus_
-and other allied forms from the Bavarian Triassic a distinct group of
-semiaquatic reptiles allied to the plesiosaurs, and his conclusions
-have never been gainsaid. In more recent years additional remains
-of these animals from Bavaria and other places in Europe have been
-described, but none are known from other parts of the earth, or from
-other than Triassic rocks. Altogether about ten genera and about twice
-as many species have been described, probably all belonging in one
-family, and all by common consent now classified with the Sauropterygia.
-
-[Illustration: FIG. 45.—Head and neck of _Nothosaurus_; photograph of
-specimen in the Senckenberg Museum, from Dr. Dreverman.]
-
-[Illustration: FIG. 46.—Pectoral girdle of _Nothosaurus_, from
-photograph by E. Fraas: _icl_, interclavicle; _cl_, clavicle; _sc_,
-scapula; _cor_, coracoid.]
-
-[Illustration: FIG. 47.—Pelvic bones of _Nothosaurus_: _il_, ilium;
-_ac_, acetabulum; _p_, pubis; _is_, ischium. (After Andrews.)]
-
-The Nothosauria were much smaller reptiles than the plesiosaurs, none
-of them perhaps exceeding the size of the smallest known plesiosaurs.
-They were semiaquatic in habit, with many curious resemblances to
-other semiaquatic reptiles of a later time known, as the dolichosaurs.
-The neck is more or less elongated, having about twenty vertebrae in
-the longest-necked forms; the body is moderately long, and broad,
-and the tail is relatively short. The vertebrae and ribs are quite
-like those of the plesiosaurs, that is, the vertebrae are gently
-concave at each end, and the dorsal ribs are attached by a single
-head to the transverse process high up on the arch; the cervical ribs
-are double-headed, precisely like those of the older plesiosaurs,
-one of the characters which insistently proves the relationships of
-the two groups. The bones of the shoulders (Fig. 46) also have many
-resemblances to the extraordinary ones of the plesiosaurs, though
-they are much less specialized. There was no sternum; the coracoids
-are large, though very much smaller than those of the plesiosaurs.
-The collar-bones are large and strong, joining each other in front
-of the coracoids and firmly united with the shoulder-blades at the
-outer extremity. Four vertebrae are united to form a sacrum, and their
-union with the hip bones (Fig. 47) was much firmer than was the
-case with the plesiosaurs. The limbs are elongated, but it will be
-observed in the figures (Fig. 48) that the radius and ulna, tibia and
-fibula, that is, the bones of the forearm and of the leg proper, are
-relatively very short as compared with the humerus and femur, a sure
-indication of the beginning of aquatic habits. The toes and fingers
-were doubtless webbed, and there was no increase in the numbers of
-bones in the digits, so conspicuous in the plesiosaurs. The external
-nostrils are large, but are not situated so far back near the eyes as
-in the plesiosaurs. There is a large pineal opening in the top of the
-skull, as in the plesiosaurs, but no sclerotic or bony plates have
-been observed in the eyes. They had ventral ribs like those of the
-plesiosaurs.
-
-[Illustration: FIG. 48.—Legs of _Lariosaurus balsami_, an Upper
-Triassic nothosaur: _h_, humerus; _r_, radius; _u_, ulna; _i_,
-intermedium; _ue_, ulnare; _f_, femur; _fi_, fibula; _t_, tibia; _a_,
-astragalus; _c_, calcaneum. (After Abel.)]
-
-No impressions of scales or bony plates have ever been found with the
-remains of the nothosaurs, and it is the belief that the skin was
-bare. A good idea of their general appearance will be gained from the
-accompanying restoration adapted from that of Professor Fraas (Fig. 44)
-and the restoration of the less highly specialized _Lariosaurus_, made
-from a very complete skeleton in the Frankfort museum (Fig. 49).
-
-It has been thought that these nothosaurs, so intermediate in structure
-between the true plesiosaurs and land reptiles, were the actual
-ancestors, but this is rather doubtful. It is probable that they were
-only very closely akin to the real ancestors, since in some ways they
-had become specialized too much, and, as we have already explained,
-highly specialized characters or organs can never go back to their
-earlier condition. The nothosaurs do prove beyond all possibility of
-doubt that the plesiosaurs were at least the descendants of animals
-closely allied to them, so closely, indeed, that it is doubtful whether
-we could distinguish external differences were all of them actually
-living at the present time.
-
-[Illustration: FIG. 49.—_Lariosaurus balsami_.]
-
-We have repeatedly seen that all aquatic animals have some or all the
-bones of the limbs shortened, and it is of interest to observe that the
-early plesiosaurs had longer forearm and foreleg bones than the later
-ones, just as we have seen was the case with the early ichthyosaurs.
-It would seem probable that all the early plesiosaurs had long necks,
-though some of the late ones in Cretaceous times had relatively short
-necks, shorter even than the known nothosaurs possessed.
-
-The nothosaurs doubtless lived about the shores of the ancient seas,
-spending much of their time in the water, leaving it perhaps when hard
-pressed by their enemies, as do some modern reptiles, or to rear their
-young. The teeth of the nothosaurs are long and slender in front,
-shorter behind. The animals must therefore have been carnivorous in
-habit, feeding probably upon such fishes as they could catch, and the
-various invertebrates which live in shallow water. The structure of the
-jaws and their attachments are quite as in the plesiosaurs, proving
-that they could not have swallowed large objects; but the skull is
-broader and flatter than that of most plesiosaurs, indicating habits
-not unlike those of the modern alligators and crocodiles.
-
-Some time we shall doubtless find remains of nothosaurs or nearly
-allied animals elsewhere than in Europe, but probably not from later
-deposits than the Triassic. So far as we now know, their geological
-range and geographical distribution were much restricted; they
-evidently wholly died out shortly after the plesiosaurs appeared.
-
-
-
-
-CHAPTER VII
-
-ANOMODONTIA
-
-LYSTROSAURUS
-
-
-Over a large area of South Africa, chiefly along the Orange River and
-its tributaries, there is an extensive series of deposits many hundreds
-of feet in thickness, usually called the Karoo beds, which, for more
-than fifty years, have been widely famous among scientific men for the
-many and remarkable vertebrate fossils which they have yielded. These
-deposits seem to represent the whole of the vast interval of time from
-the Carboniferous to the Jurassic, that is, the whole of the Permian
-and Triassic, though not many fossils have been found in the lowermost
-strata. Among the fossils of the lower strata are those of the strange
-creatures described in the following pages as _Mesosaurus_. From the
-deposits representing the Upper Permian and the Triassic the fossils
-that have been obtained are both abundant and diverse. Unfortunately,
-however, of the scores of forms that have been discovered few are known
-completely, and still fewer are known sufficiently well to enable us to
-picture the living animals.
-
-From the Upper Permian Karoo rocks two orders of reptiles have been
-recognized, the Cotylosauria, represented by more specialized forms
-than those from the Lower Permian of North America; and the order or
-group called by Broom the Therapsida. While the forms of this latter
-group have certain definite structural relationships with each other,
-they show so great a diversity among themselves that, when they shall
-be better known, it will be found necessary perhaps to separate them
-into several distinct orders.
-
-At least five groups of the Therapsida are now recognized by Broom,
-the Dromasauria, Dinocephalia, Anomodontia, Therocephalia, and
-Theriodontia. Of all these the members of the last-mentioned group
-have attracted the greatest interest among geologists and naturalists,
-because of their intimate relationships to the mammals—so intimate,
-indeed, that they seem almost to bridge over the interval between the
-two classes. From higher Karoo beds primitive representatives of the
-more crocodilian types have been discovered, forms which seem to be the
-beginning of that order described on later pages as the Parasuchia.
-
-It would lead us too far astray to mention even, let alone describe,
-the many forms of reptiles that have been discovered in the Karoo beds;
-nor indeed is it possible for anyone who has not attentively studied
-their remains to get a very clear conception of many of them, so
-incompletely have they been made known.
-
-Doubtless from among all these diverse forms there have been not a few
-which sought wider opportunities in the water, but, if so, we have
-as yet very little knowledge of them. One form only, so far as the
-writer is aware, has been credited with aquatic habits, a remarkable
-reptile belonging to the group originally called by Sir Richard Owen,
-the Anomodontia, a word meaning “lawless teeth,” and to the genus
-_Lystrosaurus_, also described by the same noted paleontologist.
-A restoration of the skeleton of _Lystrosaurus_ has recently been
-published by Watson. This restoration the writer has reproduced in
-the present pages, though he has taken the liberty of making some
-minor changes, to accord better with what he believes must have been
-the position of the shoulder-blades and the hind legs. And he would
-also suggest that the tail in life did not turn down so much at its
-extremity as depicted by Watson.
-
-Both Broom and Watson believe that this animal was a powerful swimmer,
-and thoroughly aquatic in habit. To the present writer, however, this
-does not seem so evident. He is rather inclined to believe that the
-creature was chiefly terrestrial in habit, living probably in marshy
-regions, and perhaps seeking its food in shallow waters and in the mud.
-Aside from the position of the nostrils, which it will be observed are
-rather close to the eyes, a position so characteristic of many swimming
-reptiles and mammals, there is but little indication of aquatic
-adaptations elsewhere in the skeleton.
-
-[Illustration: FIG. 50.—Skeleton of _Lystrosaurus_, as restored by
-Watson, slightly modified.]
-
-The skull is of most extraordinary form. The face is turned downward,
-leaving the nostrils high up, in front of the eyes. The jaws were
-doubtless covered with a horny shield, like that of the turtles, having
-a cutting edge. There is a single pair of elongated canine teeth,
-possibly a sexual character. The lower jaws are heavy and stout, and
-Watson has said that the animal doubtless had the ability to open its
-mouth very widely. The quadrate, the bone with which the lower jaws
-articulate, is firmly fixed to the skull, and there is a single opening
-on the side of the skull posteriorly, a character common to all the
-Therapsida.
-
-The vertebrae are stout, and they have stout spines. The tail is
-remarkably short, stout, and stumpy; it could have been of no use
-whatever in the water for propulsion or even for steering. The front
-legs are short and stout; the forearm bones are short, suggesting
-either swimming or digging habits, and the foot is short and broad.
-The pelvis or hip bones are massive and were very firmly connected
-with the backbone by the aid of six vertebrae, a very unusual number
-in reptiles. The hind legs, as figured, show no indications whatever
-of aquatic adaptation, unless possibly the very slight shortening of
-the shin may be so construed. Watson believes that the bones of the
-pelvis, indicate, aside from its strong union with the backbones,
-strong swimming powers, but of this again the present writer is very
-skeptical. The very strong ischia and the flatness of the pelvis are
-both characters found among American Permian reptiles, which do not
-show otherwise the slightest indications of water habits.
-
-If then _Lystrosaurus_ was a powerful swimmer, as has been maintained,
-it is very evident that the hind legs must have been used as the seals
-or sea-otters use them, to propel and to guide; but they in nowise
-resemble the legs of these swimming mammals. It seems altogether
-more reasonable to suppose that _Lystrosaurus_ lived in the marshes,
-feeding upon vegetable food obtained by aid of its strong jaws
-and tusks—if the tusks were possessed by both sexes; and that the
-position of the nostrils may be ascribed to causes like those which
-brought about their recession in the Phytosauria, and not to strictly
-aquatic habits. Possibly the animal had habits somewhat similar to
-those of the hippopotamus; that it was an expert swimmer appears,
-to the present writer, improbable. The powerful front legs may be
-indicative of digging habits; the animal may have used them as an aid
-to its powerful jaws and tusks in uprooting marsh and water plants.
-However, _Lystrosaurus_, whatever may have been its habits, was a
-curious reptile. It was about three feet in length, massive in all its
-structure, and doubtless of slow and sluggish gait.
-
-
-
-
-CHAPTER VIII
-
-ICHTHYOSAURIA
-
-
-Early in the eighteenth century a curious work in the Latin language
-was published by a famous physician and naturalist—a professor in the
-University of Altorf by the name of Scheuchzer—entitled _Querulae
-Piscium_, or “Complaints of the Fishes.” The work was illustrated by
-many expensively engraved figures of various fossil remains, including
-one of some vertebrae which the author referred to as “the accursed
-race destroyed by the flood”! The history of the finding of these
-famous bones is recorded by Cuvier as follows:
-
-      Scheuchzer, while walking one day with his friend Langhans
-    in the vicinity of Altorf, a village and university of
-    Nuremburg, went to the vicinity of the gallows to make some
-    researches. Langhans, who had entered the inclosure of
-    the gallows, found a piece of limestone containing eight
-    dorsal vertebrae, of a black color and shining. Seized,
-    says Scheuchzer, with a panic terror, Langhans threw the
-    fragment of limestone beyond the wall of the inclosure, and
-    Scheuchzer, picking it up, preserved two of the vertebrae
-    which he believed to be human, and which he figured in his
-    book, _Piscium Querulae_.
-
-About the same time another observer by the name of Baier discovered
-other and similar vertebrae in the vicinity of Altorf which he
-described and figured as those of a fish; and there was much earnest
-contention between Scheuchzer and Baier, as also between their friends,
-as to their supposed nature. Scheuchzer’s figure was often cited as
-indubitable evidence of the destruction of mankind by a universal
-flood, and it was not until nearly a century later that Cuvier showed
-that the bones were really those of a marine reptile.
-
-[Illustration: FIG. 51.—Restoration of _Ichthyosaurus_ with young, by
-Charles R. Knight. (By permission of the American Museum of Natural
-History.)]
-
-It must be recollected, in extenuation of so extraordinary a blunder
-on the part of so learned a man as was Scheuchzer, who, as a physician
-and professor, one would think ought to have been able to distinguish
-between vertebrae so different as are those of an ichthyosaur and a
-man, that, during all of the eighteenth century and well into the
-nineteenth, the belief was prevalent that all fossils were the relics
-of animals and plants that had perished in the great biblical flood.
-The science of geology was yet in its infancy, and there was no known
-record, other than the biblical one, of any great inundation of the
-earth’s surface which might account for the remains of sea-animals
-in rocks remote from the seas. This belief, so long held by even
-the wisest and most learned of scholars, so long welcomed by the
-theologians as proof of the literal accuracy of the Bible, was one
-of which Scheuchzer was quite convinced. His _Piscium Querulae_ was
-largely a fantastic discussion of the supposed great world-catastrophe,
-the Noachian Deluge, by which the fishes had been destroyed and long
-imprisoned in the rocks through no sin of their own.
-
-It was the same author who, in a subsequent work, described and figured
-the fossil skeleton of a large salamander which he believed to be that
-of a child destroyed in the flood, and which he called “Homo diluvii
-testis.” In this specimen, which was discovered in the Tertiary rocks
-of Oeningen, and which is still preserved among the historically as
-well as scientifically famous fossils of the museum at Haarlem under
-the name _Andrias Scheuchzeri_, Scheuchzer thought that he detected,
-not only the skeleton of a child, but even its brain, liver, muscles,
-etc.! His engraving of this “Witness of the Flood,” the “sorrowful
-skeleton of an old sinner drowned in the Flood,” as also that of
-the ichthyosaur vertebrae of Altorf, were afterward printed in the
-famous “Copper Bible” as positive proof of the literal accuracy of the
-biblical record.
-
-Earlier than the publication of these figures by Baier and Scheuchzer,
-at the very close of the seventeenth century, a Welsh naturalist
-by the name of Lluyd, in a large and beautifully illustrated work,
-figured—perhaps for the first time—remains of ichthyosaurs, which he
-believed to be those of fishes. But Lluyd accounted for these and all
-other fossil remains by a very different theory from that of Scheuchzer
-and the theologians—a theory which at one time had many adherents among
-scholars. He believed that the spawn of fishes or the eggs of other
-creatures had been carried up from the seas and lands in moist vapors
-into the clouds, whence they had descended in rain, penetrating the
-earth to give origin to the fossils; in other words, he believed that
-all fossils grew in the earth from germs of the living animals that
-inhabited the land and seas. Certainly the old philosophers were hard
-driven to make facts agree with theories!
-
-Remains of ichthyosaurs, abundant as they were and are in many deposits
-in England and Germany, attracted very little attention from the
-naturalists of the eighteenth century after the time of Scheuchzer and
-Baier, and nothing more was written about them until 1814, when Sir
-Everard Home, an English comparative anatomist, in an extensive series
-of large and finely illustrated, though rather discursive, works,
-described and figured a number of good specimens. To the animal the
-remains of which he rather vaguely and imperfectly described, he gave
-in 1819 the name _Proteosaurus_, in the belief that it was allied to
-the living _Proteus_, a salamander.
-
-In 1821 the curator of mineralogy of the British Museum—Koenig by
-name—after a more critical study of other remains, reached the
-conclusion that these animals were intermediate between the fishes
-and the reptiles, and gave to them the generic name _Ichthyosaurus_,
-meaning fish-reptile, a name by which the chief forms have ever since
-been known. Within the next few years many specimens of ichthyosaurs
-were carefully and fully described by Conybeare, Cuvier, Owen, and
-others of England, France, and Germany, making very clear all the
-more important details of their skeletal structure. Blaineville, in
-1835, thought that the ichthyosaurs constituted a distinct class of
-vertebrates equivalent to all other reptiles, the birds, and the
-mammals, which he called Ichthyosauria, the first appearance in
-literature of the name by which the order is properly known. Five years
-later, however, the famous English anatomist and paleontologist, the
-late Sir Richard Owen, united the ichthyosaurs with the plesiosaurs as
-a single order of reptiles, to which he gave the name Enaliosauria,
-meaning sea-reptiles, a name which has long been current in textbooks
-and general works on natural history. Moreover, Owen rather arbitrarily
-changed Blaineville’s name Ichthyosauria to Ichthyopterygia, a name
-which is often, though incorrectly, used to designate this order of
-reptiles. These briefly given and perhaps dry details will make clear
-how necessary is that rule of priority upon which naturalists so often
-insist. When anyone may change the names of organisms at will there
-will be no stability and no uniformity, because there is no one to
-decide, and the prestige of a great name, like that of Owen, will carry
-authority till someone else with greater authority appears. Whether or
-not the name _Proteosaurus_, first given to any member of this order,
-should take precedence over the later _Ichthyosaurus_ is still in
-doubt, since Home gave no specific name to his species, and the very
-particular purists of modern times have decided that a genus is not
-named unless the species is also! We moderns sometimes are inclined to
-impose very stringent conditions upon the older naturalists; let us
-hope that we shall be treated more leniently by the future naturalists!
-
-It will lead us too far astray to follow in detail the history of
-the further discoveries of the ichthyosaurs during the early part
-of the nineteenth century. It may briefly be said, only, that no
-other group of extinct backboned animals excited more interest among
-scientific men. One incident will suffice. More than sixty years ago,
-an interesting deduction as to the living form of the ichthyosaurs was
-made by Sir Richard Owen. He observed that many of the known skeletons,
-as they were found in their rocky matrix, had a remarkable dislocation
-of the vertebrae at a certain place near the end of the tail, and,
-although such an appendage was quite unknown in other reptiles either
-living or extinct, concluded that the living animals had a terminal,
-horizontal, fleshy fin, very much like that of the whales and
-sirenians. Sure enough, discoveries made forty years later disclosed
-impressions in the rocks, not only of a large caudal fin, but also of
-a dorsal fin, as well as outlines of the flesh-covered paddles. The
-dislocation of the vertebrae at the place where the fleshy fin joined
-the more slender tail was due to the action of currents of water, or
-simple gravitation, upon a thin vertical fin and not, as Owen supposed,
-to the twisting of the terminal part as it fell to a horizontal
-position after partial decomposition of the soft parts.
-
-About twenty-five years ago, Professor E. Fraas, the present director
-of the Stuttgart Museum, described and figured very fully, not only
-specimens showing impressions of the fins and paddles, but also others
-of well-preserved and very complete skeletons of different species
-of ichthyosaurs from the Jurassic deposits of Würtemberg, in which
-remains of these animals occur in great profusion. His researches,
-and those of several authors since then, supplementing and confirming
-or disproving those of the many observers made during the preceding
-seventy years, have finally determined almost perfectly the complete
-structure of the more typical ichthyosaurs, enabling us to infer not a
-little as to their habits and distribution in the old Jurassic oceans.
-Within the past few years the discoveries of Professor J. C. Merriam of
-California have likewise added greatly to our knowledge of the earlier
-ichthyosaurs. It may now truthfully be said that of no group of extinct
-reptiles do we have a more complete and satisfactory knowledge than of
-the ichthyosaurs.
-
-[Illustration: FIG. 52.—_Ichthyosaurus quadricissus._ Photograph of
-specimen in Senckenberg museum, from Dr. Dreverman.]
-
-Nevertheless we have yet very much more to learn about the order
-Ichthyosauria as a whole—whence they came and how they originated;
-what their nearest kin were among other reptiles; and especially, more
-about the connecting links between them and terrestrial reptiles. They
-have, as an order, so isolated a position, are so widely separated from
-all other reptiles in structure, that they have long been a puzzle to
-paleontologists. Like the whales and other cetaceans among mammals,
-we know the ichthyosaurs well in the plenitude of their power and the
-fulness of their development, but have yet only an imperfect knowledge
-of their earlier history, and none whatever of their earliest. However,
-as will be seen farther on, the recent discoveries by Merriam have
-shed much light on some of the stages of their evolution. So nearly
-perfectly were all the later ichthyosaurs adapted to their life in the
-water that it was believed by nearly all paleontologists until about
-a score of years ago that they had descended directly from fishes.
-But this belief has been quite abandoned by all, not only because the
-recent discoveries of the earlier ichthyosaurs have demonstrated a
-positive increase in the aquatic adaptations of the later forms, but
-also because a double origin of any type of animal life is quite out of
-accord with all known facts and principles of paleontology. It is quite
-possible for animals, in becoming adapted to peculiar environmental
-and food conditions, to acquire certain resemblances to other animals,
-but quite impossible for them to acquire their actual structure. The
-ichthyosaurs are true reptiles, and all reptiles must have had a common
-origin.
-
-[Illustration: FIG. 53.—_Baptanodon (Ophthalmosaurus)._ Skull from
-the side, from above, and from below (after Gilmore): _ang_, angular;
-_bs_, basisphenoid; _d_, dentary; _fr_, frontal; _j_, jugal; _la_,
-lacrimal; _mx_, maxilla; _na_, nasal; _oc_, occipital condyle; _p_,
-palatine; _pa_, parietal; _pm_, premaxilla; _po_, postorbital; _ps_,
-parasphenoid; _pt_, pterygoid; _pf_, prefrontal; _sa_, surangular;
-_sp_, splenial; _sq_, squamosal; _st_, supratemporal; _q_, quadrate;
-_qj_, quadratojugal.]
-
-[Illustration: FIG. 54.—Occiput of _Baptanodon (Ophthalmosaurus)_:
-_pa_, parietal; _soc_, supraoccipital; _sq_, squamosal; _exoc_,
-exoccipital; _op.o_, paroccipital; _sta_, stapes; _st_, supratemporal;
-_qu_, quadrate; _qj_, quadratojugal; _pt_, pterygoid; _bs_,
-basisphenoid; _sag_, surangular; _ag_, angular; _art_, articular;
-_pra_, prearticular. (After Gilmore.)]
-
-We are sometimes in doubt, however, as to whether characters resembling
-those of other animals are really acquired as adaptations to peculiar
-environments, that is, parallel, convergent, or homo-plastic
-characters, or whether they are due to heredity from remote ancestors.
-The reptilian characters of the ichthyosaurs, however, are so emphatic
-that they can only be ascribed to heredity. Ichthyosaurs are as truly
-reptilian as crocodiles or snakes, notwithstanding their fish-like form
-and habits. The ichthyosaur ancestors were once truly land reptiles—of
-that we are as sure as we well can be. Some have thought that those
-ancestors were the primitive Rhynchocephalia, but most are now
-convinced that they were among the most primitive of reptiles, a branch
-probably from the cotylosaurs or cotylosaurian ancestors. Probably of
-all the extinct forms that we know the Proganosauria come the nearest;
-indeed it is not impossible that they may have been the actual forbears
-of the ichthyosaurs.
-
-The ichthyosaurs varied in length from two to thirty feet, but the
-different species, especially all the later ones, resembled each other
-pretty closely in shape; the beak was more slender in some than in
-others, and the shapes of the fins and paddles varied not a little, as
-we shall see. The jaws were long and slender, provided with numerous
-rather small but sharp and recurved teeth, especially well fitted for
-the seizure and retention of slippery prey. The teeth were inserted,
-not in separate sockets, as are those of the crocodiles and many other
-reptiles, but in long, deep grooves, and were easily lost, indeed so
-easily lost that one late American form was originally described as
-edentulous, and it was not till a number of years had elapsed that
-the teeth were found. The nostrils were small, and situated far back
-on the sides of the face, near the eyes. The eyes were very large,
-not only in proportion to the size of the skull, but, in the largest
-species, actually attaining in some, perhaps, the size of a human head.
-The eyeball was surrounded in front by an extraordinarily large and
-strong ring of ossifications in the sclerotic membrane, giving not only
-protection to the eye under the varying pressure of the water, but
-also greater control over vision. The neck was very short, so short,
-in fact, that no construction was visible in the living animal between
-the head and body; it was capable of only slight movement. The trunk
-was elongated and relatively slender, sometimes with more than fifty
-vertebrae in it. The tail also was long and flattened, ending in all
-the later species in a large fleshy fin, resembling the caudal fin of
-many fishes in shape and doubtless also in function. There was also a
-large dorsal fin, supported by hardened or calcified sinews, in shape
-like the dorsal fin of most fishes and many cetaceans. This character
-is absolutely unique among reptiles, so far as is known, and was one of
-the extreme specializations of water life. The hind limbs were smaller,
-often much smaller than the fore ones, and both were quite fin-like in
-life, or rather flipper-like, though not at all fin-like in structure.
-The skin was smooth and bare. In brief, to quote Fraas’s words:.
-
-      The general aspect of the ichthyosaurs was very
-    dolphin-like. The body was everywhere naked and probably
-    dark in color. The head was produced in front into a
-    long, slender snout, and was closely joined to the body
-    posteriorly without indications of a neck. The body itself
-    was cylindrical, expanded in front by the large thorax and
-    abdomen, but rapidly diminishing into the long, slender, and
-    strong tail. Close behind the head were the front paddles,
-    which in some species were broad and shovel-like, in others
-    elongated and pointed. The hind paddles were smaller than
-    the front ones, sometimes greatly reduced in size, their
-    function replaced by that of the very broad tail.
-
-From the foregoing descriptions and the restoration shown in Fig. 51,
-we see how very fish-like, or rather dolphin-like, these animals were
-in the external form—so fish-like that the name _Ichthyosaurus_ is not
-misleading, though Koenig gave it in the mistaken belief that they were
-really allied to the fishes. When to these external features certain
-other fish-like details of the skeleton are added, we do not wonder
-that the early observers were so long in doubt about them. A more
-careful examination of the skeleton will, however, disclose so many
-truly reptilian characters that their external appearance and habits
-lose all significance.
-
-The vertebrae are deeply biconcave and fish-like, it is true, but a
-consideration of the reasons therefor will convince us that any other
-kind of vertebrae would be more remarkable. At the time when the
-ichthyosaurs must have originated, at the time when the first known
-ichthyosaurs appeared in geological history indeed, all reptiles had
-biconcave vertebrae, and for the most part at least deeply biconcave
-ones. The vertebrae remained fish-like throughout all their history,
-perpetuating their type until most other reptiles had developed a
-firmer one, because such vertebrae were best adapted for the quick,
-pliant movements of the spinal column so necessary for the well-being
-of the animals in the water. In the modern dolphins, animals in shape,
-size, and habits most wonderfully allied to what these old reptiles
-must have been, the small, flat-ended vertebrae are widely separated by
-disks of flexible cartilage.
-
-Not only were their vertebrae fish-like in form, but there are other
-characters in the spinal column of a primitive or generalized nature.
-As in all aquatic animals, the articulating processes between the
-vertebrae are either weak or wanting in the posterior part of the
-column. And they were not only small, but were situated, in many,
-high up, very remarkably resembling the peculiar arrangement of the
-articulations in the dolphins.
-
-There is no sacrum, that is, there were no united vertebrae posteriorly
-for the attachment and support of the pelvis, as no such support was
-needed. In only one other group of aquatic reptiles was the sacrum
-lost, though it has wholly disappeared in the cetaceans and sirenians
-among mammals. The chevron bones of the tail, usually bony arches on
-the under side of the tail for the protection of the blood-vessels, in
-crawling reptiles, were very imperfectly developed in the later forms,
-though normal in shape in the early ones. The ribs are numerous, long,
-and slender, very much resembling those of the fish-eating dolphins.
-They usually had, however, two attachments to the body of the vertebra
-and none to the arch, differing in this respect from all other animals.
-
-Of the shoulder bones, the scapula or shoulder-blade, as usual among
-water animals, is short and broad. In the place of a sternum the
-coracoids joined each other broadly in the middle, just as they did
-in the oldest known land reptiles. And there were clavicles and an
-interclavicle. Below the abdomen behind were numerous slender bones
-called ventral ribs. The pelvis is very weak, and was suspended
-below the spinal column in the fleshy walls of the abdomen. The hind
-legs were so small that little support was necessary for them, and,
-because they were not used either for the support of the body or for
-propulsion, they did not require a firm union with the skeleton.
-Doubtless had the ichthyosaurs continued to the present time, they
-would have lost entirely the hind legs, as have the cetaceans.
-
-[Illustration: FIG. 55.—Pectoral girdle of _Baptanodon
-(Ophthalmosaurus)_, an American Upper Jurassic ichthyosaur. (After
-Gilmore.)]
-
-It is in the limbs that most extraordinary differences from all other
-animals are seen. So great are these differences that it has been a
-puzzle to naturalists to understand how they could have arisen. In no
-other animals above the fishes, that is, in no other reptiles, in no
-amphibians, birds, or mammals, are there ever more than five fingers or
-five toes, the number with which air-breathing animals began. Fingers
-and toes may be lost and often are lost in all groups of life, until
-a single one in each limb may remain, as in the domestic horse. An
-increase of fingers and toes, however, seems to be an impossibility
-in evolution, and doubtless of real fingers and toes it is an equal
-impossibility. All naturalists are now agreed that a specialized
-character can never revert to a generalized condition, or rather to a
-generalized structure, that an organ once functionally lost can never
-be regained by descendants. A character once lost is lost forever;
-horses of the future can never have more than one finger or one toe in
-each limb.
-
-[Illustration: FIG. 56.—Front paddle of _Ophthalmosaurus_ (after
-Andrews): _h_, humerus; _r_, radius; _u_, ulna; _p_, pisiform; _re_,
-radiale; _int_, intermedium; _ue_, ulnare.]
-
-[Illustration: FIG. 57.—Front paddle of _Merriamia_, a Triassic
-ichthyosaur. (After Merriam.) Explanations as in Fig. 56.]
-
-And there was an increase in the ichthyosaurs, in some not only of
-the number of digits in each limb, but in all of the number of bones
-in each digit, a character found also in the unrelated mosasaurs and
-plesiosaurs. This increase in finger and toe bones, or hyperphalangy
-as it is called, is one of the most peculiar of all the adaptations to
-water life, changing the feet and hands from the ordinary walking type
-to the fish-like swimming type. The bones beyond the humerus and femur
-in the ichthyosaurs were so increased in number and so changed in form
-and relations that they bear little resemblance to the corresponding
-bones of other reptiles. They are merely polygonal platelets of bone,
-articulating on all sides and fitting closely together, permitting
-flexibility, but not much else.
-
-It is now believed that the increase, not only of additional
-digits, sometimes to as many as ten in each hand and foot, but
-of the finger and toe bones as well, was the result of a sort of
-vegetative reproduction. The margins and ends of the flippers were
-doubtless hardened by cartilage or fibrous material, and because of
-the action of the limbs this cartilagenous material broke up into
-nodules each of which took on ossification finally. Among the whales,
-where hyperphalangy also occurs, though to a less extent, it has
-been thought that the increase in number has been due simply to the
-ossification of the parts of each bone normally present, that is, to
-the epiphyses, which became separated from the shaft of each bone. But
-this explanation will hardly suffice for the fingers and toes of the
-plesiosaurs and ichthyosaurs, for there are altogether too many such
-ossifications; and besides, the bones in these animals, as in most
-reptiles, did not have epiphyses, or terminal separate ossifications of
-the bones of the skeleton.
-
-It will be observed from the figures that the arm and thigh bones
-of _Ichthyosaurus_ are very much shortened—a striking adaptation to
-water life, so conspicuously seen in the modern whales and dolphins
-as well as in the mosasaurs, thalattosaurs, etc. So characteristic
-indeed is this shortening that, were every other bone of the skeleton
-of an ichthyosaur unknown save the humerus or femur, it would be quite
-certain from these alone that the animal was thoroughly aquatic in
-habit.
-
-About sixty years ago a rather aberrant form of ichthyosaur, now
-known as _Mixosaurus_, was discovered in rocks of Triassic age, that
-is, of much greater age than any ichthyosaurs previously found, in
-which not only the forearm but also the lower leg bones were longer,
-resembling more the corresponding bones of land animals. It was from
-the examination of specimens in 1887 of these mixosaurs that the
-late Professor Baur became convinced that the ichthyosaurs were the
-descendants of land reptiles, and not directly of the fishes as they
-were universally thought to have been at that time. As Professor Baur
-very pertinently said, if the ichthyosaurs were descended from the
-fishes directly, the earliest forms should be more nearly like the
-fishes than the later ones, whereas just the opposite was the real
-fact. The arguments which he gave in support of his contention were so
-convincing that they found immediate acceptance among all naturalists.
-Fortunately within the past fifteen years many other remains of early
-ichthyosaurs from the Triassic rocks of California have been brought
-to light by Professor Merriam, remains which throw a flood of light
-upon the early, though not the earliest, history of these strange
-reptiles. He has recognized among the forms he has discovered, not
-only new species, but several new genera, and perhaps new families
-of ichthyosaurs. His studies have demonstrated so well the stages of
-evolution between the early ichthyosaurs and the later ones in their
-progressive adaptation to water life that it will be of interest to
-summarize them here.
-
-In the early ichthyosaurs locomotion was largely by the aid of the
-limbs; in the later ones almost exclusively by the aid of the caudal
-fin. In the former the paddles were larger and the bones longer, more
-like those of land animals; in the latter they were relatively smaller
-and shorter, and more fin-like. In the digits of the early forms the
-finger and toe bones were more elongated and fewer in number. The hind
-limbs were nearly as large as the front ones in the Triassic, often
-very much smaller in the later ichthyosaurs; and the increased number
-of digits occurs only in the later forms.
-
-In the Triassic ichthyosaurs, all classed in the family Mixosauridae,
-the pelvis was larger and more firmly connected with the body than in
-the later forms.
-
-The skull of the early forms was relatively shorter, as compared with
-the trunk, the jaws shorter as compared with the head, the eyes were
-relatively small, the teeth in some less numerous, and set in distinct
-sockets like those of land reptiles; the vertebrae were relatively
-longer and less fish-like, and their articulations more like those of
-land reptiles.
-
-The distal part of the tail was not bent downward so sharply, that
-is, the terminal fin was smaller, or the tail may have been simply
-flattened near its end and not really fin-like. The scapula was longer
-and less fan-like in shape.
-
-And all these are remarkable evidences of an increased adaptation
-to water life in the more recent ichthyosaurs over the older ones.
-Were someone now so fortunate as to find ichthyosaurs in late Permian
-rocks, we should doubtless have the nearly complete chain between the
-most highly specialized type of water reptiles and their terrestrial
-ancestors.
-
-[Illustration: FIG. 58.—Caudal fin of _Ichthyosaurus_, after Baur (left
-figure); caudal fin of _Mixosaurus_, after Wiman (right figure).]
-
-From the structure of the skeleton alone the early observers were
-justified in inferring much concerning the shape and habits of the
-living ichthyosaurs. Later discoveries have added so many definite
-facts that, at the present time, we know more about their habits
-than we do of any other extinct reptiles. In various places in
-England and Germany, especially in Würtemberg, the remains of
-ichthyosaurs are found in extraordinary abundance and perfection, not
-only whole skeletons lying in the positions which they had assumed
-after the decomposition of their bodies, but also often the actual
-remains, carbonized, of the skin, muscles, and ligaments, as well as
-delicate impressions of external parts. Many of these skeletons are
-obtained from the numerous stone quarries, where they are a sort of
-“by-product,” the sums received for them adding not a little to the
-income of the quarrymen. So many are obtained in this and other ways
-that specimens of ichthyosaurs are perhaps more frequently seen in the
-museums of the world than those of any other extinct backboned animal.
-Fairly complete skeletons may now be purchased of dealers in such
-things for from fifty to seventy-five dollars. As may be supposed, the
-best and most complete collections of these fossil remains are those of
-the British Museum in London and the museum in Stuttgart. From a study
-of those of the last-mentioned museum Professor Fraas has learned many
-interesting facts and reached many interesting conclusions regarding
-the life-habits of the ichthyosaurs. In the accompanying figure (Fig.
-59) is shown a photographic reproduction of a very complete specimen,
-in which not only is the outline of the whole body shown, but also much
-of the carbonized remains of the muscles and skin has been detected.
-
-[Illustration: FIG. 59.—_Ichthyosaurus quadricissus._ (From a
-photograph from B. Hauff, Paleontologisches Atelier, Holzmaden.)]
-
-The attachment of the paddles to the body was broad antero-posteriorly,
-proving conclusively that they could not have been much used in
-propulsion, either in the water or upon land, since such use would
-require a fore-and-aft movement, and a consequent twisting or rotation
-of the whole arm or leg, which, because of the broad attachment, must
-have been very difficult, if not impossible.
-
-Microscopic examination of the remains of skin preserved disclosed
-an abundance of dark pigment, indicating, Professor Fraas believes,
-that the skin was dark colored above. Doubtless, also, the under
-side, as in nearly all swimming animals of the present time, was of
-a lighter color, because such coloration rendered the animals much
-less conspicuous in the water when seen either from above or below.
-That the skin was bare is proved by many impressions or molds of it
-that have been discovered in the rocks, in which many fine creases are
-seen, but nothing suggesting scales or bony plates, save on the front
-edge of the paddles, where impressions of overlapping scales have been
-observed. This is an interesting fact, bearing witness that their land
-ancestors had been covered everywhere with scales, much like those
-of existing lizards and other reptiles. Scales or bony plates were
-not only useless to the ichthyosaurs in the water, since they could
-afford no protection, but would have been detrimental in increasing the
-resistance in swimming.
-
-That the ichthyosaurs were predaceous animals is of course evident
-from their teeth, adapted for the seizure and retention of slippery
-prey, but not for tearing or comminuting. The fossilized remains of
-food found between the ribs of some specimens, in the place where the
-stomach was, together with fossil excrement, called coprolites, usually
-attributed to these animals, prove that they fed largely upon fishes,
-squids, belemnites, and probably other invertebrates. One ichthyosaur
-specimen preserved in the Stuttgart Museum has preserved in its stomach
-contents a mass composed of the remains of more than two hundred
-belemnites.
-
-Most interesting of all is the fact that, not very rarely, embryonic
-skeletons of ichthyosaurs have been found associated with the remains
-of adult animals, in such positions that they must have been inclosed
-within the body cavity at the death of the animals. As many as seven
-such embryonic skeletons have been observed with a single specimen. At
-first it was supposed that these skeletons were of small ichthyosaurs
-which had been swallowed whole as food, since it is not at all likely
-that these predaceous reptiles were discriminative in their choice
-of food when hungry. It is not improbable that in some cases this is
-the true explanation of the smaller skeletons within the larger ones,
-but it cannot be true of all, since wherever the small skeletons are
-identifiable they have been found to belong to the same species as the
-adult, and it would be absurd to suppose an ichthyosaur bent upon its
-prey would be at all likely to select as many as seven young animals,
-all of the same size and all of its own species. Furthermore, some
-of these young skeletons have been found in such positions as would
-indicate that they were inclosed within their egg-covering at the time
-of their death. Some of these embryos measure as much as twenty inches
-in length.
-
-Because the ichthyosaurs were born alive, and because so many of their
-skeletons are found with their various parts in orderly relation
-to each other, it is inferred with much probability that they were
-inhabitants, in large part at least, if not exclusively, of the open
-and deeper oceans. Had they been oviparous they must necessarily have
-laid their eggs upon the beaches, since no reptiles of the present
-time lay eggs in the water, and we have no other indications that
-the reptiles of the past have ever done so. And such habits would
-necessitate the periodical return to land. Had they been denizens of
-shallow waters, like the mosasaurs and plesiosaurs for the most part,
-their skeletons must surely have been disturbed by the currents and
-tides, as also by predaceous fishes, breaking up or displacing them or
-carrying away their bones. In shallow waters, also, the decomposing
-bodies would have been more liable to despoliation by the many
-scavengers of the seas.
-
-The ichthyosaurs must have been quite helpless upon land, their limbs
-being of little more use for locomotion than are the fins of fishes.
-Breathing air as they did, they were of course not suffocated when
-exposed, unless, as is the case with the whales, the feeble attachment
-of the ribs prevented the action of the respiratory muscles. If
-accidentally thrown upon the beaches, they doubtless were able to
-return to their home element more easily than the fishes can, by
-flopping, wriggling, and turning. As we have seen, the food consisted
-in part, perhaps the larger part, of small invertebrates, and because
-the bones of the lower jaws were closely united, permitting little or
-none of that expansion so characteristic of the snakes, all their prey
-must have been of relatively small size. In habit the ichthyosaurs were
-doubtless, like the dolphins and gavials, inoffensive and harmless,
-so far as animals of larger size were concerned. The abundance of
-their remains often found in restricted localities, while deposits of
-like age and character not far distant may be almost free from them,
-suggests that in all probability the ichthyosaurs, or the later ones at
-least, were more or less gregarious in habit as are the sea-mammals.
-They probably lived in schools, as do the porpoises, each species
-keeping to its restricted locality and not wandering far.
-
-The ichthyosaurs began their existence, so far as we now know, about
-the middle of Triassic times and continued to near the middle of Upper
-Cretaceous, when they disappeared forever from geological history.
-As we have seen, however, the earliest forms that we know were true
-ichthyosaurs in all respects, though more primitive than the later
-ones, indicating a long previous existence of which we yet have no
-knowledge. Their remains have been found widely distributed in Triassic
-rocks of Europe, Spitsbergen, Australia, and North America. During the
-Jurassic period they lived in great numbers and variety throughout
-the region that is now Europe. In North America the only marine rocks
-of this period that we know of have yielded numerous remains. These
-American ichthyosaurs were, however, among the most specialized of all
-ichthyosaurs—the culmination of their development. They were originally
-named _Sauranodon_ in the belief that they were toothless, but in
-recent years their teeth, small and numerous, have been discovered. And
-the genus seems also to be identical with one previously named from the
-Jurassic of Europe called _Ophthalmosaurus_. The last known remains
-of ichthyosaurs have recently been found in the Benton Cretaceous of
-Wyoming. Scanty remains of ichthyosaurs are also known from Australia
-and New Zealand. Why the ichthyosaurs should have gone out of existence
-before the plesiosaurs and mosasaurs did, one cannot say; possibly
-their stock had grown old and feeble.
-
-
-
-
-CHAPTER IX
-
-PROGANOSAURIA
-
-MESOSAURUS
-
-
-There is some doubt whether those little creatures of Paleozoic times,
-to which some years ago the late Professor Baur gave the ordinal
-name Proganosauria, are really entitled to so much distinction among
-reptiles. The question of their rank has been much disputed for the
-past twenty years without any positive conclusion. Nor were they wholly
-aquatic in habit, though they did possess many aquatic adaptations.
-That they were skilful and fleet swimmers, and capable of rapid
-evolutions in the water is quite certain, and, as the oldest known
-water reptiles, they are of more than passing interest.
-
-[Illustration: FIG. 60.—_Mesosaurus_; life restoration, after McGregor,
-the posture of hind leg slightly modified.]
-
-But two genera and three or four species of the group are known, and
-of them, even, our knowledge in some respects is not as complete as
-one could desire. The first description of any member of the group
-was by the late Professor Gervais of Paris in 1867. He had only the
-anterior part of a single skeleton, from the Karoo beds of South
-Africa, to which he gave the name _Mesosaurus_, a rather meaningless
-term signifying “middle” or “intermediate” saurian. Nothing more
-was learned about any form till 1885, when the late Professor Cope
-described a specimen from the supposed Carboniferous of Brazil, which
-he believed to be closely related to _Mesosaurus_, though he had
-only a very imperfect specimen. He called it _Stereosternum_, also a
-meaningless term, since none of the animals has a “solid sternum,”
-nor any sternum at all, in fact! A few years later, in 1888 and 1892,
-the late Professor Seeley of England studied a number of specimens of
-_Mesosaurus_, adding not a little to our knowledge of the animals. More
-recently Dr. Woodward of England and Professor Osborn of America have
-given us still further information concerning them, and within the past
-few years Dr. McGregor of Columbia University has figured and described
-excellent specimens of a new species from Brazil, which he calls
-_Mesosaurus brasiliensis_. Not only were Dr. McGregor’s discoveries
-of great interest as settling many doubtful points in their structure,
-but they were still more so from the fact that he found his species
-so nearly like that from Africa that he placed it in the same genus.
-Since the proganosaurs were purely fresh-water or terrestrial animals,
-one can only wonder how they crossed from Africa to America, or, what
-is more probable, how they migrated from America to Africa, across the
-broad Atlantic Ocean, so long ago. The geologists tell us that the
-Atlantic and Pacific, in the main, have always been oceans since the
-beginning of terrestrial life upon the earth. Possibly the tribe of
-proganosaurs migrated by the very circuitous route of Europe and North
-America, or Asia and the Northwest; but that is very improbable, since
-nothing whatever resembling them has ever been found in the Northern
-Hemisphere, and it is quite certain that in the many thousands of
-years it must have taken them to travel from southern Africa to South
-America many of the reptiles must have perished on the way and left
-their remains in the rocks. The only conclusion that seems probable is
-that there was a direct land communication in those olden times between
-Africa, or at least India, and South America across what is now the
-Atlantic Ocean. Of course this route will be very difficult to prove,
-since we can never get to the bottom of the ocean to hunt for fossil
-proganosaurs. Were this peculiar distribution of the proganosaurs an
-isolated example, one might perhaps ascribe our lack of knowledge of
-any fossil proganosaurs in the Northern Hemisphere to the meagerness of
-the fossil records, but there are many other examples of similar import
-among other early animals.
-
-[Illustration: FIG. 61.—_Mesosaurus_; restoration of skeleton. (After
-McGregor)]
-
-The age of the South American proganosaurs is now believed to be lower
-or lowermost Permian, like that of the African _Mesosaurus_; possibly,
-however, the age first described to _Stereosternum_ (Carboniferous) may
-be correct.
-
-The known skeletons are all small, none exceeding a few feet in length.
-The skull, as shown in the figure by Dr. McGregor, is elongate, and
-its teeth are extraordinarily so, and very slender. The external
-nostrils are situated close to the eyes; and no sclerotic bones have
-been discovered. There are small teeth in the bones of the palate.
-The neck is elongate, composed of ten or twelve vertebrae. The trunk
-also is long and slender, and the tail is not only long, but also
-much flattened or compressed. All these are very characteristic of
-water life. The limbs, however, show a much less complete adaptation
-for swimming—not much more so in fact than do those of the living
-Crocodilia. The upper arm and the thigh bones are relatively long,
-while those of the forearm and the leg are shorter than among
-terrestrial reptiles, the first indication of swimming habits to appear
-in crawling animals. The digits are not much elongated, and they
-have no additional finger bones, save perhaps in a lately discovered
-form in Africa, in which Dr. Broom reports supernumerary bones in
-the fifth or “little” toe.[3] The fingers and toes have only blunt
-terminal bones, that is, they were not distinctly clawed, and they
-were probably connected with each other by a membrane, as in a frog’s
-foot. This webbing of the feet is probable, not only because of the
-positions in which the bones have been found, but also because of the
-great length of the “little” toe, which is the longest in the foot, a
-character quite abnormal for a land reptile and quite characteristic
-of certain aquatic mammals, like the seals and sea-otters. There is
-a strong sacrum of two vertebrae, however, the pelvis and hind legs
-being connected with the spinal column firmly, clearly proving that,
-like the crocodiles, the proganosaurs had by no means lost their land
-proclivities.
-
-[3] An additional phalange has also been observed in the fifth toe of a
-South American species.
-
-Their vertebrae, as would be expected in such old reptiles, are quite
-primitive in structure, that is, they are deeply concave in each end,
-probably being perforated for the remains of the notochord. The pelvis
-also is of the old-fashioned type, that is, without an opening or
-vacuity between the bones below. The shoulder bones are old fashioned
-too. The shoulder-blade, especially, shows a decided adaptation to
-water life in its short, fan-like shape, very much like those of the
-mosasaurs, ichthyosaurs, whales, etc. Just why swimming animals should
-have short and broad shoulder-blades has not yet been explained, but
-doubtless they afforded better attachment for those muscles used more
-especially in swimming. The ribs are remarkably flat and heavy, and
-were not very firmly attached to the vertebrae. Heavy ribs are unusual
-among free swimming animals, but do occur in the modern sirenians,
-which live on the bottoms of shallow bays, etc., feeding upon plants.
-We may perhaps infer from this peculiar structure of the ribs that
-the proganosaurs lived more on the bottoms of shallow waters, feeding
-upon such fishes or invertebrates as they could capture, coming to the
-surface to breathe from time to time. Possibly they sought the shores
-for safety from their enemies, as do the Galapagos lizards, figured
-on p. 142; and doubtless they laid and hatched their eggs on land.
-A character which suggests that the proganosaurs lived only in the
-shallow waters is the elongated neck, reminding one of those two other
-groups of swimming reptiles, the dolichosaur lizards and the nothosaurs
-of the Sauropterygia, the only known reptiles besides the plesiosaurs
-having an abnormal number of neck bones. Still more suggestive of
-shallow, fresh-water habits is the absence of eye bones, as in the
-modern crocodiles.
-
-The long snout, with the long and slender teeth, and the position
-of the external nostrils far back near the eyes, together with the
-flattened and long tail and the webbed feet, are sufficient proof of
-expert swimming habits. The legs still functioned more or less for the
-support and propulsion of the body on the land, and they probably were
-only of slight service in the water. The alligator swims sinuously
-with its front legs collapsed and extended by the side of the body;
-its hind legs are used more as propellers, with the knee flexed and
-the feet turned outward and expanded. The legs of the proganosaurs
-doubtless were used in the same way, as shown in the restoration, which
-has been modified from the original of Dr. McGregor in accordance with
-this probable use of the legs.
-
-There seems to be an incongruity between the posterior nostrils and the
-heavy flat ribs, the former suggesting free swimming and diving habits,
-the latter shallow water and bottom habits. Possibly the position of
-the nostrils has been the result of the great elongation of the face in
-front of the nostrils; and we know that their posterior position in the
-phytosaurs (Figs. 95 and 96) has not been due to swimming habits only.
-
-Nothing has been discovered to indicate the nature of the external
-covering of the body. Possibly, even probably, the skin was more or
-less covered by horny scales or plates, though it may have been quite
-bare, as in the salamanders.
-
-To which other reptiles the proganosaurs are nearest related has long
-been a subject of dispute, and still is. The more probable view,
-however, is that they were a very early branch of the most primitive
-stock of reptiles, the Cotylosauria, one that soon perished, leaving
-no descendants, unless possibly the ichthyosaurs were their progeny.
-Some writers have thought that they were the early ancestral stock of
-the plesiosaurs, and they are often classified with the Sauropterygia.
-Still others have believed that they were an early side-branch of the
-great group of Rhynchocephalia. And this doubt has been chiefly due
-to our imperfect knowledge of the bones of the cranium. As has been
-explained, very much stress in the classification of reptiles has been
-laid by students on the possession of one, two, or no openings on the
-side of the skull back of the eyes. And this part of the skull of the
-Proganosauria has not yet been satisfactorily made out. Dr. McGregor
-thought that there are two openings in the temporal region, allying the
-group with the Rhynchocephalia. Dr. Huene is more positive that there
-is but one, like that of the ichthyosaurs. In this state of indecision,
-the proganosaurs may be dignified by giving them an ordinal position by
-themselves.
-
-
-
-
-CHAPTER X
-
-PROTOROSAURIA
-
-
-PROTOROSAURUS
-
-The genus _Protorosaurus_ is of peculiar interest, as one of the first,
-if not the first, known fossil reptiles, described by Spener as long
-ago as 1710 as a crocodile, from fragmentary remains found in 1706 in
-the Permian deposits of Thuringia. Numerous other skeletons or parts
-of skeletons attracted the attention of naturalists of the eighteenth
-century, but were very imperfectly described. No name was given to the
-animal represented by the various specimens until 1840, when Herman
-von Meyer restudied all the known material and described it under the
-name _Protorosaurus speneri_. The position of the genus among reptiles
-always has been and yet is uncertain, for the reason that the structure
-of the skull, and especially the structure of the temporal region, has
-never been satisfactorily determined. Seeley, in 1887, described more
-fully the original specimen of Spener, now preserved in the museum of
-the College of Surgeons of London, and because of certain peculiarities
-which it showed proposed for its reception the order Protorosauria.
-He thought that he detected an upper temporal vacuity, like that of
-lizards, but was very uncertain about the structure of the lower
-part of the temporal region. The writer, who has examined this type
-specimen, must admit that the structure of the region here is very
-doubtful. Under the general assumption, however, that all old reptiles
-must be related to _Sphenodon_, the Protorosauria have generally been
-classified as a suborder of the Rhynchocephalia. It is merely another
-instance of the proclivity we all have to propose hypotheses, and then,
-speedily forgetting that they are hypotheses, to accept them as facts.
-
-_Protorosaurus_ was long supposed to be an aquatic reptile, but we now
-know that it was a strictly terrestrial one, probably with climbing
-habits; and the genus concerns us only by reason of its possible
-relationships to distinctly aquatic reptiles of a later age.
-
-[Illustration: FIG. 62.—Life restoration of _Araeoscelis_.]
-
-A few years ago the writer described a very slender, lizard-like
-reptile about two feet in length from the Permian of Texas under
-the name _Araeoscelis_, so named because of its slender legs. The
-structure of both the skull and the skeleton of this reptile is now
-quite satisfactorily known, so well known indeed that the accompanying
-restoration (Fig. 62) has little that is conjectural about it, at
-least so far as the form is concerned. The skull has a single, upper
-temporal opening, quite like that of lizards, but the quadrate is
-not loose below. And this is really what we should expect in the
-ancestral lizards; and everything else of the skeleton, except perhaps
-one character, is what would be expected. That one character is the
-elongation of the cervical vertebrae, which are about twice the length
-of the dorsal vertebrae following them. The cervical ribs are very
-slender bones, articulating by a single head with the centrum only. In
-these and other characters, so far as they are known, _Araeoscelis_
-seems to agree with _Protorosaurus_, and both have very hollow bones.
-
-[Illustration: FIG. 63.—Skeleton of _Pleurosaurus_. (After Lortet)]
-
-
-PLEUROSAURUS
-
-We may for the present be justified in maintaining the order
-Protorosauria for those reptiles having a single, typically upper
-temporal opening on each side, with a fixed quadrate, not including
-the ichthyosaurs. It is not improbable, however, that when more is
-known of the ancestors of the lizards, the whole group will find its
-most natural place among the Squamata. This definition will include
-a peculiar aquatic reptile that has been known for many years, but
-which has been wrongly classed in the same family as _Sphenodon_, on
-the purely gratuitous assumption that it has two temporal openings
-on each side; we now know that it has but one. This reptile, known
-scientifically as _Pleurosaurus_, was described originally by H. von
-Meyer in 1843, but we are indebted to M. Lortet for a more precise
-knowledge of the animal, and for the figure (Fig. 63) which is here
-given of the skeleton. Not a few excellent skeletons are preserved in
-the museums at Lyons and Munich. The specimen here figured, as actually
-preserved, measures about three feet in length; a part of the tail is
-missing, which is known from other specimens to have been remarkably
-long.
-
-The figures show clearly some of the remarkable aquatic adaptations of
-the animal, especially the short neck, the very long and narrow body,
-and the extraordinarily long and flattened tail. The head is elongate
-triangular in shape, resembling very much that of the mosasaurs; and
-the external nostrils are likewise situated remotely from the end
-of the snout, as in the mosasaurs. The extremity of the snout has a
-beak-like projection. The teeth are much longer, more pointed, and more
-recurved than is the case with most land reptiles, indicating their use
-for the capture and retention of slippery, quick-moving prey.
-
-The single-headed ribs are short, proving that the body was slender
-and doubtless cylindrical, more like that of a snake. The tail was
-not only enormously elongated, but it was also compressed into a flat
-and effective propelling organ in the water. This flattening of the
-tail is apparent from the skeleton, with its elongated chevrons below
-and spines above, and it is also proved by the fortunate preservation
-of the extremity of the tail of one specimen, showing not only the
-impressions of the scales in the matrix, but also the outlines that the
-soft parts had in life. To quote from Lortet, in translation: “The tail
-was covered wholly with small scales, regularly hexagonal in shape,
-shining and nacreous, larger on the under side than above. The upper
-border of the tail was surmounted by a broad crest, extending to its
-extremity, and composed of large, oval scales.” The body doubtless was
-wholly covered with scales, though it is not probable that the caudal
-crest continued along the back.
-
-[Illustration: FIG. 64.—Life restoration of _Pleurosaurus_.]
-
-The limbs begin to show an aquatic adaptation, though not very
-pronounced. They are much shorter and smaller than are those of
-land-crawling reptiles; and the bones of the second series, that is,
-the radius and ulna, tibia and fibula, are relatively short, the
-beginning of adaptation to water habits. It is very probable that the
-feet were webbed, though the fifth digit, as usual, is shorter than
-the fourth. Doubtless on land the creature moved about in a serpentine
-way, for it could not have progressed very rapidly by the aid of its
-legs alone. The hind legs are longer than the front legs, and they were
-connected firmly with the body by means of a sacrum. The number of
-vertebrae in the neck is only five. The number of dorsal vertebrae is
-forty-three, a larger number than is known in any other air-breathing
-vertebrate with legs.
-
-Upon the whole, these lizard-like, almost snake-like pleurosaurians
-present some very curious adaptations to water life. In water they were
-doubtless speedy, swimming in serpentine undulations, with the small
-legs for the most part folded against the body and only of occasional
-use. Doubtless, too, had the pleurosaurs lived longer in geological
-history, they would have become quite snake-or eel-like, just as have
-some modern salamanders.
-
-In all probability the pleurosaurs lived habitually in fresh-water,
-perhaps visiting the shores for refuge, or for the hatching of their
-young. That they were not on the way toward a terrestrial snake-like
-body is evident from the flattened tail, and especially the crest of
-scales above; the tail was like that of the sea-snakes of the present
-time. _Pleurosaurus_, then, affords the solitary instance among
-reptiles of aquatic adaptation by the diminution of both front and hind
-extremities and the acquisition of a snake-like body and snake-like
-habits.
-
-
-
-
-CHAPTER XI
-
-SQUAMATA
-
-
-The order Squamata, so called because of the dermal covering of
-overlapping horny scales, comprises the great majority of living
-reptiles. Although the scaly covering is characteristic of nearly all
-the members of the order, the most essential differences distinguishing
-them from other reptiles are, as usual, found in the skeleton, and
-especially in the skull. The quadrate bone, that to which the lower
-jaw is articulated on each side, is not wedged in immovably between
-other bones of the skull, as in all other reptiles, but is, instead,
-freely articulated with the cranium in such a way that its lower end
-moves both backward and forward, as well as inward and outward. This
-freedom of movement has in the past been thought to be due to the
-loss of a lower temporal arch, a bony bar connecting the lower end
-of the quadrate with the hind end of the upper jaw, which is very
-characteristic, for instance, of the Rhynchocephalia. Indeed, because
-of the many primitive characters which the lizards possess, it has
-generally been supposed that the order was an early branch of the
-rhynchocephalian stem. But we are now quite sure that the lizards
-are as primitive as the Rhynchocephalia, and that their origin, as
-an independent branch of the reptilian stem, goes quite as far if
-not farther back—quite sure that the ancestors of the lizards never
-had a lower temporal arcade and two temporal vacuities, but that
-the looseness of the quadrate bone has been due to the gradual loss
-of a bone which covered the whole side of the skull until only the
-upper part of it was left. In other words, the ancestral skull of
-the Squamata must have been like that of _Araeoscelis_, more fully
-described under the Protorosauria, a group than which there is perhaps
-none more closely allied to the Squamata.
-
-The bones of the roof of the mouth of the Squamata—that is, of the
-palate—are narrow and long, and are not closely articulated, as in
-most other reptiles; they often bear teeth, a primitive character. The
-teeth of all living lizards and snakes are not inserted in sockets,
-as are those of the crocodiles, but are co-ossified to the margins or
-sides of the jaws or the bones of the palate. But this is probably not
-a primitive character; doubtless the teeth of the early lizards were
-inserted in sockets like those of most other reptiles. The shoulder
-bones are absent in many and vestigial in some others. When present
-and fully developed, they comprise the shoulder-blades or scapulae,
-a single coracoid on each side, the clavicles, and an interclavicle.
-The vertebrae, except in some lizards, are procoelous, that is, with
-the body concave in front and convex behind, a peculiar structure
-that was developed only in crawling animals. In addition to the usual
-articulations for the union of the vertebrae there are also, in some
-of the lizards and mosasaurs and all of the snakes, additional ones
-called the zygosphene and zygantrum, which will be best understood
-by reference to Fig. 12, p. 28. But little less characteristic than
-the loose articulation of the lower jaws, so unique in this order of
-reptiles, is the manner of attachment of the ribs. They are always
-single-headed, articulating only with the body or lower part of the
-vertebra. The single-headed ribs of the plesiosaurs articulate with
-a projection on each side of the arch of the vertebra; those of the
-turtles to the space between the adjacent vertebrae; nearly all other
-reptiles have double-headed ribs, articulating in various ways. This
-character, it is seen, though apparently a simple one, immediately
-distinguishes a lizard or a snake from all other animals, except the
-thalattosaurs and protorosaurs.
-
-There is much difference of opinion among naturalists as to the proper
-classification of the different groups of this order of reptiles.
-Usually it is divided into four suborders, the Lacertilia or lizards;
-the Dolichosauria or long-necked lizards of the past; the Mosasauria,
-or extinct swimming lizards; and the Serpentes or Ophidia, the snakes.
-It matters very little which classification one accepts so long as it
-is remembered that the first three groups are closely related to each
-other.
-
-
-LIZARDS
-
-Popularly a lizard is any four-legged reptile covered with scales,
-but such a definition is not strictly correct, since some lizards are
-legless and some other four-legged reptiles are covered with horny
-scales, notably the tuatera or _Sphenodon_ of New Zealand, a reptile
-long classed with lizards, but now known to belong to quite a different
-order. Bearing in mind those characters given as characters of the
-order, it will be necessary to mention only those distinguishing the
-lizards from the snakes.
-
-[Illustration: FIG. 65.—Iguana. (By permission of the New York
-Zoölogical Society)]
-
-It is true that the great majority of lizards have four legs, while the
-snakes are always functionally legless, but there are some lizards,
-like the glass snakes and the amphisbaenas, or slow lizards, which
-are quite legless and there are some snakes which have small but
-functionless hind legs. As usual, more important differences are found
-in the skull. The brain-case in all snakes is surrounded on all sides
-by bone, for the better protection of the brain, with the head resting
-quite prone on the ground. The brain of the lizards, for the most part,
-is protected on the sides and in front by a simple membrane. Nearly all
-lizards have movable eyelids, while snakes do not; snakes have a single
-lung, and a protrusible tongue, which very few lizards possess; and
-the lower jaws in front are united in the snakes by a ligament only.
-Notwithstanding these differences, the snakes and lizards are closely
-related animals, and must have come from a common ancestry; among all
-reptiles the known geological history of the snakes is shortest.
-
-Lizards, on the other hand, have a very high antiquity, beginning,
-as we now know, at least as long ago as early Triassic times. They
-still have many primitive characters in their structure and are the
-least advanced type of reptiles now living, with the exception of the
-tuatera. Their remains are seldom found in the rocks, probably because
-they have always been so strictly terrestrial in habit, for the most
-part seldom frequenting even the vicinity of the water. The true
-lizards now living number about eighteen hundred kinds, classified into
-about twenty families, divided among four chief groups, of which the
-chameleons, the amphisbaenas, our common lizards, and the monitors are
-representatives.
-
-Most living lizards are inhabitants of warm climates, though some
-extend rather far north in the temperate zone. With the exception of
-New Zealand, and the polar and subpolar regions, lizards are found
-in all parts of the world. The great majority live only in high and
-dry places, though some are denizens of low and marshy places, a few
-even not being averse to the water. They are, for the most part, spry
-in their movements, some little ones scarcely six inches in length
-taxing a vigorous man’s speed to capture; and many are expert climbers
-of cliffs, trees, and even the ceilings of residences. Some, the
-remarkable little flying dragons of Ceylon, have an extraordinary
-development of the skin on the sides of the body, supported by the
-expanded ribs, forming a sort of parachute whereby the creatures
-can sail considerable distances through the air. Nearly all are
-carnivorous, feeding upon small mammals, birds, other reptiles, frogs,
-and insects; a few only are herbivorous, such as the iguanas, which are
-often used for human food. Nearly all lizards are oviparous, laying
-from two to thirty eggs. In size the great majority are small, less
-than a foot in length; but some, such as the monitors and iguanas,
-reach a length of from four to six feet, or even more, and certain
-extinct monitors of India are known to have attained a length of thirty
-feet. They are, for the most part, slender, graceful, prettily marked,
-and quite inoffensive creatures. A few are short, flat, or stumpy in
-shape, such as the so-called horned toad. One or two species only, the
-“Gila monsters,” are reputed to be venomous.
-
-[Illustration: FIG. 66.—_Amblyrhynchus cristatus_, the Galapagos
-sea-lizard. (From Brehm)]
-
-There is but a single species of lizard now living which is in any true
-sense aquatic in habit, the well-known sea-lizard of the Galapagos
-Islands, scientifically known as _Amblyrhynchus cristatus_. It is a
-large lizard, with a short rounded head, a flat tail, and webbed feet.
-Its specific name is derived from the erect fringed crest along its
-back and tail. Its habits are best given in Darwin’s words:
-
-      It is extremely common on all the islands throughout the
-    group, and lives exclusively on the rocky sea-beaches,
-    being never found, at least I never saw one, even ten yards
-    inshore. It is a hideous looking creature, of a dirty black
-    color, stupid and sluggish in its movements. The usual
-    length of a full grown one is about a yard, but there are
-    some even four feet in length; a large one weighed twenty
-    pounds. The tails are flattened sideways, and all four
-    feet are partially webbed. They are occasionally seen some
-    hundred yards from the shore swimming about. When in the
-    water this lizard swims with perfect ease and quickness, by
-    a serpentine movement of the body and flattened tail—the
-    legs being motionless and closely collapsed to the sides.
-    A seaman on board sank one, with a heavy weight attached
-    to it, thinking thus to kill it directly; but when an
-    hour afterward he drew up the line it was quite active.
-    Their limbs and strong claws are admirably adapted for
-    crawling over the rugged and fissured masses of lava, which
-    everywhere forms the coast. The nature of this lizard’s food
-    (seaweed) as well as the structure of the tail and feet,
-    and the fact of its having been seen voluntarily swimming
-    out at sea, absolutely proves its aquatic habits; yet there
-    is in this respect one strange anomaly, namely, that when
-    frightened it will not leave the island. Hence it is easy
-    to drive these lizards down to any little point overhanging
-    the sea, where they will sooner allow a person to catch
-    hold of their tails than jump into the water. They do not
-    seem to have any notion of biting; but when much frightened
-    they squirt a drop of fluid from each nostril. I threw one
-    several times as far as I could into a deep pool left by
-    the retreating tide, but it invariably returned by a direct
-    line to the spot where I stood. It swam near the bottom,
-    with a very graceful and rapid movement, and occasionally
-    aided itself over the uneven ground with its feet. As soon
-    as it arrived near the edge, but still being under water,
-    it tried to conceal itself under the tufts of seaweed, or
-    it entered some crevice. I several times caught the same
-    lizard by driving it to a point, and, though possessed of
-    such perfect powers of diving and swimming, nothing could
-    induce it to enter the water; and as often as I threw it
-    in it returned in the manner described above. Perhaps this
-    singular piece of apparent stupidity may be accounted for by
-    the circumstance that this reptile has no enemies whatever
-    on shore, whereas at sea it must often fall a prey to the
-    numerous sharks.
-
-These lizards are of much interest as indicating one of the ways in
-which true land reptiles have become aquatic in their habits. Tempted
-by the abundance of food growing in shallow water a little beyond their
-reach, the reptiles ventured farther and farther to obtain it. The tail
-gradually became a propelling organ, though the lizard still retained
-in large measure its land habits and land feet, because of the dangers
-from its water enemies. It is not at all improbable that, in course
-of time, were these Galapagos lizards left unmolested, they would
-become fleeter swimmers by the development of a terminal caudal fin
-and paddle-like legs, thus competing with their aquatic enemies and no
-longer needing recourse to the land for protection. They also serve to
-indicate that long-tailed aquatic reptiles never used their legs to an
-appreciable extent as organs of propulsion in the water.
-
-[Illustration: FIG. 67.—_Varanus_, Australian monitor lizard. (By
-permission of the New York Zoölogical Society.)]
-
-_Flat-headed lizards._—Among the living lizards there is one group,
-called the monitors, which have so many characters peculiar to
-themselves that they seem rightfully entitled to an isolated place
-among the lizards of the present time. The group includes about
-thirty species, all belonging in the one genus _Varanus_, and all
-living in India, Africa, and Australia. In size, some of the species
-of _Varanus_ are the largest of all terrestrial lizards known in the
-past or present; in other ways also they have reached the maximum of
-specialization among lizards. The head is pointed, broad, and flat,
-and the body and tail are long. They have nine vertebrae in the neck,
-a larger number than is to be found in any other terrestrial lizard.
-Unlike other lizards they have a protrusible tongue like that of the
-snakes. All are carnivorous in habit, feeding upon small backboned
-animals, insects, and especially upon eggs, which they crush between
-their teeth while holding them aloft. Most species live wholly upon the
-land, and some are arboreal. Others, especially those of the Nile, live
-about water and are excellent swimmers. The terrestrial species have
-a round tail and small external nostrils, but the water species have
-the tail much flattened, and the nostrils have large cavities, which,
-when closed under water, are said to serve as reservoirs of air for
-respiration. Of one of these swimming species Annandale writes:
-
-      _Varanus salvator_ is common in Lower Siam where it is
-    equally at home on land, in water, and among the branches of
-    trees. The eggs are laid in hollow tree trunks. When in the
-    water the lizard swims beneath the surface, the legs being
-    closely applied to the sides, and the tail functioning both
-    as oar and rudder.
-
-These lizards take to the water to escape from their land enemies and
-not for food, a habit also known among certain other lizards, and
-one precisely the reverse of that of the Galapagos lizards. It would
-seem very probable that animals of such carnivorous habits as are the
-monitors might easily learn to capture water animals for food and
-thus eventually become aquatic in habit. This inclination toward, and
-partial adaptation to, water habits in the monitors is of much interest
-because in all probability the instinct is one of long inheritance from
-those remote ancestors which gave origin to the truly aquatic members
-of the order. Though the known geological history of the monitors does
-not extend far back, they are so intimately allied in their anatomical
-structure to the aquatic and semiaquatic lizards of Cretaceous times
-that there could seem to be no doubt of the common ancestry.
-
-_Dolichosaurs._—About fifty years ago Professor Owen, the famous
-English paleontologist, described a peculiar semiaquatic lizard
-from the Cretaceous rocks of England to which he gave the name
-_Dolichosaurus_, in allusion to the slender form of the body. Just what
-relations these slender lizards have to modern lizards has long been
-a problem; some have thought that they were their progenitors, but
-there are very good reasons for doubting this. No modern lizards, save
-the monitors, have more than eight vertebrae in the neck, while these
-dolichosaurs had as many as seventeen, a remarkable specialization for
-aquatic life that could hardly have been lost by their descendants.
-For this reason the dolichosaurs have usually been considered as
-representing a distinct suborder. But they have many resemblances
-otherwise to the monitors. They were semiaquatic in habit, and never
-more than six feet in length. They are yet imperfectly known, and no
-restoration of any form has hitherto been attempted. Their peculiar
-interest lies in the elongation of the neck, quite like that of the
-wholly unrelated nothosaurs and proganosaurs, which have been described
-in the foregoing pages. Doubtless similar habits in each had like
-results, but just what these habits were in the slender lizards we do
-not yet know.
-
-_Aigialosaurs._—Within recent years a number of other lizards have
-been made known from the Lower Cretaceous rocks of Dalmatia which
-present most remarkable intermediate characters between the monitors,
-dolichosaurs, and the mosasaurs, the famous sea-lizards of Upper
-Cretaceous age. Some of these lizards had twelve or thirteen vertebrae
-in the neck, while others had but seven—an unusually short neck
-characteristic of the mosasaurs. These latter kinds, belonging to two
-or three genera, are included in a distinct group. They were long and
-slender, the head long and pointed. The teeth, conical and sharp, were
-attached in shallow pits, quite as in the mosasaurs. The lower jaws
-had a hinge just back of the teeth, as in the mosasaurs, of which the
-only trace in modern lizards is found among the monitors. Still more
-remarkable, though perhaps not so easily appreciated, is the shape of
-the quadrate bone, with a broad flaring rim for the ear cavity, quite
-unlike that of land lizards, but quite like that of the mosasaurs. In
-fact, the very peculiar skull is almost identical with that of the true
-sea-lizards. The body and tail also resemble those of the mosasaurs
-more than those of the monitors, but there is a firm attachment of the
-pelvis to the backbone, and the legs are long and lizard-like, though
-not as long as those of land lizards. The feet were webbed in life, and
-the toes have no claws, conclusively demonstrating their water habits.
-The vertebrae indeed have the same peculiar articulations, called
-zygosphenes, as in most of the mosasaurs. The largest aigialosaurs were
-about six feet in length, that is, of about the size of the smallest
-known mosasaurs.
-
-[Illustration: FIG. 68.—_Clidastes_, an American mosasaur. Life
-restoration.]
-
-We have then in the aigialosaurs nearly every known intermediate
-character that we could wish for in a connecting link between the
-mosasaurs and the monitors, lizards that were equally at home on land
-or in the water, and there can be scarcely a doubt that they were
-either the direct ancestors or closely akin to the direct ancestors of
-the strictly marine mosasaurs; and scarcely a doubt that they were the
-descendants of the actual forbears of the modern monitors, which, as we
-have seen, have acquired partial aquatic habits in escaping from their
-enemies. The dolichosaurs we can now understand were a side branch
-from these semiaquatic aigialosaurs which, specializing in another
-direction, quickly came to grief, perhaps in competition with their
-more agile and skilful short-necked kin.
-
-Taking all these facts into consideration it seems best to unite
-the monitors, dolichosaurs, and aigialosaurs into one group of the
-Lacertilia, the Platynota, intermediate in place between the true land
-lizards and the truly aquatic mosasaurs.
-
-
-MOSASAURS
-
-At St. Pietersberg, a small mountain in the vicinity of Maestricht,
-Holland, there are immense subterranean stone quarries, which have
-been worked for more than a thousand years. The stone quarried from
-them is a sandy limestone of Upper Cretaceous age containing many
-well-preserved remains of extinct animals that have long been sought
-by collectors of fossils. In 1776 Major Drouin—an officer of a near-by
-garrison, one of much military importance in those days—secured from
-one of these quarries some bones of an extinct reptile, which, though
-of interest, afforded but little information concerning the structure
-and affinities of the animal to which they had once belonged. In 1780
-a very perfect skull, in excellent preservation, of the same kind of
-an animal was obtained from the same quarry by Dr. Hofmann, an army
-surgeon of the same garrison, whose interest in such things had been
-incited by Major Drouin’s collections. This specimen, so renowned in
-science, has had a remarkable and eventful human history, in part
-related by St. Faujas de Fond, a French commissary of the “Army of the
-North,” and one of the participants:
-
-      In one of the great galleries or subterranean quarries in
-    which the Cretaceous stone of St. Pieter’s Mount is worked,
-    about five hundred paces from the entrance, and ninety
-    feet below the surface, the quarrymen exposed part of the
-    skull of a large animal in a block of stone which they were
-    engaged in quarrying. On discovering it they suspended
-    their work and went to inform Dr. Hofmann, surgeon to the
-    forces at Maestricht, who for some years had been collecting
-    the fossils from the quarry, remunerating the workmen
-    liberally for the discovery and preservation of them. Dr.
-    Hofmann, arriving at the spot, saw with extreme pleasure
-    the indication of a magnificent specimen; he directed the
-    operations of the men, so that they worked out the block
-    without injury to the fossil, and he then, by degrees,
-    cleared away the yielding matrix and exposed the
-    extraordinary jaws and teeth, which have since been the
-    subject of so many drawings, descriptions, and discussions.
-    This fine specimen which Dr. Hofmann had transported with
-    so much satisfaction to his collection, soon became,
-    however, a source of much chagrin to him. Dr. Goddin, one
-    of the canons of Maestricht, who owned the surface of the
-    soil beneath which was the quarry whence the fossil was
-    obtained, when the fame of the fossil reached his ears,
-    pleaded certain feudal rights in support of his claim to
-    it. Hofmann resisted and the canon went to law. The whole
-    chapter supported their reverend brother, and the decree
-    ultimately went against the poor surgeon, who lost both the
-    specimen and his money, for he was made to pay the costs of
-    the action. The canon, leaving all remorse to the judges
-    who pronounced the iniquitous sentence, became the happy
-    and contented possessor of this unique example of its kind.
-
-    [Translation by Leidy.]
-
-But the canon was ultimately despoiled of his ill-gotten treasure. At
-the siege of Maestricht in 1795, the famous skull to which Hofmann
-had devoted so much anxious thought and labor, fell into the hands of
-the French and was carried off as one of the spoils of war. So widely
-celebrated had the specimen become during the fifteen years which had
-elapsed since its discovery, through the writings of several noted
-scientific men, that the French general commanded his artillerists
-to spare the house in which it was known to be. The canon, however,
-shrewdly suspecting that such an unexpected and extraordinary mark of
-favor was not for his own sake but rather for the sake of the famous
-fossil, had it removed and carefully hidden in a house in the city.
-After the capitulation of Maestricht the eagerly sought-for fossil was
-not to be found, and the offer of a reward of six hundred bottles of
-wine, so the story goes, was made for its recovery. So tempting was
-the offer that, ere long, it was brought in triumph to the house of
-St. Faujas de Fond, by a half-dozen grenadiers, whence it was later
-transferred to Paris, where it now is.
-
-We may well sympathize with Dr. Hofmann in the loss of his cherished
-specimen, since, had it not been for his zeal, money, and labor,
-it would never have escaped the usual fate of such things—complete
-destruction. But we must remember that St. Faujas de Fond, the recorder
-of this history, was a Frenchman, and somewhat interested in robbing
-the reverend canon of it; possibly there is another side of the story
-which has never been told.
-
-After peace was declared, one has regretfully to add that the canon,
-not Dr. Hofmann, was reimbursed for it, or so it is said. Cuvier rather
-naïvely says that it was ceded to the Garden of Plants of Paris,
-perhaps in the way that many other things are ceded to the conqueror
-in time of war. The specimen is really a good one, even when compared
-with many found in recent years, and there is little wonder that the
-cupidity of St. Fond was incited by it. Casts of it are now or have
-been in nearly every noted museum of the world, and pictures of it
-illustrated nearly every textbook of geology published during the
-first three-quarters of the past century. It had been the subject of
-considerable controversy even before it came into the hands of Cuvier.
-Peter Camper figured and described the skull as that of a whale or
-“breathing fish”; while St. Fond himself later called it a crocodile.
-Crocodile or alligator skeletons were rare in those days, and St. Fond
-made a special trip to the British Museum to study one. But it was
-really Adrian Camper, a son of Peter Camper, who deserves the credit,
-so often wrongly ascribed to Cuvier, for the recognition of the true
-nature of the fossil. He insisted that the animal was a lizard allied
-to the living monitors, an opinion which it will be seen has finally
-been proved to be correct within very recent years.
-
-In 1808 this famous skull, and all other known remains of a similar
-nature, came under the observation of Cuvier, the renowned French
-naturalist and paleontologist, who confirmed the views of Adrian
-Camper. He fully described and figured all the known parts of the
-skeleton that had later come to light, calling the animal the great
-lizard of the Meuse, the river near which Hofmann’s specimen was found.
-Conybeare, a well-known paleontologist of England, some years later
-formally christened it _Mosasaurus_, a transliteration of Cuvier’s
-phrase, from the Latin _Mosa_, for Meuse, and _saurus_, a lizard. For
-more than half a century Cuvier’s figure of the skull of the original
-specimen appeared in works on geology over the name _Mosasaurus
-hofmanni_, or _Mosasaurus camperi_. One could wish that the former name
-for the species might prevail, in recognition of the zealous doctor who
-was so shabbily treated in his possession of the specimen.
-
-For some years the few specimens discovered by Drouin and Hofmann were
-all that were known of the mosasaurs. A few others of related forms
-were discovered in England, and some were reported from New Jersey by
-early explorers, but there was little published about the mosasaurs
-till 1843, when Dr. August Goldfuss, a noted German paleontologist,
-described and beautifully figured an excellent specimen from the
-United States. This specimen also had a rather eventful history.
-It was discovered early in the fourth decade by Major O’Fallen, an
-Indian agent, near the Great Bend of the Missouri River, whence it
-was transported by him to St. Louis and placed in his garden as a
-curiosity. It happened that Prince Maximilian of Wied, the famous
-naturalist, in his travels through the United States, saw the specimen
-and secured it, taking it to Germany on his return. He presented it
-to the Museum of Haarlem where Goldfuss saw and described it. Rather
-oddly, this specimen was of a species closely allied to the original
-one of Maestricht, a species which has since only rarely been found.
-It was called _Mosasaurus maximiliani_ by Goldfuss, though some time
-previously, it has since been found, some fragments of the same
-species were described by Harlan, an American author, under the name
-_Ichthyosaurus missouriensis_. Goldfuss’ paper was strangely overlooked
-by subsequent writers, and it was not till the discovery of numerous
-remains of mosasaurs by Leidy, Cope, and Marsh in the chalk of western
-Kansas, nearly thirty years later, that much was added to the world’s
-knowledge of these strange reptiles.
-
-[Illustration: FIG. 69.—Skeleton of _Plalecarpus_ as mounted in the
-Paleontological Exhibit. Walker Geological Museum, University of
-Chicago.]
-
-Perhaps nowhere in the world are the fossil remains of marine animals
-more abundantly and better preserved than in these famous chalk
-deposits of Kansas. The exposures are of great extent—hundreds of
-square miles—and the fossil treasures they contain seem inexhaustible.
-Long-continued explorations by collectors have brought to light
-thousands of specimens of these swimming lizards, some of them of
-extraordinary completeness and perfect preservation, so complete and
-so perfect that there is scarcely anything concerning the mosasaurs
-which one might hope to learn from their fossil remains that has not
-been yielded up by these many specimens. The complete structure and
-relations of all parts of the skeleton, impressions of the bodies made
-in the soft sediments before decomposition had occurred, the character
-of their food, the nature of the skin covering, and even some of the
-color markings of the living animals have all been determined with
-certainty. Not only from Kansas, but also from many other parts of the
-world, have remains of these animals been discovered, until now it may
-truthfully be said that no other group of extinct reptiles is better
-represented by known fossil remains than the mosasaurs. From England,
-Belgium, Russia, and France in Europe; from New Jersey, Georgia,
-Alabama, Mississippi, Texas, New Mexico, Colorado, Kansas, Nebraska,
-the Dakotas, Wyoming, and other places in the United States; from New
-Zealand and South America they have been obtained in greater or less
-abundance and perfection.
-
-[Illustration: FIG. 70.—Tooth of _Tylosaurus_.]
-
-Their geological history is relatively brief, notwithstanding their
-wide distribution over the earth in such great numbers and diversity.
-The earliest are known from near the beginning of the Upper Cretaceous
-of New Zealand, whence it is believed by some that they migrated to
-other parts of the world, appearing in North America some time later.
-They reached their culmination in size, numbers, and variety very soon,
-and then disappeared forever before the close of Cretaceous time. The
-largest complete specimen of a mosasaur known measures a little more
-than thirty feet in length, but incomplete skeletons of others indicate
-a maximum length of about forty feet. The skulls of the largest species
-are about five feet long. The smallest known adult skeletons are
-scarcely eight feet in length. There are now known at the present time
-seven or eight genera of three distinct types, all belonging to one
-family, the Mosasauridae, including about twenty-five known species.
-While a few of the genera are widely distributed over the earth, the
-species are all of restricted range, indicating, perhaps, non-migratory
-habits.
-
-The adaptation of the mosasaurs to an aquatic life was very complete,
-though perhaps not so complete as was that of the ichthyosaurs. The
-skull is flattened, narrow, and more or less elongate, but large in
-proportion to the remainder of the skeleton—nearly one-sixth of the
-entire length; that relative size doubtless is indicative of very
-predaceous and pugnacious habits. The teeth in the typical forms are
-numerous, strong, and sharp, conical in shape, and recurved. Not
-only are there numerous teeth in both the upper and lower jaws, but
-there are also two rows of strong teeth implanted in the back part of
-the palate, upon bones called pterygoids, the use of which will be
-understood later. The teeth were inserted on large, tumid, bony bases,
-rather loosely attached in shallow pits or alveoli, unlike the teeth of
-all modern lizards. Such a mode of attachment of the teeth doubtless
-had some relation to the habits of the animals concerning which we
-are not quite clear. They were easily dislodged, and, in consequence,
-of very unequal size, some full grown, some small, and others just
-appearing above the surface of the gums in the living animals. The
-frequent loss of teeth and their constant and easy replacement by new
-ones is a peculiarity of predaceous reptiles, thereby insuring their
-best functional use.
-
-The external nostrils, of large size, were situated at a considerable
-distance back of the end of the snout, but not nearly so far back or so
-near the eyes as were the nostrils of the ichthyosaurs, plesiosaurs,
-and phytosaurs. Their size and position suggest a use like that of the
-modern aquatic monitors, as mentioned on a preceding page. The eyes
-were of moderate size, those of the less purely aquatic forms being
-directed more laterally than those of species of more distinctly diving
-habits. They were protected by a stout ring of bony plates, as were the
-eyes of all truly aquatic reptiles of the past. The ears, also, in most
-if not all mosasaurs, had a thick cartilaginous ear-drum in place of a
-simple membrane, evidently, as Dollo has shown, for better protection
-under undue pressure of the water in deep diving.
-
-[Illustration: FIG. 71.—_Clidastes_, inner side of right mandible:
-_ang_, angular; _art_, articular; _cor_, coronoid; _pa_, prearticular;
-_sur_, surangular.]
-
-As in all other lizards, the bones with which the lower jaws
-articulate, the quadrates, were loosely attached at the upper end,
-permitting great freedom of movement in all directions, more even than
-the land lizards have. The lower jaws were long and powerful, armed
-with a single row of teeth on each side, from sixteen to eighteen
-in number. Just back of the teeth, a little beyond the middle, each
-mandible has a remarkable joint, quite unknown in land lizards, though
-a trace of it is found in the monitors, permitting much movement
-between the front and back parts, both laterally and vertically, though
-chiefly in the former direction. Furthermore, as in land snakes but not
-as in land lizards, the front ends of the two sides of the jaws were
-somewhat loosely attached to each other by ligaments. This looseness of
-the two sides of the jaws, not only in front but also behind, together
-with the joint in each, was of the greatest use in swallowing prey, as
-will be explained farther on.
-
-[Illustration: FIG. 72.—Skulls of mosasaurs. Upper figure, _Clidastes_,
-from the side; middle figure, _Platecarpus_, from below; lower figure,
-_Tylosaurus_, from above: _an_, angular; _bs_, basisphenoid; _c_,
-coronoid; _ep_, epipterygoid; _fr_, frontal; _j_, jugal; _l_, lacrimal;
-_m_, maxilla; _na_, nasal; _oc_, occipital condyle; _pa_, parietal,
-palatine; _pm_, premaxilla; _pf_, prefrontal; _pt_, pterygoid; _po_,
-postorbital; _q_, quadrate; _sp_, splenial; _sq_, squamosal; _tr_,
-transverse; _v_, vomer.]
-
-As in most other aquatic reptiles, the neck was short and strong, the
-vertebrae being less in number than in most other lizards. The trunk
-was long and slender, more especially so in the surface-swimming kinds,
-with from twenty-two to thirty-four vertebrae. The tail was long, no
-longer than the tail of some land lizards, but more powerful, and
-broader and flatter. It was expanded or dilated more or less toward the
-free end, that is, with the beginning of a terminal caudal fin, such
-as the more specialized ichthyosaurs and crocodiles possessed. The
-vertebrae were procoelous, that is, concave in front and convex behind,
-like those of most modern lizards and all modern snakes and crocodiles,
-but quite unlike the biconcave vertebrae of all other aquatic reptiles.
-This kind of articulation of the backbones gave greater firmness and
-strength to the spinal column, but decreased the flexibility, and its
-possession by these animals was doubtless due to their descent from
-land lizards which had already acquired it. The loss of flexibility,
-however, was partly compensated by the loss of the additional
-articulating surfaces of the tail.
-
-[Illustration: FIG. 73.—_Platecarpus_; occipital view of skull: _bo_,
-basioccipital; _eo_, exoccipital; _pf_, postfrontal; _st_, stapes;
-_pt_, pterygoid; _q_, quadrate.]
-
-As in all other aquatic reptiles, it is in the limbs that the most
-striking characteristics of these water lizards or “sea-serpents” are
-found. The legs were so completely adapted to an aquatic mode of living
-that the animals must have been practically helpless upon land, able
-perhaps to move about in a serpentine way when accidentally stranded
-upon the beaches, but probably never seeking the land voluntarily. The
-front limbs, like those of all other swimming animals having a powerful
-propelling tail, were larger than the hind ones, though not very much
-so. The bones of the first two segments, that is, the arm, forearm,
-and thigh and leg bones, were all short and broad, resembling those of
-the ichthyosaurs more than those of any other reptiles, save perhaps
-the thalattosaurs, discussed below. The articular surfaces of all the
-limb bones, as in other aquatic animals, were restricted in extent,
-indicating limited motion between the joints, though doubtless having
-great flexibility. In the most specialized types, such as _Tylosaurus_,
-the wrist and ankle bones were almost wholly cartilaginous, just as
-they are in the water salamanders, and in whales and porpoises. This
-tendency of the ends of long bones, the wrists and ankles as well as
-other bones of the skeleton, to become more cartilaginous, or less
-well ossified, in animals purely aquatic in habit is a marked one. So
-much is this the case that paleontologists always suspect water habits
-in reptiles showing it, even though but few parts of the skeleton are
-known.
-
-[Illustration: FIG. 74.—_Clidastes_; left front paddle: _c_, coracoid;
-_h_, humerus; _r_, radius; _sc_, scapula; _u_, ulna.]
-
-[Illustration: FIG. 75.—_Tylosaurus_; left front paddle: _c_, coracoid;
-_sc_, scapula; _h_, humerus; _r_, radius; _u_, ulna.]
-
-Increase in the number of bones of the digits is a more or less
-conspicuous characteristic of all mosasaurs. In those forms in which
-the wrists and ankle bones had become cartilaginous in great part, as
-many as eleven phalanges have been observed in the longest toes, though
-in other forms, those with more completely ossified wrists and ankles,
-only two or three additional bones have been developed in the longest
-fingers and toes by aquatic habits. The pliability and flexibility of
-the fingers and toes were certainly very great, but they could not
-possibly have been flexed or bent so as to grasp or seize anything;
-and of course all vestiges of claws had disappeared. Many specimens
-have been found with all the bones of the limbs, that is, the “paddle
-bones,” in the positions they occupied when the animals died. Figures
-of three such specimens, made from photographs or careful drawings by
-the writer, are shown herewith (Figs. 74-76). In several such specimens
-very clear impressions of the smooth membranes between the fingers have
-been observed, and in one specimen preserved in the collections of the
-University of Kansas the outline of the fleshy parts connecting the
-paddle with the body has been preserved.
-
-[Illustration: FIG. 76.—_Platecarpus_; right front paddle: _h_,
-humerus; _r_, radius; _u_, ulna.]
-
-It will be seen by comparison of the figures of the mosasaur paddles
-with those of the ichthyosaurs and plesiosaurs that there was a wide
-difference in their structure, though all have the characteristic
-shortening of the limb bones and increase in the numbers of the
-finger and toebones, that is hyperphalangy. It is probable that these
-differences mean a more powerful and varied use of the limbs in the
-mosasaurs. It is certain that the mosasaurs were much more predaceous
-and pugnacious in their habits than were any other truly aquatic
-backboned air-breathing animals of the past or present. They were the
-“land sharks” of the ancient seas, and probably the only ones among
-water reptiles that would be dangerous and offensive to man, were they
-all living today.
-
-For a long time it was thought that the mosasaurs had no breast
-bone, and that, in consequence, the front part of the thorax was
-expansible. Under this assumption the mosasaurs would have been much
-more snake-like in habit than they really were. The loose construction
-of the jaws doubtless permitted the swallowing of prey of considerable
-size, and the inference was that they habitually preyed upon animals of
-large size. A snake will often swallow a frog of larger diameter than
-its own body, the flexible jaws and loosely connected ribs permitting
-it to pass to the abdominal cavity. But the unyielding ring formed by
-the anterior ribs connected with the breast bone in the mosasaurs, as
-in other lizards, conclusively proves that large animals could not
-have been swallowed whole by the mosasaurs. In several instances the
-fossilized stomach contents, composed chiefly or wholly of fishes, have
-been found between the ribs of mosasaurs, and in none were the fishes
-more than two or three feet in length, though the reptiles were from
-sixteen to twenty feet long. Possibly the largest mosasaurs, those
-thirty or thirty-five feet in length, might have captured and swallowed
-fishes six or seven feet long, but in all probability their usual prey
-was of smaller relative size.
-
-[Illustration: FIG. 77.—_Platecarpus_; pelvis, from below: _p_, pubis;
-_il_, ilium; _is_, ischium.]
-
-The very loose construction of the pelvic bones, those to which
-the hind legs are articulated, is an evidence of more complete
-adaptation to water life than was or is the case with any other water
-air-breathers except the ichthyosaurs and cetaceans. The sacrum
-had entirely lost its function as a support to the pelvis and had
-disappeared, that is, the vertebrae composing it had become quite
-like the adjacent ones, by the loss of the ribs connecting them with
-the ilium. The small pelvis was suspended loosely in the walls of the
-abdomen, or at the most was feebly connected with a single vertebra
-by ligaments. It was entirely useless as a support for the legs.
-The mosasaurs could not possibly have raised their bodies from the
-ground while on land. It is well known that the land lizards and the
-crocodiles raise their bodies free from the ground while running or
-walking; none drags its body over the surface.
-
-[Illustration: FIG. 78.—Photograph of carbonized remains of scales of
-_Tylosaurus_.]
-
-In several instances complete or nearly complete skeletons of mosasaurs
-have been discovered with the different bones nearly all in the
-positions and relations they had after the decomposition of the flesh,
-together with the carbonized remains of the skin and impressions of
-the investing scales and membranes. The nature of the body covering is
-therefore known with certainty from nearly all parts of the body. The
-body everywhere, save on the membrane between the fingers and toes, and
-perhaps on the top of the skull, was covered with small overlapping
-scales, very much like those of the monitors. These scales, however,
-were small and smooth in comparison with the size of the animals, those
-of a mosasaur twenty feet in length being almost precisely the size of
-those of a monitor six feet long. The top of the skull seems to have
-been covered with horny plates, as in most lizards. In one instance
-parallel dark bars, obliquely placed, and of narrow width, formed by
-carbonized pigment, were observed by the writer. As has been stated,
-in some instances fish bones and fish scales have been observed among
-the fossilized stomach contents, and it is quite certain that the
-food of these creatures must have been composed chiefly of fishes,
-though of course it is not improbable that other small vertebrates,
-birds, pterodactyls, the young of plesiosaurs, and possibly small
-mammals, may occasionally have formed a part of their diet. That the
-mosasaurs were very pugnacious in life is conclusively proved by the
-many mutilations of their bones that have been observed, mutilations
-received during life and partly or wholly healed at the time of death.
-Bones of all vertebrates are repaired after injury by the growth of
-more or less spongy osseous material about the injured part, forming a
-sort of natural splint. This material is more or less entirely removed
-by absorption when it is no longer required for the support of the
-broken ends. Many such injured bones of the mosasaurs have been found;
-sometimes the bones of the hands and feet have grown together, and not
-infrequently the vertebrae have been found united by these osseous
-splints; occasionally even the skull itself, especially the jaws,
-attest extensive ante-mortem injuries. In a single instance the writer
-has observed the loss of a part of the tail, where it probably had been
-bitten off. It may be mentioned, however, that the bones of the tail
-had no such “breaking points” in the mosasaurs as have those of many
-land lizards, whereby a part or all may be lost as a result of even a
-trivial injury, and then regrown. Such a condition in an organ relied
-upon entirely for propulsion would have been immediately fatal to the
-existence of the mosasaurs. The large jaws and teeth are in themselves
-sufficient evidence of the fiercely carnivorous propensities of the
-mosasaurs. The constant renewal of the sharply pointed teeth, thereby
-preventing deterioration by use or accident, preserved, even in the
-oldest animals, the effectiveness of the youthful structure.
-
-We may now understand how the mosasaurs seized and swallowed their
-prey. Living constantly in the water, away from all firm objects, with
-small, short limbs quite incapable of holding struggling prey, and
-the body not sufficiently serpentine to hold it in its folds after
-the manner of snakes, the mosasaurs would have found it difficult or
-impossible to swallow fishes of even moderate size, were their jaws of
-the same construction as are those of the land lizards. If they preyed
-upon small animals only, or if they tore their prey to pieces after the
-manner of the alligators, there would have been no especial difficulty
-in deglutition. But it is certain that the animals which the mosasaurs
-devoured were not always small, and they must have been swallowed
-whole, since their teeth were not adapted, like those of the alligators
-and true crocodiles, for the rending of bodies. One who has watched a
-snake swallow a frog or another snake will appreciate the difficulties
-against which the mosasaurs contended in swallowing fishes a fifth or a
-sixth of the length of their own bodies. The ordinary snake, no matter
-where or how it seizes its prey, invariably swallows it head first. Its
-mandibles are even more loosely united in front than were those of the
-mosasaurs, and while there is no joint in the snake’s mandibles such
-as there is in the mosasaurs’, the loose union of the various bones of
-the mandibles serves the same purpose. The frog or lizard, while firmly
-held by the slender teeth, is slowly moved sideways by the alternate
-lateral action of the jaws till the head is reached. Many non-poisonous
-snakes, if they find it impracticable or impossible to reverse the
-position of their prey in this way, wrap the folds of their body about
-it, holding it firmly while they release their mouth-hold and seize
-it by the head. An amusing instance of these habits came under the
-observation of the writer not long ago, in Texas. A large “blue racer”
-(_Bascanion_), six feet four inches in length, caught an unusually
-large bullfrog by one hind leg, but in almost less time than it takes
-to relate, the head of the frog had entered the snake’s gullet and the
-mouth was closed over it, notwithstanding the vigorous muscular and
-vocal protests on the part of the frog. Wishing to secure the skull
-of the snake for his collection, the writer seized an ax standing
-conveniently by and cut the snake cleanly in two. The peristaltic
-action of the deglutitional muscles carried the frog slowly on about
-two feet farther to the ax-made orifice, from which it emerged, and,
-after a few croakings against such unkind usage, calmly hopped off into
-the near-by pool of water! Many poisonous snakes release their prey
-after killing it; other snakes may force their prey down the throat by
-pressing it against the ground.
-
-Even small fishes could not possibly have been swallowed by the
-mosasaurs in any other way than head first, since the backwardly
-projecting, and often long, spines would have rendered any other
-procedure impossible. Even after the head had entered the gullet,
-deglutition could have been effectively completed only by the aid of
-some mechanism whereby the fish could have been pulled or pushed back
-into the constricting fauces. The strong teeth of the upper jaws and
-palate held firmly the struggling prey, while the loosely united jaws,
-bending laterally at the joint back of the middle, either alternately,
-or more probably in unison, steadily forced it far enough back to be
-seized by the muscles of the fauces.
-
-The shape of the mosasaurs, though slender, does not suggest
-extraordinary speed in the water; doubtless most of the fishes that
-lived in the seas with them could swim faster than they. Their prey
-was captured, for the most part at least, by sudden and quick lateral
-movements, for which their powerful and flexible paddles admirably
-adapted them.
-
-It is a rather remarkable fact that, among the thousands of specimens
-of mosasaurs which have been collected during the past forty years in
-both Europe and North America, there never has been found one of a
-very young animal. Of almost all other animals occurring abundantly
-as fossils some specimens are sure to be discovered of young and even
-embryonic individuals. It is quite certain that all such voracious
-monsters as were the mosasaurs did not die of old age. Some specimens,
-it is true, have been found that were evidently not full grown animals,
-but the observed differences in the size of the fossil bones are not
-great. All are of adult or nearly adult animals. If the mosasaurs were
-oviparous, as were the ichthyosaurs, and probably the plesiosaurs,
-and as are some living land lizards, the apparently entire absence of
-embryonic bones associated with often nearly complete skeletons of the
-mosasaurs is inexplicable; certainly _some_ mosasaurs must have died
-a short time before the birth of their young. But embryos have never
-been discovered, though numerous skeletons inclosing fossilized stomach
-contents have been found. From this fact it would seem very probable
-that the mosasaurs were oviparous, as are most other lizards. But this,
-after all, may be a hasty inference.
-
-No known reptiles lay their eggs in the water. Perhaps there is some
-reason why the eggs of reptiles and birds, so different from those of
-fishes and amphibians, cannot hatch in water; and there is no good
-reason for supposing that the mosasaurs were exceptions to this rule.
-Unless carefully hidden or protected by the parent, the eggs or very
-young of the mosasaurs would have been subject to many and grave
-dangers. Fish eggs are usually small and produced in great numbers,
-thousands often being extruded from a single female. Among so many
-there is a greater probability that at least two will hatch and survive
-to maturity, reproducing their kind. It is unreasonable to suppose
-that the lizards of the past were more prolific of eggs than are their
-relatives now living; nor is it possible that their eggs could have
-been as small as are those of most fishes. Modern lizards seldom lay
-more than twenty-five or thirty eggs at a time; even the turtles, with
-their greater vicissitudes, seldom produce more than one hundred. The
-eggs of the mosasaurs were certainly large and few in number, and the
-young animals must have begun breathing air immediately after escaping
-from the shells. If the mosasaurs were oviparous they must have laid
-their eggs upon the shores and beaches, as do the sea-turtles and the
-Crocodilia. Nor is it at all probable that the female mosasaurs gave
-even that protection to their eggs or young that the crocodiles and
-turtles give. The young mosasaurs, perhaps reaching a foot in length,
-must have been left entirely to their own devices and their own fate at
-the very earliest stages of their independent careers.
-
-The waters in which the mosasaurs abounded swarmed with many kinds of
-predaceous fishes, to say nothing of the hordes of their own kinds,
-all carnivorous in the highest degree, to all of which the tender
-saurians must have been choice food. Possibly the shallow waters of the
-bays and estuaries may have afforded protection to the newly hatched
-reptiles. It would seem probable that the female mosasaurs went up
-the rivers for a shorter or longer distance to lay their eggs or give
-birth to their young, and that the young reptiles remained in such
-relatively protected places until of a sufficient size to cope with
-the fierce enemies of the open seas. We know practically nothing of
-the inhabitants of the lakes and rivers during all the time in which
-the mosasaurs existed; and this perhaps is the real reason why we have
-never yet found a specimen of a young mosasaur.
-
-[Illustration: FIG. 79.—Head of _Tylosaurus_.]
-
-We have seen that many skeletons of ichthyosaurs are found entire, and
-but little disturbed in position, suggesting, if not proving, that the
-animals as a rule lived and died far out in the deep seas, away from
-the disturbing effects of currents of water on their decaying bodies.
-Among the thousands collected, the great majority of the specimens
-of mosasaurs consist of a few bones or a part of the skeleton only.
-Moreover, nearly all specimens show the disturbing effects of currents
-of water; and the bones are usually associated with those of turtles,
-birds, and flying reptiles, which probably did not often venture far
-from the shores; all of which goes to prove that the mosasaurs in
-general lived in the comparatively shallow waters of the seas, and
-not far from the shores. That some were excellent divers, descending
-probably many fathoms deep in the water, is certain, because of the
-extraordinary protective structures of the eyes and ears.
-
-But the various kinds of mosasaurs differed not a little in their
-habits. Some, like _Mosasaurus_ and _Clidastes_, were doubtless chiefly
-surface swimmers, as is evidenced by their better ossified bones,
-firmer articulation, and the presence of the additional zygosphenal
-articulations of the vertebrae, wanting in other forms, as also by the
-structure of their paddles. They had a relatively long body and short
-tail, the tail having a more pronounced distal expansion than in the
-case of other forms, and the eyes looking laterally, not at all upward.
-The feet, as shown in Fig. 74, were broad and short, with most of the
-wrist and ankle bones well ossified, and with but few extra bones in
-the digits. _Tylosaurus_ (Fig. 79), on the other hand, had a more
-slender skull, the nostrils were situated farther back from the tip of
-the snout, the tail was longer and more powerful, and the feet were
-very highly specialized (Fig. 75). The wrist and the ankle were almost
-wholly cartilaginous, the fifth finger and fifth toe were much longer,
-and the number of phalanges was greatly increased. Moreover, the bones
-of the skeleton are more spongy, the joints are more cartilaginous,
-and the ears were better protected by a heavy coat of cartilage. In
-most of these respects the genus _Platecarpus_ was intermediate between
-_Clidastes_ and _Tylosaurus_ (Fig. 76).
-
-Like nearly all other lizards, the mosasaurs had a pineal opening
-in the skull, but it is not at all probable that they possessed a
-functional pineal eye.
-
-Many and varied have been the opinions of scientific men regarding
-the relationships of these animals, as has been intimated. They were
-thought to be a kind of whale or breathing fish by Peter Camper;
-crocodiles, by St. Fond; and aquatic lizards, by Adrian Camper and
-Cuvier. The late Professor Cope thought they were more nearly related
-to the snakes than to the lizards, and that they might even have been
-the ancestral stock from which the snakes have descended. Because
-of this belief he gave to them the name Pythonomorpha, meaning
-python-like, and this name, really the first ever applied to them, is
-yet often used instead of Mosasauria. A more complete knowledge of
-the mosasaurs, however, and especially the recent discoveries of the
-semiaquatic connecting links, called the aigialosaurs and described
-on a preceding page, have set at rest all doubt as to their real
-affinities. They are real lizards, differing less from the living
-monitor land lizards than do the monitors from some other land lizards,
-especially the amphisbaenas and chameleons. And to Adrian Camper is
-due the credit for the recognition of their real relationship, though
-it required more than a century to prove that he was right.
-
-[Illustration: FIG. 80.—_Globidens alabamensis._ Part of mandible, with
-teeth. (From Gilmore.)]
-
-Very recently, and since the foregoing was written, a remarkable new
-type of mosasaurs has been discovered in Alabama and Europe. Only
-fragmentary jaws, a few vertebrae, and some skull bones are known,
-so that it is impossible yet to decide how closely the new form is
-related to the true mosasaurs, but so far as the evidence goes the
-only distinguishable character is the teeth. These, instead of being
-elongated and pointed, are nearly spherical, as shown in Fig. 80. Such
-teeth could have been used only for crushing shell-fish, and not at all
-for the seizure and retention of slippery fishes. The genus, which was
-called _Globidens_ by its discoverer, Mr. Gilmore, includes two known
-species, from Alabama and Europe, the latter recently described by
-Dollo. It has been suggested that this peculiar kind of dentition was a
-more primitive or intermediate one, a kind that the first mosasaurs had
-before they became fully adapted to the water; but this is doubtful,
-since _Globidens_ comes from late Cretaceous, and must be one of the
-later types. If _Globidens_ is a true mosasaur, and it seems to be one,
-its life-habits must have been remarkably different from those that
-have long been known. Possibly when the limbs and more of the skull are
-found, _Globidens_ will prove to be of a distinctive type.
-
-
-SNAKES
-
-The chief differences between snakes and lizards have already been
-given and need not be repeated, save very briefly. Snakes are always
-functionally legless, though some have vestiges of the hind pair; the
-brain-case is wholly bony; the upper temporal bar is wanting; the
-lower jaws are united in front by ligaments only, like those of the
-mosasaurs; the vertebrae are greatly increased in number, and always
-have the additional zygosphenal articulations like those of _Clidastes_
-and _Mosasaurus_ and some lizards; there is but one lung, and the eyes
-are always without free eyelids. But these characters are really not
-very important, since every one of them is found in the lizards or
-mosasaurs, except the complete ossification of the brain-case, and even
-this is partly ossified in the mosasaurs. It is rather the presence of
-all these characters which distinguishes a snake from a lizard.
-
-The number of living snakes is nearly as great as that of the living
-lizards, and their distribution over the earth is very similar. Snakes
-are for the most part strictly terrestrial in habit. Some live more
-or less among trees, and some live in the water, though with but few
-exceptions all are fully capable of rapid progression upon land. They
-are almost invariably carnivorous in habit, swallowing their prey
-whole, and usually alive, as has been described. Some poison their prey
-or crush it to death before swallowing it. Some feed upon eggs which
-are swallowed whole and then crushed in their stomachs by projecting
-bones from the under side of the vertebrae developed for that purpose.
-In size snakes vary from a few inches in length to twenty-five or more
-feet, no known extinct forms being larger than the living anacondas
-and boas. In geological history the earliest remains known date from
-the latter part of the Cretaceous, and it is quite probable that they
-have a briefer history than that of the lizards of which they are the
-descendants. Venomous serpents are known only from comparatively recent
-geological times, and it is probable that venomosity is the latest and
-final specialization of importance in the reptilian class.
-
-[Illustration: FIG. 81.—_Hydrus bicolor_; sea-snake. (From Brehm)]
-
-Of strictly aquatic snakes there is no known geological history, and it
-is improbable that there is any such history. There are a few snakes
-now living—very venomous ones, allied to the deadly cobras—which
-have become so completely adapted to life in the water that they are
-unable to exist or even move about on land. These are the well-known
-sea-snakes of the Indian Ocean and adjacent waters. Perhaps the most
-highly specialized and typical of these is the black-banded sea-snake,
-_Distina cyanocincta_, which reaches a length of four or five feet,
-and is a rapid and excellent swimmer. From the figure (Fig. 81) it is
-seen that the body is very much flattened from side to side, and lacks
-or has but a few vestiges of the transverse scales on the under side
-so characteristic of all other snakes, and which enable them to move
-about on land. So helpless are these snakes on land that it is said
-sailors will handle them carelessly, because of their inability to bite
-while out of water, though the bite is very venomous. They never come
-on land for any purpose whatever, and their young, unlike those of
-most other snakes, are born alive. There are a number of species of
-these sea-snakes, though comparatively little is known of their habits.
-They are of especial interest as another example of the ways in which
-air-breathing land vertebrates have become adapted to water life. The
-adaptation, however, was simple, for nearly all snakes swim freely in
-water by undulatory movements; it would require not much change to
-convert an ordinary water snake into one like these sea-snakes.
-
-
-
-
-CHAPTER XII
-
-THALATTOSAURIA
-
-
-Millions of years before the first appearance of the mosasaurs in
-geological history, another group of reptiles showing many curious
-resemblances to them attempted a rather precarious existence in the
-water. Its members survived long enough to acquire many structural
-adaptations to a water life, long enough to become diversely modified,
-but not long enough, apparently, to wander far from their birthplace,
-not long enough to attain that security from their enemies and more
-ambitious competitors, the early ichthyosaurs and plesiosaurs, to
-insure them a long existence. They were only a partial success as water
-reptiles.
-
-It has been only within a few years that we have had any knowledge
-whatever of them, and that knowledge is still very incomplete, too
-incomplete to justify any attempt to picture them as living animals,
-even though we take the liberties that some of our illustrators
-of extinct animals feel warranted in assuming. The first known
-specimens of these “sea-reptiles”—for that is the meaning of the word
-Thalattosauria—were discovered and described by Professor J. C. Merriam
-less than ten years ago, and all our knowledge of these animals is due
-to the same author, who has studied attentively the known specimens,
-all of which are preserved in the museum of the University of
-California. The first discovered fragmentary specimens were confounded
-with those of early ichthyosaurs, from the Upper Triassic rocks of
-northern California with which they were associated. No specimen has
-yet been found that is even approximately complete; some parts of the
-skeleton are not yet known, even from fragmentary remains, and not till
-other and more complete specimens have been found will it be possible
-to determine the real form of the living animals or to decide what
-their nearest relationships with other reptiles were. Professor Merriam
-thinks that they were related most closely with the Rhynchocephalia
-(p. 176) of which the _Sphenodon_, or tuatera, of New Zealand is the
-only living representative, but whose direct genealogical history runs
-back nearly or quite to the time in which the thalattosaurs lived. On
-the other hand, there are so many resemblances to the mosasaurs shown
-in the remains that have been discovered, that it is possible the
-thalattosaurs were only a short-lived branch of the primitive lizards,
-which we also know were in existence at the time when the thalattosaurs
-lived. However, even though they resembled the mosasaurs, there could
-have been no direct genealogical relationships between them, for it is
-quite certain that the thalattosaurs very soon went out of existence,
-leaving no descendants. But it matters little which were the land
-forbears of the thalattosaurs; they present such distinct adaptations
-to water life—characters all their own—that their ancestral kinship may
-well be left to the future researches of the curious paleontologist.
-For the present, at least, they may well be placed in an order
-of reptiles all their own, as Professor Merriam has proposed—the
-Thalattosauria.
-
-[Illustration: FIG. 82.—Skull of _Thalattosaurus_. (After Merriam)]
-
-No thalattosaurs were large animals. If they had the same proportions
-between the lengths of head, body, and tail as the mosasaurs, none
-exceeded seven feet in length, and they may have been even shorter,
-though probably not much. The figure of the skull, as restored by
-Professor Merriam, shows many striking aquatic adaptations, in the
-elongated, pointed muzzle, in the large external nostrils, situated
-far back toward the eyes, and in the well-ossified ring of bones
-surrounding the eyeball. There is a parietal opening in the roof of
-the skull, as in the modern lizards and tuatera; but it is not known
-for certainty whether there were two openings on each side in the
-roof of the skull, as in the modern tuatera. While this character may
-seem trivial, it is really one of the most important in the reptilian
-anatomy in determining the relationship and classification of reptiles.
-The teeth are conical and pointed in the front end of the upper and
-lower jaws, but farther back they are rounded, rugose, and obtuse, and
-could have been used only for crushing hard objects, like mollusks,
-crustaceans, etc. (Fig. 82). And not only was there a row of such teeth
-on each jaw (only partly seen in the figure), but similar teeth covered
-a large part of the palate. And the lower jaws, it is seen, are rather
-massive.
-
-The vertebrae were, of course, of the more primitive kind, that is,
-with the ends concave, both in front and behind. It would have been
-strange indeed were they of any other kind, since reptiles with
-ball-and-socket joints to the vertebrae, that is, concave on one end
-and convex on the other, as in nearly all living reptiles, did not come
-into existence till long after the thalattosaurs had disappeared from
-geological history; and it is also a curious fact that such vertebrae
-appear to have originated only among animals crawling on land, so that
-they would not have been a character acquired by the thalattosaurs
-after descending into the water. It will be seen from the figure of
-a dorsal vertebra that the rib was attached by a single articular
-surface, almost exclusively to the body of the vertebra, quite like
-those of all lizards, snakes, and mosasaurs, and unlike those of
-other reptiles. This too may seem to be a trivial character to prove
-relationships with the lizards, but it is a curious fact that no two
-animals having different kinds of ribs are closely related to each
-other. Possibly, however, this looser mode of attachment of the ribs
-in the thalattosaurs was one of their peculiar adaptations to a water
-life, and may not have been derived from their land ancestors.
-
-[Illustration: FIG. 83.—Dorsal vertebra of _Thalattosaurus_. (After
-Merriam.)]
-
-[Illustration: FIG. 84.—_Thalattosaurus_: bones of front extremity:
-_s_, scapula; _c_, coracoid; _h_, humerus; _r_, radius; _u_, ulna.
-(After Merriam.)]
-
-Of the limbs, only a few bones are known, but these are very
-instructive. The arm bones, as shown in Fig. 84, are strikingly like
-those of the mosasaurs, as will be seen by comparing the figure on p.
-157. The humerus is a little more elongated than that of the mosasaurs,
-more nearly like the mosasaurian femur. The shoulder-blade and the
-coracoid are imperfectly ossified, as is seen from the figure—another
-characteristic of aquatic life. What the fingers and toes were like
-cannot be said; probably they were bound together by membrane, forming
-swimming paddles similar to those of the mosasaurs. Some of the bones
-referred to the pelvis are known, but it is not known whether they are
-united to the spinal column by a sacrum, as in land animals. Nor is
-anything certainly known of the hind leg or much of the tail. Since the
-front legs show marked aquatic adaptations, it is altogether certain
-that the hind legs will be found to be modified more or less, though
-not so much modified as the front legs, because, as we have seen, the
-front legs are always more specialized in aquatic animals than the
-hind ones, even as the hind legs are more specialized than the front
-ones in land animals. Possibly the hind legs will be found to be more
-like those of the Thalattosuchia, as shown on p. 212, that is, partly
-terrestrial in character. Doubtless the tail was long and flattened,
-possibly with a terminal fin-like dilation, though this is less
-probable.
-
-As regards the habits and food of the thalattosaurs, no better summary
-can be given than that of Professor Merriam, in his own words:
-
-      The remains of thalattosaurs are known only in purely marine
-    deposits containing little or no material of terrestrial
-    origin. They are associated with a fauna consisting of
-    numerous forms, both vertebrate and invertebrate, which
-    are not known to have existed away from marine areas. In
-    the structure of the skeleton we find the abbreviated and
-    broadened proximal segments of the limbs, the slender snout
-    with prehensile terminal teeth, and the median superior
-    nostrils, indicating a purely aquatic type. There can
-    scarcely be room for doubt that the thalattosaurs as a group
-    were typical marine forms. The larger and more specialized
-    species comprised in the genus _Thalattosaurus_ were
-    strictly natatory. They may have visited the shore, but,
-    like the plesiosaurs, were better fitted for swimming
-    than for crawling. Of the smaller _Nectosaurus_
-    we unfortunately do not know the limbs. They may have
-    been considerably less specialized, and the animal
-    to a correspondingly greater degree a shore-dweller.
-    _Nectosaurus_ is, however, found in the same deposits
-    with other forms and appears to be as common as the others;
-    so that it is safe to consider it as having passed the
-    greater part of its life away from the shore.
-
-    From what we know of the vertebral column of
-    _Thalattosaurus_ it appears that the animal had
-    a relatively short neck and a long dorsal region, the
-    proportions being nearly those in the vertebral column of
-    some mosasaurs. Only the anterior portion of the caudal
-    region is known. The slender, rounded neural spines with
-    well-developed articulating processes seen here are not
-    such as commonly appear in forms with a highly specialized
-    sculling tail, and it is hardly probable that a caudal fin
-    of large size was developed.
-
-    The anterior limbs evidently formed paddles of moderate
-    size. The posterior pair may have been larger, in
-    compensation for lack of a strong sculling tail. It is,
-    however, possible, that as in _Geosaurus_ (of the
-    thalattosuchian crocodiles) the hind limbs were not
-    typically natatory, and the distal end of the tail was
-    vertically expanded.
-
-    No specimens have yet been found which are well enough
-    preserved to show any remains of the stomach contents,
-    and we have no definite evidence concerning the food of
-    the thalattosaurs, more than is furnished by the general
-    structure of the animal. The character of the paddles, the
-    form of the skull, and the presence of slender prehensile
-    teeth in the terminal portions of the jaws would indicate
-    that they fed in part upon some swiftly moving prey which
-    was caught by a quick snap of the jaws, deglutition being
-    assisted by the curved teeth of the pterygoids. The heavy
-    vomerine and posterior mandibular teeth may have been used
-    for crushing the light shells of ammonites, which existed in
-    vast numbers in the same seas.
-
-
-
-
-CHAPTER XIII
-
-RHYNCHOCEPHALIA
-
-
-In some of the small islands near the northeast coast of New Zealand
-certain small and peculiar, lizard-like reptiles, known as tuateras,
-have long been known. For many years they were supposed, even by
-scientific men, to be real lizards, so much do they resemble in
-external appearances and in habits the lizards of other parts of the
-earth. It was early observed, however, that they presented certain
-remarkable internal differences from the real lizards or Lacertilia,
-though it was not till about twenty-five years ago that the importance
-of these differences was recognized by the late Professor Cope, who
-separated them into a distinct order quite co-ordinate with the
-lizards, crocodiles, and turtles. These little reptiles, seldom
-reaching a length of two feet, have now become so scarce that the New
-Zealand government protects them by law from unnecessary destruction;
-nevertheless it will probably be only a short time before they become
-extinct, the end of a long genealogical line. No other living reptiles
-have retained more of the old-fashioned or primitive characters than
-this _Sphenodon_ or _Hatteria_, as the animal is called, and because
-of them it is of peculiar interest to zoölogists, and especially
-paleontologists.
-
-The differences of these beaked lizards from the true lizards are
-especially noticeable in the skull, and more especially in the
-arrangement of the bones which give articulation to the lower jaws
-(Fig. 8). In the lizards and snakes the quadrate bone is loosely
-articulated at its upper end with the cranium, and has no inferior
-bar or arch connecting its lower end with the jugal and the back part
-of the upper jaw. _Sphenodon_, on the contrary, has the quadrate
-bone firmly fixed to its adjacent bones at both ends, and is quite
-immovable. The vertebrae are biconcave like those of all early
-reptiles, not concavo-convex as are the vertebrae of most other living
-reptiles. The intercentra or hypocentra, little wedge-shaped bones
-between the centra below, are more persistent in _Sphenodon_ than
-in any other living land animals except the gecko lizards. Upon the
-whole the tuatera is the most old-fashioned of living reptiles, and in
-consequence it has nearly lost out in competition with new things.
-
-[Illustration: FIG. 85.—_Sphenodon punctatum_, or tuatera. (From
-specimen in the Yale University museum.)]
-
-With these living tuateras we have nothing further to do, since they
-are land animals, living about the beaches of the New Zealand islands,
-and only occasionally venturing into the water, hiding from their
-enemies in the holes in the rocks. But, from some of their antecedents,
-from some of their direct forbears perhaps, there have gone off at
-different times various branches, whose descendants wandered into
-foreign lands or into foreign places, and lived and flourished for a
-brief time and then became extinct. Some of these went down into the
-water and became more or less aquatic in habit; some, indeed, changed
-their forms and habits so greatly that they are often, perhaps rightly,
-segregated into different orders. Whether or not they should be called
-Rhynchocephalia matters little, however. It is merely a matter of
-opinion as to how great the changes should be in order to entitle the
-offspring to a genealogical tree all its own. Of these branches there
-are two, whose relationships seem to be definite, the Choristodera and
-Thalattosauria, though there is more doubt about the latter than the
-former. A third group, that included _Pleurosaurus_, seems, from more
-recent discoveries, to belong to a different line of descent and has
-been described under the Protorosauria.
-
-In the direct line of ancestry there is no known form that was
-distinctly aquatic. The oldest known of these, perhaps, is that shown
-in Fig. 86, _Sapheosaurus_ from the Jurassic of Solenhofen. Its
-resemblance to the modern tuatera is great, and doubtless its habits
-were very similar, though its rather long tail and rather short neck
-possibly indicate subaquatic habits.
-
-[Illustration: FIG. 86.—_Sapheosaurus_, an Upper Jurassic
-rhynchocephalian. (After Lortet.)]
-
-
-CHORISTODERA
-
-Among the many reptiles of the past which have sought a more congenial
-or a safer home in the water few have had a more interesting history,
-or a briefer one, than those to which the late Professor Cope gave
-the name Choristodera in 1876. Many students of repute consider the
-group an order, others a suborder of the Rhynchocephalia. The group,
-whether order or suborder, are interesting because of their long and
-devious migrations from western North America to Europe, or vice versa,
-through rivers and ponds; interesting also because of the persistence
-of certain old-fashioned traits that clung to them long after their
-disappearance in other animals. Perhaps these traits were among the
-causes of their merely moderate success as animals of the water, traits
-that led to their early dissolution. Like the proganosaurs, which they
-must have resembled in external appearance not a little, they wandered
-from their birthplace in the western continent, to perish in the
-eastern; and like them their span of existence was short.
-
-Their history among mankind, too, is brief. The first known specimens,
-from western North America, were described by Professor Cope in 1876,
-under the name _Champsosaurus_. In the following year Professor
-Gervais of Paris made known another form from Rheims, which he called
-_Simoedosaurus_, so closely allied to the American that even yet
-they have not been sharply distinguished. Some years later these
-European specimens were more fully described by the well-known Belgian
-paleontologist, Dr. Dollo, but it has been only within the past few
-years that our knowledge of the animals has been made at all complete
-by the discovery and description of several excellent skeletons of
-_Champsosaurus_ by Mr. Barnum Brown of New York.
-
-[Illustration: FIG. 87.—_Champsosaurus_; skeleton, as mounted in
-American Museum. (Brown.)]
-
-These semiaquatic reptiles never grew very large—not more than four
-or five feet in length; nor did they ever succeed in becoming fully
-at home in the water, certainly no more so than our modern alligators
-and crocodiles. They remained to the end of their comparatively brief
-existence essentially land animals, probably seeking their food in the
-water but fleeing to the land for protection and for the breeding of
-their young. Their chief water adaptations are seen in the elongate
-face and flattened swimming tail. Their legs remained essentially
-terrestrial, and could have been of but little use in the water for
-propulsion; the feet even were doubtfully webbed, or if so, not more
-than are those of the alligator. Singularly, like the proganosaurs,
-their ribs were heavy and stout, also suggesting bottom-crawling
-habits, like those of the living Galapagos lizards. The skull was
-lightly built, and the face was long and slender, like that of the
-gavials and proganosaurs; but, like those of the former and unlike
-those of the latter, the nostrils were situated at the extreme tip.
-The hind legs were firmly attached to the body by the sacrum; and no
-sclerotic bones of the eyes have been discovered. The neck was neither
-unusually long nor unusually short. The body was probably covered with
-horny scales.
-
-[Illustration: FIG. 88.—Restoration of _Champsosaurus_.]
-
-[Illustration: FIG. 89.—_Champsosaurus_; skull from above. (After
-Brown.)]
-
-To the student of paleontology these animals are of interest because of
-the retention of several primitive traits which had long disappeared in
-other known reptiles. While the vertebrae had ceased to be perforated
-by the notochord, as in the early reptiles, they were still shallowly
-biconcave. The first bone of the neck, the atlas, had changed but
-little from that of their very ancient forbears of Permian times, and
-the bones of the palate still retained numerous teeth scattered over
-it, like those of the same Paleozoic ancestors. Most primitive and
-old fashioned of all was the pelvis, which was so unlike that of all
-known contemporary or later reptiles that, were a paleontologist to
-see it without knowing whence it came, he would be almost sure to say
-that it belonged to a Paleozoic, or at least a Triassic, reptile, and
-not only to an early reptile but a very primitive one at that. This
-peculiarity consists in the absence of any opening between the ischium
-and pubis, which is characteristic of every living vertebrate with
-legs. And these and other old-fashioned characters could not possibly
-have been new developments; they must have existed in all the ancestors
-of the Choristodera from Paleozoic to early Tertiary times, though not
-a single other reptile is known to have possessed them, for the greater
-part of this time. Perhaps when Asia and northwestern America have
-been more thoroughly explored for vertebrate fossils, some of their
-ancestors which perished on their great migration from the western to
-the eastern continent in late Cretaceous times will be discovered.
-
-[Illustration: FIG. 90.—Pectoral girdle of _Champsosaurus_. (After
-Brown.)]
-
-[Illustration: FIG. 91.—_Champsosaurus_; pelvic bones. (After Brown.)]
-
-The choristoderans began their existence, so far as is now known, in
-North America in late Cretaceous times and died out in both Europe
-and North America in early Tertiary times. That is, they were one
-of the few branches of reptilian life which not only witnessed the
-extinction of the great dinosaurs and plesiosaurs, but the advent also
-of the early placental mammals. They lived millions of years after the
-proganosaurs became extinct, and, similar as they are in form, there
-is no relation between them. Moreover, in all probability they did not
-migrate to the eastern continent over the same route.
-
-The structure of the head and teeth of the Choristodera clearly
-indicates a fish-eating habit, or at least a diet of soft-bodied, free
-swimming invertebrates. The legs and ribs, as also the armor of ventral
-ribs, like those of the plesiosaurs, point very insistently toward a
-bottom-crawling habit while in the water.
-
-
-
-
-CHAPTER XIV
-
-PARASUCHIA
-
-
-The first known specimen of the order of reptiles now generally
-known as the Parasuchia was found in Würtemberg, Germany, in 1826
-and very briefly and inadequately described[4] two years later by
-Professor George Jaeger. The specimen was a sorry one, and was sadly
-misinterpreted by Jaeger. It consisted chiefly of casts of the alveoli
-or sockets of a number of teeth, more or less connected by corroded or
-decomposed portions of the jaws. He recognized the casts as teeth of
-a peculiar reptile, but mistook the roots for crowns, and, naturally
-concluding that such obtuse teeth would be of use only for the
-mastication of vegetable food—about the last kind of food to which the
-phytosaurs were addicted—called the animal _Phytosaurus_, meaning plant
-saurian. Because of differences he observed in the shapes of the teeth
-he thought that they belonged to two distinct species, which he called
-_cylindricodon_ and _cubicodon_; but the differences were due simply to
-the different positions they held in the jaws.
-
-[4] “The author showed drawings and some specimens of two hitherto
-unknown reptiles from the white, coarse-grained sandstone, of which one
-in the form of the skull resembles the gavial, but is distinguished by
-the cylindrical form of the lateral teeth of the jaws; he therefore
-calls it provisionally _cylindricodon_, and a second species or genus,
-of which, however, so far only fragments of the jaws have been found,
-because of the four-cornered form of the teeth, _cubicodon_, while at
-the same time for the genus or family, to which the remains of these
-animals have belonged, he proposes the name _Phytosaurus_, since the
-teeth seem to be more adapted to a vegetable diet, even though they
-have not been worn away, as in _Iguanodon_.”—_Isis_ (1828), p. 441
-(translation).
-
-Fourteen years later Hermann von Meyer, the renowned German
-paleontologist, described and figured other remains of the same or an
-allied reptile under the name _Belodon plieningeri_. In subsequent
-papers during the next twenty-three years von Meyer very fully
-described and beautifully illustrated the skulls and other remains
-of this and other species, all of which he referred to the genus
-_Belodon_, the name by which for many years the animals were generally
-known in scientific literature. Von Meyer thought that he recognized in
-_Belodon kapfii_, the species most often figured in textbooks, the same
-animal that Jaeger had previously described.
-
-Von Meyer was not at all certain about the relationships of his
-_Belodon_, though he recognized its affinity with the crocodiles. It
-was Huxley who, in a famous paper on the evolution of the crocodiles,
-published in 1875, united _Belodon_ and another genus from the Trias
-of Scotland, which he called _Stagonolepis_, with the Crocodilia as
-representatives of the suborder Parasuchia, one of the three into which
-he divided the order. Huxley admitted that the relationships between
-the Parasuchia and the Mesosuchia or Eusuchia, the other suborders
-which he proposed, were not as intimate as those between the latter
-two, which were separated solely on the structure of the palate and
-vertebrae, as has been explained in chap. xv. As early as 1869 the
-late Professor Cope recognized certain forms which had been previously
-described from Carolina as belonging to the group, calling them
-_Belodon_, but it was not until 1896 that E. Fraas separated _Belodon
-planirostris_ of von Meyer as a member of a distinct genus, to which he
-gave the name _Mystriosuchus_.
-
-Here, as a part of the order Crocodilia, the phytosaurs remained
-till within very recent years, though there have been some mild
-protests against the association, especially by Marsh, Zittel, and
-Baur. The famous English paleontologist, Richard Owen, located the
-“Belodontia,” as the phytosaurs were often called, in his order
-Thecodontia, based chiefly upon the manner of the insertion of the
-teeth in sockets. But this has long since been shown to have little
-value in the classification of reptiles. Various authors have written
-about the phytosaurs in later years, notably Cope, Fraas, Huene, and
-Jaekel, but it was J. H. McGregor who first definitely separated the
-phytosaurs into a distinct order, in a careful revision of the American
-forms. He called the order Parasuchia, after Huxley, dividing into
-two suborders, the Phytosauria, after Jaeger, and the Aetosauria, a
-group which, for lack of a better place, had previously been classed
-with the Crocodilia, either as a member of the Parasuchia or as an
-independent suborder by Zittel (the Pseudosuchia). More recently
-Huene has shown that certain African reptiles from the Lower Trias
-had certain very definite characters entitling them to an independent
-position, for which he proposed the order Pelycosimia. Upon the whole,
-however, these characters seem to be primitive parasuchian, and the
-group may provisionally be placed in the order Parasuchia, as a third
-suborder, the Pelycosimia. The order Parasuchia, then, until we know
-much more about the latter two groups, may be conveniently divided into
-three suborders, the Phytosauria, Aetosauria or Pseudosuchia, and the
-Pelycosimia, all of Triassic age.
-
-McGregor was quite right in retaining for the suborder the name
-Phytosauria, suggested by Jaeger in 1828, inappropriate as the word is
-etymologically, but was hardly justified in substituting the generic
-name _Phytosaurus_ for the long and well-known _Belodon_, because it
-is quite impossible to say that Jaeger’s very fragmentary specimen
-upon which he based the genus _Phytosaurus_ really is the same as
-_Belodon_. Professor Fraas very kindly showed the writer the original
-type-specimen of Jaeger, now preserved in the Stuttgart Museum,
-and both are agreed that it is impossible to prove the identity of
-_Belodon_ and _Phytosaurus_ from the very fragmentary and imperfect
-specimen. It is quite as probable, for instance, that _Phytosaurus_ and
-_Mystriosuchus_ are identical as that _Phytosaurus_ and _Belodon_ are.
-Unfortunately, this is not the only case in vertebrate paleontology
-where the fragmentary specimens to which names have been given are
-inadequate to determine the species, or genus, or even the family
-to which they belong; there have been very many such instances. The
-pioneers in paleontology were often justified in naming small and
-obscure fragments of bones, or single bones. One would be justified
-even yet in giving a name to an indeterminable fragment of a bird bone
-from the Triassic formation, because the discovery of a bird of any
-kind in that formation would be very important for science, even if its
-precise kind might never be recognized from the specimen. Nevertheless,
-the custom is a very reprehensible one when indiscriminately followed.
-For these reasons the writer disagrees with McGregor in substituting
-the inappropriate name _Phytosaurus_ for _Belodon_, the name by which
-the most typical forms were so long known.
-
-The Aetosauria, which have long been known from a marvelous specimen
-found in Würtemberg many years ago and described by the elder Fraas,
-need not detain us long. They were relatively small reptiles about
-two feet long, almost completely incased in a bony armor, and purely
-terrestrial in habit. The skull even yet is not perfectly known, and
-it is possible that when it is the group may have to be dissociated
-from the phytosaurs. The nostrils were not posterior, and the skull is
-short. Other specimens of the same group have been described from the
-Upper Triassic rocks of Massachusetts.
-
-The Pelycosimia of Huene are very interesting as showing apparently
-primitive forms with which the true phytosaurs may have been intimately
-related ancestrally. They, too, have a rather short skull with the
-nostrils in front, and were not at all aquatic in habit. Not much is
-known about the single genus that is located in the group, aside from
-the skull and a few limb bones.
-
-
-PHYTOSAURIA
-
-The Phytosauria, so far as known, were all reptiles of considerable
-size, greatly resembling the crocodiles, and especially the gavials
-in form and habit, but differing very greatly in having the external
-nostrils situated far back near the eyes; in having no false palate
-so characteristic of the Crocodilia; in having a more primitive
-shoulder-girdle, consisting of a short coracoid, interclavicle, and
-clavicles; and in having the ordinary type of pelvis, that is, with
-the pubis entering into the acetabular articulation for the femur.
-They were all, like the crocodiles, covered more or less by a bony
-armor; there are two openings on each side of the temporal region;
-there is no pineal opening; the vertebrae are gently biconcave,
-precisely like those of the early or mesosuchian crocodiles; there
-is always an opening of considerable size, called the preorbital
-foramen, in front of the eyes, as in some crocodiles, many dinosaurs,
-and most pterodactyls; there is also an opening through the back
-part of the mandibles as in crocodiles; and the double-headed ribs
-are attached exclusively to the transverse process of the arch,
-precisely as in the crocodiles, dinosaurs, and pterodactyls. From
-all these it is evident that the phytosaurs are related most nearly
-to the crocodiles and dinosaurs, and are probably an early branch
-of the stem from which they, the pterodactyls and the birds, arose,
-a branch that persisted only a short time, geologically speaking,
-and went entirely out of existence at the close of Triassic times,
-leaving no descendants behind. Nevertheless, in this comparatively
-brief life-span they developed not a few distinctive forms and became
-widely distributed over the earth. Their remains are known from the
-Upper Trias of Germany, England, and Scotland, India, South Africa,
-and from Massachusetts, North and South Carolina, and many places
-in the Rocky Mountains. No true phytosaurs are yet known from South
-America, but in all probability they will be discovered there when
-the Triassic deposits of that continent have been better explored
-for fossils. In the Rocky Mountains, especially, their remains are
-widely scattered, they have been found in many localities in Wyoming,
-Colorado, Oklahoma, Utah, and New Mexico. Though for the most part
-their known remains from these localities are yet fragmentary, not
-less than four distinct genera have been described from these regions:
-“_Belodon_,” _Angistorhinus_, _Paleorhinus_, and _Episcoposaurus_.
-From the Carolinas and Massachusetts a single genus, though described
-under numerous names, has been made known, originally called by Emmons
-_Rutiodon_ (_Rhytidodon_). And from Europe and India at least as many
-more different genera are known. All these genera are, however, so
-closely allied that they are placed in the single family Belodontidae.
-
-[Illustration: FIG. 92.—Restoration of _Mystriosuchus_, an Upper
-Triassic phytosaur.]
-
-[Illustration: FIG. 93.—Skull of _Mystriosuchus_, a phytosaur: _pm_,
-premaxilla; _m_, maxilla; _na_, nasal; _f_, frontal; _p_, prefrontal;
-_l_, lacrimal; _pf_, postfrontal; _po_, postorbital; _pa_, parietal;
-_sg_, squamosal; _qj_, quadratojugal; _pl_, palatine; _t_, transverse;
-_in_, internal nares; _en_, external nares; _pt_, pterygoid; _bs_,
-basisphenoid; _eo_, exoccipital. (After McGregor.)]
-
-[Illustration: FIG. 94.—Dorsal vertebrae of phytosaur: _az_, anterior
-zygapophysis; _pz_, posterior zygapophysis; _d_, _c_, articulations of
-rib.]
-
-[Illustration: FIG. 95.—Scapula and coracoid of _Rutiodon
-carolinensis_, an American phytosaur. (After McGregor.)]
-
-[Illustration: FIG. 96.—_Belodon_; restoration of head, from above.]
-
-[Illustration: FIG. 97.—_Mystriosuchus_: restoration of head, from
-above.]
-
-In _Belodon_ (Fig. 96), the earliest known and most typical genus,
-perhaps, the moderately elongated face has a high crest reaching nearly
-to its front end, and this type is known both from Europe and from New
-Mexico. Others have the face long and slender, even longer and more
-slender than in the ancient teleosaur crocodiles or the modern gavials.
-In some forms the teeth are cylindrical and slender throughout, and
-there may be as many as fifty on each jaw, or two hundred in all; while
-in others only the anterior teeth are cylindrical and the posterior
-teeth are flattened and serrate along their cutting edges. In the body
-not very great differences have been observed. Some are more slender
-than others, and there are minor differences in the shapes and sizes
-and numbers of the bony scutes along the back and on the throat.
-
-But they are all alike in their essential characters, a very long
-beak with numerous teeth; the foremost ones on the expanded, more
-or less spoon-shaped front extremity, are more or less, sometimes
-greatly, elongated. The jaws may be likened to a long and slender
-pair of tongs with nipping teeth at the front end. The strong, long,
-and flattened tail is sufficient evidence that the phytosaurs were
-excellent swimmers, but, aside from that and the posterior location of
-the external nostrils, directly over the internal, few other aquatic
-adaptations are observed in the skeleton. There are no sclerotic bony
-plates about the eyes, or at least none have so far been discovered,
-although among the numerous known specimens they would confidently be
-expected were they really present in the skeleton; and the presence of
-bony armor negatives markedly aquatic habits.
-
-Doubtless on the whole the habits of the phytosaurs were not very
-unlike those of the modern gavials, which they so strongly resemble
-in form, size, and general characters. But they differ very greatly
-from the gavials in the extreme posterior position of the nostrils,
-and in the greatly elongated teeth of the front end of the beak,
-teeth which must have had some especial and peculiar use. Nor is the
-position of the nares to be accounted for satisfactorily by reference
-to aquatic habits. It has been suggested that the creatures used the
-very long and slender beak in prodding and probing in the sand and
-mud for soft-bodied invertebrates, worms and the like, for which the
-teeth would be especially fitted; and that the posterior position of
-the nostrils may be in part, perhaps wholly, accounted for by this
-habit, which permitted the reptiles to breathe without extricating the
-beak from the mud or shallow waters. That the animals were wholly and
-intensely carnivorous in habit is attested by their teeth; although
-they are called “plant saurians,” they never had anything to do with
-plants in the way of food. Unfortunately so far no specimens have
-ever been found showing the remains of stomach contents, nor have any
-been found showing impressions of the form of the body or of any of
-its parts. Until such specimens are found, as they doubtless will be
-eventually, one can be less sure of the precise details in their life
-reconstructions. However, the skeleton is now known nearly completely,
-and this suffices to give a very approximately correct idea of what the
-animals were like when alive.
-
-
-
-
-CHAPTER XV
-
-CROCODILIA
-
-
-The order of reptiles to which the name Crocodilia is technically
-applied comprises less than twenty-five living species, popularly
-known as crocodiles, alligators, caimans, and gavials. They are often
-of great size, ugly and repulsive in appearance, cruel and vicious
-in habit, wholly carnivorous, and denizens, almost exclusively, of
-fresh-water lakes or rivers in tropical and subtropical regions; a few
-only venture into the sea near the shores. They are all excellent and
-powerful swimmers, but are by no means exclusively aquatic in habit,
-many of them spending a large part of the time on the shores; and they
-invariably seek the land for the deposition and hatching of their eggs.
-In size they are the largest of living reptiles, some of the existing
-species reaching a length of twenty-five feet, while some extinct
-species were probably fully twice that length.
-
-The geological history of the crocodiles is a very ancient one,
-reaching back at least as far as the early Jurassic and probably to
-the Triassic. The culmination of the order, at least so far as size,
-variety, and numbers are concerned, was doubtless before the close of
-the Mesozoic. The early crocodiles, however, were of a more generalized
-structure in some respects, though specialized in others, because of
-which naturalists in the past have usually divided the order into three
-or four chief subdivisions, or suborders, two of which, the Mesosuchia
-and the Thalattosuchia, became extinct before or during Cretaceous
-time. The third suborder, the Parasuchia of many textbooks, has now
-been unanimously separated by paleontologists from the Crocodilia as an
-independent order. The fourth suborder of the textbooks, the Eusuchia,
-a word meaning _true_ crocodiles, appeared in geological history, so
-far as we yet know, shortly before the extinction of the Mesosuchia,
-and is best known from the forms now living, all of which belong to
-it. Although the modern crocodiles can hardly be called, as a group,
-purely aquatic reptiles, we shall find it of interest, because of their
-intimate relation to the older and more strictly marine forms, to speak
-of them somewhat in detail.
-
-
-MODERN CROCODILES, EUSUCHIA
-
-The crocodiles of the present—and we use the word in the technical
-sense of Crocodilia—because of their general resemblance to the
-lizards, or true “saurians,” were classed with them by the older
-naturalists, whence comes the popular name alligator, a corruption
-of the Spanish _el lagarto_, or “the lizard,” given to some of
-the South American forms by early explorers. But this resemblance
-is a superficial one only, as was early recognized by comparative
-anatomists. The crocodiles, indeed, are only remotely related to the
-lizards.
-
-[Illustration: FIG. 98.—Senegal crocodile. (By permission of the New
-York Zoölogical Society.)]
-
-The head or cranium is flattened and broad, the facial part or snout
-sometimes greatly elongated and slender, and the external nostrils
-are always situated at the front end. The bones of the upper surface
-of the cranium and face have many pit-like depressions. The neck is
-short and stout, and but little movable. The body is somewhat depressed
-and flattened, not cylindrical and slender, as in the more typical
-water reptiles. The tail is much elongated and compressed, forming a
-powerful means of propulsion in swimming, its breadth being increased
-by a vertical row of horny plates above. The limbs are of the ordinary
-elongated type—ambulatory rather than swimming legs—and are not of much
-use for propelling the body in the water; the front legs indeed are
-usually held close to the body while the animal is swimming. The toes,
-however, are partially connected by webs, to a slight extent only in
-the alligators and crocodiles, but much more so in the long-snouted
-gavials. The feet have five toes in front and four behind; and the loss
-of the fifth toe can only be ascribed to terrestrial habits. The body
-is covered more or less with horny scutes or scales, beneath which are
-several rows of thickened, pitted, bony plates on the dorsal side, and
-sometimes also on the under side, forming a more or less extensive
-bony armor. The eyes have movable lids, as in most lizards, and the
-ear-opening is small.
-
-But the external appearance of these reptiles is not sufficient to
-distinguish them widely from other groups, and we must resort to
-the internal structure, especially that of the skeleton, for the
-more essential differential characters. The most crucial of these,
-the one which more than any other determines their relationships,
-consists in the position and shape of the bone with which the lower
-jaw articulates, the quadrate bone, so characteristic of reptiles. As
-in the plesiosaurian and ichthyosaurian skulls, it is firmly united
-with the adjoining bones, not articulating freely with them, as in the
-lizards and snakes. But this fixed relation of the bones is very unlike
-that of the plesiosaurs, ichthyosaurs, and turtles, in that it is held
-in place by _two_ bony bars or arches, the upper extending forward to
-unite with the bones at the back part of the orbit, the lower, with
-the hind extremity of the upper jaw. The lower jaws are rigidly united
-in front, sometimes for a long distance; they have, almost always,
-a hole or opening through the hinder part, known in but few other
-reptiles. The bones of the palate are all firmly united, forming a
-nearly complete roof, very unlike the condition in the mosasaurs and
-lizards. The palate also is very peculiar in the development of a
-plate of bone below the nasal chambers, forming a complete bony canal
-on each side through which the respiratory air passes far back to the
-internal opening of the nostrils above the pharynx, and not, as in
-other reptiles—save the immediate ancestors of the mammals—entering the
-mouth at the front end. This peculiar arrangement of the air-passages,
-so like that of ourselves, has much to do with the water habits of the
-crocodiles, as we shall see.
-
-The teeth are conical in shape, and are always restricted to the edges
-of the jaws, above and below. They are inserted deeply and firmly in
-sockets, and are replaced frequently by new ones growing beneath them,
-pushing the older ones out as their usefulness becomes impaired by
-injury or by use. In some species there are as many as thirty teeth in
-each side of the jaws, above and below, although the broad-headed kinds
-have a smaller number.
-
-[Illustration: FIG. 99.]
-
-[Illustration: FIG. 100.
-
-FIG. 99.—Skull of _Alligator mississippiensis_, from below.
-
-FIG. 100.—The same, from above: _bo_, basioccipital; _bs_,
-basisphenoid; _f_, frontal; _j_, jugal; _l_, lacrimal; _m_, maxilla;
-_n_, nasal; _p_, parietal; _pa_, palatine; _pm_, premaxilla; _pf_,
-prefrontal; _pr_, postfrontal; _pt_, pterygoid; _q_, quadrate; _qj_,
-quadratojugal; _tr_, transverse.]
-
-The neck is short, as has been stated, but it always includes in living
-forms nine vertebrae, a number probably slightly in excess of that
-of their terrestrial forbears. By the peculiar mode of attachment of
-the short “hatchet-shaped” ribs, much lateral movement of the neck
-is prohibited, nor is any very great vertical movement possible. The
-vertebrae of the whole column, save the atlas, the second sacral, and
-the first caudal—which is a very remarkable anomaly—are concave in
-front and convex behind, agreeing in this respect with those of all
-other living reptiles, save the turtles, the tuatera, and some lizards.
-The ribs of the neck have their two heads attached, one to the body of
-the vertebra, the other to the arch, but those of the dorsal region,
-though double-headed, have both become attached to the transverse
-projection of the arch, a seemingly trivial character, but one which
-immediately distinguishes all crocodiles from all other water reptiles,
-and from all terrestrial reptiles, indeed, save the Parasuchia,
-Pterosauria, and Dinosauria. The pelvis is firmly attached to the
-spinal column by two sacral vertebrae.
-
-[Illustration: FIG. 101.—Vertebrae of gavial from the side (cervical),
-and from in front (dorsal): _az_, anterior zygapophysis; _pz_,
-posterior zygapophysis; _d_, diapophysis; _r_, cervical rib; _c_,
-articulation for head; _t_, for tubercle of dorsal rib.]
-
-The collar-bones, or clavicles, are wanting in crocodiles; there is a
-slender interclavicle; and the shoulder-blade and coracoid are well
-developed (Fig. 102). The bones of the pelvis are loosely united with
-each other as they are in most reptiles (Fig. 104). The pubes, the
-anterior bones below, unlike those of all other reptiles, do not help
-to form the acetabulum or socket for the articulation of the thigh
-bone, nor do they articulate with each other. This single character
-sharply distinguishes a crocodile from all other reptiles, living or
-extinct, and is almost the only character that separates the order from
-the dinosaurs, aside from the peculiar structure of the nasal passages
-in the skull. On the under side of the body, connected with the front
-end of the pubes, there are seven or eight pairs of abdominal ribs,
-corresponding to the plastron of the turtles and similar to those of
-the ichthyosaurs and plesiosaurs. The mosasaurs have no such ribs.
-
-[Illustration: FIG. 102.]
-
-[Illustration: FIG. 103.
-
-FIG. 102.—Scapula (_sc_) and coracoid (_cor_) of gavial.
-
-FIG. 103.—Front foot of crocodile: _u_, ulna; _r_, radius; _re_,
-radiale; _ue_, ulnare; _p_, pisiform.]
-
-Furthermore, the crocodiles differ from all other living reptiles in
-having a four-chambered heart, like that of birds and mammals, that
-is, a heart with two auricles and two ventricles. This more perfect
-structure of the circulatory organs does not, however, insure at all
-times a complete separation of the pure or arterial blood from the
-impure or venous blood, since the blood may be more or less intermixed
-outside of the heart by a connection between the venous and the
-arterial systems. Whether these imperfectly developed organs, so
-suggestive of a higher and more perfect mode of respiration, are the
-vestiges of what were once among some reptiles functional structures,
-or whether they are rudiments of a higher organization, developing
-independently in these creatures, cannot be positively determined,
-but it seems very probable that, far back in geological times, some
-reptiles, especially the pterodactyls and dinosaurs, had their
-respiratory and circulatory systems more like those of the birds and
-mammals of today. Unfortunately, however, if such was the case, we may
-never be able to prove it, although proof would not be impossible;
-stranger things than fossil hearts have been found by paleontologists!
-
-The stomach, moreover, in the crocodiles is fashioned somewhat after
-that of the birds, with an imperfect division into crop and gizzard.
-Some crocodiles of today have the habit of swallowing hard pebbles,
-as do many birds. There is an old myth that the crocodile of the Nile
-swallows a pebble on each of its birthdays, thus giving reliable
-information as to its age by the number found in its gizzard at
-its death! And this habit has been suggested for some of the most
-ancient crocodiles, the teleosaurs, by the recurring presence of
-siliceous pebbles found with the remains of their skeletons. And we
-have seen this pebble-swallowing habit was also characteristic of the
-plesiosaurs, with whose remains “stomach-stones,” or gastroliths, as
-they have been called, are often found.
-
-[Illustration: FIG. 104.—Pelvis of crocodile: _il_, ilium; _is_,
-ischium; _pu_, pubis.]
-
-All of these various characters of the skeleton and fleshy parts are
-pretty conclusive evidence that the crocodiles, ugly creatures that
-they are, today enjoy the highest rank among cold-blooded animals. They
-are perhaps in some respects of not so high a type of reptiles as were
-some of the extinct reptiles, but that they have survived so long, so
-many millions of years, is pretty good evidence of endurance, to say
-the least.
-
-Living crocodiles belong to three distinct groups or families: the
-true crocodiles and alligators; the long-snouted crocodiles or Borneo
-gavials; and the true gavials of India. Members of the first of these
-families are really only subaquatic, or amphibious in habit; they move
-about on land with entire freedom, and often seek their food there.
-Certain marked aquatic characters they do possess, in the skull and
-tail, as we shall see. They are indigenous to southern China, India,
-Africa, Madagascar, the southern part of the United States, Central
-America, and the northern part of South America. The members of this
-family are distinguished by the more or less broad and flat head, the
-possession of comparatively few teeth of large size, and by having the
-toes less completely webbed. The crocodiles proper differ from the
-caimans and alligators especially in the arrangement of the teeth.
-During later geological times, that is, during early Tertiary times,
-the geographical range of the Crocodilidae was much more extended
-than it is at present, the remains of many often very large species,
-being found in the lake deposits of the northwestern parts of the
-United States, Great Britain, Germany, France, etc. Yet earlier, in
-the late Cretaceous rocks of the United States, in Texas, and Wyoming
-especially, there have been found rather scanty remains of a gigantic
-crocodile which must have been nearly fifty feet in length when living.
-
-The second family, the Tomistomidae, or long-snouted crocodiles,
-comprises but two living species, both restricted at the present time
-to Borneo. These crocodiles have a moderately slender snout, because
-of which they are sometimes called gavials, though it is not nearly so
-slender as that of the true Gangetic gavial. This family is probably
-older than either of the other living ones, and is the only one known
-with certainty to have lived during much of the Cretaceous times,
-several species of considerable size having been found in New Jersey
-and Europe. Their feet are better webbed than are those of the true
-crocodiles and alligators, the front feet partly, the hind feet wholly
-so. In general structure they seem to be the most primitive of the
-living Crocodilia, and may have been the ancestors of all modern forms.
-
-[Illustration: FIG. 105.—Gavial. (By permission of the New York
-Zoological Society)]
-
-The third family, the Gavialidae, also comprises but two living
-species, both restricted in habitat to the rivers of India. Of these
-the famed gavial of the Ganges is the better known and the more highly
-specialized. The skull of this species has an exceedingly long and
-slender snout; the teeth are numerous, small, and slender; and the feet
-are more fully webbed than are those of other members of the order. In
-habits the gavials are more distinctly aquatic than are the crocodiles
-and alligators. They feed almost exclusively upon small fishes, for
-the seizure and retention of which their small and sharply pointed
-teeth are admirably adapted. The hind feet are relatively long, a
-character that will be better understood when comparison is made with
-those of the Thalattosuchia. Although attaining a large size, fully
-twenty-five feet in length, they are comparatively harmless animals,
-never attacking human beings or other large animals, as do some of the
-crocodiles proper. The gavials have lived a long time in the Indian
-regions, the Gangetic gavial itself having been found in deposits
-of Pleiocene age, perhaps the oldest known of all living species of
-air-breathing vertebrates. Some of the extinct gavials of the same
-region attained a length of nearly or quite fifty feet, possibly the
-longest, if not the largest, of all swimming reptiles of ancient or
-modern times. Extinct gavials have been reported from South America,
-but are not yet fully known.
-
-While the fish-eating gavials swallow their prey whole, the crocodiles,
-caimans, and alligators prey upon all living animals that come within
-their reach, whether large or small, and they will often leave the
-water to seize their intended victims, such as pigs, sheep, birds, or
-even human beings. Their teeth, as has been already stated, are much
-larger, longer, and more irregular in size than those of the gavials.
-Their victims are often drawn under the water and drowned, the peculiar
-posterior position of the internal nostrils permitting the animals to
-breathe with the mouth and to firmly hold their prey under water, while
-the extremity of the snout and the external nostrils are above the
-surface.
-
-As the firm, unyielding bony palate, the fixed position and
-articulation of the lower jaws, and their rigid attachment to each
-other in front do not permit creatures of large size to enter the
-gullet whole, the crocodiles and alligators must tear their food to
-pieces, which they do by quick, strong jerks from side to side, aided
-by the powerful tail; or they may twist off a limb or some other part
-of their victims by a rapid rotation of the whole body, two assisting
-in this operation, rotating in opposite directions.
-
-Living crocodiles lay from twenty to sixty eggs, according to the
-species; these eggs are sometimes the size of a goose egg, and are
-covered with a hard shell. They are laid either in a deep excavation
-in the sand and covered over by the parent; or under leaves and straw.
-The female remains on guard until the eggs are hatched, of which she
-is apprized, it is said, by a peculiar noise uttered by the partly
-imprisoned young. She thereupon reopens the nest, and guides her
-liberated infants to the water, where she leaves them to their fate.
-Whether this remarkable habit is one that has been acquired in recent
-times or not is uncertain, but because it has been observed in a
-number of unrelated forms, it is probable that the instinct is of long
-inheritance, and may account for certain peculiarities of structure in
-some of the ancient members of the order. Doubtless the habit arose
-because of the unprotected places in which the eggs are necessarily
-laid on the shores and beaches, and because the eggs are comparatively
-so few in number. The sea-turtles likewise lay their eggs in hollows
-scooped out of the sand of the beaches, but the parents give no further
-care to their eggs, nor to their newly hatched offspring, a neglect
-which is compensated for by the much larger number of eggs they lay,
-because of which the chances are much greater that a few will survive
-the more numerous vicissitudes to which the eggs and young turtles are
-exposed.
-
-
-ANCIENT CROCODILES, MESOSUCHIA
-
-The name Mesosuchia, meaning “middle crocodiles,” by which the ancient
-members of the Crocodilia have generally been known, was given by
-Huxley in the belief that they were intermediate between the “true”
-or modern crocodiles and an ancient group which he united with the
-order under the name “Parasuchia.” A fuller and better knowledge of
-the members of this last group has proved very conclusively that they
-are really less allied to the crocodiles than are some other orders of
-reptiles, the dinosaurs for instance, and should be properly classed
-by themselves as a distinct order. And, more recently, it has also
-become quite apparent that the old crocodiles should not be separated
-so widely from the modern ones as Huxley proposed; that the differences
-distinguishing them from the recent members of the order are really
-not of more than family importance. We thus have left but two chief
-divisions of the Crocodilia, the Eusuchia and Thalattosuchia; and the
-latter group even, by some authors, perhaps rightly, are included under
-the true crocodiles as a family only.
-
-[Illustration: FIG. 106.—_Teleosaurus_; skull, from above.]
-
-These older crocodiles, the Mesosuchia of Huxley, comprise a
-considerable number of extinct forms which lived as far back as the
-early part of the Jurassic, and continued nearly to, if not actually
-into, Cenozoic time, that is, to the Eocene. They differ from all
-living forms, chiefly in having, not concavo-convex but biconcave
-backbones, that is, the more primitive vertebrae with which all
-reptiles began. Nor was the internal opening of the nasal passages so
-far back in the mouth as in the later forms. In other respects they
-did not differ very greatly from some of those now living. All the
-earliest kinds that we know of—the teleosaurs—had a long, slender
-snout, resembling very much that of the modern gavials. And they were,
-for the most part, incased in a more complete bony armor, on both the
-dorsal and the ventral sides; and the front legs were smaller than
-those of the gavials even. The resemblance of the living teleosaurs to
-the modern gavials must have been very great, although the heavier bony
-armor indicates a less exclusively aquatic life. They probably lived
-more in the shallow waters of the seas near the shores.
-
-Near the close of the Jurassic appeared for the first time, so far as
-we now know, broad-headed mesosuchian crocodiles, forms having less
-numerous and stronger teeth, and resembling closely modern alligators.
-It has been believed that these broad-headed kinds were of later origin
-than the more slender-nosed teleosaurs, but a moment’s consideration
-will make it evident how improbable such an evolution must be. The
-crocodiles must have descended from strictly terrestrial reptiles, and
-no terrestrial reptiles have a slender nose. That they should have
-acquired a slender face in adaptation to water habits and then returned
-to the more primitive land type with a broad face and less strictly
-aquatic habits is contrary to all our experience in paleontology. From
-this it is altogether probable that broad-faced crocodiles of later
-times must have been the descendants of broad-faced kinds that were
-in existence during all the Jurassic times, but of which we as yet
-have no knowledge. These broad-faced Jurassic crocodiles were, for the
-most part, small creatures, much smaller than the teleosaurs even, and
-smaller than any species of crocodiles now living. Their remains are
-known only from fresh-water or shore deposits, and are, for the most
-part, associated with those of land and fresh-water animals. About the
-time of their first known appearance in geological history, the small
-mammals and birds had also become more or less abundant, and it was
-suggested by Owen that these land animals had something to do with the
-development of the ancient amphibious crocodiles. Perhaps this was the
-case with respect to their greater abundance and development, and with
-certain peculiarities of their structure, but that the gavial-like
-teleosaurs should have come back to the land and reverted to a more
-primitive form seems quite improbable.
-
-During Cretaceous times, especially in America, numerous forms of
-these old mesosuchian crocodiles were doubtless in existence, both
-slender-nosed and broad-nosed, and some of them must have been of
-considerable size, though none known was as large as some of the
-late crocodiles. This type, with biconcave vertebrae, continued to
-live on, in both North and South America, to the latter part of
-Cretaceous times, and it is even possible that some continued on
-into the Tertiary. But long before the close of the Cretaceous,
-the modern kind appeared, those with concavo-convex vertebrae, and
-more posterior internal nostrils. The earliest are known from New
-Jersey (_Thoracosaurus_, _Holops_), so like the Borneo gavials of
-today that they are properly classified in the same family, the
-Tomistomidae or Gavialidae. If all the later, procoelian type, that
-is, those with concavo-convex vertebrae, originated from a single form
-when the amphicoelian or mesosuchian type became extinct, Huxley’s
-classification into the Mesosuchia and Eusuchia would perhaps be
-proper, but we have much reason to suppose that the change in the kinds
-of vertebra and in the position of the nostrils was only incidental,
-and may have occurred in more than one line of descent, that is, it
-may have occurred in the broad-headed kinds of the Jurassic to the
-broad-headed crocodiles of today, as also in the gavial-like forms of
-the Cretaceous to the gavials of the present. And this is the reason
-why naturalists no longer recognize the classification of Huxley,
-which, partly perhaps because of the prestige of his name, has so long
-been accepted in our chief works on natural history.
-
-
-MARINE CROCODILES, THALATTOSUCHIA
-
-While the ancient crocodiles of which we have spoken resembled the
-modern ones so closely in form of body and probably in habits, there
-were certain others of the old Jurassic seas which departed so widely
-both in structure and in habits, from their associates that they are by
-some authors given a place wholly by themselves as a distinct group.
-This has been called by Professor Fraas the Thalattosuchia, a word
-meaning “sea-crocodiles.” They were a very early side-branch from the
-great genealogical tree of the Crocodilia, a branch which departed so
-widely from their associates in adapting themselves to a peculiar and
-aberrant mode of existence that they cannot be considered as typical
-crocodiles, although so closely related to them in other respects
-that therecannot be the least doubt regarding their ancestry. None of
-the crocodiles which we have considered, whether ancient or modern,
-can truthfully be called purely aquatic. They never ceased to use
-their limbs for locomotion on land, more or less of the time, or for
-the support of the body; and many of them have subsisted, in part at
-least, on land animals. How easy it may have been for some of them
-to become almost wholly emancipated from land habits we may easily
-conjecture. The gavials, as we have seen, are more at home in the
-water than upon land; their food is chiefly found in the water; but,
-so long as their habits restrict them chiefly to fresh-water, or to
-the vicinity of the shores, their limbs continue to be used as much
-for crawling as for swimming. Were the gavials to be driven out to
-sea by the stress of fresh-water conditions or attracted thereto by a
-greater abundance of more easily obtainable or better food, so far from
-land that they no longer would have much use for their legs for the
-support or propulsion of their bodies, in the course of time they would
-doubtless change to a more purely aquatic type. And in that change
-there would be material modifications of their structure: their limbs
-would become better adapted to movements in the water; the skin would
-become smoother, and the bony and horny scales would be lost, since
-they would be not only useless in the water, but actually detrimental
-to the well-being of the animals; and the tail would develop into a
-more powerful organ of propulsion, as a means of increasing their speed
-in obtaining food or in escaping their enemies, such as the sharks.
-In fact, we can only imagine that in the transformation precisely
-those modifications would occur which we actually find in these old
-sea-crocodiles, the Thalattosuchia. And they are of especial interest
-to us here because nowhere do we find a better example of Nature in the
-act of transforming a terrestrial or subterrestrial animal into a truly
-aquatic one.
-
-[Illustration: FIG. 107.—_Geosaurus_, an Upper Jurassic thalattosuchian
-crocodile, drawn from restoration and figures by Fraas.]
-
-
-The group comprises only a few forms, so far as known. All were of
-modest size among extinct reptiles, from ten to twenty feet in length,
-and all are from the Upper Jurassic deposits of Europe. They did
-not exist very long, probably because they found it impossible to
-discard old habits and old structures entirely and become absolutely
-emancipated from the land; their breeding habits possibly were too
-deeply impressed into their structure readily to change, as did those
-of other sea-reptiles. Some of their remarkable aquatic adaptations
-have long been known, but only within a dozen years has our knowledge
-of them become at all complete. Three or four genera have been
-described, but only a few forms are well known, of which _Geosaurus_
-may be taken as most typical. To this we shall confine our descriptions.
-
-[Illustration: FIG. 108.—_Geosaurus_; skull from side and from above.
-(After Fraas.)]
-
-The skull of _Geosaurus_ is rather small in comparison with the length
-of the body, smaller proportionally than in any living crocodile, but
-not much smaller than that of the teleosaurs. The snout is long and
-slender, much like that of the teleosaurs and gavials, but the bones
-of the whole upper surface are quite smooth, not roughened and pitted
-like those of modern forms. The skull of _Dakosaurus_, another genus
-of thalattosuchians, is much less elongate than that of _Geosaurus_,
-but has the other characteristics of _Geosaurus_. The eyes are provided
-with a stout ring of sclerotic bones, with a pupillary opening of less
-than one inch. We have seen that all other strictly aquatic reptiles
-have similar eye bones, but no other crocodiles have them. The internal
-openings of the nostrils are large and long, but they are not situated
-far back, as in the modern crocodiles, not even so far back as in the
-early teleosaurs. They had no need of the peculiar breathing apparatus
-of the amphibious crocodiles, since all their prey must have been
-water-breathing creatures. Their eyes were directed laterally, not
-more or less upward, as in their nearest relatives. Nearly all other
-crocodiles have an opening through the hind end of the lower jaw, but
-the thalattosuchians did not. The teeth were about as numerous as in
-the modern gavials, but they projected freely only a short distance
-above the gums in life, and they were very slender and sharply pointed,
-excellently well adapted for catching smooth and slippery fishes.
-Their vertebrae, like those of all other reptiles of their time,
-were biconcave. Those of the neck resembled those of the teleosaurs,
-save that there were only seven, fewer than is the case with any
-other members of the order. In becoming adapted to their peculiar
-mode of life these crocodiles lost two vertebrae from the neck. All
-modern crocodiles have two ribs attached to the first vertebra; the
-thalattosaurs had but one, another evidence of primitive characters.
-While the number of vertebrae in the neck was reduced, in the back it
-was increased to eighteen; all other crocodiles have but fifteen or
-sixteen. The trunk was long, another adaptation to water life. There
-were two firmly united vertebrae in the sacrum, as in the modern forms.
-The reason for the persistence of this terrestrial character we shall
-see later.
-
-[Illustration: FIG. 109.—Tail, scapula (_sc_), and coracoid (_c_) of
-_Geosaurus_. (After Fraas.)]
-
-The tail was very long and strong, nearly as long as all the remainder
-of the body, and relatively much longer than in other crocodiles. It is
-of interest to observe that the head, neck, body, and tail had almost
-the same relative proportions as those of the great sea-lizards, the
-mosasaurs. The terminal bones of the tail are very peculiar, and very
-different from the corresponding bones of other crocodiles. While the
-spines of the tail bones along the anterior part are only moderately
-stout and long, and are directed obliquely backward, near the terminal
-part they become suddenly much broader and are directed upward, and, a
-little farther along, obliquely forward. The chevron bones on the under
-side also here become broader and longer. The end of the tail curves
-markedly downward to end in a slender point. It will be remembered that
-a similar downward curvature of the end of the tail observed in nearly
-all specimens of ichthyosaurs induced in Owen the belief that the
-animals had a fleshy terminal fin, a belief which later discoveries of
-the carbonized remains of the flesh confirmed. The peculiar structures
-observed in various specimens of these sea-crocodiles, even though no
-impressions or remains of the fleshy parts have been discovered, is
-quite conclusive evidence that these animals also had a broad, fleshy,
-terminal fin. No other explanation of the structure is possible.
-
-[Illustration: FIG. 110.—_Geosaurus._ Elongate hind leg, and
-paddle-like front leg. (After Fraas.)]
-
-The ribs are not at all stout and are not much curved. They are
-directed posteriorly in the known specimens preserved in the matrix
-in such a way as to indicate a slender thorax and abdomen, not the
-broad body of the modern crocodiles. The abdominal ribs, that is,
-those protecting the region on the under side of the body between the
-breast bone and the pelvis, are strongly developed in _Geosaurus_. The
-sternum, always present in other crocodiles, is wanting in _Geosaurus_.
-The shoulder-blades and coracoids, often changed in shape in water
-reptiles, are not unlike those of the amphibious crocodiles, but are
-smaller and flatter.
-
-The fore limbs, to use Professor Fraas’s words, “are among the most
-interesting of all the peculiarities of _Geosaurus_,” and show very
-clearly that these animals were excellent swimmers. The humerus is
-remarkably short and broad; the two bones of the forearm, the radius
-and ulna, are broad, rounded, or angular plates, not long bones, as
-in other crocodiles; the wrist bones also are broad and plate-like.
-The three bones of the thumb, that is of the digit which received
-most strongly the impact of the water in swimming, are also broad and
-flat. All of these bones are marvelously aquatic in type, as will be
-evident from a comparison of them with the corresponding bones of the
-ichthyosaurs and mosasaurs. The bones of the other fingers, however,
-were not much changed from the ordinary crocodilian form, as a further
-comparison of them with the fingers of a land crocodile will show.
-Furthermore the whole limb or paddle was very small in comparison with
-the hind leg, and it was attached very near to the head. The relative
-proportions of the front and hind limbs in the geosaurs, gavials, and
-alligators are instructive as showing the progressive decrease in size
-of the front legs from the subaquatic, through the semiaquatic, to
-the almost purely aquatic type. The hind legs, strangely enough, were
-not very different in size and structure from those of the gavials or
-teleosaurs. The thigh bone is long and slender, though the bones of the
-leg and ankle are somewhat shortened and flattened, as are also those
-of the first toe. There were no claws on the hind feet, a distinctly
-aquatic adaptation, and the toes were certainly webbed. The pelvis,
-while not especially stout, is of good size, and was firmly attached to
-the sacrum.
-
-Perhaps all these characters may best be summed up in the words of
-Professor Fraas, as translated:
-
-      We recognize in _Geosaurus_ an unusually slenderly
-    built crocodile, in appearance very different from all true
-    crocodiles. The smooth, rounded skull, with its greatly
-    elongated and slender snout, and the deep-lying, small eyes,
-    reminds one most of the ichthyosaurs. The skull merges into
-    the slender, elongated trunk without a visible neck, and
-    the body was provided neither above nor below with horny or
-    bony armor, but was, probably, as in the whales, covered
-    with a smooth, soft skin. The anterior extremities, attached
-    far forward, are developed as paddles, and served rather
-    as organs of equilibration than as a means of propulsion,
-    which was the function of the elongated hind legs and the
-    extraordinarily strong and powerful tail, which supported
-    at its end a large fin. The entire impression given of
-    the animal is that of an excellent swimmer, with all the
-    peculiar aquatic adaptations. In the skeleton, however, all
-    the characters of the original crocodiles are preserved.
-    Most remarkable are the laterally placed eyes, protected
-    by the stout sclerotic bones, and the overhanging bones of
-    the orbits. So, too, the large temporal openings of the
-    skull, doubtless due to the absence of the bony plates in
-    the integument, give to the animal a strangely abnormal
-    appearance for a crocodile.
-
-We have observed that all the truly aquatic air-breathing animals,
-save the plesiosaurs, have either lost the hind legs or else have them
-greatly reduced in size, and the disproportionately large size of
-these members in _Geosaurus_ seems inexplicable. But an explanation is
-not, I think, hard to find. In the adaptation to water life the first
-to become modified for the control of the body are the front legs.
-The hind legs never have any really important use when the tail is a
-powerful propeller. The hind legs of the geosaurs are still essentially
-legs and not paddles, and they were doubtless used either occasionally
-for propulsion on land, or perhaps for pushing the body about on
-the bottom of shallow waters. And the presence of a well-developed
-ventral armor of bony ribs possibly also indicates more or less of the
-terrestrial crawling habit. As soon as the hind legs cease to be used
-for crawling they take on only a feeble use for the equilibration of
-the body, and speedily become small, until finally they disappear.
-That the hind legs of these creatures were of some use in the water
-is certain, because of the modifications in their structure, and
-especially because of the loss of the claws; but that they were of
-important use as propellers is hardly probable. We may therefore infer
-that the thalattosuchians, while distinctively sea-reptiles, had not
-entirely lost their land habits. Moreover, it is highly probable that
-their egg-laying habits, which would hardly change with a greater
-adaptation to water life, compelled the animals recurrently to visit
-the shores. To have finally lost their hind legs they must have become
-viviparous in habit, since it seems to be impossible for any true
-air-breathers to be hatched in water. Perhaps this insurmountable habit
-was the final cause of their extinction in competition with the truly
-viviparous aquatic flesh-eaters. The thalattosuchians had but a brief
-existence in geological history, during the latter part of the Jurassic
-period only, so far as certainly known, nor did they become widely
-dispersed over the earth; they are known from Europe, possibly from
-Brazil.
-
-
-
-
-CHAPTER XVI
-
-CHELONIA
-
-
-No order of reptiles of the past or present is more sharply and
-unequivocally distinguished from all others than the Chelonia or
-Testudinata. No order has had a more uniformly continuous and
-uneventful history. None now in existence has had a longer known
-history, and of none is the origin more obscure. The first known
-members of the order, in Triassic times, were turtles in all respects,
-as well or nearly as well adapted for their peculiar mode of life as
-are those now living, and were they now living they would attract no
-especial attention from the ordinary observer and but little from the
-naturalist. From time to time some have gone after better things,
-and have come to grief, but the main line has remained with fewer
-improvements, fewer evolutional changes, than any other group of higher
-vertebrates. The turtles seem very early to have adapted themselves
-so well to their peculiar mode of life, to have intrenched themselves
-so thoroughly in their own province, that no other creatures have
-been able to overcome them, or to drive them from it. The remains of
-no other air-breathing vertebrates are so omnipresent in the rocks
-as those of the turtles; they may be expected wherever fossils of
-air-breathing animals are found, though unfortunately often only in
-scattered and broken fragments. The loose union of their skeletal bones
-and their general habits of life in shallow waters left their bodies as
-food for scavengers, or for dismemberment by the tides and currents.
-
-Relationships with other reptiles they really have none. Some have
-thought that the plesiosaurs were their first cousins, others the
-Placodontia, an indeterminate group of extinct reptiles usually placed
-with the Anomodontia. But their relationship with neither of these is
-closer than with the crocodiles, dinosaurs, or pterodactyls. They are
-the only reptiles that we know, besides the cotylosaurs, which have no
-holes in the temporal roof of the skull, and as the cotylosaurs were
-the most primitive and the oldest of reptiles, this fact incontestably
-proves that the turtles had a very ancient origin, though we know
-them no farther back than the later Triassic. They are the only order
-of reptiles of which not a single member is known to have teeth, or
-even vestiges of them. Until recently only a single specimen has been
-known from the Trias, and of that only the casts of the shell; but
-the shell was as fully developed and as complete as that of a modern
-alligator snapper, which it resembled much in form and in size. And
-doubtless the habits of this ancient _Proganochelys_ were similar
-to those of the alligator snapper. The early cotylosaurian reptiles
-were all littoral-or marsh-loving animals, and more or less aquatic,
-and doubtless the early turtles continued in the same environments
-and with the same habits after acquiring a shell for protection and
-losing their teeth, which for some inexplicable reason they seemed no
-longer to need. Until near the close of the Jurassic period probably
-all turtles were amphibious animals of the marshes, spending much,
-perhaps the larger part, of the time in the water, good swimmers, and
-yet good crawlers. With the beginning of the Cretaceous, however, some
-of them became ambitious for new and untried modes of life. Various
-ones went down into the sea and became marine animals, reaching the
-zenith of their prosperity and the maximum of size before the close
-of the period, but continuing in diminished size and numbers to the
-present time, if we may consider the leather-back turtle as really
-their descendant. Others in the Cretaceous took to the rivers and
-ponds, and became almost as thoroughly aquatic in their thin shape
-and soft covering; and their lineal descendants still continue in the
-rivers of the Northern Hemisphere. Still others, in the Age of Mammals,
-took to the upland, and competed with the mammals in the open places
-and prairies, reaching their maximum in Miocene-Pliocene times, when
-for some unknown reason the giants among them were driven from the
-mainlands to continue a precarious existence to the present time in
-some of the larger islands.
-
-[Illustration: FIG. 111]
-
-[Illustration: FIG. 112
-
-FIGS. 111 and 112.—_Graptemys._ (From Hay.)
-
-FIG. 111.—Carapace: _cp1_, _cp2_, etc., costal plates; _cs1_, _cs2_,
-etc., costal scutes, horny; _n1_, _n2_, etc., neural bones; _nup_,
-nuchal bone; _nus_, nuchal scute; _py_, pygal bone; _spy_, suprapygal;
-_spy 2_, second suprapygal, or postneural; _vs1_, _vs2_, etc.,
-vertebral scutes; 1, 2, 3-12 on right side, marginal scutes; 1, 2, 3-12
-on left side, peripheral bones.
-
-FIG. 112.—Plastron: _ab_, abdominal scutes; _an_, anal scutes;
-_ent_, entoplastron (interclavicle); _epi_, epiplastron (clavicle);
-_fem_, femoral scute; _g_, gular scute; _hum_, humeral scute; _hyo_,
-hypoplastron bone; _hypo_, hypoplastron; _in_, inguinal scute; _py_,
-pygal bone; _xiph_, xiphiplastron.]
-
-Were there no turtles living we should look upon the fossil forms
-as among the strangest of all vertebrate animals—animals which had
-developed the strange habit of concealing themselves inside of
-their ribs, for that is literally what the turtles do. The box or
-shell of an ordinary turtle is composed of the backbones and ribs,
-to which are soldered a shell of bony skin plates above, with the
-clavicles, interclavicle, and ventral ribs below. Except in the strange
-leather-back turtle described farther on, these plates form definite
-series. Ten of them cover the spines of the dorsal vertebrae, in the
-mid-line, one over each, of which the turtles have the smallest number
-of any known reptiles. There are eight on each side over the ribs,
-united by suture with each other and with the middle series; and, in
-addition, there are twenty-six bones surrounding them and attached to
-them. All these bones compose what is called the carapace, which forms
-a complete roof in the more terrestrial types, more or less imperfect,
-with vacuities between the bones in the marine forms. On the under
-side, in addition to the clavicles and the interclavicle, there are
-three pairs of enlarged ventral ribs that go to form the plastron,
-solid and complete in land turtles, with openings in the water forms.
-And in the land forms the plastron is more or less firmly united with
-the carapace.
-
-[Illustration: FIG. 113.—_Toxochelys_; coracoid and scapula.]
-
-In the skeleton contained within the box thus formed is the very
-peculiar pectoral girdle, composed of scapula and coracoid, the scapula
-so peculiar that the controversy as to its homologies is not yet quite
-settled. Most authors, until recently, have believed that its peculiar
-shape (Fig. 113) is due to the co-ossification of the procoracoid
-with the scapula instead of as usual its loss or union with the true
-coracoid, so called. We are now pretty sure that this is not true,
-since in reality there is no such bone as the procoracoid, the bone
-so called being the real or true coracoid; and because, in the second
-place, the long anterior projection called the procoracoid is really
-only an outgrowth of the scapula itself and not a fused, separate bone.
-Hence the bone is properly called the scapula-proscapula, and not the
-scapula procoracoid, as it usually has been. The coracoids are elongate
-and flattened and without the usual supracoracoid foramen, so generally
-present in reptiles. The only other reptiles having a similar structure
-of the scapula are the plesiosaurs, and it has been because of this
-apparent resemblance that some good paleontologists have thought the
-turtles and plesiosaurs were allied. The sacrum is composed of two
-vertebrae only, and the pelvis of the usual three bones, the ilium, the
-ischium, and the pubis, all covered over by the shell.
-
-[Illustration: FIG. 114.—Pelvis of _Chelone_, from below: _pu_, pubis:
-_is_, ischium; _il_, ilium (in acetabulum).]
-
-In every known turtle the neck is composed invariably of eight
-vertebrae, but they are peculiar in many respects. In the earliest
-known turtles the neck vertebrae were, as would be supposed, biconcave,
-but they soon became very variable in all; in each neck some are
-biconcave, some biconvex, some opisthocoelous, and some procoelous. And
-Dr. Hay tells us that the neck has increased in length in the later
-forms.
-
-The skull also is very peculiar in that it has some very primitive
-characters and others very aberrant. The temporal roof, as has been
-said, has no holes through it, though it is often reduced by the
-emargination of the borders, whether from below or behind, until in
-some the whole temporal region is exposed, and not at all covered over.
-There is no parietal foramen, so constantly present in all the early
-reptiles and in the lizards and the tuatera of modern times. There
-are no teeth or vestiges of teeth, but the jaws have usually a horny
-cutting edge, which seems to be quite as serviceable; in the river
-turtle the lips are fleshy. There is no transverse or transpalatine
-bone. There is a single vomer only, not paired as in other reptiles,
-whence comes the doubtful theory that the vomers of other reptiles
-are not the real vomers originally so named in mammals, and hence
-often called prevomers. The vomer of the turtles under this theory is
-believed to be the real homologue of the mammalian bone. The palate is
-always slightly, sometimes nearly wholly, underfloored, as in mammals,
-carrying the internal nostrils far back in the mouth. In the occipital
-region of the skull there is a separate bone on each side called the
-paroccipital or opisthotic, which has been indistinguishably fused with
-the exoccipital in all other reptiles except the ichthyosaurs since
-Triassic times.
-
-[Illustration: FIG. 115]
-
-[Illustration: FIG. 116
-
-FIGS. 115 and 116.—_Trachemys._ (From Hay.)
-
-FIG. 115.—Skull from above: _fr_, frontal; _ju_, jugal; _pa_, parietal;
-_paoc_, paroccipital; _pfr_, prefrontal; _pof_, postfrontal; _pro_,
-proötic; _qu_, quadrate; _sq_, squamosal; _soc_, supraoccipital.
-
-FIG. 116.—Skull from below: _alv_, alveolar surface of maxilla; _boc_,
-basioccipital; _bap_, basisphenoid; _exoc_, exoccipital; _mx_, maxilla;
-_pal_, palatine; _paoc_, paroccipital; _pmx_, premaxilla; _pro_,
-proötic; _pt_, pterygoid; _qu_, quadrate; _qj_, quadratojugal; _sq_,
-squamosal; _vom_, vomer.]
-
-In the feet the numbers of phalanges—that is, the bones of the free
-digits—are like those of mammals, that is, two in the first and three
-in each of the other four digits. The land tortoises have lost some of
-these, while the river turtles have either gained one or two in the
-fourth finger and fourth toe, or else have enjoyed an uninterrupted
-descent from the primitive reptiles which normally possessed that
-number. All other reptiles, save those phylogenetically allied to the
-primitive mammals, that is, the Theriodontia and their allies, have
-normally the phalangeal formula 2, 3, 4, 5, 4. It was partly because
-of this similarity of the numbers of toe bones that the turtles have
-been classed in the great group of reptiles that includes the ancestors
-of the mammals; that is, under this theory, the turtles would enjoy a
-nearer relationship to the mammals and to man himself than any other
-living reptiles! But this classification has been shown to be quite
-artificial.
-
-[Illustration]
-
-[Illustration: FIG. 117.—Limbs of _Colpochelys_, a recent sea-turtle:
-_H_, humerus; _R_, radius; _U_, ulna; _r_, radiale; _i_, intermedium;
-_u_, ulnare; _p_, pisiform; _c_, centrale; _T_, tibia; _F_, fibula;
-_a_, astragalus; _m_, fifth metatarsal. (From Wieland.)]
-
-From what has been said, it will be surmised that the Chelonia
-represent in themselves one of the primary subdivisions of the class
-Reptilia, and that, unlike most others, the order has enjoyed a most
-remarkable longevity. And doubtless they are one of the primary
-branches of the reptilian stock, which has remained distinct since
-Permian times at least, if not since Carboniferous, isolated and
-remarkably homogeneous, giving off no branches which departed far from
-the main stock, and on the whole leading a singularly placid existence
-for ten or more million years.
-
-In most textbooks the order Chelonia is divided into three suborders,
-the Pleurodira, the Cryptodira, and the Trionychoidea. In recent
-years, however, the earlier members of the older group of Pleurodira
-have been separated into a fourth suborder, the Amphichelydia, a group
-characterized by some not very important differences in the plastron
-and skull, and including those forms in which the cervical vertebrae
-are amphicoelous. This group continued to Eocene times before it
-became extinct, and consisted of archaic forms which persisted after
-all the other suborders had come into existence. The Cryptodira,
-especially characterized by the manner in which they withdraw the head
-and neck within the shell by an =S=-like vertical flexure, are known
-from the Lower Jurassic and are still the dominant group of today,
-with more than one hundred and forty living species. The Pleurodira
-in the narrower sense are first known from their remains in the Upper
-Cretaceous of North America and are still represented by about forty
-species, living in the Southern Hemisphere. They are distinguished from
-the other groups by the manner in which they withdraw the neck and head
-into the shell, by a horizontal, sidewise flexure. The third suborder,
-the Trionychoidea, also began in Cretaceous times, so far as we know,
-and are represented by about seventy living species, chiefly in the
-Northern Hemisphere. They are especially characterized by the absence
-of bony marginal plates and the soft epidermis.
-
-With the exception of the land tortoises, all turtles from the
-beginning of their career as an order to the present time have been
-more or less at home in the water. In some, like the marine forms, the
-adaptation to aquatic life has produced marked changes in structure: in
-the loss of the horny dermal shields and in the loss of bone tissue;
-in the flattening of the shell, and in the development of the front
-legs into swimming flippers, with a loss of the claws. In the absence
-of a guiding tail, which is always small in the marine turtles,
-propulsion must of course be wholly by the aid of the limbs. As oar
-propellers the marine turtles show some of the peculiar characters
-of the plesiosaurs. With a like short and broad body, a more or less
-elongated and flexible neck, there could be no sinuosity of the body in
-swimming. As an oar-like organ the humerus became flattened, and its
-muscular attachments, as in the plesiosaurs, descended far down the
-shaft, giving greater mechanical advantage. Unlike all other aquatic
-vertebrates, the turtles never developed real hyperphalangy. Only in
-the river turtles is there a possibility of an increase in the bones of
-the fourth digit.
-
-To discuss in general the structure and habits of the living chelonians
-would extend this chapter to an undue length, and would add nothing
-to the many excellent works on natural history accessible to the
-student. We have therefore contented ourselves with a brief outline of
-the geological history of the order, with especial reference to their
-aquatic habits.
-
-
-SIDE-NECKED TURTLES. PLEURODIRA
-
-The suborder of Chelonia, generally known as the snake-necked or
-side-necked turtles or tortoises, comprises about forty living
-species, confined to South America, Africa save the northernmost part,
-Madagascar, New Guinea, and Australia. In Australia they are the only
-members of the order known—another instance of the peculiar isolation
-of the fauna of that region. In the past they lived in North America
-during Upper Cretaceous times, the earliest known forms of the group
-in its restricted sense, of which seven species are described by Hay.
-In Eocene times they are also known from Europe and Asia, from both of
-which regions they have long since disappeared.
-
-The Pleurodira, as the term indicates, are easily distinguished from
-all other turtles by the way in which they withdraw the head within the
-shell. Instead of withdrawing it by an =S=-shaped flexure of the neck
-between the shoulder-blades, as do other turtles, these bend the neck
-laterally in a horizontal plane, bringing the head within the margins
-of the shell in front of one or the other foreleg; and the margins of
-the shell are produced here in an eave-like fashion for the greater
-protection of the head. In the structure of the shell, which is always
-fully developed into a box, these turtles do not differ very much from
-the Cryptodira, though there may be some extra bones in the plastron,
-as also in the skull. The nasal bones are always, the lacrimals
-sometimes, well developed; the latter never, the former rarely, found
-in other groups. The lower jaws articulate a little differently,
-and the external ear is always fully surrounded by bone. Very
-characteristic is the bony union of the pelvis with the plastron below,
-which never occurs in other turtles, unless it be the Amphichelydia.
-
-The side-necked turtles are all of fresh-water habit, similar to that
-of the fresh-water tortoises spoken of farther on. The neck is often
-very long and snake-like, which accounts for one of the names given
-to these turtles; because it is withdrawn into the shell sidewise, it
-has more distinctively ball-and-socket joints between the vertebrae,
-with distinct transverse processes for the attachment of the necessary
-side-moving muscles. The feet in all are more or less webbed and armed
-with strong claws.
-
-The largest and perhaps the best known of all living side-necked
-turtles is the giant Amazon turtle of South America, which sometimes
-has a shell nearly three feet in length. Its feet are broadly webbed,
-and the shell is rather flat in the adult; it is an excellent swimmer
-in the waters of the Orinoco and Amazon. Six or seven species of
-the genus to which it belongs are known, all of them South American
-except one that lives in Madagascar and one fossil found in the Eocene
-of India. This remarkable distribution is but one more of the many
-instances known in zoölogy and paleontology that seem to prove an early
-land connection between India and South America. Had the migration
-between the two continents occurred by way of Asia and Bering straits,
-as did that of hosts of mammals, one would certainly expect to find
-some evidence of it in the North American Tertiary rocks, which, so
-far, is lacking.
-
-
-CRYPTODIRA
-
-The chief families of the Cryptodira turtles are the Chelydridae,
-or snappers; the Emydidae, or marsh tortoises; the Testudinidae, or
-land tortoises; the Chelonidae, or sea-turtles; the Protostegidae, or
-ancient sea-turtles; and the Dermochelydidae, or leather-backs. Other
-doubtful or smaller groups, both living and extinct, may be omitted, or
-incidentally mentioned.
-
-
-SNAPPING TURTLES
-
-The family of snapping turtles, the Chelydridae, are of interest
-because of their peculiar geographical distribution at the present
-time. Only four species are known, three of them from North America,
-the fourth from New Guinea. The family is one of the most primitive of
-living turtles, though no members of it are known with certainty from
-earlier rocks than the Oligocene. In all probability, also, they have
-retained, more than have any other group of turtles, unless it be some
-of the fresh-water tortoises, the primitive habits of the earlier or
-earliest turtles, though of course there have been modifications, both
-in structure and in habits. The three species of the United States
-include two of the snapping turtles proper and the alligator turtles of
-the southern states, which sometimes reach a length of three feet. All
-the species are largely aquatic in habit, powerful and active swimmers,
-with webbed feet and strong claws, and both on the land and in the
-water they are bold and fierce. They have a relatively large head and
-very strong jaws. Agassiz saw one bite off a piece of a plank an inch
-in thickness, and they can usually be raised from the ground by any
-object which they seize. The carapace and plastron are much reduced,
-and are rather loosely united. The shell is not large enough for the
-complete withdrawal of the head and legs within it, and the tail is
-unusually large and strong. The common snapping turtle, _Chelydra
-serpentina_, is found from Canada to Ecuador, and its remains have been
-found with those of the mammoth and mastodon in Pleistocene deposits;
-and related species of the same genus have been reported from the
-Miocene of England.
-
-
-FRESH-WATER OR MARSH TORTOISES
-
-The family of turtles or tortoises (Emydidae) represented at the
-present time by the common terrapin, painted tortoise, and box tortoise
-of the United States, and commonly called fresh-water turtles or
-tortoises, comprises the largest group of living chelonians—nearly a
-third of all existing members of the order. They are widely distributed
-over all parts of the earth except Australia, and are of very varied
-habits. Some are almost exclusively aquatic; others, like the painted
-tortoise, are partially so, while others, especially the common box
-tortoise, are almost as exclusively terrestrial as the true land
-tortoises, dying even, if forced to live long in water.
-
-The shell in the more aquatic forms is depressed or flattened, but
-in the terrestrial kinds may be as highly arched as in the true land
-tortoises. The feet are adapted primarily for walking, but nearly
-always have the toes webbed, and the digits are longer than are those
-of the land tortoises. Only the two or three middle toes have claws.
-Some species have developed hinges in the plastron, whereby they may be
-completely closed up after the head and legs are withdrawn within the
-shell. Most of the species are carnivorous in habit, but a few, like
-the box tortoise, are strictly vegetarian.
-
-Geologically the fresh-water tortoises have a not very ancient history,
-going back no farther than do the land tortoises, that is, to the
-beginning of the Cenozoic or Age of Mammals. Fully fifty species
-are known from the Tertiary rocks of North America, or more than
-three-fourths as many as are now living upon the earth.
-
-The family at most can be said to be only amphibious in habit, and has
-no striking aquatic adaptations, since the shell is well developed and
-is covered with horny shields. The flattened shell of the more aquatic
-forms is characteristic, as is also the greater degree of webbing
-between the toes.
-
-
-LAND TORTOISES
-
-Perhaps the last of the more noteworthy specializations of
-the Chelonia, and indeed among the last of the more important
-specializations of the Reptilia, are the upland tortoises, of which
-the common “gopher” of the southern states is almost the only remnant
-in North America. They formed a part of the great hegira of forest and
-marsh animals to the open prairies, away from the lowlands and water
-which the turtles had inhabited almost exclusively for millions of
-years.
-
-[Illustration: FIG. 118.—_Testudo sumeirei_, a giant upland tortoise.
-(From Hay, after Rothschild.)]
-
-They began their career, Dr. Hay thinks, at about the beginning of
-the Cenozoic, that is, with the great development of the mammals, and
-reached the maximum of their development in the Miocene; and they
-have been on the decline ever since. In the Northern Hemisphere, at
-least, the slowly cooling climate throughout the Eocene, and a decided
-decrease in moisture, brought about the prairies and prairie plants
-before its close. Just as the horses, rhinoceroses, camels, and other
-herbivorous mammals took to these open places for the better and more
-abundant food found therein, so also the lowland tortoises found better
-food and fewer enemies there, for they are all strictly herbivorous in
-habit. The mammals became more conspicuous to their enemies when they
-went into the open, and it was only by the development of speed, more
-sober coloration, and perhaps greater cunning that they found safety
-from them. The tortoises were handicapped by low intelligence, and they
-could not develop speed, for they were not constructed to that end. But
-they did find protection in their bony shell, which became thicker,
-higher, and more convex, and with smaller openings. To quote Dr. Hay:
-“We may suppose that it would be much more difficult for a carnivorous
-animal to effect an entrance into such a shell than into one depressed,
-and whose borders may be spanned by the jaws of their enemies.” Perhaps
-also the highly arched form of the shell gave greater capacity for the
-lungs, and the tortoises in general, it is said, do have better lung
-capacity than the more aquatic or lowland types of turtles. Possibly,
-also, the heavier shell lessened the evaporation of the body fluids,
-and made the tortoises less dependent upon the vicinity of water.
-Certain it is that the common box tortoise, of like form and habits,
-occurs not rarely on the arid plains, far from water.
-
-The neck and legs became fully retractile within the shell; the digits
-were shortened up, without a vestige of webbing membrane between them;
-the phalanges were reduced in number to two in each toe, and nearly all
-the toes have well formed claws. The feet are placed squarely upon the
-ground, and the body is elevated in walking. They can swim, when by
-accident they are thrown into the water, only as any terrestrial mammal
-can.
-
-About forty species of land tortoises are known throughout the world
-at the present time, though North America, the probable original home
-of the tribe, has but three, all small. The larger species are all now
-denizens of islands, especially the Galapagos Islands, where the giant
-tortoises have long been famous. And many of our living forms have
-changed but little since Eocene times. In the Oligocene and Miocene
-they inhabited western North America in enormous numbers. In the Bad
-Lands of South Dakota one can often see the remains of a dozen or more
-of these giant tortoises at one time, specimens varying from one to
-three feet in length of shell. In river deposits, those of the late
-Miocene or early Pliocene, the writer has seen areas of an acre or more
-literally strewn with their remains, as though droves of them had been
-overwhelmed and perished together. About fifty species of these land
-tortoises are known from the American Tertiary, thirty-two of them
-belonging to the modern genus _Testudo_, which comprises the giant
-tortoises of the Galapagos. The largest known species of the group is
-one of _Testudo_ from the Pliocene of India, which had a shell six feet
-in length. Why the larger species became extinct in Pliocene times on
-the mainland to survive only in the islands is not known; possibly
-their carnivorous enemies became too cunning and too numerous.
-
-
-SEA-TURTLES. CHELONIDAE
-
-The sea-turtles, or Chelonidae comprise five or six living species,
-inhabitants for the most part of tropical and subtropical oceans, of
-which the green or edible turtle (_Chelone_), the hawksbill turtle
-(_Caretta_), and the loggerhead (_Eretmochelys_ [Fig. 119]) are the
-best known. They are all thoroughly aquatic in habit, and of large
-size, from three to five feet in length. The carapace is heart-shaped,
-and reduced, that is, with large openings between the ribs; the
-plastron also is reduced and loosely united to the carapace. The neck
-is short and the head is not retractile within the shell. The temporal
-region of the skull is roofed over. The four legs form large and
-powerful flippers, and the hind legs are relatively small. The body is
-flattened and the tail is small. The aquatic characters of the limbs
-are seen especially in the broad and strong humerus, with the radial
-crest for the attachment of powerful muscles situated far down on
-the shaft; in the relative shortness of the radius and ulna, and the
-large size of the latter bone; in the flattened carpal bones; and in
-the great elongation of the digits and the absence of all but one or
-two of the claws. Unlike the leather-back turtle and the Cretaceous
-sea-turtles, the carapace and plastron are completely covered with
-horny shields, from which indeed the tortoise shell of commerce is
-derived. Except the green turtle, all members of the family are
-carnivorous.
-
-[Illustration: FIG. 119.—_Eretmochelys_, loggerhead turtle. (By
-permission of the New York Zoölogical Society.)]
-
-Extinct members of the family are known from scanty remains in Cenozoic
-and late Cretaceous rocks. From the earlier Cretaceous deposits of the
-plains more primitive allied forms occur, often classed in distinct
-families of which _Toxochelys_ (Fig. 120) and _Desmatochelys_ are the
-more noteworthy. The latter genus, especially, might well have been an
-ancestor of all the modern forms. About three feet in length, it had
-all the essential characteristics of the sea-turtles, in its thin form,
-roofed-over skull, reduced carapace, loose plastron, and flipper-like
-limbs. The single known specimen, preserved in the museum of the
-University of Kansas, came from the lower rocks of the Upper Cretaceous
-of Nebraska. Yet earlier, at the close of the Jurassic, there were
-shore turtles of considerable size that had begun to develop a fondness
-for the open seas; to acquire a depressed form and lightened shell, the
-limbs still retaining, however, more of the terrestrial or crawling
-form. They are grouped as a separate family, the Thalassemydae,
-and include the first of the Chelonia to depart from the marsh and
-fresh-water habits which for long ages, perhaps, had limited the
-activities and evolution of the turtles.
-
-[Illustration: FIG. 120.—Carapace of _Toxochelys bauri_, an Upper
-Cretaceous sea-turtle: _ep_, epineural. (After Wieland.)]
-
-
-ANCIENT SEA-TURTLES. PROTOSTEGIDAE
-
-[Illustration: FIG. 121.—_Toxochelys latiremis_; front leg: _hum_,
-humerus; _rad_, radius; _ul_, ulna; _int_, intermedium; _uln_, ulnare;
-_p_, pisiform; _cen_, centrale. (From Wieland.)]
-
-[Illustration: FIG. 122.—_Desmatochelys lowii_; skull from above and
-below.]
-
-Forty-four years ago the late Professor E. D. Cope, one of the
-greatest naturalists America has ever produced, in almost the earliest
-exploration of the great Cretaceous fossil deposits of western
-Kansas, discovered and collected a remarkable specimen of one of
-the most extraordinary turtles that is known even yet. By an error
-somewhat natural for those times, when the theory of evolution was
-just beginning to attain acceptance by naturalists, he thought that
-the specimen, notwithstanding its monstrous size, represented a very
-primitive kind of turtle, and gave to it the name _Protostega gigas_,
-meaning gigantic first roof! The late Professor George Baur, to whom
-paleontology owes so much, showed that, far from being a primitive
-turtle, _Protostega_ was really one of the most specialized types of
-the order. Professor Cope’s account of the discovery of the specimen is
-of so much interest that it may be quoted here:
-
-“In the very young tortoise or turtle the ribs are separate, as in
-other animals. As they grow older they begin to expand at the upper
-side of the upper end, and with increased age the expansion extends
-throughout the length. The ribs first come in contact where the
-process commences, and in the land tortoise they are united at the
-end. In the sea-turtles the union ceases a little above the ends. The
-fragments of the _Protostega_ were seen by one of the men projecting
-from a ledge of a low bluff. After several square feet of rock had
-been removed, we cleared up the floor and found ourselves well repaid.
-Many long, slender pieces of two inches in width lay upon the ledge.
-They were evidently ribs, with the usual heads, but behind each head
-was a plate-like the flattened bowl of a huge spoon, placed crosswise.
-Beneath these stretched two broad plates, two feet in width, and no
-thicker than binder’s board. The edges were fingered and the surface
-was hard and smooth. All this was quite new, among fully grown animals.
-Some bones of a large paddle were recognized, and a leg bone. The
-shoulder-blade of a huge tortoise came next, and further examination
-showed that we had stumbled on the burial place of the largest species
-of sea-turtle yet known. But the ribs were those of an ordinary turtle
-just hatched, and the great plates represented the bony deposit in the
-skin, which, commencing independently in modern turtles, unite with
-each other at an early day. But it was incredible that the largest
-of known turtles should be but just hatched, and for this and other
-reasons it has been concluded that this ‘ancient mariner’ is one of
-those forms, not uncommon in old days, whose incompleteness in some
-respects points to the truth of the belief that animals have assumed
-their modern perfection by a process of growth from more simple
-beginnings.”
-
-Later studies by Doctors G. Baur, E. C. Case, O. P. Hay, and especially
-G. R. Wieland, of the abundant and excellent material, preserved in the
-museums of Yale and Kansas universities and the Carnegie Institution,
-and especially the discovery by Wieland in 1895 of an allied and yet
-larger form which he called _Archelon_, have determined practically
-every detail of the structure of this remarkable group of sea-turtles.
-A surprisingly complete specimen of _Archelon_ is mounted in the museum
-of Yale University.
-
-[Illustration: FIG. 123.—_Archelon ischyros_; skeleton from above: _n_,
-nuchal, _r_, _r_, _r_, ribs; _m_, _m_, peripheral bones; _h_, humerus;
-_r_, radius; _u_, ulna; _t_, tibia; _fi_, fibula. (From Wieland.)]
-
-About a half-dozen species and two genera of the family have so far
-been described, all coming from the Upper Cretaceous deposit of Kansas
-and South Dakota, the genus _Archelon_ from later rocks than those
-which have yielded _Protostega_.
-
-The general form and structure of _Archelon_ will best be understood
-from the accompanying figures after Wieland (Figs. 123, 124, 125) and
-the restoration of the living animal as interpreted by the writer
-(Fig. 126). If the leather-back turtle, described farther on, is really
-the descendant of these or allied turtles, as many authors believe, it
-of course represents the very highest aquatic specialization of all
-Chelonians. If, on the other hand, as some believe, the leather-back
-is the end of a long and independent line of descent, then _Archelon_
-represents the highest aquatic specialization of all other turtles.
-
-In size, at least, _Archelon_ attained the maximum of the order,
-reaching a length of more than twelve feet, and a weight of more than
-three tons. Except that the shell was not heart-shaped or elongated as
-in all modern sea-turtles, but nearly circular in outline, it had all
-the aquatic adaptations of the sea-turtle in a yet higher degree.
-
-[Illustration: FIG. 124.—_Archelon_ from below, without plastron: _h_,
-humerus; _r_, radius; _u_, ulna; _sc_, scapula; _c_, coracoid; _p_,
-pubis; _i_, ischium. (From Wieland.)]
-
-[Illustration: FIG. 125.—_Archelon_; skeleton from below: _hp_,
-hyoplastron; _hpp_, hypoplastron. (From Wieland.)]
-
-The shell was depressed; the dermal plates covering the ribs had almost
-entirely disappeared, remnants only of their upper ends remaining; the
-skull (Fig. 127) had the temporal region wholly roofed over; the neck
-was short and not retractile. The front legs were strong flippers,
-the humerus was long and stout, with the crest for the attachment
-of muscles far down on the shaft; the digits were greatly elongated
-and clawless, etc. The plastron only was less reduced than in the
-case of the modern sea-turtles. No traces of horny shields have been
-discovered. As to the nature of the covering and the general appearance
-of the turtle when alive, Dr. Wieland has kindly given the writer his
-views, as follows:
-
-“After direct study or fairly close examination of all the fossil
-material of importance thus far collected representing the
-Protostegidae, it seems certain that in all the members of the group
-an external leathery layer was well developed. In no instance is there
-the slightest trace of horny shield sulci, or grooves; though it seems
-probable that there was some gradation toward a thin and perhaps even
-slightly horny hide. In _Archelon ischyros_ the reduced condition
-of the carapace and the presence of the continuous row of large,
-median, supraneural elements render it quite certain that there was a
-development of leathery hide comparable to that of _Dermochelys_. The
-same may be said of _Protostega gigas_. But _Archelon Marshii_ had a
-less reduced carapace, and the leathery skin was probably less well
-developed; and _Protostega Copei_, in which no trace of supraneurals
-remains, must have made some approach to the horn-shield condition.
-A more distinct suggestion of transition from the leathery to the
-horny shield covering may be seen in the very different contemporary
-Cretaceous form, _Toxochelys Bauri_, where ossified epi-or supraneurals
-occupy quite exactly the nodal relation of the five vertebral horn
-shields of later turtles, like _Lytoloma_, though there are not the
-slightest traces of sulci.
-
-[Illustration: FIG. 126.—_Archelon ischyros_, a gigantic sea-turtle
-from the Upper Cretaceous of South Dakota.]
-
-[Illustration: FIG. 127.—Skull of _Archelon ischyros_: _pa_, parietal;
-_f_, frontal; _pm_, premaxilla; _pf_, prefrontal; _ptf_, postfrontal;
-_m_, maxilla; _j_, jugal; _qj_, quadratojugal; _sur_, surangular; _d_,
-dentary; _an_, angular. (After Wieland.)]
-
-“From a purely anatomical standpoint I have suggested that _Archelon_
-had seven dorsal keels corresponding to those of _Dermochelys_. There
-is much excellent reason for regarding dermogene ossification as
-essentially double-layered throughout the Reptilia.
-
-“In any restoration of _Archelon ischyros_ only the mid-line should
-be accentuated as a series of rather sharp supraneural crests. These
-are shown to have been present by the characteristic groove-like
-median pits with radiating striae, which are such a prominent feature
-of epineurals. It is reasonable to believe that the pits mark the
-attachment of horny crests developed in the leathery hide. Such
-were doubtless projected, more or less keel-like, to a height of
-one or two inches, and thus gave to the mid-line of the carapace,
-when seen laterally, a distinctly sinuous outline not unlike that of
-_Toxochelys_.”
-
-As regards the habits of these ancient sea-turtles, we may offer
-tolerably certain conjectures. In the opinion of the writer, the
-less reduced plastron indicates a bottom-feeding habit, a view that
-is strengthened by the more rounded form of the shell, like that of
-the river turtle. All in all it would seem that _Protostega_ and
-_Archelon_ lived habitually on the soft bottoms of the shallower
-seas, feeding upon the hordes of large shell-fish, for which their
-powerful parrot-like beak was admirably adapted. That the species of
-_Protostega_ did not commonly frequent the deeper oceans is indicated
-by the general absence of their remains in the deeper water deposits.
-The writer, in a long collecting experience, always found their remains
-associated with those of the smaller _Toxochelys_, toothed birds,
-pterodactyls, and the smaller mosasaurs.
-
-Perhaps no one can speak more authoritatively as to the habits of these
-gigantic sea-turtles of the Cretaceous than Dr. Wieland:
-
-“With regard to the general habits and appearance of _Archelon_ much
-might doubtless be said if the present-day sea-turtles were more
-familiar objects. Dr. Hay thought that _Archelon ischyros_ was a clumsy
-or even a sluggish, mainly littoral animal, moving slowly about the
-bottom of quiet inlets in quest of shell-fish; I, on the contrary,
-much struck by the powerful flippers, and especially by the flattening
-of the humerus, with its low radial crest and obviously strong
-musculature, have held that unusual swimming power and adaptation to a
-strictly marine life were indicated. Perhaps, as usual where experts
-differ, it is probable that both views are in part correct, and that
-_Archelon_ was only a moderately good swimmer. It may be noted that,
-notwithstanding the almost circular body, the femoral notch, that for
-the hind leg, lies far back, so that it is not necessary, on the score
-of bulk, to assume slowness of motion, or the inability to pursue a
-sea-going life. Furthermore, it is now known that the development of
-the digits fell little short of that seen in _Colpochelys_ (Fig. 117)
-or _Eretmochelys_, truly marine turtles.
-
-“Therefore, while there can be no doubt that _Archelon_ was strictly
-carnivorous in habit, and well able to navigate the open seas, it
-is not likely that it fed on other than relatively slow-moving prey.
-Lydekker looked upon the broad mandibles and broad palate of _Lytoloma_
-as specializations for a mussel diet; and very similarly in _Archelon_,
-while the decurved beak would easily transform him into a most
-formidable enemy, the heavy premaxillaries and vomer, and the flat but
-deep lower jaw, suggest an adept crusher of crustaceans. The presence
-of vast quantities of _Nautilus dekayi_, which I found accompanying one
-of the specimens, was doubtless accidental, but it plainly suggests
-that this cephalopod was one of the teeming sources of food in the
-_Archelon_ environment.
-
-“The huge bulk of the mature _Archelon_ might account for the shearing
-off and loss of the flippers of younger forms caught between the shells
-of the ‘elder boatmen of the Cretaceous seas,’ as Cope has called them,
-during any sudden rush while herding on the shores. But probably the
-young turtles did not much frequent the shores at either egg-laying or
-other times. Whence it is much more likely that it was a mosasaur or
-some of the gigantic fishes like _Portheus_ which bit off the right
-hind flipper in the type-specimen of _Archelon ischyros_, well above
-the heel, as I have described it. That this happened rather early in
-life is shown by the arrested growth of the right femur and remaining
-portions of the tibia and fibula, which are all uniformly 10 per cent
-smaller than the corresponding bones of the left flipper.”
-
-While there were many small fishes in the Niobrara seas which the
-Protostegas inhabited, the most striking thing in the fauna is the
-great abundance of molluscal shells, especially _Ostrea congesta_.
-And with them were great hordes of larger pelycypod mollusks, some of
-them of enormous size. Some of the largest reach a diameter of nearly
-four feet, with shells so thin that one can hardly understand how they
-could have supported such large, oyster-like creatures. One can imagine
-that such shell-fish might have afforded an almost inexhaustible
-source of food for the large turtles; and several times the writer has
-found remains of _Protostega_ associated with such shells. From all
-of which evidence it seems very probable indeed that Dr. Wieland is
-right in imputing to these gigantic turtles a shell-feeding habit, a
-habit which required neither speed nor great prowess; and perhaps the
-formidable beak was used more in social quarrels than for food-getting.
-That these marine turtles departed from the usual reptilian habit of
-laying their eggs upon land is improbable. The tortoise shell turtles
-of the Bahamas lay three or four hundred eggs in a hollow scooped out
-in the sand and then leave the young to their own devices; certainly
-many a one is gobbled up by birds of prey or other enemies on their way
-to the water. Perhaps the young _Archelon_ lost its hind leg in some
-such mishap.
-
-
-LEATHER-BACK MARINE TURTLES
-
-The most remarkable member of the Chelonia now living is _Dermochelys
-coriacea_ (Fig. 128), the great leathery or leather-back turtle of
-the warmer parts of the Atlantic, Indian, and Pacific oceans, the
-sole member of the family Dermochelydidae. It is the largest of
-all living turtles and the most thoroughly aquatic of all, whether
-living or extinct. It sometimes reaches a length of six feet, or
-half that of the largest known extinct forms, and weighs a thousand
-or more pounds. Agassiz saw a specimen that he said weighed a ton.
-Unlike other turtles, it has a carapace quite peculiar to itself,
-composed of a layer of thin, irregularly polygonal bones forming a
-mosaic, completely hidden in the thick skin, and entirely free from
-the skeletal bones beneath them. The larger of these skin bones form
-seven rows above, which appear in the living animal as sharp keels
-running the whole length of the shell. On the under side there are five
-rows of smaller-sized bones, under which there are vestiges of bones
-representing the normal plastron of turtles. The limbs are powerful,
-flattened paddles, not unlike those of _Eretmochelys_, but wholly
-destitute of claws. The front paddles are much larger than the hind
-ones; the humerus is long and flattened, and the digits are elongated.
-The leather-back is a powerful and effective swimmer, going long
-distances. Its habits are not well known; its food is chiefly fish,
-crustaceans, and mollusks.
-
-[Illustration: FIG. 128.—_Dermochelys coriacea._ (From Brehm.)]
-
-So very different is the structure of its shell that some excellent
-naturalists regard _Dermochelys_ as the equivalent in rank of all other
-turtles combined, the sole representative of the suborder Athecae, as
-distinguished from the Thecophora. Dr. Hay, whose authority on fossil
-turtles is of the highest, believes that its line of ancestry has been
-distinct from that of all other turtles from Triassic times at least.
-Others believe that the leather-back is merely a highly specialized
-form derived from the ordinary shelled type, a descendant of some of
-the marine turtles of Cretaceous times. In support of the primitive
-ancestry of the leather-back Dr. Hay offers the following:
-
-“The writer holds the view that the earliest turtles possessed
-practically two kinds of shell, one purely dermal, consisting probably
-of a mosaic of small bones arranged in at least twelve longitudinal
-zones. Each zone probably consisted of a row of larger bones bordered
-on each side by smaller bones. Each of these bones was covered by a
-horny scute. The nearest approach to such a dermal shell is in our days
-seen in _Dermochelys_. Beneath the skin there seems to have existed a
-carapace more or less complete, which consisted of a nuchal, a median
-row of neurals, eight pairs of costals, a pygal, probably one or more
-supraneurals, and about eleven peripherals on each side. To what extent
-the neurals and the costal plates had become anchylosed to the neural
-spines and the ribs respectively, it is now impossible to determine.
-Nor can we say to what extent the various elements of the carapace had
-become connected with one another. There was a subdermal plastron which
-was composed of at least eleven bones.
-
-“According to the author’s view, as time went on the external,
-mosaic-like shell disappeared in most turtles, while a more efficient
-armor was developed out of the subdermal elements. In the ancestors of
-_Dermochelys_, however, the dermal armor was retained, while the more
-deeply seated one disappeared, with the exception of the nuchal bone.”
-
-Such a hypothesis as the foregoing satisfactorily explains the
-extraordinary mosaic shell of the leather-back, and is perhaps an
-acceptable explanation of the rather strange fact that the horny
-shields of turtles do not correspond with the bones below them, as
-might be expected. Unfortunately this hypothesis lacks sufficient
-proof. About the only evidence that is offered in its support is the
-existence of a row of bones along the middle line in the Cretaceous
-_Toxochelys_, and notably in _Archelon_, both aquatic forms. It is
-urged that these bones, the epineurals of Wieland, are really the
-remains of an external layer that persisted in these turtles. However,
-they might have been new ossifications, such as we know did occur in
-not a few of the land tortoises later over the tail and limbs. Aside
-from _Proganochelys_ in the vast interval of time from the Triassic to
-the Eocene no other evidence of such an external dermal layer has been
-discovered. The chief argument against such divergent ancestry of the
-turtles in two chief lines of descent is the fact that in its other
-structure _Dermochelys_ shows great resemblance to other sea-turtles of
-the Cretaceous times—so much resemblance that it seems impossible that
-the ancestors of the leather-back should have paralleled them in almost
-everything except the shell.
-
-On the other hand, those who disagree with this view believe that the
-modern leather-back is the descendant of such Cretaceous marine turtles
-as _Protostega_ or _Archelon_, some of which had lost nearly all of
-the costal plates and had the neurals and marginals reduced. It is
-urged that some of these early marine forms, after they had practically
-lost the ordinary bones of the carapace, for some reason or other found
-a bony shell again necessary for their welfare. Possibly they had
-become littoral in habit; possibly they again became subject to new and
-dangerous enemies in their unprotected condition, notwithstanding their
-great size; perhaps the zeuglodons were among their enemies. Now, as we
-have seen, an animal never takes a back track and recovers a thing it
-has once lost. It was impossible for the ancestors of the leather-back
-again to acquire an orthodox shell, and they forthwith proceeded to
-acquire quite another kind that would serve the same purpose.
-
-Possibly the truth lies between the variant views, in the theory
-recently expressed by Versluys: “The shell of tortoises and turtles is
-formed by a combination of two layers of dermal ossifications, a thecal
-layer and a more superficial epithecal layer, the latter generally
-represented by the marginals only. The leather-back is a member of the
-Cryptodira, and is allied to the other marine turtles. The problem of
-the origin of the aberrant shell of the leather-back seems to find its
-solution in the hypothesis that it is a secondary proliferation of the
-marginals and such other epithecal elements as were present in its
-thecophorous ancestors.”
-
-In other words, Versluys believes that Hay’s and Wieland’s views
-of the primitive double layer of exoskeletal bones is essentially
-correct, but that _Dermochelys_ was derived from later forms in which
-some of them, only, as in _Archelon_, had remained. Baur’s contention
-that “_Dermochelys_ is not the least, but the most specialized marine
-turtle” seems to have been fully justified.
-
-
-RIVER TURTLES. TRIONYCHOIDEA
-
-No reptile is more familiar or more exasperating to the river fisherman
-than the turtle, variously known as the river, soft-shelled, or mud
-turtle. It lives, often in great numbers, in most of the rivers, ponds,
-and bayous of the interior east of the Rocky Mountains, and especially
-in those of sluggish current and muddy bottoms. It is voraciously
-carnivorous in habit, feeding upon the smaller fish, mussels, and such
-other living food as it can capture. With its long, sinuous neck and
-snake-like head, and soft, mottled skin, it is repulsive enough to most
-persons, but is especially annoying to the fisherman, since it devours
-with impunity his bait so long as he feeds it, and can seldom be caught
-on the hook because of its hard and bony mouth, in which only by good
-luck will the hook catch. And the luckless string of fish that the
-fisherman leaves in the water may be almost completely devoured in a
-few hours by these fiercely predaceous feeders. However, if so annoying
-while seeking for better game, it in part makes up for the annoyance it
-causes by furnishing in its own body a not unpalatable food for those
-who like to eat reptiles.
-
-[Illustration: FIG. 129.—_Trionyx_, river turtle. (By permission of the
-New York Zoölogical Society.)]
-
-The river turtles will be readily recognized from the accompanying
-illustration (Fig. 129). They are very flat, covered with a soft,
-smooth skin, with a long, sinuous neck and a small, snake-like and
-vicious-looking head which has a protuberant snout with the external
-nasal orifice at its end. Their feet are webbed and somewhat
-paddle-like, but always with three stout claws—whence comes the name of
-the group—on the anterior digits, which are used for burrowing in the
-mud and excavating holes for their eggs. These turtles burrow more or
-less in the mud, with the long neck free, lying in wait for their prey,
-and coming to the surface from time to time to breathe. As the shape
-of the body and the paddle-like feet would suggest, they are active
-swimmers and purely aquatic in habit, never leaving the water unless
-compelled to. They bury their hard-shelled eggs on the shores only a
-few feet from the water, and leave them to their fate. If the pools
-in which they live dry up, they burrow deeply in the mud and await
-the rains and floods. In captivity they feed upon all kinds of food,
-vegetable as well as animal, and are active and aggressive.
-
-[Illustration: FIG. 130.—_Aspideretes_, a trionychoid turtle from the
-Basal Eocene of New Mexico; skull from above. (From Hay.)]
-
-Because of certain peculiarities, they are usually classed in a
-separate suborder all their own, the Trionychoidea, especially
-distinguished from the Cryptodira, which in general they resemble in
-most respects, aside from the absence of the usual horny dermal plates,
-in the lack of a marginal row of bony plates around the carapace—not a
-very important distinction. Less than thirty living species are known,
-all of them exclusively, or chiefly of fresh-water habit. Six species
-are known from North America; the remainder inhabit Africa, south of
-the Sahara Desert, southern India, and most of the East Indian islands;
-none is known from Australia. No species lives in South America and
-none is known to have lived there in past times. During Eocene,
-Oligocene, and Miocene times these fresh-water turtles lived in the
-region of Europe in great numbers, but for some inexplicable reason
-they became extinct there and never returned. Nearly seventy species of
-the Trionychoidea, belonging in two families, are described by Dr. Hay
-from the Tertiary rocks of North America, more than twice the number
-now living throughout the world. Some of these were of relatively
-large size, measuring fully two feet in the length of the shell. And in
-some places they must have been very abundant. The writer has seen, in
-the Bad Lands of the Continental Divide, their weathered-out remains so
-numerous that they might be raked into windrows miles in length along
-the sloping bluffs, all in small fragments, for their bones, like those
-of most turtles, are only loosely united by sutures and readily drop
-apart before fossilization. Their shells may be readily distinguished
-from those of all other turtles by the granulated, pitted, or
-sculptured exterior surface, that was covered by the skin in life;
-other turtles have the surface smooth below the horny shields, the
-margins of which are marked on the bones by grooves or sulci; the few
-marine turtles of the past that were probably covered with a soft skin
-instead o£ horny shields had the shell smooth and much less completely
-ossified.
-
-[Illustration: FIG. 131.—_Aspideretes_, a trionychoid turtle from the
-Eocene of New Mexico; front leg. (From Hay.)]
-
-As to the origin of the soft-shelled turtles there has been not a
-little difference of opinion. The earliest ones known in geological
-history date back only to about the middle of the Cretaceous; perhaps
-they branched off from the horny-shelled turtles somewhat earlier, but
-probably not much. There are some, however, who think that this group
-of turtles was very primitive, perhaps the most primitive, but the
-writer agrees with Dr. Hay in rejecting this view. Unlike those of all
-other turtles, the fourth digit in front and hind feet has one or two
-more phalanges than have other turtles. We have seen that the oldest
-known reptiles had the digital formula 2, 3, 4, 5, 3 or 4. Most other
-turtles have the same numbers of bones in the digits that mammals have,
-that is, two phalanges in the thumb and big toe and three in each of
-the other digits. The river turtles have a larger number in the fourth
-digit, either four or five. It seems to be a law that evolution is
-irreversible, and if so could the river turtles have been descended
-from forms with a less number of phalanges? But, the skeleton of the
-Trionychoidea resembles the more specialized turtles in so many ways
-that one can hardly believe they were all accidental or parallel.
-
-We may then assume that at about the time that the ordinary marsh
-turtles took to the sea to become marine, others took advantage of
-the fresh-water ponds and rivers, and in doing so, like the marine
-turtles, lost their horny epidermal shields, and became thinner in
-shape, thereby reducing the resistance to the water. Instead, however,
-of reducing the costal plates over the ribs, they retained them intact
-and complete for some reason or other, but lost instead the marginal
-row of bones, unlike the marine turtles which retained them even after
-they had lost nearly all of the costal plates. Possibly also they
-regained additional bones in the fourth digit, a sort of hyperphalangy
-like that of the more strictly aquatic reptiles. Or, possibly, they may
-have descended from some branch of the turtles which had not yet lost
-these bones, retaining them because they were still serviceable for
-swimming. We know nothing yet about the structure of the feet of the
-early turtles, and it is possible that not all had acquired the reduced
-phalangeal formula.
-
-In the development of aquatic habits the river turtles do not show
-the same degree of specialization in the limbs that the strictly
-marine forms do. The humerus (Fig. 131) is a slender bone, with the
-tuberosities for the attachment of the muscles situated near the
-proximal end. The radius and ulna are relatively short, and the foot is
-long. The hind legs, as would be supposed, are less highly specialized
-as swimming paddles, and are relatively smaller. Nevertheless the
-Trionychoidea present an interesting type of adaptation to water
-habits, both in body and in limbs.
-
-
-
-
-INDEX
-
-
-    Adaptation to aquatic life, 59.
-    Aetosauria, 187.
-    Aigialosaurs, 146.
-    Alligator, _197_.
-    Amblyrhynchus, _142_.
-    Andrews, C. W., 75.
-    Angistorhinus, 190.
-    Anomodontia, 102.
-    Aquatic reptiles, adaptation of, 59.
-    Araeoscelis, _133_, 138.
-    Archelon, 234, _236_, _238_, 239.
-    Archosauria, 33.
-    Aspideretes, _246_, _247_.
-
-    Baptanodon, _113_, _114_, _117_.
-    Baur, George, 119, 120, 185, 234.
-    Belodon, 185, 189, _191_.
-    Belodontia, 185.
-    Bêche, De la, 73.
-    Bogalobou, 75.
-    Broom, Robert, 5, 102, 103, 129.
-    Brown, Barnum, 93, 179.
-    Buckland, Dean, 75, 77.
-
-    Cacops, _35_.
-    Camper, Adrian, 149, 166.
-    Camper, Peter, 149, 166.
-    Captorhinus, _49_.
-    Caretta, 230.
-    Carpus, 38.
-    Casea, _55_.
-    Case, E. C., 234.
-    Champsosaurus, _179_, _180_, _181_, _182_.
-    Chelone, _220_, 229.
-    Chevrons, 32.
-    Choristodera, 178.
-    Classification of reptiles, 13.
-    Clavicles, 37.
-    Cleithrum, 36.
-    Clidastes, _147_, _154_, _155_, _157_, 166.
-    Collection of fossils, 10.
-    Colpochelys, _222_.
-    Conybeare, Rev., 73, 110, 149.
-    Cope, E. D., 126, 176, 178, 185, 231, 233.
-    Coracoid, 36.
-    Cotylosauria, 16.
-    Cryptodira, 226.
-    Cretaceous of Kansas, _8_.
-    Crocodiles, ancient, 204;
-      marine, 207;
-      modern, 195.
-    Crocodilia, 15, 194.
-    Crocodilus, _195_.
-    Cuvier, Georges, 73, 97, 107, 110, 149.
-
-    Darwin, Charles, 142.
-    De Fond, St. Faujas, 148.
-    Dermochelys, 241, _242_.
-    Desmatochelys, 231, _232_.
-    Dimetrodon, _36_, _51_.
-    Dinosauria, 18.
-    Dolichosaurs, 145.
-    Dolichobrachium, 54.
-    Dollo, Louis, 167, 179.
-
-    Edaphosaurus, _23_.
-    Elasmosaurus, _79_, _84_, _86_, _87_.
-    Enaliosauria, 75.
-    Eosauravus, 52.
-    Episcoposaurus, 190.
-    Eretmochelys, _230_.
-    Eryops, _31_, _47_.
-    Eusuchia, 195.
-    Exoskeleton, 43.
-    Extinct reptiles of North America, 52.
-
-    Femur, 41.
-    Fibula, 41.
-    Foot, 42.
-    Fraas, Eberhard, 74, 75, 99, 111, 115, 185, 213.
-
-    Gastroliths, _92_, 200.
-    Gavial, Borneo, 201;
-      Gangetic, _198_, _199_, _202_.
-    Gavialidae, 203.
-    Geological Ages, 46.
-    Geosaurus, _208_, _210_, _211_, _212_, 214.
-    Gervais, Professor, 126.
-    Gilmore, Charles, 113, 167.
-    Globidens, _167_.
-    Goldfuss, August, 151.
-    Graptemys, _218_.
-
-    Hadrosaurus, 56.
-    Hand, 38.
-    Hauff, B., 122.
-    Hay, Oliver P., 220, 227, 228, 234, 242.
-    Hofmann, Dr., 148.
-    Holops, 207.
-    Home, Everard, 110.
-    Homo diluvii testis, 108.
-    Huene, Friedrich von, 131, 185.
-    Humerus, 38.
-    Huxley, Thomas, 185, 207.
-    Hydrus, _169_.
-    Hyperphalangy, 118.
-    Hypocentrum, 36.
-
-    Ichthyosauria, 17, 107.
-    Ichthyosaurus, _108_, _112_, 119, 121, _122_.
-    Iguana, _140_.
-    Ilium, 39.
-    Interclavicle, 37.
-    Intercentrum, 30.
-    Ischium, 39.
-
-    Jaeger, George, 184.
-    Jaekel, 185.
-
-    Karoo beds, 102.
-    Koenig, 110.
-
-    Labidosaurus, _22_, _26_, _50_.
-    Laecertilia, 140.
-    Lariosaurus, _99_, _100_.
-    Leather-back turtles, 241.
-    Leidy, Joseph, 151.
-    Limnoscelis, _20_, _47_.
-    Lizards, 140;
-      flat-headed, 144;
-      Galapagos, 142.
-    Lull, Richard, 54.
-    Lystrosaurus, 103, _104_.
-    Lortet, M., 135.
-
-    McGregor, J. H., 126, 129, 131, 185, 186, 189.
-    Mandible, 25.
-    Mantell, Dr., 75.
-    Marsh, O. C., 54, 185.
-    Merriam, J. C., 112, 120, 171, 174.
-    Merriamia, _118_.
-    Mesosaurus, 126, _127_, _128_.
-    Mesosuchia, 185, 204.
-    Meyer, Hermann von, 75, 87, 132, 134, 184.
-    Mixosaurus, 119.
-    Monitor lizards, 144.
-    Mosasauria, 148, 166.
-    Mosasaurus, 148;
-      hofmanni, 149;
-      maximiliani, 151.
-    Münster, Georg von, 97.
-    Mudge, B. F., 93.
-    Mystriosuchus, 185, _188_, _189_, _191_.
-
-    Nares, 23.
-    Nectosaurus, 175.
-    Nothosauria, 95.
-    Nothosaurus, _96_, _97_, _98_.
-
-    O’Fallen, Major, 151.
-    Ophiacodon, _30_, _32_, _37_, _38_, _40_, _42_.
-    Ophidia, 168.
-    Ophthalmosaurus, _118_, 125.
-    Orders of reptiles, 16.
-    Osborn, H. F., 126.
-    Ostodolepis, _33_.
-    Owen, Richard, 75, 103, 110, 111, 185.
-
-    Paleorhinus, 190.
-    Paliguana, 5.
-    Parasuchia, 18, 184.
-    Parietal foramen, 23.
-    Pectoral girdle, 34.
-    Pelvic girdle, 39.
-    Pelvis, 39.
-    Pelycosauria, 186.
-    Pelycosimia, 187.
-    Phytosauria, 18, 187.
-    Phytosaurus, 186, 187.
-    Pineal foramen, 23.
-    Platecarpus, _151_, _155_, _156_, _158_, _159_, 166.
-    Platynota, 148.
-    Plesiosauria, 77.
-    Plesiosaurus, _74_.
-    Pleurodira, 224.
-    Pleurosaurus, _134_, _136_, 177.
-    Polycotylus, 80.
-    Proatlas, 32.
-    Proganochelys, 217.
-    Proganosauria, 17.
-    Proteosaurus, 110.
-    Protorosauria, 17, 132.
-    Protorosaurus, 132.
-    Protostega, 233, 234.
-    Protostegidae, 231.
-    Pseudosuchia, 185.
-    Pterosauria, 18.
-    Pubis, 39.
-    Pythonomorpha (Mosasauria), 166.
-
-    Range of Reptilia, _45_.
-    Rhachitomous vertebrae, 17.
-    Rhynchocephalia, 17, 176.
-    Rhytidodon, 190.
-    Ribs, 33.
-    River turtles, 244.
-    Rutiodon, _190_.
-
-    Sacrum, 32.
-    Sapheosaurus, _178_.
-    Sauranodon (Baptanodon), 125.
-    Sauropterygia, 17, 73.
-    Scheuchzer, 107.
-    Seeley, H. G., 75, 126, 132.
-    Seymouria, _21_, _48_.
-    Shoulder-girdle, 34.
-    Simoedosaurus, 179.
-    Skeleton of reptiles, 19.
-    Skull of reptiles, 21.
-    Snakes, 168.
-    Spener, 132.
-    Sphenodon, _24_, 132, _176_.
-    Squamata, 17, 138.
-    Stegocephalia, 48.
-    Stereosternum, 126.
-    Sternum, 37.
-    Stomach-stones, 200.
-
-    Tarsus, 42.
-    Teeth, 21, 25.
-    Teleosaurus, _205_.
-    Temporal openings, 23.
-    Testudo, _228_.
-    Thalattosauria, 17, 171.
-    Thalattosaurus, _172_, _173_, _174_.
-    Thalattosuchia, 207.
-    Therapsida, 16.
-    Theromorpha, 16.
-    Thaumatosaurus, _74_.
-    Thoracosaurus, 207.
-    Tibia, 41.
-    Tomistomidae, 201.
-    Tortoises, 216;
-      fresh-water, 226;
-      land, 227;
-      marsh, 226.
-    Toxochelys, _219_, _231_, _232_.
-    Trachemys, _221_.
-    Trimerorhachis, _25_.
-    Trinacromerum, _77_, _81_, _83_, _85_, _88_, _89_.
-    Trionychoidea, 244.
-    Trionyx, _245_.
-    Tuatera, 176. _See_ Sphenodon.
-    Turtles, 216;
-      river, 244;
-      sea, 229;
-      ancient sea, 231;
-      side-necked, 224.
-    Tylosaurus, _153_, _155_, _157_, _160_, _165_, 166.
-
-    Varanus, _144_.
-    Varanops, _53_.
-    Ventral ribs, 34.
-    Vertebrae, 28;
-      notochordal, 29;
-      rhachitomous, 31.
-    Versluys, 244.
-
-    Watson, D. M. S., 103.
-    Wieland, G. R., 234, 236, 239, 243.
-    Woodward, A. S., 126.
-
-    Zittel, Carl von, 185.
-
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-<p style='text-align:center; font-size:1.2em; font-weight:bold'>The Project Gutenberg eBook of Water Reptiles of the Past and Present, by Samuel Wendell Williston</p>
-<div style='display:block; margin:1em 0'>
-This eBook is for the use of anyone anywhere in the United States and
-most other parts of the world at no cost and with almost no restrictions
-whatsoever. You may copy it, give it away or re-use it under the terms
-of the Project Gutenberg License included with this eBook or online
-at <a href="https://www.gutenberg.org">www.gutenberg.org</a>. If you
-are not located in the United States, you will have to check the laws of the
-country where you are located before using this eBook.
-</div>
-
-<p style='display:block; margin-top:1em; margin-bottom:1em; margin-left:2em; text-indent:-2em'>Title: Water Reptiles of the Past and Present</p>
-<p style='display:block; margin-top:1em; margin-bottom:0; margin-left:2em; text-indent:-2em'>Author: Samuel Wendell Williston</p>
-<p style='display:block; text-indent:0; margin:1em 0'>Release Date: February 3, 2022 [eBook #67314]</p>
-<p style='display:block; text-indent:0; margin:1em 0'>Language: English</p>
-  <p style='display:block; margin-top:1em; margin-bottom:0; margin-left:2em; text-indent:-2em; text-align:left'>Produced by: Peter Becker and the Online Distributed Proofreading Team at https://www.pgdp.net (This file was produced from images generously made available by The Internet Archive)</p>
-<div style='margin-top:2em; margin-bottom:4em'>*** START OF THE PROJECT GUTENBERG EBOOK WATER REPTILES OF THE PAST AND PRESENT ***</div>
-
-<hr class="chap x-ebookmaker-drop" />
-
-<p class="f120">THE UNIVERSITY OF CHICAGO PRESS<br />CHICAGO, ILLINOIS</p>
-<p class="f150 space-above2"><i>Agents</i></p>
-<p class="center">THE CAMBRIDGE UNIVERSITY PRESS<br />LONDON AND EDINBURGH</p>
-<p class="center">THE MARUZEN-KABUSHIKI-KAISHA<br />TOKYO, OSAKA, KYOTO</p>
-<p class="center">KARL W. HIERSEMANN<br />LEIPZIG</p>
-<p class="center">THE BAKER &amp; TAYLOR COMPANY<br />NEW YORK</p>
-
-<hr class="chap x-ebookmaker-drop" />
-
-<h1>WATER REPTILES OF THE<br />PAST AND PRESENT</h1>
-
-<p class="center space-above3">BY</p>
-<p class="f120"><span class="smcap">Samuel Wendell Williston</span></p>
-<p class="center space-below2"><i>Professor of Paleontology in the<br />
-University of Chicago</i></p>
-
-<div class="figcenter">
-  <img  src="images/a003.jpg" alt="" width="150" height="140" />
-</div>
-
-<p class="center space-above3">THE UNIVERSITY OF CHICAGO PRESS<br />
-CHICAGO, ILLINOIS</p>
-
-<p class="center"><span class="smcap">Copyright 1914 by<br />
-The University of Chicago</span></p>
-
-<p class="center">All Rights Reserved<br />
-Published October 1914</p>
-
-<p class="center">Composed and Printed By<br />
-The University of Chicago Press<br />Chicago, Illinois, U.S.A.</p>
-
-<hr class="chap x-ebookmaker-drop" />
-
-<div class="chapter">
-<p><span class="pagenum" id="Page_v">[Pg v]</span></p>
-<h2 class="nobreak">PREFACE</h2>
-</div>
-
-<p>It was just forty years ago that the writer of these lines, then an
-assistant of his beloved teacher, the late Professor B. F. Mudge,
-dug from the chalk rocks of the Great Plains his first specimens of
-water reptiles, mosasaurs and plesiosaurs. To the youthful collector,
-whose first glimpse of ancient vertebrate life had been the result of
-accident, these specimens opened up a new world and diverted the course
-of his life. They were rudely collected, after the way of those times,
-for modern methods were impracticable with the rifle in one hand and
-the pick in the other. Nor was much known in those days of these or
-other ancient creatures, for the science of vertebrate paleontology was
-yet very young. There were few students of fossil vertebrates—Leidy,
-Cope, and Marsh were the only ones in the United States—and but few
-collectors, of whom the writer alone survives.</p>
-
-<p>Those broken and incomplete specimens, now preserved in the museum of
-Yale University, will best explain why this little book was written.
-The author offers it, so far as lies within him, as an authoritative
-and accurate account of some of the creatures of earlier ages which
-sought new opportunities by going down from the land into the water.
-So far as possible he has endeavored to make the text understandable,
-and, he hopes, of interest also, to the non-scientific reader. He will
-not apologize for such scientific terms as remain, since only by their
-use can precision be attained: there are no common English equivalents
-for them. The reader will find their explanations in the chapter on the
-skeleton of reptiles, and especially in the illustrations.</p>
-
-<p>The author has had the opportunity during recent years of critically
-studying nearly all the reptiles described in the following pages,
-but, if that were the only source of his information, the accounts of
-many would have been meager. He has endeavored, briefly at least, to
-mention the names of all those to whom we are chiefly indebted for our
-knowledge, but in such a work as this it is manifestly impracticable to
-give due credit to every one.
-<span class="pagenum" id="Page_vi">[Pg vi]</span></p>
-
-<p>To the friends who have been of assistance in various ways he tenders
-his sincere thanks: to Professor E. Fraas for photographs and the kind
-permission to reproduce some of his excellent illustrations; to Dr.
-Dreverman, of the Senckenberg Museum, for several excellent photographs
-for reproduction or restoration; to Dr. Hauff, of Holzmaden, for an
-excellent photograph of an ichthyosaur; to Dr. H. F. Osborn, of the
-American Museum, for permission to reproduce the spirited restoration
-of ichthyosaurs drawn by Mr. Knight; to Professors Schuchert and Lull,
-and Dr. Wieland, of Yale University; to Dr. Hay and Mr. Gilmore, of the
-National Museum, to Mr. Barnum Brown and Dr. McGregor, of the American
-Museum, and to Professor Merriam, of the University of California, for
-photographs and other favors.</p>
-
-<p class="author"><span class="smcap">Samuel W. Williston</span></p>
-<p><span class="smcap">University of Chicago</span><br />
-<span class="ws3">July, 1914</span></p>
-
-<hr class="chap x-ebookmaker-drop" />
-
-<div class="chapter">
-<p><span class="pagenum" id="Page_vii">[Pg vii]</span></p>
-<h2 class="nobreak">CONTENTS</h2>
-</div>
-
-<table border="0" cellspacing="0" summary="TOC" cellpadding="2" >
-  <tbody><tr>
-      <td class="tdr"><span class="smcap">chapter</span></td>
-      <td class="tdr" colspan="3"><span class="smcap">page</span></td>
-   </tr><tr>
-      <td class="tdr">I.</td>
-      <td class="tdl_ws1 fontsize_120" colspan="2"><span class="smcap">Introduction</span></td>
-      <td class="tdr"><a href="#Page_1">&nbsp;1</a></td>
-   </tr><tr>
-      <td class="tdr">II.</td>
-      <td class="tdl_ws1 fontsize_120" colspan="2"><span class="smcap">Classification of Reptiles</span></td>
-      <td class="tdr"><a href="#Page_13">13</a></td>
-   </tr><tr>
-      <td class="tdr">III.</td>
-      <td class="tdl_ws1 fontsize_120" colspan="2"><span class="smcap">The Skeleton of Reptiles</span></td>
-      <td class="tdr"><a href="#Page_19">19</a></td>
-   </tr><tr>
-      <td class="tdr">IV.</td>
-      <td class="tdl_ws1 fontsize_120" colspan="2"><span class="smcap">The Age of Reptiles</span></td>
-      <td class="tdr"><a href="#Page_44">44</a></td>
-   </tr><tr>
-      <td class="tdr">V.</td>
-      <td class="tdl_ws1 fontsize_120" colspan="2"><span class="smcap">Adaptation of Land Reptiles
-                           to Life in the Water</span><span class="ws3">&nbsp;</span></td>
-      <td class="tdr"><a href="#Page_59">59</a></td>
-   </tr><tr>
-      <td class="tdr">VI.</td>
-      <td class="tdl_ws1 fontsize_120" colspan="2"><span class="smcap">Order Sauropterygia</span></td>
-      <td class="tdr"><a href="#Page_73">73</a></td>
-   </tr><tr>
-      <td class="tdr">&nbsp;</td>
-      <td class="tdr">&nbsp;</td>
-      <td class="tdl_ws1">Plesiosauria.</td>
-      <td class="tdr">&nbsp;</td>
-   </tr><tr>
-      <td class="tdr">&nbsp;</td>
-      <td class="tdr">&nbsp;</td>
-      <td class="tdl_ws1">Nothosauria.</td>
-      <td class="tdr">&nbsp;</td>
-   </tr><tr>
-      <td class="tdr">VII.</td>
-      <td class="tdl_ws1 fontsize_120" colspan="2"><span class="smcap">Order Anomodontia</span></td>
-      <td class="tdr"><a href="#Page_102">102</a></td>
-   </tr><tr>
-      <td class="tdr">&nbsp;</td>
-      <td class="tdr">&nbsp;</td>
-      <td class="tdl_ws1">Lystrosaurus.</td>
-      <td class="tdr">&nbsp;</td>
-   </tr><tr>
-      <td class="tdr">VIII.</td>
-      <td class="tdl_ws1 fontsize_120" colspan="2"><span class="smcap">Order Ichthyosauria</span></td>
-      <td class="tdr"><a href="#Page_107">107</a></td>
-   </tr><tr>
-      <td class="tdr">IX.</td>
-      <td class="tdl_ws1 fontsize_120" colspan="2"><span class="smcap">Order Proganosauria</span></td>
-      <td class="tdr"><a href="#Page_126">126</a></td>
-   </tr><tr>
-      <td class="tdr">&nbsp;</td>
-      <td class="tdr">&nbsp;</td>
-      <td class="tdl_ws1">Mesosaurus.</td>
-      <td class="tdr">&nbsp;</td>
-   </tr><tr>
-      <td class="tdr">X.</td>
-      <td class="tdl_ws1 fontsize_120" colspan="2"><span class="smcap">Order Protorosauria</span></td>
-      <td class="tdr"><a href="#Page_132">132</a></td>
-   </tr><tr>
-      <td class="tdr">&nbsp;</td>
-      <td class="tdr">&nbsp;</td>
-      <td class="tdl_ws1">Protorosaurus.</td>
-      <td class="tdr">&nbsp;</td>
-   </tr><tr>
-      <td class="tdr">&nbsp;</td>
-      <td class="tdr">&nbsp;</td>
-      <td class="tdl_ws1">Pleurosaurus.</td>
-      <td class="tdr">&nbsp;</td>
-   </tr><tr>
-      <td class="tdr">XI.</td>
-      <td class="tdl_ws1 fontsize_120" colspan="2"><span class="smcap">Order Squamata</span></td>
-      <td class="tdr"><a href="#Page_138">138</a></td>
-   </tr><tr>
-      <td class="tdr">&nbsp;</td>
-      <td class="tdr">&nbsp;</td>
-      <td class="tdl_ws1">Lizards.</td>
-      <td class="tdr">&nbsp;</td>
-   </tr><tr>
-      <td class="tdr">&nbsp;</td>
-      <td class="tdr">&nbsp;</td>
-      <td class="tdl_ws1">Mosasaurs.</td>
-      <td class="tdr">&nbsp;</td>
-   </tr><tr>
-      <td class="tdr">&nbsp;</td>
-      <td class="tdr">&nbsp;</td>
-      <td class="tdl_ws1">Snakes.</td>
-      <td class="tdr">&nbsp;</td>
-   </tr><tr>
-      <td class="tdr">XII.</td>
-      <td class="tdl_ws1 fontsize_120" colspan="2"><span class="smcap">Order Thalattosauria</span></td>
-      <td class="tdr"><a href="#Page_171">171</a></td>
-   </tr><tr>
-      <td class="tdr">XIII.</td>
-      <td class="tdl_ws1 fontsize_120" colspan="2"><span class="smcap">Order Rhynchocephalia</span></td>
-      <td class="tdr"><a href="#Page_176">176</a></td>
-   </tr><tr>
-      <td class="tdr">&nbsp;</td>
-      <td class="tdr">&nbsp;</td>
-      <td class="tdl_ws1">Choristodera.</td>
-      <td class="tdr">&nbsp;</td>
-   </tr><tr>
-      <td class="tdr">XIV.</td>
-      <td class="tdl_ws1 fontsize_120" colspan="2"><span class="smcap">Order Parasuchia</span></td>
-      <td class="tdr"><a href="#Page_184">184</a></td>
-   </tr><tr>
-      <td class="tdr">&nbsp;</td>
-      <td class="tdr">&nbsp;</td>
-      <td class="tdl_ws1">Phytosauria.</td>
-      <td class="tdr">&nbsp;</td>
-   </tr><tr>
-      <td class="tdr">XV.</td>
-      <td class="tdl_ws1 fontsize_120" colspan="2"><span class="smcap">Order Crocodilia</span></td>
-      <td class="tdr"><a href="#Page_194">194</a></td>
-   </tr><tr>
-      <td class="tdr">&nbsp;</td>
-      <td class="tdr">&nbsp;</td>
-      <td class="tdl_ws1">Eusuchia.</td>
-      <td class="tdr">&nbsp;</td>
-   </tr><tr>
-      <td class="tdr">&nbsp;</td>
-      <td class="tdr">&nbsp;</td>
-      <td class="tdl_ws1">Mesosuchia.</td>
-      <td class="tdr">&nbsp;</td>
-   </tr><tr>
-      <td class="tdr">&nbsp;</td>
-      <td class="tdr">&nbsp;</td>
-      <td class="tdl_ws1">Thalattosuchia.</td>
-      <td class="tdr">&nbsp;</td>
-   </tr><tr>
-      <td class="tdr">XVI.</td>
-      <td class="tdl_ws1 fontsize_120" colspan="2"><span class="smcap">Order Chelonia</span></td>
-      <td class="tdr"><a href="#Page_216">216</a></td>
-   </tr><tr>
-      <td class="tdr">&nbsp;</td>
-      <td class="tdr">&nbsp;</td>
-      <td class="tdl_ws1">Side-necked Turtles.</td>
-      <td class="tdr">&nbsp;</td>
-   </tr><tr>
-      <td class="tdr">&nbsp;</td>
-      <td class="tdr">&nbsp;</td>
-      <td class="tdl_ws1">Snapping Turtles.</td>
-      <td class="tdr">&nbsp;</td>
-   </tr><tr>
-      <td class="tdr">&nbsp;</td>
-      <td class="tdr">&nbsp;</td>
-      <td class="tdl_ws1">Fresh-water or Marsh Tortoises.</td>
-      <td class="tdr">&nbsp;</td>
-   </tr><tr>
-      <td class="tdr">&nbsp;</td>
-      <td class="tdr">&nbsp;</td>
-      <td class="tdl_ws1">Land Tortoises.</td>
-      <td class="tdr">&nbsp;</td>
-   </tr><tr>
-      <td class="tdr">&nbsp;</td>
-      <td class="tdr">&nbsp;</td>
-      <td class="tdl_ws1">Sea-Turtles.</td>
-      <td class="tdr">&nbsp;</td>
-   </tr><tr>
-      <td class="tdr">&nbsp;</td>
-      <td class="tdr">&nbsp;</td>
-      <td class="tdl_ws1">Ancient Sea-Turtles.</td>
-      <td class="tdr">&nbsp;</td>
-   </tr><tr>
-      <td class="tdr">&nbsp;</td>
-      <td class="tdr">&nbsp;</td>
-      <td class="tdl_ws1">Leather-back Marine Turtles.</td>
-      <td class="tdr">&nbsp;</td>
-   </tr><tr>
-      <td class="tdr">&nbsp;</td>
-      <td class="tdr">&nbsp;</td>
-      <td class="tdl_ws1">River Turtles.</td>
-      <td class="tdr">&nbsp;</td>
-   </tr>
- </tbody>
-</table>
-
-<hr class="chap x-ebookmaker-drop" />
-
-<div class="chapter">
-<span class="pagenum" id="Page_1">[Pg 1]</span>
-<h2 class="nobreak" id="CHAPTER_I">CHAPTER I<br />
-<span class="h_subtitle">&nbsp;<br />INTRODUCTION</span></h2>
-</div>
-
-<p>In most persons the word reptile incites only feelings of disgust and
-abhorrence; to many it means a serpent, a cold, gliding, treacherous,
-and venomous creature shunning sunlight and always ready to poison. Our
-repugnance to serpents is so much a part of our instincts, or at least
-of our early education, that we are prone to impute to all crawling
-creatures those evil propensities which in reality only a very few
-possess. Were there no venomous serpents—and there are but two other
-venomous reptiles known—we should doubtless see much to admire in
-those animals now so commonly despised; because a few dozen kinds, like
-the rattlesnakes, copperheads, and cobras, protect themselves in ways
-not unlike those used by man to protect himself, we unjustly abhor the
-thousands of other kinds, most of which are not only innocent of all
-offense toward man, but are often useful to him.</p>
-
-<p>There are now living upon the earth more than four thousand kinds or
-species of cold-blooded animals which we call reptiles, all of which
-are easily distinguishable into four principal groups: the serpents
-and lizards, the crocodiles, the turtles, and the tuatera. Their
-habits and forms are very diverse, but they all possess in common
-certain structural characters which sharply distinguish them from
-all other living creatures. A reptile may be tersely defined as a
-cold-blooded, backboned animal which breathes air throughout life.
-And yet, it is not quite certain that this definition is strictly
-correct when applied to all the reptiles of the past, since it has
-been believed that certain extinct ones may have been warm-blooded.
-By this definition, short as it is, we at once exclude a large number
-of cold-blooded, air-breathing, backboned animals which were formerly
-included by scientific men among the true reptiles, and even yet are
-popularly often so included—the amphibians or batrachians. These
-animals, now almost wholly represented by the despised toads, frogs,
-<span class="pagenum" id="Page_2">[Pg 2]</span>
-and salamanders, were, very long ago, among the rulers of the land,
-of great size and extraordinary forms. But they have dwindled away,
-both in size and in numbers, till only a comparatively few of their
-descendants are left, none of them more than two or three feet in
-length, and all of them sluggish in disposition and of inoffensive
-habits. While we may speak of the amphibians as air-breathing, they
-are, with few exceptions, water-breathers during the earlier part of
-their existence. Some may pass their whole lives as water-breathers,
-while a few begin to breathe air as soon as hatched from the egg; but
-these are the marked exceptions.</p>
-
-<p>In many respects the internal structure of the amphibians of the
-present time is widely different from that of reptiles, though there
-can be no doubt that the early amphibian ancestors of the modern
-toads, frogs, and salamanders were also the ancestors of all living
-and extinct reptiles, and it is a fact that the living amphibians
-differ more from some of the ancient ones than those early amphibians
-did from their contemporary reptiles. Discoveries in recent years have
-bridged over nearly all the essential differences between the two
-classes so completely that many forms cannot be classified unless one
-has their nearly complete skeletons. We know that some of the oldest
-amphibians, belonging to the great division called Stegocephalia,
-were really water-breathers during a part of their lives, because
-distinct impressions of their branchiae, or water-breathing organs,
-have been discovered in the rocks with their skeletal remains, but we
-are not at all sure that some of the more highly developed kinds were
-not air-breathers from the time they left the egg; indeed, we rather
-suspect that such was the case.</p>
-
-<p>We are also now quite certain that, from some of the early extinct
-reptiles—the immediate forbears probably of the great dinosaurs—the
-class of birds arose, since the structural relationships between
-birds and reptiles are almost as close as those between reptiles and
-amphibians.</p>
-
-<p>Huxley believed that the great class of mammals arose directly from
-the amphibians, and there are some zoölogists even yet who think that
-he was right. But paleontologists are now quite sure that they were
-<span class="pagenum" id="Page_3">[Pg 3]</span>
-evolved from a group of primitive reptiles, known chiefly from Africa,
-called the Theriodontia; quite sure because nearly all the connecting
-links between the two classes have already been discovered—to such
-an extent, indeed, that really nothing distinctive of either class
-is left save the presence or absence of the peculiar bone called the
-quadrate, the bone with which the lower jaw articulates in birds and
-reptiles; and certain elemental parts of the lower jaw itself. And even
-these bones, in certain mammal-like reptiles, had become mere vestiges.
-Even the double condyle of the mammal skull, with which the vertebrae
-articulate, so like those of the amphibian skull that Huxley based his
-belief of the amphibian origin of the mammals chiefly upon it, has now
-been found in certain reptiles. Warm-bloodedness, one of the diagnostic
-characters of birds and mammals, is not really very important, since
-it must have arisen in these two classes independently, and we may
-easily conceive that the earliest mammals were cold-blooded or that the
-immediate ancestors of the mammals were warm-blooded.</p>
-
-<p>It is an interesting fact in the history of the vertebrates, as of
-all other groups of animals and plants, that the chief divisions
-arose early in geological history. Every known order of amphibians
-and reptiles, unless it be that including the blind-worms, was
-differentiated by the close of the Triassic period. The frogs are now
-known from the Jurassic. The mammals and birds also quite surely date
-their birth from the Triassic. And this early differentiation of the
-chief groups is doubtless due to the fact that the potentialities of
-diverse evolution are limited by specialization. It is apparently a law
-that evolution is irreversible, that it never goes from the special to
-the general, that an organism or an organ once extinct or functionally
-lost never reappears. And it is also a law in evolution that the parts
-in an organism tend toward reduction in number, with the fewer parts
-greatly specialized in function, just as the most perfect human machine
-is that which has the fewest parts, and each part most highly adapted
-to the special function it has to subserve. And these laws explain why
-it is that no highly specialized organism can be ancestral to others
-differing widely from it. The more radically distinct an organism
-is from its allies, the earlier it must have branched off from the
-genealogical tree.
-<span class="pagenum" id="Page_4">[Pg 4]</span></p>
-
-<p>The many new discoveries of extinct forms so often intermediate, not
-only between the larger groups, but between many of the lesser ones as
-well, are making the classification of the vertebrates increasingly
-difficult. At one time it was sufficient to define a reptile as a
-cold-blooded animal with a single occipital condyle, that is, with
-a single articular surface between the skull and the first vertebra
-of the neck; a mammal as a warm-blooded animal with two articular
-surfaces; but these definitions are no longer strictly correct.
-Connecting links do not break down classification, as one might think,
-but they do often spoil our fine systems and compel our classifiers to
-take a wider view of nature than their own narrow province affords.</p>
-
-<p>We can never hope that most, or even the greater part, of all the
-animals which have lived in the past will ever become known to us,
-even imperfectly. Doubtless the species of the past geological ages
-outnumbered many times, perhaps hundreds of times, all those now
-living, since many of these latter are merely the remnants of far
-more varied and extensive faunas. At times the conditions for the
-preservation of the remains of animal life have been more favorable
-than at others, and, under such favorable conditions, a fairly good
-glimpse is sometimes given us of the fauna of some isolated epoch
-and locality in the earth’s history. Those animals which lived in
-and about the water have been preserved in greater numbers and more
-perfectly than the strictly land animals, since fossils are due to
-the preserving action of water, with few exceptions. Of those animals
-which lived upon the land or in the air only the rarest of accidents
-carried the skeletons into the lakes, seas, and oceans. And, even when
-they had been covered by sediments at the bottoms of lakes and seas
-and hidden away from adverse agencies, it has often happened that the
-great erosions of later ages have carried away and destroyed the rocks
-in which they were inclosed. The records of long intervals of time
-have thus been lost in all parts of the world. That we are able to
-obtain even an imperfectly continuous history is due to the fact that
-the intervals thus lost are not everywhere contemporaneous, that the
-missing records of one place may be filled out in part elsewhere. But
-<span class="pagenum" id="Page_5">[Pg 5]</span>
-this substitution of records from a distance can never make the history
-complete. If, in human history, we had only the records for one century
-in China, for another in England, and for yet another in South America,
-how imperfect indeed would be our knowledge of human progress. Animals
-and plants are never quite alike in remote regions, and they never have
-been. The living reptiles of North and South America are today almost
-entirely different, and, were their fossil remains to be discovered a
-million years hence, it would be very difficult to decide that they had
-once lived contemporaneously; difficult, though perhaps not impossible,
-since some are so nearly alike that their relationships or possible
-identity would probably be established after long search. This will
-serve to make clear how very difficult it is, for the most part, to
-correlate exactly the geological formations in remote regions of the
-earth, or even sometimes in adjacent regions where the fossils are
-scanty, or the conditions under which the animals had lived were very
-different.</p>
-
-<p>There are long periods of time, millions of years at a stretch perhaps,
-throughout which our knowledge amounts to little or nothing concerning
-many land reptiles which we are sure must have existed abundantly. No
-better example of our oftentimes scanty knowledge can be cited than
-the following. Until within the past fifteen years it was thought that
-true land lizards, of which there are about eighteen hundred species
-now living, dated back in their history no farther than about the
-close of the great Secondary Period, or the Age of Reptiles. But a
-single skull of a true land lizard has been discovered in the Triassic
-deposits of South Africa, a skull of a form so nearly like that of the
-modern iguana of America that its discoverer, Dr. Broom, has called it
-<i>Paliguana</i>. The lizards must have been in existence, probably
-many thousand species of them, during all the great interval of time
-between the Middle Triassic and the close of the Cretaceous, since it
-is a law which can have no exception, that a type of life once extinct
-never reappears. The “ancient iguanas” of the Trias must have been the
-forbears of many, if not all, of the lizards of later times, though
-nothing is known of their descendants through a period of time which
-can be measured only by millions of years.
-<span class="pagenum" id="Page_6">[Pg 6]</span></p>
-
-<p>However, notwithstanding these imperfections of our geological records,
-we know very much more about extinct reptiles than we do about living
-ones, so far at least as those parts capable of preservation in the
-rocks are concerned. Were our knowledge of reptiles confined to the
-forms now living upon the earth it would be relatively very incomplete
-since, aside from the lizards and snakes, they are merely the remnants
-of what was once a mighty class of vertebrates.</p>
-
-<p>Not only do we learn from the remains preserved in the rocks the
-precise shape and structure of the bones of the skeleton and their
-precise articulations, but we are often able to determine not a little
-regarding the forms which the living animals had by the impressions
-made by the dead bodies in the soft sediment which inclosed them
-before decomposition of the softer parts had ensued, sediments which
-afterward solidified into hard rock. But these impressions are, with
-rare exceptions, only those of profiles or of flattened membranes.
-The rounded bodies of life do not retain their shape long enough for
-the sediment to harden; in most cases the flesh has decomposed before
-being entirely covered by sediment. Sometimes the integument and
-scales in a carbonized condition are actually preserved, retaining
-some of the actual structure of the organized material. The carbon
-pigment of the skin has sometimes been preserved in patterns indicating
-the color-markings in some of these ancient reptiles; and even the
-microscopic structure has been detected in carbonized remains of
-organs. Fossil stomach contents, the bony remains of unhatched young,
-as well as the delicate impressions of skin and membrane, all add to
-our knowledge of the structure and habits of the animals which lived so
-long ago. Many other things also may be learned, or at least inferred,
-concerning the living animals and their habits from the positions in
-which the skeletons are found, from the nature of the rocks which
-inclose them, or from the character and abundance of other fossils
-found with them. The frequent discovery of bones which had been injured
-and mended during life, or the living amputation of members, often
-tell of the characteristics of the creatures. So, too, the climatic
-conditions under which the animals lived may often be inferred with
-<span class="pagenum" id="Page_7">[Pg 7]</span>
-tolerable certainty; the presence of “stomach-stones” reveals something
-of the food habits, and even of the structure of the alimentary canal, etc.</p>
-
-<p>All this information is gained slowly, often very slowly, and with
-much labor and pains. Rarely or never is it the case that all the
-information obtainable concerning any one kind of an extinct animal
-is furnished by a single specimen. Skeletons are very seldom, perhaps
-never, found quite complete, with all their parts in their natural
-positions; and the nature of the matrix inclosing them usually prevents
-a study of all parts of any specimen. If a newly discovered fossil
-is widely different from the corresponding parts of any creature
-previously known, whether living or extinct, we cannot infer very much
-from a few bones as to what the remainder of the skeleton is like.
-Such inferences or guesses in the past have often resulted in grievous
-error, and self-respecting paleontologists are now very reluctant to
-speculate much concerning extinct animals from fragments of a skeleton,
-no matter what those fragments or bones may be; future discoveries are
-sure to reveal errors. It is, therefore, only by the accumulation of
-much material, and by the careful study and comparison of all known
-related animals, that reliable conclusions can be reached. Often it
-requires scores of specimens to determine the exact structure of a
-single kind of animal, and, as the collection and preparation of
-fossil skeletons are tedious and expensive, our knowledge sometimes
-increases very slowly. In recent years, however, there have been many
-more students of extinct backboned animals than formerly, and there are
-now many museums and universities which spend annually large sums of
-money in the collection and preparation of such fossils. This greater
-activity of the last twenty years is bringing to light many new and
-strange forms, as well as completing our knowledge of those previously
-imperfectly known.</p>
-
-<p>It is commonly, but erroneously, believed that the bones of extinct
-animals are usually found in excavations made for the purpose. It
-is true that not a few specimens of fossils have been discovered
-in excavations made for other purposes, such as railway cuttings,
-quarries, wells, etc., but if no others were found our knowledge of the
-animals of the past would be very meager indeed. Fossils are, for the
-<span class="pagenum" id="Page_8">[Pg 8]</span>
-most part, found by deliberate search over the denuded rocks in which
-they occur. Methods of search and collection will best be understood by
-the following description of the noted fossil-bearing rocks of western Kansas.</p>
-
-<div id="FIG_1" class="figcenter">
-  <img  src="images/fig1.jpg" alt="" width="600" height="461" />
-  <p class="center"><span class="smcap">Fig. 1.</span>—A characteristic
-     chalk exposure in western Kansas,<br /> a hundred acres or more in extent.</p>
-</div>
-
-<p>About the middle of Cretaceous times, there extended from the Gulf of
-Mexico on the south to or nearly to the Arctic Ocean on the north a
-narrow inland ocean or sea, a few hundred miles in width, covering what
-is now the western part of Kansas and the eastern part of Colorado,
-and separating the North American continent into two distinct bodies
-of land. This ocean, because of its location, bordered on both sides
-by low-lying lands—the Rocky Mountains had not then been pushed
-up—doubtless was comparatively calm and placid, free from violent
-storms and high tides. That the climate, in the region of Kansas at
-least, was warm or even subtropical is fairly certain, since plants
-allied to those now living in warm, temperate, or subtropical regions
-were then living much farther to the north; and since the animals which
-<span class="pagenum" id="Page_9">[Pg 9]</span>
-then lived in this sea were only such as would be expected in waters of
-warm temperature. Its tributary rivers could have been neither large
-nor swift-flowing, since the sediment at its bottom was free, or nearly
-free, from in-brought material. This was at least the case not very
-far from its shores. Its slowly falling sediment was composed, almost
-exclusively, of microscopic shells of animals and plants, foraminifera
-and coccoliths. The deposits thus made are almost identical with those
-now forming in various parts of the world in clear but not deep waters,
-away from the immediate coasts of the continents, almost pure chalk.
-Animals dying in this inland sea fell slowly to the bottom during or
-after decomposition of their softer parts, and the slowly increasing
-sediments covered up and buried the preservable parts. The many
-predaceous fishes and other scavengers with which the waters abounded
-often tore the decomposing bodies apart, separating and displacing the
-bones of the skeleton; and the currents of the shallow waters washed
-others apart. Often the teeth of fishes and other carnivorous animals
-are found imbedded in the bones, and many are the scars and toothmarks
-observed in the fossil bones.</p>
-
-<p>After the ocean had dried up and the bottom had been raised far above
-the present level of the oceans, other deposits made in lakes and by
-the winds covered deeply the consolidating sediments, burying them for
-millions of years with all that they contained. Long-continued erosion
-by winds and rains has again laid bare many parts of the old ocean
-bottom, and has washed them out into ravines and gullies. Many hundreds
-of square miles of this chalk are now laid bare in western Kansas, upon
-which the growth of vegetation has been prevented by the arid climate.
-Here and there may now be discovered protruding from the sloping or
-precipitous surfaces of this exposed chalk bones or parts of bones of
-the old animals buried so long ago in the soft sediment of the ancient
-ocean bottom.</p>
-
-<p>The sharp-eyed searcher after fossils detects these protruding, often
-broken and weather-worn, petrified bones, which themselves betray the
-presence often of other parts of their skeletons still concealed in the
-chalky hillside. Fortunate is he if he has discovered a specimen soon
-<span class="pagenum" id="Page_10">[Pg 10]</span>
-after it appeared at the surface, before the rains have washed away
-and destroyed most of the remains that had been there preserved. Still
-more fortunate is he if all or nearly all of the original skeleton has
-been preserved together in its natural relations. After days, perhaps
-weeks, of labor, the specimen is secured and shipped to the laboratory.
-Those parts which have been washed out of the chalky rock before the
-discovery of the specimen are always more or less injured and for the
-most part lost, their fragments strewn down the hillside, for erosion
-is always slow and many years may have elapsed since first the specimen
-had appeared at the surface. More frequently, perhaps, a few strokes
-of the pick and shovel disclose but one, two, or three bones remaining
-in the rocks. The specimen, if large, or composed of many bones, is
-carefully uncovered sufficiently to show its extent, and then, so far
-as possible, removed in large blocks of the rock. The bones themselves,
-notwithstanding their petrifaction, are usually soft and easily broken,
-and their separate removal from the matrix may require weeks or even
-months of labor, work which cannot be done prudently in the field.</p>
-
-<p>Of many specimens the rock matrix is so hard that the task of removing
-it from the bones is slow and difficult, indeed well-nigh impossible,
-for the bones are usually softer than their surrounding matrix. On the
-other hand, the matrix may be so soft and friable that it cannot be
-quarried out in blocks. In such cases the separate divisions, as large
-as they can be excavated and safely handled, are carefully covered with
-thick bandages of burlap and plaster-of-paris, often strengthened with
-rods of iron or boards. The skeleton of a single animal treated in this
-way may require weeks and even months to collect, prepare, and mount in
-the museum.</p>
-
-<p>From what has been said the reader will understand how it is possible
-to make an approximately accurate picture of extinct animals as they
-appeared in life—approximately accurate, never absolutely so. The
-flesh and other soft parts of an animal are never petrified, though it
-is a common belief that they may be. Petrified men and women are still
-occasionally shown in cheap museums, but they are always frauds. Many
-times has the writer been called upon to express an opinion as to the
-nature of some concretion which the discoverer was sure was a petrified
-<span class="pagenum" id="Page_11">[Pg 11]</span>
-snake, turtle, or even some part of the human body, because of fancied
-resemblances in shape and size. Not too emphatically can it be said
-that anything dug from the earth having the shape of a living animal
-and alleged to be petrified is either an accidental resemblance or
-a deliberate humbug—if we except such extraordinary casts as those
-of Pompeii. The Cardiff Giant and the Muldoon are still fresh in the
-memory of some of us. There have been a few instances where flesh has
-been preserved in the North, frozen for thousands of years, but frozen
-fossils are very different from petrified fossils. Flesh decays before
-it possibly can be petrified, and only rarely is the residue of flesh,
-tendons, and skin, that is, the carbon and mineral matters, preserved.</p>
-
-<div id="FIG_2" class="figcenter">
-  <img  src="images/fig2.jpg" alt="" width="600" height="451" />
-  <p class="center"><span class="smcap">Fig. 2.</span>—Removing
-        a specimen of fish in a block from<br /> the chalk of western Kansas.</p>
-</div>
-
-<p>One may sometimes restore extinct animals as in life, knowing fully the
-shape and structure of the skeleton, and still be far from the real
-truth. All elephants of the present time have a bare or nearly bare
-skin. If all that we knew of the extinct mammoth were derived from the
-<span class="pagenum" id="Page_12">[Pg 12]</span>
-skeleton we should never have suspected that the creature was clothed
-during life with long and abundant hair, such as has been found
-with the frozen bodies in Siberia. Nor should we suspect that the
-dromedary and Bactrian camels of today have large masses of fat on
-their backs, if we knew only their skeletons. It must therefore be
-remembered that all restorations of extinct animals, representing them
-as in life, are merely the sum of our knowledge concerning them, as
-close approximations to the real truth as it is possible to make. Or,
-rather, they should be such approximations; unfortunately many such
-restorations have been made by artists wholly unacquainted with the
-anatomy of the creatures they attempt to represent, often adorned with
-appendages drawn from a too vivid imagination.</p>
-<hr class="chap x-ebookmaker-drop" />
-
-<div class="chapter">
-<p><span class="pagenum" id="Page_13">[Pg 13]</span></p>
-<h2 class="nobreak" id="CHAPTER_II">CHAPTER II<br />
-<span class="h_subtitle">&nbsp;<br />CLASSIFICATION OF REPTILES</span></h2>
-</div>
-
-<p>There is very much doubt, very much uncertainty, among paleontologists
-about the classification of reptiles. No two writers agree on the
-number of orders, or the rank of many forms. Some recognize twenty or
-more orders, others but eight or nine. And this doubt and uncertainty
-are due chiefly to the many discoveries of early forms that have been
-made during the past twenty years. The many strange and unclassifiable
-types which have come to light in North America, South Africa, and
-Europe have thrown doubt on all previous classificatory schemes,
-have weakened our faith in all attempts to trace out the genealogies
-of the reptilian orders; and classification is merely genealogy.
-It is only the paleontologist who is competent to express opinions
-concerning the larger principles of classification of organisms,
-and especially of the classification of reptiles. The neozoölogist,
-ignorant of extinct forms, can only hazard guesses and conjectures
-as to the relationships of the larger groups, for he has only the
-specialized or decadent remnants of past faunas upon which to base
-his opinions. About some things we can be quite confident; about some
-groups opinions have crystallized, and we all agree, except perhaps on
-trifles. The dinosaurs, the pterodactyls, the crocodiles, for instance,
-offer only minor problems to perplex the systematist, but the origin
-and the relations, not only of these, but also of nearly all the
-others, are still involved in obscurity. The question, whence came the
-ichthyosaurs, the plesiosaurs, the turtles, etc., seems almost as far
-from solution as it did fifty years ago. With every problem solved a
-dozen more intrude themselves upon us. Hence, classification simply
-represents the present condition of our knowledge, our present opinions
-as to genealogies. It was the fashion a dozen years ago to draw all
-sorts of genealogical trees on the slightest pretext, to trace in
-beautifully clear lines the precise descent of all kinds of animals;
-<span class="pagenum" id="Page_14">[Pg 14]</span>
-and very few have been worth the paper on which they were printed.
-When facts are numerous enough, conclusions are patent even to the
-novice; when facts are few and obscure, one can guess about as well as
-another. In general, it may be said that the older a group of animals
-is the more abstruse are the problems presented; first, because of the
-lack of abundant material; second, because the forms speak to us in an
-unfamiliar language that we cannot easily interpret. The classification
-of the mammals approaches more nearly the ultimate truth than does that
-of any other group of organisms, because we know more about the extinct
-forms than we do of any other class, and also because we know more
-about the living forms than we do about any other living animals.</p>
-
-<p>Species of reptiles are, for the most part, vague quantities in
-paleontology; they can be determined with assurance only by the
-comparison of abundant material. Adult characters in mammals are
-apparent in the ossification of the skeleton, and size can be used
-within moderate limits in the determination of species; but size in
-reptiles means but little; no one could possibly say that the skeleton
-of an alligator six feet in length is not that of an adult animal if
-he knew nothing else about the Crocodilia. So also the compression and
-malformations of bones from the processes of fossilization obliterate
-specific characters in great part. Nor are specific characters easily
-distinguishable in the skeletons of living reptiles. The genus,
-therefore, among fossil reptiles is practically the unit, and we may
-be sure that for every well-defined genus we discover there existed
-numerous minor variations, which, had we the living animals to study,
-we should call species. We classify the living Crocodilia into two
-families, about four well-defined genera—perhaps even five or six—and
-about twenty-five species. Of the living lizards there are about
-eighteen hundred species, twenty families, and four larger groups or
-suborders. In all probability the lizards have never been more abundant
-and more varied than they are at the present time. Possibly these
-proportions of species, genera, families, and suborders may represent
-approximately the proportions that have existed at some time or other
-in most of the other groups which we call orders—approximately only,
-<span class="pagenum" id="Page_15">[Pg 15]</span>
-for we can never be quite sure that we evaluate the structural
-characters of different groups of organisms quite equally. The absence
-of a molar tooth in a mammal would ordinarily indicate a genus, the
-absence of a tooth in a reptile might not indicate even a variety or
-a race. Whence it follows that classification of organisms is not
-and never will be an exact science. The value of characters used in
-classification is very unequal, as we have seen. No two persons see
-these characters from the same viewpoints, and in consequence no
-two persons whose opinions are worth while ever wholly agree as to
-classification.</p>
-
-<p>The following scheme differs only in minor details from the more
-conservative of the generally accepted views, and those differences
-are, for the most part, the writer’s own opinions, to be taken for
-what they are worth. It may be said decisively that no classification
-of the reptiles into major groups, into super-families or subclasses
-that has so far been proposed is worthy of acceptance; there is no
-such subclass as the Diapsida or Synapsida, for instance. And we have
-very much more to learn about the early reptiles before any general
-classification of the reptiles can be securely founded. It is very
-probable that the primary radiation of the reptiles into the various
-lines of descent, into its main branches, occurred much earlier than
-we have been disposed to believe; that before the close of Paleozoic
-time, perhaps before the close of the Carboniferous, all the great
-groups of reptiles had gone off from the main stem, and that since then
-only smaller and smaller branches have appeared. There have been no new
-orders of reptiles in all probability since Triassic times, and perhaps
-none since Permian.</p>
-
-<p>Taxonomists are often disposed to cut the Gordian knots of
-relationships by raising the ranks of the animals they study to
-independent positions. More than thirty independent orders of reptiles
-have been proposed by different students, and quite as many of mammals
-and of birds; possibly after more forms have been discovered there will
-be as many proposed for the amphibians. Sometimes, indeed, it is better
-to make such independent groups than to unite lesser ones on doubtful
-evidence. But the writer, for one, believes that it is more worthy of
-the thoughtful scientific student to seek for relationships than for
-differences. It is far easier to destroy than to construct, to make new
-<span class="pagenum" id="Page_16">[Pg 16]</span>
-genera, families, and orders than to unite those already proposed. To
-raise every proposed suborder of reptiles to an order, as has been
-proposed by various writers, and the orders to subclasses, only leaves
-classification where it was; nothing has been added to taxonomy save a
-lot of new names to perplex and annoy the student.</p>
-
-<p class="space-below2">In the following scheme of classification three
-groups provisionally called orders are prefixed by an asterisk.</p>
-
-<table  border="0" cellspacing="0" summary="Reptile Orders" cellpadding="2" >
-<caption class="fontsize_150"><b>CLASS&nbsp;REPTILIA</b></caption>
-  <tbody><tr>
-      <td class="tdl_space-above1 fontsize_120">Order</td>
-      <td class="tdl_space-above1 fontsize_120"><b>COTYLOSAURIA</b></td>
-      <td class="tdl" colspan="2">&nbsp;</td>
-   </tr><tr>
-      <td class="tdl">&nbsp;</td>
-      <td class="tdl" colspan="3"><p class="classes">Primitive reptiles with notochordal
-                vertebrae, imperforate temporal region, persistent intercentra; two coracoids;
-                plate-like pelvis, with all or most of the amphibian skull elements; short
-                legs and short neck; phalangeal formula primarily 2, 3, 4, 5, 3(4).</p></td>
-   </tr><tr>
-      <td class="tdl">Suborder</td>
-      <td class="tdl"><b>Diadectosauria</b></td>
-      <td class="tdl" colspan="2">Permocarboniferous, North America.</td>
-   </tr><tr>
-      <td class="tdl">&nbsp;</td>
-      <td class="tdl"><b>Pantylosauria</b></td>
-      <td class="tdl" colspan="2">Permocarboniferous, North America.</td>
-   </tr><tr>
-      <td class="tdl">&nbsp;</td>
-      <td class="tdl"><b>Labidosauria</b></td>
-      <td class="tdl" colspan="2">Lower Permian, North America.</td>
-   </tr><tr>
-      <td class="tdl">&nbsp;</td>
-      <td class="tdl"><b>Pareiasauria</b></td>
-      <td class="tdl" colspan="2">Upper Permian, Europe, Africa.</td>
-   </tr><tr>
-      <td class="tdl bb">&nbsp;</td>
-      <td class="tdl bb"><b>Procolophonia</b></td>
-      <td class="tdl bb" colspan="2">Triassic, Europe, Africa.</td>
-   </tr><tr>
-      <td class="tdl fontsize_120">Order</td>
-      <td class="tdl fontsize_120"><b>CHELONIA</b></td>
-      <td class="tdl" colspan="2">&nbsp;</td>
-   </tr><tr>
-      <td class="tdl">&nbsp;</td>
-      <td class="tdl" colspan="3"><p class="classes">Temporal region imperforate.
-            Head and limbs more or less retractile within a box formed chiefly by
-            the exoskeleton.</p></td>
-   </tr><tr>
-      <td class="tdl">Suborder</td>
-      <td class="tdl"><b>Pleurodira</b></td>
-      <td class="tdl" colspan="2">Triassic to recent.</td>
-   </tr><tr>
-      <td class="tdl">&nbsp;</td>
-      <td class="tdl"><b>Cryptodira</b></td>
-      <td class="tdl" colspan="2">Jurassic to recent.</td>
-   </tr><tr>
-      <td class="tdl bb">&nbsp;</td>
-      <td class="tdl bb"><b>Trionychoidea</b></td>
-      <td class="tdl bb" colspan="2">Cretaceous to recent.</td>
-   </tr><tr>
-      <td class="tdl fontsize_120">Order</td>
-      <td class="tdl fontsize_120"><b>THEROMORPHA</b></td>
-      <td class="tdl" colspan="2">&nbsp;</td>
-   </tr><tr>
-      <td class="tdl">&nbsp;</td>
-      <td class="tdl" colspan="3"><p class="classes">Primitive
-               reptiles with notochordal vertebrae, perforate
-               temporal region, persistent intercentra; two coracoids;
-               plate-like pelvis with median vacuity; no free
-               dermosupraoccipitals in skull; longer legs and neck;
-               phalangeal formula 2, 3, 4, 5, 3(4).</p></td>
-   </tr><tr>
-      <td class="tdl">Suborder</td>
-      <td class="tdl"><b>Pelycosauria</b> (<i>sens. lat.</i>)</td>
-      <td class="tdl" colspan="2">Permocarboniferous, North America,</td>
-   </tr><tr>
-      <td class="tdl">&nbsp;</td>
-      <td class="tdl">&nbsp;</td>
-      <td class="tdr" colspan="2">Europe.&emsp;&nbsp;</td>
-   </tr><tr>
-      <td class="tdl">&nbsp;</td>
-      <td class="tdl"><b>Dromasauria</b></td>
-      <td class="tdl" colspan="2">Upper Permian, Africa.</td>
-   </tr><tr>
-      <td class="tdl bb">&nbsp;</td>
-      <td class="tdl bb"><b>Dinocephalia</b></td>
-      <td class="tdl bb" colspan="2">Middle and Upper Permian, Africa.</td>
-   </tr><tr>
-      <td class="tdl fontsize_120">Order</td>
-      <td class="tdl fontsize_120"><b>THERAPSIDA</b></td>
-      <td class="tdl" colspan="2">&nbsp;</td>
-   </tr><tr>
-      <td class="tdl">&nbsp;</td>
-      <td class="tdl" colspan="3"><p class="classes">Reptiles
-              with a single temporal perforation on each side;
-              vertebrae not notochordal; intercentra not persistent;
-              pelvis with vacuity; skull bones reduced; teeth heterodont;
-              phalangeal formula, 2, 3, 3, 3, 3.</p></td>
-   </tr><tr>
-      <td class="tdl">Suborder</td>
-      <td class="tdl"><b>Anomodontia</b></td>
-      <td class="tdl" colspan="2">Permo-Trias, Africa, North America.</td>
-   </tr><tr>
-      <td class="tdl">&nbsp;</td>
-      <td class="tdl"><b>Therocephalia</b></td>
-      <td class="tdl" colspan="2">Upper Permian, Africa.
-                     <span class="pagenum" id="Page_17">[Pg 17]</span></td>
-   </tr><tr>
-      <td class="tdl bb">&nbsp;</td>
-      <td class="tdl bb"><b>Theriodontia</b></td>
-      <td class="tdl bb" colspan="2">Trias, Africa.</td>
-   </tr><tr>
-      <td class="tdl fontsize_120">Order</td>
-      <td class="tdl fontsize_120"><b>SAUROPTERYGIA</b></td>
-      <td class="tdl" colspan="2">&nbsp;</td>
-   </tr><tr>
-      <td class="tdl">&nbsp;</td>
-      <td class="tdl" colspan="3"><p class="classes">Aquatic
-           reptiles with a single temporal vacuity; no
-           supratemporal bone, or quadratojugal; ribs single-headed,
-           diapophysial; coracoids large, meeting in middle line,
-           single; neck long, tail short.</p></td>
-   </tr><tr>
-      <td class="tdl">Suborder</td>
-      <td class="tdl"><b>Nothosauria</b></td>
-      <td class="tdl" colspan="2">Triassic, Europe.</td>
-   </tr><tr>
-      <td class="tdl">&nbsp;</td>
-      <td class="tdl"><b>Plesiosauria</b></td>
-      <td class="tdl" colspan="2">Triassic to close of Cretaceous,</td>
-   </tr><tr>
-      <td class="tdl bb">&nbsp;</td>
-      <td class="tdl bb">&nbsp;</td>
-      <td class="tdr bb" colspan="2"> cosmopolitan.&emsp;&nbsp;</td>
-   </tr><tr>
-      <td class="tdl fontsize_120">⃰Order</td>
-      <td class="tdl fontsize_120"><b>PROGANOSAURIA</b></td>
-      <td class="tdl" colspan="2">&nbsp;</td>
-   </tr><tr>
-      <td class="tdl bb">&nbsp;</td>
-      <td class="tdl bb" colspan="3"><p class="classes">Primitive
-          aquatic reptiles; single (? upper) temporal
-          perforation; neck elongate; nares posterior; vertebrae
-          notochordal; intercentra persistent; pelvis plate-like;
-          phalangeal formula 2, 3, 4, 5, 4(6). Permocarboniferous,
-          Africa, South America.</p></td>
-   </tr><tr>
-      <td class="tdl fontsize_120">Order</td>
-      <td class="tdl fontsize_120"><b>ICHTHYOSAURIA</b></td>
-      <td class="tdl" colspan="2">&nbsp;</td>
-   </tr><tr>
-      <td class="tdl bb">&nbsp;</td>
-      <td class="tdl bb" colspan="3"><p class="classes">Reptiles
-          with all aquatic adaptations; a single, upper
-          temporal perforation; both supratemporal and squamosal
-          present; a single coracoid. Middle Triassic to Benton
-          Cretaceous, cosmopolitan.</p></td>
-   </tr><tr>
-      <td class="tdl fontsize_120">⃰Order</td>
-      <td class="tdl fontsize_120"><b>PROTOROSAURIA</b></td>
-      <td class="tdl" colspan="2">&nbsp;</td>
-   </tr><tr>
-      <td class="tdl bb">&nbsp;</td>
-      <td class="tdl bb" colspan="3"><p class="classes">A single,
-           upper temporal vacuity, quadrate fixed (neck
-           vertebrae elongate); bones hollow; cervical ribs
-           single-headed, articulating with centrum; pelvis plate-like.
-           Permian, North America, Europe.</p></td>
-   </tr><tr>
-      <td class="tdl fontsize_120">Order</td>
-      <td class="tdl fontsize_120"><b>SQUAMATA</b></td>
-      <td class="tdl" colspan="2">&nbsp;</td>
-   </tr><tr>
-      <td class="tdl">&nbsp;</td>
-      <td class="tdl" colspan="3"><p class="classes">A single,
-           upper temporal vacuity, or, secondarily none;
-           quadrate loosely articulated with cranium; teeth on palate;
-           intercentra more or less persistent; a single coracoid; ribs
-           single-headed, central.</p></td>
-   </tr><tr>
-      <td class="tdl">Suborder</td>
-      <td class="tdl"><b>Lacertilia</b></td>
-      <td class="tdl" colspan="2">Trias to recent.</td>
-   </tr><tr>
-      <td class="tdl">&nbsp;</td>
-      <td class="tdl"><b>Mosasauria</b></td>
-      <td class="tdl" colspan="2">Upper Cretaceous, cosmopolitan.</td>
-   </tr><tr>
-      <td class="tdl bb">&nbsp;</td>
-      <td class="tdl bb"><b>Ophidia</b></td>
-      <td class="tdl bb" colspan="2">Upper Cretaceous to recent.</td>
-   </tr><tr>
-      <td class="tdl fontsize_120">⃰Order</td>
-      <td class="tdl fontsize_120"><b>THALATTOSAURIA</b></td>
-      <td class="tdl" colspan="2">&nbsp;</td>
-   </tr><tr>
-      <td class="tdl bb">&nbsp;</td>
-      <td class="tdl bb" colspan="3"><p class="classes">Aquatic
-           reptiles; two (?) temporal vacuities; ribs
-           single-headed, attached to centrum; single coracoid;
-           no intercentra. Trias, California.</p></td>
-   </tr><tr>
-      <td class="tdl fontsize_120">Order</td>
-      <td class="tdl fontsize_120"><b>RHYNCHOCEPHALIA</b></td>
-      <td class="tdl" colspan="2">&nbsp;</td>
-   </tr><tr>
-      <td class="tdl">&nbsp;</td>
-      <td class="tdl" colspan="3"><p class="classes">Two
-            temporal vacuities on each side; palate with teeth;
-            intercentra persistent; a single coracoid; teeth acrodont;
-            ribs articulating with centrum and arch.</p></td>
-   </tr><tr>
-      <td class="tdl">Suborder</td>
-      <td class="tdl"><b>Rhynchosauria</b></td>
-      <td class="tdl" colspan="2">Triassic, Europe.</td>
-   </tr><tr>
-      <td class="tdl">&nbsp;</td>
-      <td class="tdl"><b>Sphenodontia</b></td>
-      <td class="tdl" colspan="2">Triassic to recent.</td>
-   </tr><tr>
-      <td class="tdl">&nbsp;</td>
-      <td class="tdl"><b>Choristodera</b></td>
-      <td class="tdl" colspan="2">Uppermost Cretaceous, lowermost</td>
-   </tr><tr>
-      <td class="tdl bb">&nbsp;</td>
-      <td class="tdl bb">&nbsp;</td>
-      <td class="tdl bb" colspan="2">&nbsp;&nbsp;Eocene, North America, Europe.
-                  <span class="pagenum" id="Page_18">[Pg 18]</span></td>
-   </tr><tr>
-      <td class="tdl fontsize_120">Order</td>
-      <td class="tdl fontsize_120"><b>PARASUCHIA</b></td>
-      <td class="tdl" colspan="2">&nbsp;</td>
-   </tr><tr>
-      <td class="tdl">&nbsp;</td>
-      <td class="tdl" colspan="3"><p class="classes">Subaquatic
-              reptiles, with two temporal vacuities; an
-              antorbital vacuity; no false palate; pubis entering
-              acetabulum; ribs double-headed, diapophysial.</p></td>
-   </tr><tr>
-      <td class="tdl">Suborder</td>
-      <td class="tdl"><b>Phytosauria</b></td>
-      <td class="tdl" colspan="2">Upper Trias, cosmopolitan.</td>
-   </tr><tr>
-      <td class="tdl">&nbsp;</td>
-      <td class="tdl"><b>Pelycosimia</b></td>
-      <td class="tdl" colspan="2">Trias, Africa.</td>
-   </tr><tr>
-      <td class="tdl bb">&nbsp;</td>
-      <td class="tdl bb"><b>Pseudosuchia</b></td>
-      <td class="tdl bb" colspan="2">Trias, Europe, North America.</td>
-   </tr><tr>
-      <td class="tdl fontsize_120">Order</td>
-      <td class="tdl fontsize_120"><b>CROCODILIA</b></td>
-      <td class="tdl" colspan="2">&nbsp;</td>
-   </tr><tr>
-      <td class="tdl">&nbsp;</td>
-      <td class="tdl" colspan="3"><p class="classes">Two
-            temporal vacuities; teeth thecodont; a false palate;
-            pubis excluded from acetabulum; single coracoid; ribs
-            double-headed, diapophysial; subaquatic or aquatic.</p></td>
-   </tr><tr>
-      <td class="tdl">Suborder</td>
-      <td class="tdl"><b>Eusuchia</b></td>
-      <td class="tdl" colspan="2">Jurassic to recent.</td>
-   </tr><tr>
-      <td class="tdl bb">&nbsp;</td>
-      <td class="tdl bb"><b>Thalattosuchia</b></td>
-      <td class="tdl bb" colspan="2">Upper Jurassic, Europe.</td>
-   </tr><tr>
-      <td class="tdl fontsize_120">Order</td>
-      <td class="tdl fontsize_120"><b>DINOSAURIA</b></td>
-      <td class="tdl" colspan="2">&nbsp;</td>
-   </tr><tr>
-      <td class="tdl">&nbsp;</td>
-      <td class="tdl" colspan="3"><p class="classes">Ambulatory
-              reptiles, with two temporal vacuities; no false palate;
-              pubis entering acetabulum; ribs double-headed, diapophysial.</p></td>
-   </tr><tr>
-      <td class="tdl">Suborder</td>
-      <td class="tdl"><b>Theropoda</b></td>
-      <td class="tdl" colspan="2">Upper Trias to close of Cretaceous, cosmopolitan.</td>
-   </tr><tr>
-      <td class="tdl">&nbsp;</td>
-      <td class="tdl"><b>Orthopoda</b></td>
-      <td class="tdl" colspan="2">Close of Trias to close of Cretaceous, cosmopolitan.</td>
-   </tr><tr>
-      <td class="tdl bb">&nbsp;</td>
-      <td class="tdl bb"><b>Sauropoda</b></td>
-      <td class="tdl bb" colspan="2">Upper Jurassic, Lower Cretaceous, cosmopolitan.</td>
-   </tr><tr>
-      <td class="tdl fontsize_120">Order</td>
-      <td class="tdl fontsize_120"><b>PTEROSAURIA</b></td>
-      <td class="tdl" colspan="2">&nbsp;</td>
-   </tr><tr>
-      <td class="tdl">&nbsp;</td>
-      <td class="tdl" colspan="3"><p class="classes">Volant
-           reptiles; fourth finger greatly elongated to support
-           patagium; neck vertebrae elongated; bones hollow; ribs
-           double-headed, diapophysial; a single coracoid; no clavicles
-           or interclavicle; two temporal vacuities.</p></td>
-   </tr><tr>
-      <td class="tdl">Suborder</td>
-      <td class="tdl"><b>Pterodermata</b></td>
-      <td class="tdl" colspan="2">Jurassic, Europe.</td>
-   </tr><tr>
-      <td class="tdl">&nbsp;</td>
-      <td class="tdl"><b>Pterodactyloidea</b></td>
-      <td class="tdl" colspan="2">Upper Jurassic to Upper Cretaceous,</td>
-   </tr><tr>
-      <td class="tdl">&nbsp;</td>
-      <td class="tdl">&nbsp;</td>
-      <td class="tdl" colspan="2">&nbsp;&emsp;Europe, North America.</td>
-   </tr>
- </tbody>
-</table>
-
-<hr class="chap x-ebookmaker-drop" />
-
-<div class="chapter">
-<p><span class="pagenum" id="Page_19">[Pg 19]</span></p>
-<h2 class="nobreak" id="CHAPTER_III">CHAPTER III<br />
-<span class="h_subtitle">&nbsp;<br />THE SKELETON OF REPTILES</span></h2>
-</div>
-
-<p>The bony framework, or skeleton, that which gives form and stature
-to the body, and which serves for the support of the soft parts and
-the attachment of muscles, is, with rare exceptions, all that is ever
-preserved of fossil animals. Because, therefore, students of extinct
-animals must rely so much, if not exclusively, upon the skeleton
-much attention has been given to the study of comparative osteology,
-the science of bones. Not only are most of the bones of the skeleton
-characteristic of the genus to which they belong, but the more
-general plan of the skeleton, or parts of the skeleton, is likewise
-characteristic of the larger groups. The paleontologist may become so
-expert in deciphering the characters of single bones, or even parts
-of bones—often all that are known of animals new to science—that he
-is able to hazard guesses as to the general structure of the skeleton
-to which they belong. But such guesses usually will approximate the
-real truth only in the degree that the bones upon which they are based
-approximate like bones of other animals that are better known. Not all
-parts of the skeleton are equally characteristic of the type of animal
-which possessed them. A tooth of a mammal may positively determine the
-species to which it belongs, while the toe bone of the same animal
-might not enable one to guess at its family, even. As a rule one can
-seldom be quite sure of the species of a reptile unless the larger part
-of the skeleton, or at least the skull, is available, although almost
-any bone of the skeleton, if one is expert, will permit a decision as
-to the family, if not the genus.</p>
-
-<p class="space-below2">One must often depend upon the positions and
-relations of the bones, as found in the rocky matrix, for the final
-determination of many characters. One can, for instance, never be sure
-of the number of bones in the neck, trunk, tail, or feet of a reptile,
-until specimens have been found with all such bones in position. It is
-<span class="pagenum" id="Page_20">[Pg 20]</span>
-for this reason that much care is exercised in the collection of
-specimens of fossil animals, and especially of fossil reptiles,
-to preserve all parts of the skeleton, so far as possible, in the
-relations they occupied in the rocks until they can be studied in the
-laboratory. Many grievous errors have been made in the past by hasty
-inferences from fragmentary and poorly collected specimens.</p>
-
-<div id="FIG_3" class="figcenter">
-  <img  src="images/fig3.jpg" alt="" width="600" height="105" />
-  <p class="center"><span class="smcap">Fig. 3.</span>—<i>Limnoscelis</i>,
-    a subaquatic cotylosaur, from<br /> the Permocarboniferous of New Mexico.</p>
-</div>
-
-<p>Because of the reliance which must be placed upon the skeleton it
-will be necessary to speak somewhat in detail of its structure in
-the reptiles, and to use not a few terms in its description that are
-unfamiliar to the general reader. So far as possible technical terms
-will be avoided, though some must be used, as there are no equivalents
-in the English language for them. The reader may use this chapter as a
-sort of explanatory index or glossary for the better elucidation of the
-necessary details of the following chapters.</p>
-
-<p>It is needless to say that the skeleton of a reptile is arranged on
-essentially the same plan as that of our own; the bones have the
-same names that they have in our own skeleton, but there are more of
-them, and the individual bones, as a general rule, are less highly
-specialized, that is, are not so well adapted for special functions.
-In a word, the skeleton of a reptile for the most part is generalized,
-though particular parts may be highly specialized for particular uses.
-As a rule, if not as a law, the course of evolution has been to reduce
-<span class="pagenum" id="Page_21">[Pg 21]</span>
-the number of parts and to adapt those which remain more closely to
-their special uses, either by increase in size, or by modifications of
-their shape and structure.</p>
-
-<h3>SKULL AND TEETH</h3>
-
-<p>The skull of reptiles is much more primitive or generalized in
-structure than is that of mammals, to such an extent, indeed, that
-there is yet much doubt as to the precise homologies of some of the
-bones composing it; and, inasmuch as the names were originally given,
-for the most part, to the bones of the human skull, there is still
-some confusion among students as to the proper names in all cases, a
-confusion that doubtless will not be wholly dissipated until we know
-much more about the early or more primitive reptiles than we do at present.</p>
-
-<div class="figcontainer">
-  <div class="figsub">
-   <img id="FIG_4" src="images/fig4.jpg" alt="" width="200" height="243" />
-   <p class="center">Fig. 4</p>
-  </div>
-
-  <div class="figsub">
-   <p class="space-below2">&nbsp;</p>
-   <img  id="FIG_5" src="images/fig5.jpg" alt="" width="300" height="139" />
-   <p class="center space-above2">Fig. 5</p>
-   </div>
-   <p class="blockquot"><span class="smcap">Fig. 4.</span>—<i>Seymouria</i>,
-    a primitive cotylosaurian. Skull, from above: <i>pm</i>, premaxilla;
-   <i>n</i>, nasal; <i>l</i>, lacrimal; <i>p</i>, prefrontal; <i>f</i>,
-   frontal; <i>pf</i>, postfrontal; <i>it</i>, intertemporal; <i>st</i>,
-   supratemporal; <i>sq</i>, squamosal; <i>ds</i>, dermosupraoccipital;
-   <i>t</i>, tabulare; <i>j</i>, jugal; <i>po</i>, postorbital; <i>m</i>,
-   maxilla; <i>s</i>, surangular; <i>ang</i>, angular; <i>pa</i>, parietal.</p>
-
-   <p class="blockquot space-below2"><span class="smcap">Fig. 5.</span>—<i>Seymouria</i>,
-   skull from the side. Explanations as in fig. 4.</p>
-</div>
-
-<p>As in other parts of the skeleton, there has been a reduction in the
-number of parts of the reptile skull from that of the more primitive
-forms, and a better adaptation of those which remain for the special
-uses they subserve. This reduction in number has been caused in part by
-the actual loss of bones, in part by the fusion of contiguous ones. The
-most primitive reptiles had no less than seventy-two separate bones in
-<span class="pagenum" id="Page_22">[Pg 22]</span>
-the skull;<a id="FNanchor_1" href="#Footnote_1" class="fnanchor">[1]</a>
-the human skull has but twenty-eight inclusive of the ear bones. There
-is but little variation, either in the number or in the relations of
-bones, in the mammalian skull. If one knows the human skull thoroughly
-he can easily understand the structure of the skull of any mammal. The
-same cannot be said of the skulls of reptiles; one would be greatly
-puzzled in the comparison of the skulls of turtles and crocodiles, if
-he knew nothing about other forms. And it is safe to formulate another
-general law in evolution here: Characters which have been longest
-inherited are least liable to change. The earliest reptiles had at
-least four pairs of bones which have disappeared in all later reptiles;
-and they had some bones in pairs which have fused in later reptiles,
-either with their mates or with contiguous bones. The crocodile has
-at least two pairs of bones which have disappeared in turtles. On the
-other hand, the turtle has at least one pair of free bones which have
-been fused with adjacent bones in the crocodiles, and one pair that
-is fused which is free in the latter. The lizard has one pair of bones
-that has been wholly wanting in other reptiles for millions of years,
-while on the other hand it has lost some bones that are present in
-all other modern reptiles. The four parts of the occipital bone of
-mammals, basioccipital, exoccipitals, and supraoccipital, are almost
-invariably free and there is a single occipital condyle, except in the
-Theriodontia.</p>
-
-<div id="FIG_6" class="figcenter">
-  <img  src="images/fig6.jpg" alt="" width="300" height="363" />
-  <p class="blockquot space-below2"><span class="smcap">Fig. 6.</span>—<i>Labidosaurus</i>, a cotylosaur.
-     Skull from above: <i>pm</i>, premaxilla; <i>n</i>, nasal; <i>m</i>,
-     maxilla; <i>l</i>, lacrimal; <i>p</i>, prefrontal; <i>fr</i>,
-     frontal; <i>pf</i>, postfrontal; <i>po</i>, postorbital; <i>j</i>,
-     jugal; <i>pa</i>, parietal; <i>sq</i>, squamosal; <i>ds</i>,
-     dermosupraoccipital; <i>pf</i>, parietal foramen.</p>
-</div>
-
-<p>In this reduction or fusion of parts, or in addition thereto, there has
-been a general lightening-up of the whole skull-structure in reptiles
-from the rather massive and protected form of the older to the lighter,
-less protected, and more fragile type of the later ones, since speed,
-<span class="pagenum" id="Page_23">[Pg 23]</span>
-greater agility, better sense organs, and doubtless greater brain power
-have rendered unnecessary or useless the older kinds, just as modern
-methods and modern arms have rendered useless the coat of mail of the
-Middle Ages.</p>
-
-<div id="FIG_7" class="figcenter">
-  <img  src="images/fig7.jpg" alt="" width="600" height="365" />
-  <p class="blockquot space-below2"><span class="smcap">Fig. 7.</span>—<i>Edaphosaurus</i>, a theromorph
-     reptile from the Permian of Texas. Skull with single temporal vacuity.</p>
-</div>
-
-<p>The old reptiles had a continuous covering or roof for the skull,
-pierced only by the openings for the nostrils in front—the nares—the
-orbits for the eyes near the middle, and a smaller median opening
-back of them for the so-called “pineal eye.” The temporal region,
-that is, the region back of the orbits on each side, was completely
-roofed over by bone for the support and protection of the jaw muscles.
-In later reptiles this region has been lightened, either by holes
-that pierce it or by the emargination of its free borders, as in the
-turtles. The openings have occurred in different ways, and with the
-loss of different bones in various lines of descent. In one large
-group of reptiles, comprising the pterodactyls, dinosaurs, phytosaurs,
-crocodiles, and rhynchocephalians, there are two openings on each side,
-called the supratemporal and lateral temporal vacuities. In another
-still larger group there is a single vacuity on each side, all members
-of which it has been thought were markedly related to each other. Some
-of these, the lizards, snakes, and mosasaurs, the ichthyosaurs, and
-<span class="pagenum" id="Page_24">[Pg 24]</span>
-probably the proganosaurs, have the single opening high up on the
-side, corresponding apparently to the supra temporal vacuity of the
-double-arched forms, as those with two openings are called. Many
-others, however, like the whole order Therapsida and the Theromorpha,
-have the single opening lower down and bounded differently; their
-relationships are doubtful, since it is very much of a question how the
-single opening has arisen. There have been many theories to account for
-the origin of the temporal vacuities, but all are yet speculations.
-Notwithstanding these doubts, which more recent discoveries have
-intensified, there can be none that the structure of this region of the
-skull offers important and reliable characters for the classification
-of the reptiles into the larger groups, but, unfortunately, we are
-very uncertain yet as to what this classification should be. We are
-confident that all those reptiles having two temporal vacuities on each
-side are related to each other; we are yet very much in doubt as to the
-classification of all other reptiles, or at least all others having
-only a single temporal vacuity on each side.</p>
-
-<div id="FIG_8" class="figcenter">
-  <img  src="images/fig8.jpg" alt="" width="600" height="326" />
-  <p class="blockquot space-below2"><span class="smcap">Fig. 8.</span>—<i>Sphenodon</i>
-     (tuatera). Skull from side and above: <i>pm</i>, premaxilla;
-     <i>n</i>, nasal; <i>prf</i>, prefrontal; <i>f</i>, frontal;
-     <i>pf</i>, postfrontal; <i>p</i>, parietal; <i>po</i>, postorbital;
-     <i>sq</i>, squamosal; <i>m</i>, maxilla; <i>j</i>, jugal; <i>qj</i>,
-     quadratojugal; <i>q</i>, quadrate; <i>c</i>, coronoid; <i>sa</i>,
-     surangular; <i>art</i>, articular; <i>pa</i>, prearticular; <i>d</i>,
-     dentary; <i>an</i>, angular.</p>
-</div>
-
-<p>Better evidences of relationships, or the absence of relationships, are
-offered by the presence of certain bones in the skulls in some orders
-<span class="pagenum" id="Page_25">[Pg 25]</span>
-that are lost in others, since it may be accepted as an axiom that new
-bones have not appeared in the skulls of reptiles, birds, or mammals;
-and that no bone which has once disappeared has ever been functionally
-regained by the descendants of those that lost it. The presence,
-then, of an extra bone in the temporal region of the lizards or the
-ichthyosaurs is proof that they have had a long and independent descent
-from reptiles which possessed it.</p>
-
-<p>The mandible of the earliest reptiles was composed of not less than
-seven separate and distinct bones, as shown in the <a href="#FIG_9">accompanying
-figures</a>. The mandible of no modern reptile has more than six, and some
-have fewer. The mandible of mammals is composed of a single bone,
-the dentary; those reptiles, the Theriodontia, which doubtless were
-ancestral to the mammals in Triassic times, have all the bones, except
-the dentary, much reduced, or even vestigial. The prearticular bone, as
-shown, so far as known, has been absent in all reptiles since Triassic
-times, except the ichthyosaurs, plesiosaurs, <i>Sphenodon</i>, and
-turtles, all reptiles of ancient origin. The coronoid bone primitively
-extended the whole length of the teeth on the inner side; in all
-reptiles, except the plesiosaurs, since Triassic times it is either
-reduced to a small bone back of the teeth or is absent. So also the
-splenial has been greatly reduced in size in all later reptiles and may
-be wanting as in <i>Sphenodon</i> and modern turtles. The articular of
-reptiles, it is now generally believed, is represented in mammals by
-one of the ear bones, the quadrate by another.</p>
-
-<div id="FIG_9" class="figcenter">
-  <img  src="images/fig9a.jpg" alt="" width="600" height="208" />
-  <img  src="images/fig9b.jpg" alt="" width="600" height="158" />
-  <p class="blockquot space-below2"><span class="smcap">Fig. 9.</span>—Mandible of
-    <i>Trimerorhachis</i>, a stegocephalian amphibian, ancestrally related
-    to the reptiles: <i>A</i> from within; <i>B</i> from without. The
-    coronoid is composed of three bones, the true coronoid (<i>cor</i>),
-    the intercoronoid (<i>icor</i>), and the precoronoid (<i>pc</i>). The
-    splenial is composed of two, the true splenial (<i>sp</i>) and the
-    postsplenial (<i>psp</i>). The prearticular (<i>pa</i>) is broad,
-    the dentary (<i>d</i>) is small; and the angular (<i>an</i>) is only
-    slightly visible on the inner side.</p>
-</div>
-
-<div id="FIG_10" class="figcenter">
-  <img  src="images/fig10a.jpg" alt="" width="600" height="163" />
-  <img  src="images/fig10b.jpg" alt="" width="600" height="146" />
-  <p class="blockquot space-below2"><span class="smcap">Fig. 10.</span>—Mandible
-     of <i>Labidosaurus</i>, a cotylosaur reptile: <i>A</i> from within;
-     <i>B</i> from without. The coronoid (<i>cor</i>) is a single bone,
-     but extends far forward. The splenial (<i>sp</i>) is also a single
-     bone, replacing the two of the amphibians. The <i>prearticular</i>
-     (<i>pa</i>) is narrower, and the angular (<i>ang</i>) appears broadly
-     on the inner side. The dentary (<i>d</i>) is much larger and the
-     surangular (<i>sa</i>) is distinct. The articular (<i>art</i>) is small.</p>
-</div>
-
-<div id="FIG_11" class="figcenter">
-  <img  src="images/fig11.jpg" alt="" width="600" height="123" />
-  <p class="blockquot space-below2"><span class="smcap">Fig. 11.</span>—Mandible
-     of <i>Alligator</i>, a modern, highly specialized reptile, from within.
-     The coronoid (<i>cor</i>) is small and is situated far back; the
-     splenial (<i>sp</i>) does not extend to the symphysis; the prearticular
-     (<i>pa</i>) has disappeared, or has fused with the angular (<i>an</i>)
-     or articular (<i>art</i>). The dentary (<i>d</i>) has become the chief
-     bone of the mandible.</p>
-</div>
-
-<p>The teeth of reptiles are of much less importance, as a rule, in the
-determination of relationships than are the teeth of mammals. Rarely
-are their shapes of specific, and often not of generic, importance,
-though their number and relative sizes may be. The teeth of mammals,
-as a rule, are forty-four or less in number, and they are always
-inserted in distinct sockets in the jaw bones. Among reptiles they
-are indefinite in number, and may be attached to any of the bones
-of the palate and sometimes also to the coronoid of the mandibles.
-<span class="pagenum" id="Page_26">[Pg 26]</span>
-Furthermore, except in those reptiles related to the immediate
-ancestors of the mammals, they are alike or nearly alike in the
-jaws, that is, homodont, not distinguishable into incisors, canines,
-and molars. They may be inserted in separate sockets (thecodont),
-in grooves, or simply be co-ossified to the surface of the bone
-(acrodont). And they are usually reproduced indefinitely by new teeth
-growing at the side of the base or below them. More usually they are
-<span class="pagenum" id="Page_27">[Pg 27]</span>
-pointed and curved; sometimes they are flattened, with sharp cutting
-edges in front and behind in the more strictly carnivorous reptiles;
-in those of herbivorous habits they are more dilated and roughened on
-the crown, not pointed; in not a few they are low, broad, and flat
-and are used only for crushing the hard shells of invertebrates. With
-the very few exceptions among certain dinosaurs, they never have more
-than one root for attachment. The evolutional tendency for reptiles,
-as for the mammals, is to loose teeth, especially those of the palate.
-Among living reptiles it is only the most primitive types, such as
-the lizards, snakes, and the tuatera, which have teeth on the palatal
-bones, and in none are there teeth on the vomers, as was the rule in
-the ancient reptiles. The lizards may have them on pterygoids and
-palatines, and the tuatera has them on the palatines only. There may be
-as many as eighty on each jaw, above and below, and hundreds of smaller
-ones on the palate, or they may be reduced in number to five or six,
-or even to a single one; some reptiles, like the turtles and later
-pterodactyls, have none. The teeth of reptiles are composed of the same
-kinds of tissues as are the teeth of mammals, that is, of dentine and
-enamel, but the enamel is always thin, perhaps because the teeth are so
-<span class="pagenum" id="Page_28">[Pg 28]</span>
-easily replaced that a thicker protective covering is not needed.
-The arrangement of the dentine in primitive reptiles is complicated,
-that is, plicated or folded in labyrinthine figures, like that of
-many stegocephalian amphibians, the Labyrinthodontia, especially.
-This labyrinthine structure of the dentine persisted longest in the
-ichthyosaurs.</p>
-
-<h3>VERTEBRAE AND RIBS</h3>
-
-<p>The spinal column or backbone of reptiles, as in all air-breathing
-vertebrates, is made up of a variable number of separate segments
-called vertebrae, permitting flexibility. Each vertebra is composed of
-a body, or centrum, and an arch on the dorsal side for the protection
-of the spinal cord. Various projections from the vertebra, called
-processes, serve for the attachment of ligaments or muscles, for
-articular union with adjacent vertebrae, or for the support of ribs,
-and these processes have characteristic differences in different
-reptiles. The pair in front and behind, for articulation with the
-adjoining vertebrae, may become obsolete or even lost in swimming
-reptiles, as we shall see; they are called zygapophyses. In not a few
-reptiles there is an additional pair for zygapophysial articulation
-in front and behind, called zygosphene and zygantrum, for the greater
-strengthening of the column; they are especially characteristic of
-snakes and certain lizards. In certain other reptiles, especially the
-long-necked dinosaurs, there is an additional pair arranged differently
-from the zygophene, that have received the names hyposphene and hypantrum.</p>
-
-<div id="FIG_12" class="figcenter">
-  <img  src="images/fig12.jpg" alt="" width="600" height="176" />
-  <p class="blockquot space-below2"><span class="smcap">Fig. 12.</span>—Procoelous
-         vertebra of snake: <i>za</i>, zygantrum; <i>zs</i>,
-         zygosphene; <i>ps</i>, posterior zygapophysis.</p>
-</div>
-
-<p>On the top of the arch is the spine or spinous process, which may vary
-<span class="pagenum" id="Page_29">[Pg 29]</span>
-enormously in size and length; sometimes it is flattened or dilated
-above for the support of an exoskeleton, or it may be heavy and
-massive for the attachment of strong muscles and ligaments. In the
-modern basilisk lizards and in the ancient <i>Dimetrodon</i> and
-<i>Edaphosaurus</i> from the Permian rocks of Texas these spines are
-of enormous length, some of them nearly four feet long in reptiles not
-twice that length. Slender crawling reptiles usually have no spines, or
-only vestigial ones. On the sides of the arch there may be a distinct
-transverse process for the articulation of the rib.</p>
-
-<p>In all early reptiles the ends of the body or centrum are concave,
-as they are in nearly all fishes. Such a conformation, called
-amphicoelous, gives great flexibility to the spinal column, but only
-moderate strength, since the intervening spaces are filled with
-cartilage in life. In all living reptiles, with few exceptions, the
-body is concave, like a saucer, in front and correspondingly convex
-behind, and the intervening cartilage has largely disappeared. Such a
-mode of union, called procoelous, adds greatly to the strength of the
-backbone, enabling it to receive greater shocks or greater pressure
-without dislocation; or to sustain the greater strain of muscles used
-in running swiftly or in climbing. Among living reptiles, only the
-gecko lizards and the tuatera have biconcave vertebrae. Some extinct
-reptiles, such as some of the dinosaurs, animals that walked erect upon
-their legs, had their vertebrae convex in front and concave behind
-(opisthocoelous). Birds, though walking erect, have a very different
-and more complicated articulation of the cervical vertebrae, and
-certain reptiles, like the turtles, have very complicated cervical
-vertebrae.</p>
-
-<p>In the embryos of all vertebrate animals there appears first an
-elongated fibrous rod, called the notochord, in the place of the future
-spinal column. This rod may persist through life, never ossifying, as
-was the case with all the earliest fishes, and is the condition in some
-living ones. As the embryo grows, however, the separate segments, or
-vertebrae, ossify about this rod in all reptiles, forming bony rings,
-perforate at first in the middle for the more or less constricted
-notochord. This stage was the permanent condition in all the earliest
-reptiles and in some later ones. Such animals are said to have
-<span class="pagenum" id="Page_30">[Pg 30]</span>
-notochordal vertebrae, the notochord more or less continuous, like a
-string of beads, the beads representing the enlargements between the
-contiguous vertebrae.</p>
-
-<div id="FIG_13" class="figcenter">
-  <img  src="images/fig13.jpg" alt="" width="600" height="328" />
-  <p class="blockquot space-below2"><span class="smcap">Fig. 13.</span>—Notochordal
-     cervical vertebrae, with intercentra, of <i>Ophiacodon</i>, a primitive
-     theromorph reptile from the Permocarboniferous of New Mexico:
-     <i>pa</i>, proatlas; <i>an</i>, arch of atlas; <i>o</i>, odontoid;
-     <i>ax</i>, axis.</p>
-</div>
-
-<p>In many early amphibians, and probably in all the earliest ones, as
-well as in the fishes from which they were derived, the vertebra is
-more complicated in that it is composed of at least three pairs of
-separate bones, two of which united with each other, the third finally
-disappearing in modern animals, or at the most represented by a mere
-vestige called the intercentrum. The dorsal pair of these bones, called
-the neurocentra, forms the arch of the vertebra. The ventral posterior
-pair, called the pleurocentra, increases in size and unites to form the
-centrum or body of the vertebra; while the ventral anterior pair, early
-united with each other, is called the hypocentrum or intercentrum,
-persistent in all early reptiles as a vestige between the centra on
-the ventral side. This divided condition of the vertebra is persistent
-in the first vertebra, the atlas of all higher animals, in which the
-so-called body is the hypocentrum or intercentrum, the arch is the
-neurocentrum, while the pleurocentra have fused more or less with the
-anterior part of the next vertebra, the axis, to form the so-called
-odontoid. That this is the real explanation of the structure of the
-<span class="pagenum" id="Page_31">[Pg 31]</span>
-atlas is proved by the various stages of its evolution in the
-reptiles, from the earliest (<a href="#FIG_15">Fig. 15</a>) in which it scarcely
-differs from rhachitomous—as this structure is called—vertebrae of an early
-amphibian, to the modern in which the structure is nearly like that of mammals.</p>
-
-<div id="FIG_14" class="figcenter">
-  <img  src="images/fig14.jpg" alt="" width="400" height="392" />
-  <p class="blockquot space-below2"><span class="smcap">Fig. 14.</span>—Rhachitomous
-    dorsal vertebra of <i>Eryops</i>: <i>n</i>, neurocentrum or arch;
-    <i>pl</i>, pleurocentrum; <i>i</i>, intercentrum or hypocentrum;
-    <i>az</i>, anterior zygapophysis; <i>pz</i>, posterior zygapophysis;
-    <i>d</i>, diapophysis, for tubercle of rib; <i>p</i>, parapophysis, for
-    head of rib.</p>
-</div>
-
-<p>In front of the atlas, that is, between it and the skull, there was, in
-all early reptiles, as well as in some later ones, like the crocodiles
-and tuatera, the remnant of what is believed to have been another
-vertebra, of which only the arch remains, and which is called the
-proatlas. In its earliest condition it articulated with the skull in
-front and the arch of the atlas behind.</p>
-
-<p>As in mammals, the vertebrae of the different regions have received
-distinctive names, cervical, dorsal, lumbar, sacral, and caudal. The
-numbers of each region are far more variable than they are among
-mammals, the total number of vertebrae in the column varying from
-about thirty to more than five hundred, in certain snakes. Nor are the
-different regions always easily distinguishable, especially those in
-front of the sacrum. In the earliest reptiles there was practically
-no neck, and only two vertebrae, the atlas and axis, that properly
-can be called cervical. Very soon, however, the reptiles developed a
-longer neck with seven vertebrae, a number that has remained singularly
-constant in higher animals, especially in the mammals. In most modern
-reptiles there are from seven to nine; in a few lizards, five. But the
-number was much more inconstant among the older reptiles; some of the
-plesiosaurs had as many as seventy-six cervical vertebrae; some of the
-older lizards even had as many as eighteen.
-<span class="pagenum" id="Page_32">[Pg 32]</span></p>
-
-<p>Ordinarily the cervical vertebrae differ from those behind them only
-in the small size or fusion of their ribs; sometimes, however, as in
-the Protorosauria and Pterosauria, the vertebrae may be much elongated.
-The dorsal vertebrae of reptiles vary in number from ten in turtles and
-some dinosaurs to forty-three in <i>Pleurosaurus</i>; and under the
-name dorsal we include the so-called lumbar, as there is seldom any
-real distinction between the two series, save the smaller size or the
-co-ossification of the ribs of the latter.</p>
-
-<div class="figcontainer">
-  <div class="figsub">
-   <img id="FIG_15" src="images/fig15.jpg" alt="" width="200" height="236" />
-   <p class="center"><span class="smcap">Fig. 15.</span>—<i>Ophiacodon</i>,<br />
-          a primitive theromorph<br /> reptile: proatlas, atlas,<br />
-          and axis, with ribs.</p>
-  </div>
-  <div class="figsub">
-   <p class="space-below2">&nbsp;</p>
-   <img  id="FIG_16" src="images/fig16.jpg" alt="" width="350" height="189" />
-   <p class="center space-above2"><span class="smcap">Fig. 16.</span>—Sacrum
-                of <i>Chelone</i>.</p>
-   </div>
-</div>
-
-<p>The sacrum in reptiles primitively consisted of a single vertebra,
-which bore a large rib on each side for the support of the pelvis. Very
-early, however, a second or even a third vertebra was added to it from
-behind. The number two is the rule among reptiles, both ancient and
-modern; among crawling reptiles the number never exceeds three, but
-among ambulatory and flying reptiles the number may be as great as in
-any mammal.</p>
-
-<p>The number of caudal vertebrae in reptiles is exceedingly variable,
-from a dozen or fifteen up to a hundred and fifty or more. In snakes
-but two regions are distinguishable, the caudal and precaudal, and the
-number altogether may reach nearly five hundred. With the exception
-of the first few basal caudal vertebrae (pygals) and the minute ones
-at the extreme tip, all caudal vertebrae of reptiles bear a slender,
-usually <b>Y</b>-shaped bone below in the interval between the centra,
-for the protection of the vessels and nerves. Because of their shape
-they have been called chevrons, and are really outgrowths from the intercentra.
-<span class="pagenum" id="Page_33">[Pg 33]</span></p>
-
-<p>The ribs of reptiles are of more importance in classification than
-one would suppose. The primitive rib was a slender, curved bone,
-with the vertebral end dilated to articulate continuously with the
-intercentral space—that between the centra and the anterior part of
-the arch. And this is the condition still remaining in the tuatera.
-Very soon, however, the lower end of the articular surface (capitulum)
-became separated from the upper (tubercle) by a notch, and the ribs
-became distinctly double-headed. And this mode of articulation is
-the rule among mammals. Among later reptiles, however, there were
-many modifications. In nearly all the head migrated a little backward
-on the centrum. By the loss of the tubercle in lizards, the head
-became truly single-headed, and attached solely to the body; and this
-condition is characteristic of the order Squamata. In another large
-group the head of the rib gradually migrated up on the arch and on
-the transverse process (diapophysis), so that both head and tubercle
-are attached to the diapophysis; and this condition is equally
-characteristic of the orders of reptiles known collectively as the
-Archosauria—the crocodiles, pterodactyls, dinosaurs, and phytosaurs.
-In the Sauropterygia, the ribs are single-headed and attached to the
-end of the diapophysis. Finally in most ichthyosaurs the capitulum and
-tubercle both articulate with the body of the vertebra.</p>
-
-<div id="FIG_17" class="figcenter">
-  <img  src="images/fig17.jpg" alt="" width="400" height="278" />
-  <p class="blockquot space-below2"><span class="smcap">Fig. 17.</span>—<i>Ostodolepis</i>, a primitive
-      theromorph reptile. Vertebrae from in front and side, with primitive
-      double-headed rib and intercentrum.</p>
-</div>
-
-<p>Ribs primitively were probably attached to all the vertebrae to the end
-of the tail. In the earliest reptiles that we know they are present on
-all vertebrae as far back as the tenth or twelfth caudal only, those of
-the caudal for the most part co-ossified with the centra. The ribs of
-the neck vertebrae more quickly disappeared, or became fused with the
-vertebrae, and only in the crocodiles among living reptiles are there
-ribs on the atlas. The sacral ribs, on the other hand, became much
-<span class="pagenum" id="Page_34">[Pg 34]</span>
-larger and stouter and developed an articulation at their outer ends
-for the support of the ilium (<a href="#FIG_16">Fig. 16</a>).</p>
-
-<p>The so-called ventral ribs are slender ossifications in the connective
-tissue under the skin, on the under side of the body, and are
-characteristic of most reptiles. The anterior ones doubtless fused
-together more or less to form the sternum or breast bone, which was
-otherwise absent in the early reptiles.</p>
-
-<h3>PECTORAL OR SHOULDER GIRDLE</h3>
-
-<p>Those bones which form the framework for the support of the anterior
-extremity in vertebrate animals are known collectively as the pectoral
-girdle. In our own skeleton there are but two on each side, or four in
-all, the scapula or shoulder-blade, and the clavicle or collar-bone. A
-third bone, however, is represented in all mammals by a mere vestige
-which early unites with the scapula and is called the coracoid
-process. In the lowest forms of mammals, the Monotremata, of which the
-<i>Ornithorhynchus</i> and <i>Echidna</i> are the only examples, not
-only is this coracoid bone largely developed, articulating with the
-sternum or breast bone, but there is an additional coracoid bone in
-front of this; and there is also an interclavicle. Indeed, the pectoral
-girdle in these mammals is more primitive or generalized in structure
-than it is in any living reptiles, composed of scapula, coracoid,
-metacoracoid, and clavicle on each side and an interclavicle in the
-middle. No living reptiles have the metacoracoid, and, as is the case
-with many mammals, some reptiles have no clavicles.</p>
-
-<p>Primitively, that is, in all the old reptiles, the girdle is composed
-of scapula, coracoid, metacoracoid, clavicles, and interclavicle,
-while in some of the very oldest there is yet another bone, more or
-less of a vestige, derived from the ancestral amphibians and called
-the cleithrum or supraclavicle. The scapula is more or less elongated
-in crawling and climbing reptiles; more slender and bird-like in those
-which walked erect after the manner of birds and mammals; shorter and
-more fan-shaped in the swimming reptiles, as we shall see. In some
-pterodactyls, unlike all other known animals, the scapula articulated
-at its upper end with the backbone, giving a much firmer support for
-<span class="pagenum" id="Page_35">[Pg 35]</span>
-the anterior extremities. Only in those reptiles allied to the
-ancestors of the mammals has the scapula ever had a spine or projection
-on its dorsal side.</p>
-
-<div id="FIG_18" class="figcenter">
-  <img  src="images/fig18.jpg" alt="" width="600" height="204" />
-  <p class="blockquot space-below2"><span class="smcap">Fig. 18.</span>—<i>Cacops</i>,
-       a Permian stegocephalian, ancestrally allied to the primitive reptiles,
-       with rhachitomous vertebrae and large cleithrum above the scapula.</p>
-</div>
-
-<p>Of the two coracoid bones in the original pectoral girdle the posterior
-one began to disappear early and is entirely lost in all reptiles that
-lived later than Triassic times, though it still persists in the lowest
-mammals, as we have seen. In most later reptiles the remaining coracoid
-has become less firmly attached to the scapula than it was in the older
-reptiles. It usually has a small foramen piercing it near the middle of
-the upper border or end, the supracoracoid foramen. The clavicle, while
-more constant among reptiles than among mammals, has been lost in some,
-the Crocodilia, for instance, as also the dinosaurs and pterodactyls.
-<span class="pagenum" id="Page_36">[Pg 36]</span>
-The interclavicle is more constant in reptiles, a more or less
-<b>T</b>-shaped bone underlying the coracoids where they join, or the
-breast bone; but there were some reptiles that lost it, the dinosaurs
-and pterodactyls, for instance. In the turtles both the clavicles and
-the interclavicle form a part of the under shell or plastron.</p>
-
-<div id="FIG_19" class="figcenter">
-  <img  src="images/fig19.jpg" alt="" width="400" height="466" />
-  <p class="blockquot space-below2"><span class="smcap">Fig. 19.</span>—Scapula
-        (<i>sc</i>), coracoid (<i>cor</i>), and metacoracoid (<i>mcor</i>)
-         of <i>Dimetrodon</i></p>
-</div>
-
-<p>The cleithrum is known in only a few of the old reptiles; it is a
-more or less slender bone which lies along the upper front margin of
-the scapula, articulating at its lower end with the upper end of the
-clavicle on each side.
-<span class="pagenum" id="Page_37">[Pg 37]</span></p>
-
-<p>The breast bone or sternum, while not properly a part of the pectoral
-girdle, may be mentioned here. In reptiles it is rarely well developed
-or even ossified, the flying reptiles known as the pterodactyls being
-the most notable exceptions. It was a comparatively late development in
-this class, the earliest ones not possessing it even in a cartilaginous
-condition. It was doubtless evolved from the more or less numerous and
-slender ossifications on the under side of the body called ventral
-or abdominal ribs, after the coracoids had become reduced and more
-slender. Whenever it is present the coracoid articulates with it
-on each side in front. In most lizards it remains as a cartilage
-throughout life.</p>
-
-<div id="FIG_20" class="figcenter">
-  <img  src="images/fig20.jpg" alt="" width="500" height="326" />
-  <p class="blockquot space-below2"><span class="smcap">Fig. 20.</span>—Clavicles
-         and interclavicle of <i>Ophiacodon</i>, a theromorph reptile from
-         the Permocarboniferous of New Mexico.</p>
-</div>
-
-<h3>ANTERIOR EXTREMITY</h3>
-
-<p>The upper arm bone, or humerus, like most other bones of the
-extremities, has been greatly modified by the habits of the different
-reptiles. In running and climbing reptiles it is always slender, while
-in burrowing reptiles it is short and stout and much expanded at the
-extremities, like the humerus of the mole among mammals. And we shall
-<span class="pagenum" id="Page_38">[Pg 38]</span>
-also see how greatly modified it was among the swimming reptiles.
-The humerus of flying reptiles has an enormous process on the side,
-corresponding to the attachment of the deltoid muscle. The head of the
-humerus, for articulation with the glenoid cavity of the scapula, is
-rounded in all reptiles, except the pterodactyls, and the articulation
-is always at the extremity. At the lower extremity the protuberance
-at the outer or radial side is called the ectocondyle; that on the
-inner or ulnar side, the entocondyle. Between the two at the end are
-the articular surfaces for the radius and ulna, the capitellum and
-trochlea. A little above each of these condyles there is usually, on
-one side or the other or on both, a foramen or hole for the passage of
-arteries or nerves. That on the inner side, which is characteristic of
-all early reptiles and of many mammals, is called the entepicondylar
-foramen; that on the outer side, the ectepicondylar foramen; the latter
-is present in the lizards, and both are found in the tuatera and some
-of the early reptiles.</p>
-
-<div id="FIG_21" class="figcenter">
-  <img  src="images/fig21.jpg" alt="" width="600" height="350" />
-  <p class="center space-below2"><span class="smcap">Fig. 21.</span>—Anterior
-        extremity of <i>Ophiacodon</i>.</p>
-</div>
-
-<p>The radius and ulna are always distinct bones in reptiles, and always
-freely movable on each other; they are usually shorter than the humerus,
-but in some springing and climbing reptiles they are quite as long.</p>
-
-<p>The carpus or wrist of reptiles consists primitively of eleven
-distinct, irregularly shaped bones, which articulate more or less
-closely with each other in three rows. Those of the first row, all true
-carpals, are known usually as the radiale, intermedium, ulnare, and
-pisiform, corresponding quite with the bones of the human wrist known as
-<span class="pagenum" id="Page_39">[Pg 39]</span>
-the scaphoid, lunar, cuneiform, and pisiform. The second row has but
-two bones, on the radial side, known as the centralia; while the
-third row has a bone to correspond to each of the metacarpals, five
-in number, and collectively known as the carpalia. Some or indeed all
-of these bones may be either absent or unossified, that is, remaining
-through life as nodules of cartilage. Seldom, however, are there less
-than nine bones in the carpus of reptiles.</p>
-
-<p>The metacarpals, like the digits, primitively were five in number, and
-seldom are there less, though the fifth is sometimes lost, and rarely
-also the first. They are more or less elongate bones, increasing in
-length from the first to the fourth, with the fifth usually shorter.
-The first and the fifth are usually more freely movable on the wrist
-than are the other three.</p>
-
-<p>The number of joints or phalanges in the fingers of all primitive
-reptiles is that of the modern lizards and the tuatera, that is, two
-on the first finger or thumb, three on the second, four on the third,
-five on the fourth, and three on the fifth. The crocodiles have one
-less phalange on the fourth digit; the turtles have usually two less
-on the fourth and one less on the third, that is, with precisely the
-same arrangement that is found in our own fingers and that of mammals
-in general, two on the thumb and three on each of the other fingers.
-As exceptions the river turtles have four bones in the fourth digit.
-And this mammal-like and turtle-like arrangement of the phalanges was
-that of those early reptiles, the Theriodontia, from which the mammals
-arose. The last or ungual phalange of reptiles is usually claw-like,
-that is, sharp, curved, and pointed, but sometimes it is more nail-or
-hoof-like.</p>
-
-<h3>PELVIC OR HIP GIRDLE</h3>
-
-<p>The pelvic girdle or pelvis in reptiles and higher animals consists of
-three bones on each side, often closely fused in adult reptiles and
-together known as the innominate bone. The upper or dorsal one of these
-three bones—that to which the sacrum is attached—is the ilium; the
-one on the lower or ventral side in front is the pubis; and that on
-the ventral side behind is the ischium. On the outer side, where these
-three bones meet, is a cup-like depression, sometimes a hole, called
-<span class="pagenum" id="Page_40">[Pg 40]</span>
-the acetabulum, for the articulation of the head of the thigh bone,
-homologous with the glenoid articulation of the pectoral girdle, which,
-as we have seen, was originally formed by three bones, the scapula,
-coracoid, and metacoracoid, the two latter bones, like the pubis and
-ischium, meeting in the middle line below. In all the primitive and
-early reptiles the pubis and ischium form a continuous plate of bone
-without holes in it, except a small one just below the acetabulum in
-the pubis, called the obturator foramen, and corresponding to the
-supracoracoid foramen of the coracoid. One may almost always recognize
-these two bones by the presence of the foramen. This “plate-like”
-condition of the pelvis has been lost in all late and modern reptiles
-by the appearance of a larger or smaller vacuity between the pubis
-and ischium, either paired, when it corresponds quite with the
-so-called obturator opening of mammals, or singly in the middle. This
-old-fashioned character, like the old-fashioned type of pectoral
-girdle, disappeared entirely about the close of the Mesozoic period,
-the Choristodera, described in the following pages, being the last of
-the kind.</p>
-
-<div id="FIG_22" class="figcontainer">
-  <div class="figsub">
-   <p class="space-above2">&nbsp;</p>
-   <img src="images/fig22a.jpg" alt="" width="250" height="158" />
-  </div>
-  <div class="figsub">
-    <img src="images/fig22b.jpg" alt="" width="250" height="377" />
-   </div>
-   <p class="blockquot space-below2"><span class="smcap">Fig. 22.</span>—Pelvis
-     of <i>Ophiacodon</i>: <i>A</i> from side; <i>B</i> from above; <i>pu</i>,
-     pubis; <i>il</i>, ilium; <i>is</i>, ischium.</p>
-</div>
-
-<p>The ilium in reptiles usually has a more or less prolonged process
-or projection turned backward by the side of the anterior caudal
-vertebrae, but in those animals which walked erect on the hind legs,
-<span class="pagenum" id="Page_41">[Pg 41]</span>
-the dinosaurs and pterodactyls, as also some of the more erect-walking
-reptiles ancestral to the mammals, this process was directed forward,
-as in birds and mammals. The crocodilia, unlike all other known
-reptiles, have the pubes excluded from the acetabulum, and they do not
-meet in a median symphysis. This character alone will distinguish any
-crocodilian from all other reptiles. But there is some doubt as to the
-homology of the bones usually called pubes in the crocodiles. Some of
-the bipedal dinosaurs have the pubis forked, the anterior part directed
-downward and forward, and not meeting its mate in a symphysis, the
-posterior process long and slender, lying below the long ischium, as
-in birds. Indeed, when this peculiarity of the dinosaurian pubis was
-first discovered, it was thought to be an evidence of the immediate
-relationship of birds; its structure is now interpreted differently.</p>
-
-<h3>POSTERIOR EXTREMITY</h3>
-
-<p>The thigh bone or femur in reptiles, like the humerus, is variable
-in size and shape. Only in those reptiles that walked erect is the
-articulation of the head set off from the shaft of the bone by a
-distinct neck. In others the articulation is at the extreme top of
-the bone, since the thigh bones are habitually turned more or less
-directly outward from the acetabulum and the long axis of the body.
-The more or less pronounced rugosities at the upper end of the femur,
-for the attachment of muscles, called trochanters, are not easily
-distinguishable into the greater and lesser, as in mammals. Sometimes,
-as in the erect-walking dinosaurs, there is a more or less pronounced
-process on the shaft lower down, called the fourth trochanter, for the
-attachment of caudal muscles. On the back part of the shaft there is a
-ridge or line for the attachment of muscles, corresponding to the linea
-aspera of the mammalian femur. The projections at the lower end on the
-sides are called condyles.</p>
-
-<p>The two bones of the leg, or shin, are usually shorter than the thigh
-bones, though in running and leaping animals they may be quite as long
-or even longer. That on the inner or big toe side is called the tibia,
-and articulates with the distal end of the femur, but chiefly with its
-inner condyle. It has a more or less well-developed crest in front
-above for the attachment of the extensor muscles directly, since there
-<span class="pagenum" id="Page_42">[Pg 42]</span>
-never is a patella in reptiles, and only rarely sesamoid bones of any
-kind. The fibula, at the little-toe side of the leg, is usually more
-slender than the tibia, though it may be larger in swimming reptiles
-and even in some running forms. It disappeared in some of the later
-pterodactyls. Its upper articulation has a more gliding and somewhat
-rotary motion on the outer condyle of the femur, turning the foot
-outward in extension of the leg.</p>
-
-<div id="FIG_23" class="figcenter">
-  <img  src="images/fig23.jpg" alt="" width="450" height="510" />
-  <p class="blockquot space-below2"><span class="smcap">Fig. 23.</span>—Right
-       hind foot of <i>Ophiacodon</i>: <i>a</i>, astragalus; <i>c</i>,
-       calcaneum; <i>c1</i>, <i>c2</i>, centralia; 1, 2, 3, 4, 5, tarsalia.</p>
-</div>
-
-<p>The tarsus of reptiles differs from that of mammals, in that the
-chief movements of extension and flexion of the foot upon the leg
-occur within the tarsus rather than between the tarsus and leg bones.
-Primitively the tarsus of reptiles consisted of nine bones, two in the
-first row, two in the second, and five in the third, but in all modern
-reptiles the bones of the middle row and the fifth one in the third row
-have disappeared; in some lizards and turtles the two of the first row
-are fused. The two bones of the proximal row correspond quite to the
-astragalus and calcaneum, the astragalus articulating with both tibia
-and fibula proximally, the calcaneum with the latter only. The oldest
-known tarsus of any vertebrated animal, one from the Coal Measures
-of Ohio, has this structure, while in all the early amphibians there
-were three bones, the tibiale, intermedium, and fibulare. Some of the
-later swimming reptiles, like the ichthyosaurs and plesiosaurs, have
-apparently this amphibian structure, with three bones that are usually
-called tibiale, intermedium, and fibulare, but it is very doubtful
-indeed whether they are homologically the same. In the middle row two
-centralia are known in one or two very ancient reptiles, but for the
-<span class="pagenum" id="Page_43">[Pg 43]</span>
-most part there is only a single centrale, and even that is usually
-lost in later reptiles. The third row, like the third row of the
-carpus, had a distinct bone for each digit originally, but the fifth
-one was very soon lost and has never reappeared. The structure of
-the digits and number of bones are quite like those of the hands,
-except that the fifth toe has four bones instead of three, that is,
-the phalangeal formula was 2, 3, 4, 5, 4. As a rule in terrestrial
-reptiles, as in terrestrial mammals, the hind foot is more specialized
-than the front ones.</p>
-
-<p>Most reptiles have an external covering or exoskeleton of horny plates
-or scales or bony scutes. Horny scales are of course not preservable
-as petrifactions, though in many instances their actual carbonized
-remains or their impressions have been detected. Such information comes
-only rarely, though doubtless in the course of time we shall obtain
-it for most extinct reptiles. In the mosasaurs, for instance, very
-perfect impressions showing the detailed structure of the scales have
-been frequently found. Similar impressions were long since observed by
-Lortet in <i>Pleurosaurus</i>, and in not a few dinosaurs impressions
-of most wonderful perfection have been found. It is only in the water
-reptiles, probably, that all external coverings tended to disappear.</p>
-
-<p>Bony dermal plates or scutes are less common among reptiles, though by
-no means rare. The turtles, as is well known, are almost completely
-inclosed in such an exoskeleton, bones which have coalesced more or
-less to form a box or carapace within which the head and limbs may be
-withdrawn for protection. In the modern crocodilians also the body is
-more or less protected by small bone plates forming rows on the back
-and sometimes on the under side. The ancient phytosaurs had similar
-plates. Not a few of the dinosaurs were more or less covered with bony
-scutes and sometimes with large bony plates or spines. Some modern
-lizards have bony plates over the body instead of horny scales.</p>
-
-<hr class="chap x-ebookmaker-drop" />
-
-<div class="chapter">
-<p><span class="pagenum" id="Page_44">[Pg 44]</span></p>
-<h2 class="nobreak" id="CHAPTER_IV">CHAPTER IV<br />
-<span class="h_subtitle">&nbsp;<br />THE AGE OF REPTILES</span></h2>
-</div>
-
-<p>Geologists divide the history of the earth, since life first appeared
-upon it, into four general eras, the Proterozoic, Paleozoic, Mesozoic,
-and Cenozoic, that is, into eras of first life, ancient life, middle
-life, and recent life. These divisions were made long ago by geologists
-when it was believed that extraordinary changes, great cataclysmic
-revolutions, marked their limits.</p>
-
-<p>With a fuller knowledge of the life of the past we know that evolution
-has been continuous and uninterrupted; possibly accelerated or retarded
-at times, but without break. Were the earth’s history to be written
-anew, with our present knowledge, and with an unbiased mind, it is
-very doubtful whether many of the time divisions would have the same
-limits that they have now—whether the Paleozoic would terminate with
-the Carboniferous, or the Permian, or the Trias, or whether indeed we
-should think it necessary to make any primary divisions whatsoever. In
-other words, our greater knowledge of living and extinct organisms,
-and of the rocks which contain fossils, has made the problems of
-classification much more complex than they seemed to be formerly. It
-is much easier to classify organisms or rocks, or anything else, when
-we know only a few isolated kinds—much easier to draw divisional
-lines. Geological history is like a volume in which pages, leaves, and
-even whole chapters either are missing or are printed in languages
-which we understand only imperfectly. Where the lost or unknown parts
-belong, the largest divisions may be made, and possibly such may have
-been epochs of unusual activity, of diastrophic changes which greatly
-accelerated organic evolution. No one can say just where the dividing
-line should be drawn between the rocks of Paleozoic and Mesozoic age,
-or between the Mesozoic and Cenozoic, for there is none; the most
-that we can hope for is to make the divisions everywhere in the world
-conform to those first made for local reasons.
-<span class="pagenum" id="Page_45">[Pg 45]</span></p>
-
-<div id="FIG_23A" class="figcenter">
-  <p class="f120">Click image to enlarge.</p>
-  <a href="images/fig23a_hr.jpg">
-  <img  src="images/fig23a.jpg" alt="" width="600" height="385" /></a>
-  <p class="blockquot space-below2"><span class="smcap">Fig. 23</span><i>a</i>.—Range
-       of the Reptilia.Heavy lines indicate occurrence in North America.</p>
-</div>
-
-<p><span class="pagenum" id="Page_46">[Pg 46]</span>
-The periods of the Paleozoic era are the Cambrian, Ordovician,
-Silurian, Devonian, Carboniferous, and Permian, in the order as given;
-those of the Mesozoic era are the Triassic, Jurassic, and Cretaceous;
-those of the Cenozoic era, the Eocene, Oligocene, Miocene, Pliocene,
-Pleistocene, and Recent. As a relic of an old classification we still
-often divide the Cenozoic into two quite arbitrary divisions, the
-Tertiary and the Quaternary, the latter including the Pleistocene and
-Recent only. The same may be said regarding the limits of each of
-these periods as of the eras; the sole problem is to make each period
-contemporaneous throughout the world, an exceedingly difficult problem,
-because no faunas or floras have ever been the same over the whole
-earth. Indeed, with the exception of some of the lowliest and most
-generalized forms, or man himself, no species are the same throughout
-the earth today. Inasmuch as we must depend upon the fossils in the
-rocks for the determination of the ages, where none is quite the
-same in strata of remote localities the identification becomes very
-difficult or even impossible. Nor are the periods, as accepted, of
-equal or even approximately equal duration; the Cretaceous period, for
-instance, was longer than all the remainder of the Mesozoic, longer
-perhaps than all the time which has elapsed since its close.</p>
-
-<p>The earliest animals with a backbone, or rather the earliest that we
-call vertebrates—for some vertebrates have no vertebrae—began their
-existence, so far as we know, in late Ordovician times, as attested
-by fish bones in Ordovician rocks of Colorado and Utah. The first
-evidences of the existence of air-breathing vertebrates in geological
-history are footprints preserved in the uppermost Devonian rocks of
-Pennsylvania. We call them amphibian because they resemble footprints
-associated with amphibian skeletons in later formations, and because
-the foot itself is still the most important difference we know between
-fishes and the higher animals.
-<span class="pagenum" id="Page_47">[Pg 47]</span></p>
-
-<div id="FIG_24" class="figcenter">
-  <img  src="images/fig24.jpg" alt="" width="600" height="440" />
-  <p class="blockquot space-below2">
-       <span class="smcap">Fig. 24.</span>—Permocarboniferous landscape
-       (adapted from Neumayr) with restoration of <i>Eryops</i>, a
-       stegocephalian amphibian ancestrally allied to the reptiles; and
-       <i>Limnoscalis</i>, a cotylosaur (in water).</p>
-</div>
-
-<p><span class="pagenum" id="Page_48">[Pg 48]</span>
-In the rocks of the next great time division, the Mississippian, as we
-call it in America, corresponding more or less closely with the Lower
-or Subcarboniferous of other parts of the world, numerous footprints
-of amphibians have been discovered, but no fossil remains except a
-few from near its close in Scotland. From the Upper Carboniferous, or
-Pennsylvanian, however, not only numerous footprints but the actual
-skeletons, or impressions of skeletons, have long been known in Europe
-and America. Until recently all these footprints and skeletons were
-supposed to be exclusively amphibian. We are now almost sure that some
-of them belonged to reptiles of lowly type, the earliest coming from
-near the middle of the Pennsylvanian of Linton, Ohio. The amphibians of
-this period were, for the most part, salamander-like creatures of from
-a few inches to two or three feet in length. They all belong to the
-group collectively known as the Stegocephalia, except that very near
-the close of the period there appeared small, slender, small-legged
-aquatic forms which seem to be the ancient representatives of the real
-salamanders of modern times. Some of the Stegocephalians had become
-greatly specialized as legless, snake-like, or eel-like creatures.</p>
-
-<div id="FIG_25" class="figcenter">
-  <img  src="images/fig25.jpg" alt="" width="600" height="297" />
-  <p class="blockquot space-below2">
-     <span class="smcap">Fig. 25.</span>—Restoration of <i>Seymouria</i>,
-     the most primitive of known cotylosaur reptiles. From the Permian of
-     Texas, about two feet long.</p>
-</div>
-
-<p>By the beginning of Permian times tremendous changes had taken place
-in the land life. The small amphibians of the Carboniferous types
-dwindled away, soon to disappear, and their places were taken by others
-of peculiar types, for the most part larger; and by many and diverse
-kinds of reptiles—water reptiles, marsh reptiles, land reptiles, and
-even climbing tree reptiles. From the uppermost Carboniferous and Lower
-<span class="pagenum" id="Page_49">[Pg 49]</span>
-Permian rocks of the United States more than fifty genera and twice
-that many species of amphibians and reptiles have been made known in
-recent years, and doubtless as many more will be discovered in the
-future. From other parts of the world the history of reptiles of the
-Lower Permian is yet scanty, two or three forms from South America, as
-many more from Africa, and a half-dozen or so from Europe are all; and
-of these very few are known at all well.</p>
-
-<div id="FIG_26" class="figcenter">
-  <img  src="images/fig26.jpg" alt="" width="600" height="389" />
-  <p class="center space-below2">
-     <span class="smcap">Fig. 26.</span>—<i>Captorhinus</i>, a cotylosaur
-     reptile from Texas.</p>
-</div>
-
-<p>We classify all the known forms of reptiles from the Lower Permian
-under three or four orders, the Cotylosauria, Theromorpha or
-Pelycosauria, Proganosauria, and possibly the Protorosauria, but the
-classification is yet provisional, representing merely the present
-stage of our knowledge. The Proganosauria and Protorosauria, including
-distinctively aquatic reptiles, will be more fully described in
-the following pages. To give even a brief description of the more
-terrestrial reptiles of this, the earliest known reptilian fauna, would
-be beyond our purpose; the accompanying life restorations by the author
-of some of the more typical and better known forms, based upon nearly
-perfect skeletons, will suffice.</p>
-
-<p>From the reptiles and amphibians of the Lower Permian of Texas and New
-Mexico to the ichthyosaurs of the Middle Triassic of California there
-is a complete gap in the records of the land life of North America. We
-do not know what became of all the remarkable animals of the Permian.
-There are few traces of their descendants elsewhere known, unless it
-be in South Africa. From the Middle and Upper Permian of South Africa
-and Russia, a marvelous reptilian fauna has been made known in recent
-<span class="pagenum" id="Page_50">[Pg 50]</span>
-years. More than a hundred species of six or seven groups, and at least
-two orders have been described. Of these the Cotylosauria are the
-continuation of the American order, but include more specialized forms,
-the Pareiasauria and the Procolophonia, all of them, like the more
-primitive American forms, characterized by the imperforate temporal
-region. The Therapsida, likewise, seem to be the continuation of the
-American Theromorpha, so closely allied to them that it is difficult
-to draw a distinguishing line between them. On the other hand, these
-African reptiles merge through the Theriodontia into the mammals in the
-Triassic. They are all terrestrial, crawling reptiles, except a few
-which are described on a later page under the Anomodontia.</p>
-
-<div id="FIG_27" class="figcenter">
-  <img  src="images/fig27.jpg" alt="" width="600" height="264" />
-  <p class="center space-below2">
-    <span class="smcap">Fig. 27.</span>—Restoration of <i>Labidosaurus</i>,
-    a cotylosaur reptile from Texas, about three feet long. </p>
-</div>
-
-<p>The records of the lower part of the Triassic period are scanty
-everywhere in the world, save perhaps in Africa. Before the close of
-the period, however, probably every important group of cold-blooded
-air-breathing animals had made its appearance in geological history,
-if we except the snakes; even the mammals had appeared, and possibly
-the birds. The Cotylosauria, Theromorpha, and Therapsida disappeared,
-the latter giving birth to the mammals; the nothosaurs and plesiosaurs,
-the ichthyosaurs, dinosaurs, crocodiles, phytosaurs, rhynchocephalians,
-lizards, and turtles have all left records of their existence in Upper
-Triassic rocks; and the pterodactyls had also, in all probability,
-begun their career, though none is surely known till the Jurassic.
-<span class="pagenum" id="Page_51">[Pg 51]</span></p>
-
-<p>During Jurassic times all these orders of reptiles waxed prosperous
-and powerful, and branched out in many ways and in countless numbers;
-many new kinds of each appeared—the marine crocodiles, the quadrupedal
-dinosaurs, etc.—but no order or suborder, so far as we know,
-disappeared before its close. And this prosperity continued on into
-the Lower Cretaceous and for many even into the Upper Cretaceous. The
-largest dinosaurs disappeared in the Lower Cretaceous, so far as our
-knowledge goes, but the old-fashioned crocodiles continued on into
-the Upper, to give place to the new-fashioned kinds. The ichthyosaurs
-lingered on for a while on the western continent, but the mosasaurs
-appeared, and the plesiosaurs reached their highest evolution and
-continued to the end. The flying reptiles attained the zenith of
-their evolution, but disappeared before the close. The marine turtles
-attained the maximum of specialization and size. The upright-walking
-dinosaurs continued on unabated to the close of the period; and a new
-kind of dinosaurs appeared near the end.</p>
-
-<div id="FIG_28" class="figcenter">
-  <img  src="images/fig28.jpg" alt="" width="600" height="426" />
-  <p class="center space-below2">
-      <span class="smcap">Fig. 28.</span>—Restoration of <i>Dimetrodon</i>,
-     a pelycosaur reptile from the Permian of Texas;<br/> about eight feet long.</p>
-</div>
-
-<p><span class="pagenum" id="Page_52">[Pg 52]</span>
-With the opening of the next great era—the Cenozoic or Tertiary—the
-reptiles dwindled away to their present insignificant position, while
-the birds and mammals appeared in great numbers and varied forms. The
-Age of Reptiles was closed and the Age of Mammals had begun.</p>
-
-<p>The history of the reptiles during the Cenozoic is an uneventful one;
-they ceased their dominion upon land, in the water, and in the air.
-Their remains are scanty, for the most part, in the rocks of the
-Tertiary, and such as are known differ only in details from those now
-living. The land tortoises only, like the mammals of Oligocene and
-Miocene times, seized the opportunities of open prairies and prospered.
-A few of the late Mesozoic forms continued a short while into the
-Eocene. No new groups, perhaps few new families, came into existence
-during the greater part of this time; it was the age only of land
-tortoises and the poisonous snakes among reptiles.</p>
-
-<h3>EXTINCT REPTILES OF NORTH AMERICA</h3>
-
-<p>The oldest known fossil reptile of North America, or indeed of the
-world, is represented by a single specimen, lacking the skull, from
-black shales of Middle Pennsylvanian age overlying a coal seam at
-Linton, Ohio. The specimen was originally described as an amphibian,
-but was later recognized by Professor Cope as a true reptile. It
-was more fully described by the writer under the name <i>Eosauravus
-Copei</i>, who agreed with Cope as to its reptilian nature. Until the
-skull is discovered, however, the precise relationships of the animal
-must remain doubtful.</p>
-
-<p>The next later rocks that have yielded reptilian remains are those
-of Illinois and Texas formerly supposed to be of Permian age. Later
-evidence, furnished by invertebrates, however, seems to prove that
-the lowermost of the strata are of uppermost Carboniferous age. The
-Illinois deposits, so far as known, are of very limited extent,
-consisting practically of a single bone-bed in black shale in the
-immediate valley of the Kaskaskia River near Danville. The known
-fossils from this bone-bed—all isolated bones—are preserved in the
-museum of the University of Chicago, and include the types of several
-genera later recognized in the Texas deposits.
-<span class="pagenum" id="Page_53">[Pg 53]</span></p>
-
-<p>The deposits of Texas, extending northward through Oklahoma to the
-south line of Kansas, are of considerable extent, for the most part
-lying along the Wichita River and its tributaries, north of Seymour,
-Texas. They are composed chiefly of red clays and sandstones of
-fresh-water or delta origin, perhaps eight hundred feet in total
-thickness. Beds of like character and yielding similar fossils are also
-known from northern New Mexico on the tributaries of the Chama River.
-Their chief characters, as well as restorations of some of the more
-noteworthy forms, have already been given.</p>
-
-<p>No vertebrate fossils are known in America from the Upper Permian and
-Lower Triassic. Marine limestones of Middle and Upper Triassic age
-of Nevada and northern California have yielded numerous remains of
-primitive ichthyosaurs, the only known remains of the thalattosaurs,
-and a few others of doubtful affinities, all of which have been
-described by Dr. Merriam. The Upper Triassic exposures, of considerable
-extent, occur between the Pitt River and Squaw Creek in Shasta County,
-California. Reptilian remains from the Middle Triassic are so far known
-only from the limestones of West Humboldt and New Pass regions of
-western and central Nevada.</p>
-
-<div id="FIG_29" class="figcenter">
-  <img  src="images/fig29.jpg" alt="" width="600" height="285" />
-  <p class="center space-below2">
-    <span class="smcap">Fig. 29.</span>—Restoration of <i>Varanops</i>, a
-    theromorph reptile from the Permian of Texas;<br /> about four feet
-    long.</p>
-</div>
-
-<p>Land reptiles of Middle and Upper Triassic age are known from many
-widely separated localities in the United States, but chiefly from the
-<span class="pagenum" id="Page_54">[Pg 54]</span>
-extensive “red beds” of the Rocky Mountain region. The fossils from
-these beds occur for the most part at least in the horizon called
-the Shinarump. Its age is usually considered to be Upper Triassic,
-but the character of the fossils seems to indicate possibly the
-Middle Triassic. Aside from the stereospondylian amphibians, the last
-of the Stegocephalia, the vertebrates from this horizon and these
-regions are chiefly Phytosauria. A few anomodonts, or what seem to be
-anomodonts—the only record of their occurrence outside of Africa—are
-known from Wyoming and Utah. And a single specimen from the Wind
-River red beds, described by the writer as <i>Dolichobrachium</i>,
-may represent reptiles allied to the dinosaurs. Phytosaur fossils of
-this horizon have been discovered in Utah, the Wind River Mountains,
-and near Laramie City in Wyoming; in southwestern Colorado; in western
-Texas; and in various places in New Mexico and Arizona. Doubtless when
-these fossiliferous beds are more thoroughly explored many new and
-interesting reptiles will be discovered.</p>
-
-<p>Phytosaur remains, probably of about the same age as the Rocky Mountain
-ones, have long been known from the Triassic of North Carolina.
-From somewhat more recent Triassic deposits in Connecticut and
-Massachusetts, several skeletons of small carnivorous dinosaurs, and
-various parasuchian remains have been described by Marsh, Lull, and
-Talbot. And these beds have long been famous in Massachusetts for their
-footprints, for the most part originally referred to birds, but now
-pretty well known to have been made by dinosaurs and amphibians.</p>
-
-<p>No vertebrate fossils of Lower or even Middle Jurassic age are known
-from North America. From the Baptanodon beds of Wyoming, limestones of
-about two hundred feet in thickness, four genera of plesiosaurs, the
-very peculiar ichthyosaur from which the beds take their name, and a
-few bones of an ancient crocodile are known.</p>
-
-<p>Immediately overlying the Baptanodon beds, the Morrison beds, of from
-two hundred to four hundred feet in thickness, probably of Uppermost
-Jurassic and Lowermost Cretaceous age, have yielded an exceedingly rich
-vertebrate fauna, consisting chiefly of dinosaurs. Discovered first in
-the vicinity of Morrison, Colorado, in 1877, hundreds of tons of bones
-<span class="pagenum" id="Page_55">[Pg 55]</span>
-have been collected from these beds for various museums. The dinosaurs
-include many genera of all three suborders, varying in size from that
-of a cat to some of the largest known land animals. Of other reptiles a
-very few jaws of a true rhynchocephalian, a fragment of a wing bone of
-a pterodactyl, numerous turtles, and crocodiles, only, are known. The
-beds are predominantly black-clay shales, intercalated with sandstones,
-and all are of fresh-water origin.</p>
-
-<p>From beds definitely known as Lower Cretaceous (Trinity) in Oklahoma,
-a few bones of a sauropod dinosaur are known, and from nearly
-corresponding rocks in southern Kansas, plesiosaurs, crocodiles,
-turtles, and carnivorous dinosaurs are known from sparse remains.
-Doubtless the Potomac beds of Virginia, which have yielded bones of
-various dinosaurs, are also of Lower Cretaceous age.</p>
-
-<div id="FIG_30" class="figcenter">
-  <img  src="images/fig30.jpg" alt="" width="600" height="391" />
-  <p class="center space-below2">
-    <span class="smcap">Fig. 30.</span>—Restoration of <i>Casea</i>, a
-    theromorph reptile from the Permian of Texas,<br /> about four feet long.</p>
-</div>
-
-<p>With the exception of a single vertebra of doubtful affinities and the
-cast of a turtle-shell no vertebrate fossils have ever been discovered
-in the extensive sandstones of Dakota age, the lowermost of the
-Upper Cretaceous. From the next horizon above the Dakota, the Benton
-<span class="pagenum" id="Page_56">[Pg 56]</span>
-Cretaceous, chiefly marine limestones, at least three genera of
-plesiosaurs are known from Kansas, Texas, and Arkansas, with two or
-three more from the limestone shales of Wyoming. A few specimens of
-armored dinosaurs, two genera of ancient crocodiles, nearly the last of
-their kind, some marine turtles, and a few vertebrae of ichthyosaurs,
-the last of the order known anywhere in the world, are also known from
-the Benton Cretaceous of Wyoming.</p>
-
-<p>Continuous with the Benton limestones above in Kansas are the famous
-beds of Niobrara chalk; perhaps no fossil deposits in the world are
-more famous. Exposures covering hundreds of square miles in western
-Kansas, almost pure chalk, have furnished fossil-hunters during the
-past forty years literally thousands of specimens of mosasaurs,
-hundreds of pterodactyls, and scores of plesiosaurs and marine turtles,
-in addition to the famous birds with teeth and countless fishes of
-diverse kinds. Two or three specimens of spoon-billed dinosaurs have
-been found in these deposits, but no other reptiles of any kinds. Beds
-of like age in Colorado and New Mexico have furnished a few specimens
-of mosasaurs.</p>
-
-<p>From the marine beds of Fort Pierre age, next above the Niobrara in the
-west, have come some excellent specimens of two genera of mosasaurs,
-three or four forms of plesiosaurs, a few pterodactyls, the largest of
-all marine turtles, and still fewer specimens of dinosaurs, in Kansas,
-South Dakota, Wyoming, and Montana. From deposits of approximately like
-age in Mississippi, Alabama, and New Jersey, many incomplete specimens
-were found years ago of mosasaurs, plesiosaurs, and turtles, the last
-of the amphicoelian crocodiles, the first of the procoelian crocodiles,
-and the famous specimen of <i>Hadrosaurus</i> which served for the
-Hawkins restoration, the first attempt of its kind.</p>
-
-<p>From the uppermost Cretaceous beds of America, the Lance, Judith
-River, or Belly River beds as they are variously called, have come
-the remains of a marvelous reptilian fauna. These beds may be grouped
-together though not all contemporaneous, and there is dispute about
-their age, some excellent paleontologists insisting that the uppermost
-are really of Eocene age. From Colorado east of Denver, from eastern
-Wyoming, from Montana, and especially from the vicinity of Edmonton
-<span class="pagenum" id="Page_57">[Pg 57]</span>
-in Canada, as also occasionally in western Texas and New Mexico,
-have come many marvelous specimens of dinosaurs, huge bipedal
-carnivorous dinosaurs, great spoon-billed aquatic dinosaurs, armored
-stegosaurian dinosaurs, and many kinds of the great horned dinosaurs,
-the Ceratopsia, so far known only from these beds. Here at the very
-close of the Age of Reptiles, at the close of the Age of Dinosaurs,
-are found the ultimate specializations of all the chief groups of
-dinosaurs except the long-necked quadrupedal dinosaurs which gave up
-the ghost in Lower Cretaceous times. Many were provided with horns and
-spines, some indeed seemed to have bristled with spines throughout,
-a sure sign that they were approaching the end of their career. The
-modern type of crocodiles had usurped the ancient forms of the early
-Cretaceous, and reached the largest size of their race perhaps, though
-but few specimens are known. Here also in these beds we find the
-first representatives of lizards and snakes in America, though snakes
-have been described from earlier strata, perhaps, in Brazil. Those
-archaic, old-fashioned rhynchocephalians described on a later page as
-the Choristodera appeared also for the first time in these beds, and
-persisted for a little while in the Eocene, in Europe and America. And
-with all these there has very recently been described the last of the
-plesiosaurs, whose race went out with the dinosaurs at the very close
-of the Mesozoic. It is needless to say that the turtles also occur,
-for, as a general rule, wherever vertebrate fossils are found, in rocks
-of the land or the sea, marine or fresh-water, there will be some bones
-of turtles among them.</p>
-
-<p>With the beginning of the Cenozoic the record of the reptiles
-becomes relatively scanty in America. In the warm waters of the old
-Eocene lakes and rivers of Wyoming lived countless crocodiles, true
-crocodiles of modern aspect and of large size. But, as the climate
-of North America grew progressively colder, the crocodiles retreated
-to the south, till, in the Oligocene, the scanty remains of the last
-crocodiles are found in the American Tertiary. On the other hand, as
-the open lands appeared toward the close of the Eocene, and in the
-Oligocene and Miocene, the land tortoises throve and grew greatly in
-size. In the Bad Lands of South Dakota one may see their remains in
-almost incredible numbers. And in equally great numbers are these land
-<span class="pagenum" id="Page_58">[Pg 58]</span>
-tortoises, in shape much like the common box tortoise of today, but
-vastly larger, found in the rocks of the late Miocene or early Pliocene
-age in western Kansas. And these are the last records of the big
-tortoises in North America; their descendants are perhaps yet living in
-the Galapagos Islands.</p>
-
-<p>The history of the lizards and snakes, the only other reptiles found
-in the Cenozoic rocks of America, is very brief. A few specimens from
-the Lower Eocene of Wyoming; a few skinks and amphisbaenas from the
-Oligocene Bad Lands of South Dakota, and some bones of a python-like
-snake in the early Eocene of Wyoming are about all that we know of the
-Squamata in the Tertiary. Doubtless snakes and lizards were just as
-abundant then as now, though but few were preserved, for they are and
-always have been distinctly terrestrial animals, that only by accident
-fell into places where they could be fossilized.</p>
-
-<p>The author has collected reptile bones from nearly all of the horizons
-here mentioned and believes that the list is complete.</p>
-<hr class="chap x-ebookmaker-drop" />
-
-<div class="chapter">
-<p><span class="pagenum" id="Page_59">[Pg 59]</span></p>
-<h2 class="nobreak" id="CHAPTER_V">CHAPTER V<br />
-<span class="h_subtitle">&nbsp;<br />ADAPTATION OF LAND REPTILES<br />
-TO LIFE IN THE WATER</span></h2>
-</div>
-
-<p>In the never-ceasing struggle for existence all forms of life upon the
-earth, whether consciously or unconsciously, are continuously striving
-for improvement; striving to flee from adverse environments, or to
-adapt themselves better to those which must be endured; to escape
-their enemies, or to find means whereby they may withstand them; to
-find more or better food, or to prevent others from despoiling them
-of what they have. There is always more or less of unrest, more or
-less of discontent, if such terms may be used of the lower organisms.
-It sometimes happens with groups of organisms that by reason of
-unusual or extraordinary traits they become so perfectly adapted to
-their environments, to their surroundings, or so easily adaptable to
-changes in their environments, that they remain for long ages securely
-protected and little changed. But, as with man himself, improvement
-is usually the result of adversity—adversity which stimulates but
-does not destroy. And the word improvement, translated into biological
-language, means simply specialization, that specialization which adapts
-the organism better to its mode of life, which fits it the better to
-excel its less ambitious or less capable competitors. No animals or
-plants are perfect; if they were, there would be no advancement, no
-struggle. If all physical conditions stood still, or remained uniform,
-perhaps life would stand still, but conditions never have and never
-will stand still, and life must change to meet changed conditions.</p>
-
-<p>Thus it is that which makes life easier, which lessens the dangers
-of destruction, which insures the continued prosperity of the race,
-is seized upon and utilized by all plants and animals, so far as
-<span class="pagenum" id="Page_60">[Pg 60]</span>
-possible. As said long ago by Tennyson,<a id="FNanchor_2" href="#Footnote_2" class="fnanchor">[2]</a>
-the first law of life is not the preservation of self, but the
-prosperity of the race. Whatever the causes may be whereby the
-offspring are better adapted to conquer in the struggle for existence,
-whatever may be the laws governing changes and specialization, whether
-heredity, Mendelism, mutation, natural selection, or Lamarckism, we
-call the process evolution.</p>
-
-<p>To escape from the severe competition of the overcrowding animals
-of the sea, some of those creatures we call fishes long ago became
-air-breathers and took possession of the unoccupied land. From among
-the myriads which were driven into unbreathable water, by accident or
-by their enemies, or led there in the search for more easily acquired
-or better food, some survived and found that the oxygen of the air was
-quite as breathable as that of the water. Steadily their progeny became
-better and better adapted to the unusual life until they ceased to be
-fishes and became amphibians, from which have arisen in like manner all
-the reptiles and birds and mammals that live or have lived upon the earth.</p>
-
-<p>With more and better powers, developed under better opportunities, not
-a few of these descendants have repeatedly sought safety from their
-newly acquired enemies of the overcrowded land, or a better supply of
-food in the sea; gradually, perhaps incidentally at first, as we shall
-see is the case with some lizards today, but later with increased
-adaptation to their new surroundings, they become truly sea or water
-animals, no longer able to live upon the land. In these changed
-conditions and with concomitantly changed habits they never reverted to
-the primitive condition of fishes, never became water-breathing animals
-again, for that would be actual retrogression, a seeming impossibility
-in evolution. Nor indeed does it seem possible that a land creature
-after its reversion to water life ever can return to the land again.</p>
-
-<p>A fish through long ages of evolution has become well adapted to its
-environments; its shape is the best for speed or varied evolutions in
-the water; its teeth and mouth-organs are best suited for the food it
-requires. Now it is evident that if animals of very different habits
-and form should go back to the water and seek to compete with creatures
-already well adapted to their surroundings, they must, so far as
-<span class="pagenum" id="Page_61">[Pg 61]</span>
-possible, acquire like forms and like habits. And any improvement on
-such forms and habits that their higher development permits them to
-attain will of course be of advantage in their competitive struggles.
-A fish makes most use of its tail fin for propulsion. It follows
-that a land animal seeking to compete with it under like conditions
-must acquire a tail fin or some other organ which subserves its
-purpose as fully. The body fins are of little use to a fish, save for
-equilibration, for preserving its position, for stopping quickly, or
-for changing the direction of its movements quickly—very different
-functions from those of the corresponding organs, the limbs, of higher
-vertebrates. There are few better examples of predaceous, fish-eating
-fishes than the common gar-pike of our rivers, fishes with a slender
-body covered with very smooth scales, a strong tail, a short neck, and
-long jaws armed with numerous slender and sharp teeth. Such a fish,
-darting into a school of smaller fishes, by quick, sudden changes of
-movement, actively opening and closing its jaws, is sure to seize some
-of its sought-for prey. In a direct trial of speed with its victims it
-would most likely be worsted.</p>
-
-<p>There have been many animals of high and low rank which in the
-past and present have gone back from a terrestrial existence to a
-life in the water, finding at last a congenial home away from the
-shores. Or, perhaps, like the monitor lizards of today, they have
-found temporary safety in the water when hard pressed by their land
-enemies, and finally found, not only protection, but an abundant
-supply of easily obtainable food therein. As in every vocation of
-life there have been many failures in such attempts, many partial
-successes only. But not a few have found abounding and enduring
-success and final prosperity—success that has led possibly to undue
-adaptation to surroundings, and to the acquirement of great size,
-for that has been the invariable end of water air-breathers of long
-duration—specializations which finally prevented them from meeting new
-exigencies. It seems to be a law of evolution that no large creatures
-can give rise to races of smaller creatures; and as we shall see, the
-largest sea-animals have been the final evolution of their respective races.</p>
-
-<p>There are no better examples of such success today, nor has there been
-<span class="pagenum" id="Page_62">[Pg 62]</span>
-in all the geological ages, so far as we know, more perfect examples
-of the adaptation of air-breathing animals to an aquatic life than the
-great whalebone whales. In Eocene times their ancestors were walking
-and running land animals; of that there can be not the slightest doubt,
-since we cannot conceive, as did the older naturalists, of their direct
-descent from the fishes while having all the essential structure of
-mammals, i.e., lungs, circulatory system, manner of breeding and
-rearing the young, etc. Of the living whales, or Cetacea, there are
-now in existence two very distinct types, so different from each other
-that some have supposed them to have been evolved from different
-types of land mammals. One of these is best exemplified by the great
-baleen whale, having a broad, short head and no teeth. It feeds upon
-crustaceans chiefly, which are strained from the water by the great
-fringe or net of “whalebone.” The other type is seen in the porpoise
-or dolphin. These cetaceans have numerous, pointed and recurved teeth,
-which they use as did many of the reptiles, hereinafter described, for
-the seizure and retention of fishes and other swimming animals. So
-great have been the changes in all these cetaceans, in the adaptation
-to an aquatic life, that we are almost at a loss to conjecture from
-what kinds of land animals they have descended. The great zeuglodont
-whales of early Tertiary times have long been thought to be a sort of
-connecting link between them and their land ancestors, and it is still
-probable that they were. The forms of zeuglodont whales that have been
-discovered in Africa within recent years bear so much resemblance
-in their skull and teeth to the contemporary carnivores, that many
-paleontologists think, with good reason, that they were descended from
-them, that is, from the ancestors of all our dogs, cats, weasels,
-bears, etc., of modern times. And we have much reason to believe that
-future discoveries will bring further and more decisive proof of their
-origin before many years have elapsed. The modern Sirenia, the dugongs
-and manatees, exclusively aquatic mammals, which feed upon seaweeds at
-the bottoms of shallow bays and harbors, or in the mouths of rivers,
-are now known, practically with certainty, to be the descendants in
-these same African regions of the earliest ancestors of our sheep,
-oxen, and horses, known so certainly that they are often classed with
-them, or at least with the elephants, which approach them in their
-ancestral line even more closely.
-<span class="pagenum" id="Page_63">[Pg 63]</span></p>
-
-<p>A third type of living aquatic air-breathers is seen in the seals,
-sea-lions, etc. They are much less highly specialized, however, than
-the whales or sirenians, since they are still capable of considerable
-freedom upon land, which they recurrently seek for the breeding of
-their young. They still retain the primitive covering of hair, lost
-almost entirely by the cetaceans and sirenians and functionally
-replaced for the conservation of heat by a thick layer of blubber.
-Instead of losing the hind legs and developing the tail as a propelling
-organ like the whales, the seals encountered precisely the reverse
-experience. The hind legs have been developed into most efficient
-paddles or sculls, and the tail has been for the most part lost.
-They are fish-eaters, it is true, but they do not have the long jaws
-possessed by the porpoises and toothed whales.</p>
-
-<p>In the sea-otters, beavers, and even the muskrats, we have examples
-of less complete adaptation of land mammals to water life, the most
-of them showing the beginnings at least of structural adaptations
-similar to those of the seals. From an attentive examination of all
-these animals, living as well as extinct, which have attained partial
-or complete success as air-breathing water animals, we find certain
-laws existing, if we may call them such, which we may discuss a little
-in detail. As we have seen in the comparison of the whale with the
-seal, the methods of adaptation have not always been the same, and some
-recent writers have endeavored to classify aquatic animals under many
-groups, to which they have given learned technical names, most of which
-will not concern us here in dealing with the reptiles only.</p>
-
-<p>Beginning with the head, we find that all those reptiles and most of
-the mammals which have become aquatic fish-eaters have an elongated
-skull, or rather an elongated face. The jaws are long and slender, and
-the teeth are not only numerous but also sharp and slender, much like
-those of the gar-pike, indeed. It is remarkable, too, that in most
-such animals the external nostrils are situated, not at the extremity
-of the snout, as in all terrestrial mammals and reptiles, but far back
-near the eyes. In the whales this position of the nostril enables the
-animals to breathe without continuous muscular exertion while floating
-on the surface; that is, the nostrils are at the top of the head. In
-the sirenians, on the other hand, which live habitually at the bottom
-<span class="pagenum" id="Page_64">[Pg 64]</span>
-of shallow waters, coming to the surface to breathe only, the nostrils
-are situated so that they are the first to emerge, that is, they are
-near the front end. The crocodiles, with a more or less elongated face,
-as also the Choristodera, described farther on, are exceptions, since
-their nostrils are at the extremity of the snout. Both of these types,
-however, notwithstanding the elongation of the face, are only partly
-aquatic in habit, and in the crocodiles the breathing organs have
-undergone a strange modification in accordance with habits peculiarly
-their own, as will be explained later on. Whether this recession of the
-nostril toward the eyes can be explained in all cases by the peculiar
-breathing habits is, however, doubtful. Possibly in some cases, such as
-the phytosaurs, described later, the creatures used their long beaks
-to probe in the mud while breathing. Possibly the posterior position
-has been in some cases rather the result of the elongation of the face,
-leaving the nostrils behind in some forms, or carrying them forward in
-others. Nevertheless posterior nostrils always indicate more or less
-aquatic habits.</p>
-
-<p>In all the earliest reptiles, as we have seen, the neck was short,
-like that of their immediate progenitors, the ancient amphibians. The
-shoulders were close to the skull, with not more than two vertebrae
-that could be called cervical. It happens that most of the earliest
-reptiles, as we know them, were more or less amphibious in habit, and
-all of them were probably good swimmers; nevertheless in all likelihood
-reptiles began their career as a class with a very short neck. The
-earliest known distinctly terrestrial reptiles had a moderately long
-neck composed of six or seven cervical vertebrae. It may therefore be
-assumed with much probability that all later reptiles with a greater
-or less number of cervical vertebrae are specialized animals, so far
-as the neck is concerned. Most living reptiles have eight cervical
-vertebrae; a few have nine, and still fewer have but five. Birds may
-have as many as twenty-four, while all mammals, with two or three
-exceptions, have the primitive number seven. Among extinct reptiles,
-however, there were not a few with more numerous neck vertebrae, some
-having the enormous number of seventy-six.</p>
-
-<p>An ordinary fish has apparently no neck whatever, the trunk being
-<span class="pagenum" id="Page_65">[Pg 65]</span>
-seemingly attached to the head, nearly as in the primitive amphibians
-and primitive reptiles. It is evident that a movable neck of
-considerable length would not only be of no use to the swiftly
-swimming fish, but a positive disadvantage to it. The body is quickly
-and easily turned by the powerful tail fin, and a long neck could be
-of no use that the tail would not better subserve. It is therefore
-of interest to learn that, as a rule, aquatic animals of all kinds
-having a powerful propelling tail have also a short neck, acquired
-either by the loss of neck vertebrae, or, as in the mammals, by the
-shortening and coalescence of the normal number of seven. There are
-very few exceptions to this rule of a short neck and a long tail.
-Those strange little reptiles of Paleozoic times, the first that we
-know that returned to the water, the Proganosauria, have not only a
-long, flattened tail, but also an unduly elongated neck of from nine to
-twelve vertebrae.</p>
-
-<p>On the other hand, certain unrelated reptiles of the past, the
-dolichosaurs, nothosaurs, and plesiosaurs, with a short non-propelling
-tail, developed a long neck—sometimes an excessively long one in the
-plesiosaurs. The turtles, some of which have attained a high adaptation
-to water life, have invariably a short tail and a freely movable,
-relatively long neck, a neck which Dr. Hay tells us has increased
-in length from the beginning of their race by the simple elongation
-of the vertebrae, as in the giraffe, and never by the addition of
-vertebrae. We may then account it a rule that swimming animals with
-a long neck have a short tail, and those with a short tail have a
-long flexible neck. Even in the plesiosaurs there is some variation
-of the length of the tail in correlation with the neck. Short-tailed
-animals must necessarily propel themselves through the water by the aid
-of their legs, especially the hind legs. If one watches an actively
-swimming alligator he will observe that the front legs are folded or
-collapsed by the side of the body, while the hind legs, much bent,
-are used only slightly in propulsion. The animal swims by a marked
-sinuous or serpentine movement, like that of a snake upon land,
-extending throughout the tail and part of the body, at least. An animal
-propelling itself by its limbs could not move sinuously, and use its
-legs actively at the same time, and it is probable that the long neck
-has been evolved compensatorily.
-<span class="pagenum" id="Page_66">[Pg 66]</span></p>
-
-<p>With this shortening of the neck and sinuosity of movement there is
-developed in every case a long trunk as well as a long tail. The trunk
-becomes more slender and cylindrical, more like that of a snake, with
-an actual increase of the bones composing it, reaching the great number
-of forty-three vertebrae in that most sinuous of all water reptiles
-with legs, <i>Pleurosaurus</i> of the Protorosauria. And the tail,
-primitively having perhaps sixty or seventy vertebrae, may have as
-many as one hundred and fifty in the more typical aquatic forms. This
-elongation of trunk and tail must be of great advantage to the swimming
-reptile, just as the racing scull is a more perfect type of speedy
-craft than a flat-bottomed scow. Dr. Woodward has said that the fate of
-all fishes, if they continue their evolution long enough, is to become
-eel-like.</p>
-
-<p>Not only was the tail greatly elongated in swimming reptiles, but it
-was also more or less flattened. In the beginning of water adaptation
-the flattening was throughout the tail, as in the living alligators and
-crocodiles. As the adaptation to water life became more perfect, the
-flattening became more and more restricted to the extremity; that is,
-the flattening begins like that of a salamander and in the end becomes
-like that of a fish, a terminal fin. And some of the actual stages in
-the evolution of the fish-like fin have been observed by Dr. Merriam
-in the earlier and more primitive ichthyosaurs of California. In those
-animals swimming chiefly in a horizontal direction the tail fin has
-become like that of fishes, that is, vertical; but in those animals
-which use the tail chiefly for ascending and descending rapidly in the
-water the fin is developed in a horizontal position, examples of which
-are seen in the flukes of whales and sirenians.</p>
-
-<p>All animals living upon the land require firm articulations between the
-different bones of the skeleton, and especially between the vertebrae,
-for the support and control of the body. Among aquatic animals there
-is a strong tendency toward looseness of joints, with increasing
-flexibility. Fishes have the articular processes between the arches of
-the vertebrae feebly or not at all developed, and the centra or bodies
-of the vertebrae have thick pads of cartilage between them. Firm union
-between the vertebrae would restrict freedom of movement, and firmness
-<span class="pagenum" id="Page_67">[Pg 67]</span>
-is not required when the body is surrounded on all sides by water
-of nearly the same specific gravity as the body itself. And it is
-doubtless for the same reasons that the articulations of all strictly
-aquatic reptiles have for the most part become looser and less firm,
-especially those between the different vertebrae.</p>
-
-<p>The same looseness of articulation is also found in the ribs of
-aquatic animals. In most animals, and in all those which walk erect,
-like the mammals, each rib is firmly attached to the backbone by two
-distinct joints, the head and tubercle, with an interval between
-them. This double attachment prevents much in-and-out movement of the
-ribs and gives a firm support for the attachment of the muscles of
-respiration, as well as for those supporting the viscera. This firmness
-is unnecessary in animals living always in the water, and the ribs
-therefore in all aquatic animals tend to become single-headed and
-loose. The lower or capitular articulation has been lost in part, or
-almost wholly, in many cetaceans. It has been said that a whale cast up
-on land will die of suffocation, not for the lack of air, for it is an
-air-breathing animal like ourselves, but because it can no longer use
-its respiratory muscles attached to the loosely articulated ribs; it
-suffocates because the ribs collapse.</p>
-
-<p>As would be expected, the greatest modifications of structure in the
-adaptation of air-breathers to water life are found in the limbs. No
-other parts of the body have such different functions in water and on
-land as the limbs and fins. The limbs of a dog, or a cat, or a man
-are feeble organs for swimming in comparison with the fins of a fish,
-and if the land animal must compete with fishes to prey upon them for
-food it must acquire like swimming powers. As a matter of fact, the
-limbs of all typically aquatic air-breathing animals have lost nearly
-all external resemblance to the legs of walking and running animals,
-and have become more or less fin-like in function—fin-like in shape
-and function, but never fin-like in actual structure. No creature can
-go back and begin over again, any more than a man can again become a
-child with all its possibilities for improvement and development. If
-an animal cannot modify the organs it already possesses so as to adapt
-them to new and changed uses by the aid of evolutionary forces it must
-<span class="pagenum" id="Page_68">[Pg 68]</span>
-fail in the struggle. It can never acquire new material, never get new
-fingers and toes, new organs or parts of organs; all its possibilities
-lie in the improved and new uses it can make of the material which it
-received from its ancestors.</p>
-
-<p>The beginning of aquatic adaptation of the limbs lies in the membranous
-webs between the toes of frogs, salamanders, ducks, seal, otters, etc.,
-where the feet are used largely or entirely for propulsion through
-the water, in the absence of a propelling tail. And this membrane,
-in the majority of cases, is the extent of aquatic adaptation in
-air-breathing animals. In those animals, however, such as most of the
-reptiles described in the following pages, where the tail has developed
-as the propelling organ, the limbs lose to a greater or less extent
-their propelling function and become merely organs of equilibration
-and control. Of the two pairs of fins of fishes it is evident that
-the anterior ones have the more important equilibrational function;
-the hind ones have a much less important use as guiding organs; as
-a matter of fact, in not a few fishes the hind or pelvic fins have
-actually migrated forward to supplement the function of the pectoral
-fins. It is for these reasons that those animals best adapted of all
-for life in the water—the whales and sirenians—have lost the hind
-legs completely. In other tail-propelled air-breathers the hind legs
-have become progressively smaller and less powerful than the front
-ones. In all short-tailed water animals, however, where the legs, and
-especially the hind legs, have the important function of propulsion to
-subserve, they still retain the large size and firm connections with
-the body, examples of which will be seen in the seals, sea-otters,
-marine turtles, and plesiosaurs.</p>
-
-<p>Because the legs are no longer needed for the support or propulsion of
-the body in long-tailed air-breathers, their connection with the body
-becomes less and less firm, long before their entire disappearance. In
-animals using the legs for crawling or walking the bones of an arm and
-thigh are elongated, and the joints are always well formed, permitting
-varied, extensive, and firm movements. Just the reverse is the tendency
-in all those animals that propel themselves by the aid of the tail in
-the water, since here what is needed is broad, short limbs, not long
-and slender ones.
-<span class="pagenum" id="Page_69">[Pg 69]</span></p>
-
-<p>Most reptiles have five digits on each hand or foot; the bones of the
-wrist and ankle are well formed, as in mammals, and the digits are
-elongate, with a very definite arrangement of the bones composing them,
-as already described, never exceeding five in any one finger or toe.</p>
-
-<p>In the paddles of water reptiles, as the limbs are usually called,
-the bones of the first segment, that is, the humerus and femur, are
-always greatly shortened in those having a propelling tail, and even
-in some with a short tail, such as the seals, and in a lesser degree
-in the sea-otters. On the other hand, in those animals which use the
-legs chiefly for direct propulsion these bones are elongated, as
-exemplified by the plesiosaurs and marine turtles. In all save the
-seals and their kind, and the otters, whose legs are used rather as
-sculls than as oars, the bones of the next segment, the radius and
-ulna of the front pair, the tibia and fibula of the hind pair, are
-always shortened, and one can tell the stage of aquatic adaptation, as
-exemplified, for instance, in the plesiosaurs and ichthyosaurs by the
-degree of shortening of these bones. Indeed, the first suggestion in
-any crawling animal of water habits is shown in the relative lengths of
-the epipodial bones, as these bones are called. Furthermore, cursorial
-or terrestrial habits are suggested by the relative size of the smaller
-bone of the leg, that on the little-toe side, the fibula. In birds,
-pterodactyls, and most running animals, it disappears in part or
-wholly. In swimming animals it tends to grow larger than the tibia, as
-will be conspicuously seen in the paddle of the mosasaurs.</p>
-
-<p>The bones of the wrist change in two ways: by becoming cartilaginous,
-as in whales and salamanders, or by becoming more firmly ossified
-and more closely united, as in the plesiosaurs. The digits always
-are elongated, often extraordinarily so, either by the elongation of
-individual bones or phalanges, or by the development of new bones.
-These new bones, when they occur, are new growths, not the reproduction
-of the old elements of fishes, and there may be as many as twenty
-such new elements or phalanges in a single digit. There is one marked
-exception among reptiles to this hyperphalangy, as the increased number
-of phalanges is called, and that is the turtles. As we have seen, in
-<span class="pagenum" id="Page_70">[Pg 70]</span>
-the elongation of the neck among turtles there never has been an
-actual increase in the number of vertebrae; so also in the elongation
-of the digits the normal number of three in each digit has never been
-exceeded, except among the river turtles, where there are four in the
-fourth digit—possibly a relic of original conditions rather than
-the beginning of hyperphalangy; but the individual bones have become
-greatly elongated. In living reptiles, birds and mammals of the land,
-the fifth toe is always shorter than the fourth. In the seals, the
-sea-otter, and to a less degree in the muskrat, the fifth toe has
-become elongated. And the elongation of this toe is the first and
-most decisive indication of a webbed foot of strong propelling power
-among the aquatic reptiles of the past, as exemplified especially
-by the proganosaurs. Finally, in one order of extinct reptiles, the
-ichthyosaurs, there has been an actual increase in the number of
-digits, in some to as many as nine in each paddle.</p>
-
-<p>In addition to all these modifications of the skeleton, the bones
-themselves tend to become softer and more spongy in aquatic animals.
-The bones of the whale, as is well known, are very spongy in texture,
-and those of the seals and sea-lions contain an unusually large amount
-of oily matter. So, too, the bones of the extinct water reptiles—of
-many of them at least—were more spongy than those of their land
-relatives; and this is due in part perhaps to their lessened use as
-muscular supports, in part perhaps to the necessity of a lessened
-specific gravity. As a rule sea-animals need to be of the same specific
-gravity as the water in which they live, or a little less. The bones
-of the living sirenians, the manatees and dugongs, so far from being
-light and porous, are unusually dense and solid. The sirenians live
-habitually at the bottom of shallow waters, feeding upon vegetable
-growths; and doubtless their bottom-feeding habits account for the
-solidity of the bones. A whale would float to the top, while a
-dugong would sink to the bottom, on the relaxation of all muscular
-movement. And we shall see that certain reptiles in the past had in all
-probability like bottom-feeding habits, because of the solidity of the
-bones of their skeletons.</p>
-
-<p>Many birds and fishes have a peculiar ossification of the usually
-tendinous outer covering of the eyeball, called the sclerotic membrane.
-<span class="pagenum" id="Page_71">[Pg 71]</span>
-These ossifications form a flattened or somewhat projecting conical
-bony ring about the pupil of the eye. The individual bones are flat
-and more or less imbricated plates, with some motion between them.
-Accommodation for vision in reptiles, birds, and fishes is not the
-simple process that it is in mammals, where it is controlled by
-simple ciliary muscles which compress the lens, causing it to assume
-a more spherical or a more flattened form, thus changing the focus.
-In reptiles accommodation is effected by the compression of the
-eyeball by means of external muscles, elongating it and causing its
-front part to expand or project. The imbricated sclerotic plates
-permit this expansion and contraction of the eyeball. Under great
-internal or external air pressure the cornea, the only unprotected
-part, must necessarily change its contour unless some compensatory
-force is brought to bear to counterbalance it; and this doubtless was
-the function of the sclerotic plates so commonly present in aquatic
-reptiles.</p>
-
-<p>Among terrestrial reptiles there are not a few examples of the
-ossification of such sclerotic plates, notably among the skink lizards.
-Every known form of extinct reptiles of aquatic habit had them, and
-even some of the subaquatic dinosaurs, like <i>Diplodocus</i> and
-<i>Trachodon</i>. One may say with assurance that it is impossible
-for any reptile to become thoroughly adapted to aquatic life without
-acquiring large and strong sclerotic plates.</p>
-
-<p>Most land reptiles are or were covered by horny scales or bony plates;
-the pterodactyls are the only order of terrestrial reptiles with
-no such covering of which we have any evidence. Such coverings are
-wholly unneeded for animals living in the water. Not only are they
-unnecessary, but the increased resistance to the water would be more or
-less detrimental to rapid swimming. It is for these reasons doubtless
-that bony plates or horny scales disappeared for the most part from the
-skin of all truly aquatic reptiles and mammals.</p>
-
-<p>The foregoing are the chief acquired characteristics of aquatic
-air-breathing animals and especially aquatic reptiles in adaptation
-to their new mode of life. The resemblances, sometimes striking,
-thus brought about in animals of very different origin and remote
-relationships have often been mistaken for evidences of kinship, that
-<span class="pagenum" id="Page_72">[Pg 72]</span>
-is, direct inheritance from common ancestors. Such acquired
-resemblances in unrelated animals are known as parallel or convergent
-evolution. It has often been difficult to distinguish between
-convergent evolution and direct evolution, and difficulties still
-perplex and trouble the student of natural history in every branch
-of life. Not till all such problems are solved can we hope to attain
-the true classification of animals and plants. The whales a century
-ago were considered merely breathing fishes; the ichthyosaurs until a
-quarter of a century ago were supposed to be the direct descendants of
-fishes; lizards and crocodiles were grouped together in a single order;
-and salamanders were called reptiles not very long ago.</p>
-
-<p>Perhaps the reader will be able from the foregoing to understand
-and appreciate better some of the difficulties that confront the
-paleontologist in his attempts to solve the problems of past life; to
-understand why he sometimes makes mistakes, for he has by no means
-yet learned all the permutations of the skeleton in any class of
-vertebrates, and is not sure that the laws he accepts are not subject
-to modifications and exceptions. If he is truly scientific he hesitates
-long in prophesying or conjecturing.</p>
-
-<hr class="chap x-ebookmaker-drop" />
-
-<div class="chapter">
-<p><span class="pagenum" id="Page_73">[Pg 73]</span></p>
-<h2 class="nobreak" id="CHAPTER_VI">CHAPTER VI<br />
-<span class="h_subtitle">&nbsp;<br />SAUROPTERYGIA</span></h2>
-</div>
-
-<p>Very scanty are the early human records of those strange reptiles
-known as the plesiosaurs. Were one to search through the many works
-published during the latter half of the seventeenth century and all
-of the eighteenth, devoted to “lapides petrifacti,” “figured stones,”
-“reliquia diluvii,” or by whatever other fanciful names fossils were
-known, here and there he would probably find descriptions and figures
-of bones of these reptiles. It would hardly seem that plesiosaurian
-bones could have been overlooked by the curious, so abundant are they
-in many places. But there is no such history of the early discovery
-of the plesiosaurs as there is of the ichthyosaurs and mosasaurs.
-Their birth into human history was very formal and proper, under the
-ministrations of a learned doctor of science, the renowned Conybeare,
-of whom we shall speak again. It was he, who with De la Bêche, late
-Director of the British Geological Survey, described for the first
-time, in 1823, one of these reptiles, to which he gave the name
-<i>Plesiosaurus</i>, meaning “like a lizard.” He distinguished the
-plesiosaurs from ichthyosaurs, with which it is possible that they had
-previously been confounded, and gave a good description of considerable
-material. Cuvier, a little later, gave a more complete description
-of the same remains which had served Conybeare and De la Bêche for
-their original description, and for the first time made it evident
-that fossil plesiosaurs were widely and abundantly distributed over
-the earth. The closing sentence of Cuvier’s chapter devoted to the
-discussion of these creatures in his <i>Ossemens Fossiles</i> was
-really prophetic, not only of the many discoveries of the plesiosaurs
-yet to be made, but of all other extinct animals as well: “I doubt not
-that, in a few years it may be, I shall be compelled to say that the
-work which I have today finished, and to which I have given so much
-labor is but the first glimpse of the immense creations of ancient times.”
-<span class="pagenum" id="Page_74">[Pg 74]</span></p>
-
-<div id="FIG_31" class="figcenter">
-  <img  src="images/fig31.jpg" alt="" width="600" height="391" />
-  <p class="blockquot space-below2"><span class="smcap">Fig. 31.</span>—Restoration
-     of <i>Plesiosaurus guilelmi imperatoris</i> (left figure) and
-     <i>Thaumatosaurus victor</i> (right figure), Liassic plesiosaurs.
-     (From E. Fraas.)</p>
-</div>
-
-<p><span class="pagenum" id="Page_75">[Pg 75]</span>
-In quick succession there followed many other discoveries of
-plesiosaurs, not only in England but elsewhere in Europe. The famous
-English anatomist and paleontologist, Sir Richard Owen, to whom we
-owe, perhaps, more than to anyone else our present knowledge of these
-animals, the eccentric Hawkins of England, the learned von Meyer of
-Germany, and, in later times, more especially Seeley and Andrews of
-England, Fraas of Germany, Bogalobou and Riabanin of Russia, as well
-as many others, have brought to light during the past century many and
-varied forms of those sea-reptiles. Blaineville in 1835 gave to the
-plesiosaurs an ordinal rank under the class Ichthyosauria, and even the
-astute Owen in 1839 united them with the ichthyosaurs as a suborder of
-his Enaliosauria, or “sea-saurians.” He called them Sauropterygia, or
-“reptile-finned,” and these terms, Enaliosauria, Ichthyopterygia, and
-Sauropterygia, have long persisted in works on natural history because
-of the prestige of Owen’s name. As we shall see later, the plesiosaurs
-are really of remote kinship to the ichthyosaurs, and there is no such
-natural group as the Enaliosauria. It often takes years to distinguish
-between apparent and real relationships among living organisms, and
-both of these groups of sea-saurians have had a sorry experience in the
-treatment they have received from nomenclators.</p>
-
-<p>Perhaps because of the writings of Dean Buckland in his famous
-<i>Bridgewater Treatise</i>, in large part a theological disquisition,
-though of real scientific merit, the ichthyosaurs and plesiosaurs
-early became widely and popularly known, and, even to this day, these
-reptiles, together with the dinosaurs, first made known by Rev. Dr.
-Mantell, are often supposed to be the most typical and horrid of
-monsters. Many and fabulous are the tales that have been told of
-them in literature both grave and gay. The preacher adduced them as
-evidences of the great world-catastrophe told in biblical history, and
-the German student sings of them to the tune of the “Lorelei”:</p>
-
-<div class="poetry-container"><div class="poetry"><div class="stanza">
-    <div class="verse indent0">Es rauscht in Schachtelhalmen, verdächtig leuchtet das Meer;</div>
-    <div class="verse indent0">Da schwimmt mit Thränen in Auge ein Ichthyosaurus einher.</div>
-    <div class="verse indent0">Ihn jammert der Zeiten Verderbniss, denn ein sehr bedenklicher Ton</div>
-    <div class="verse indent0">War neuerlich eingerissen in der Liasformation.</div><span class="pagenum" id="Page_76">[Pg 76]</span>
-    <div class="verse indent0">Der Plesiosaurus, der alte, der jubelt in Saus und Braus;</div>
-    <div class="verse indent0">Der Pterodactylus selber flog jungst betrunken nach Haus.</div>
-    <div class="verse indent0">Der Iguanodon, der Lümmel, wird frecher zu jeglicher Frist;</div>
-    <div class="verse indent0">Schon hat er am hellen Tage die Ichthosaura geküsst.</div>
-</div></div></div>
-
-<p>We now know that they were not the monsters of horrid mien that they
-were once supposed to be: the largest plesiosaurs, were they living
-today, would find unopposable foes in the vicious and cruel crocodiles.
-They were relatively stupid and slow, cruel enough to the smaller
-creatures, but of limited prowess. But in structure and habits they are
-among the most remarkable of all the animals of the past or present.</p>
-
-<p>Although their remains are among the most abundant and widely
-distributed of all fossil reptiles, the plesiosaurs as a whole are less
-perfectly known than either the ichthyosaurs or the mosasaurs, and it
-has been within a comparatively few years only that an approximately
-complete knowledge of any form has been obtained. This is partly due
-to the fact that the order comprises vastly more kinds, more species,
-genera, and families than does any other order of marine reptiles;
-partly because their remains, though widely distributed over the earth,
-and in rocks of many geological epochs, are seldom found completely
-preserved; usually specimens comprise only a few bones or single bones,
-and complete skeletons are rare. Were there but few kinds, the many
-specimens discovered would mutually supplement each other, finally
-completing our knowledge; but the fragments of many kinds only add to
-our confusion. Nevertheless, because the plesiosaurs lived so long in
-geological history, their remains are found in rocks of many different
-kinds, and since it is improbable that any of them had great specific
-longevity, it is very probable that all these described species, or
-most of them, often made known from single bones, will eventually be
-found to be distinct, and that many more will be added to them. It does
-not seem improbable that within the next forty or fifty years not less
-than a hundred species of plesiosaurs will have been discovered in
-North America alone. At the present time perhaps that many have been
-described from the whole world.</p>
-
-<p>When Blaineville gave the name Plesiosauria to the aquatic reptiles
-<span class="pagenum" id="Page_77">[Pg 77]</span>
-described by Conybeare, Cuvier, and others, he had no
-knowledge of others of an intermediate kind between them and
-land reptiles. His group-term then can be properly applied only
-to the truly aquatic forms, and Owen’s name Sauropterygia becomes
-available in a wider sense to include all the known types belonging
-to the order of which the plesiosaurs form a part. Of this order
-then there are two clearly marked divisions or suborders, the
-Plesiosauria and the Nothosauria, the former having a complete
-aquatic adaptation, the latter only a partial one. While the two
-suborders are evidently allied, some authors have suggested that
-their differences are only familial; others have thought that they
-are really orders. We shall see how close the relationships are.</p>
-
-<h3>PLESIOSAURIA</h3>
-
-<p>It was Dean Buckland who facetiously likened the plesiosaurs to a snake
-threaded through the shell of a turtle, and the simile was not an
-inapt one in his day. The vernacular designation of them—long-necked
-lizards—conveys the same impression of their chief peculiarity, but
-the name is less applicable than it once was, since recent discoveries
-have brought to light forms with a relatively short neck.</p>
-
-<p>Though the plesiosaurs are nearly perfectly adapted to an aquatic
-life, the adaptation was, in many respects, of a very different kind
-from that of the ichthyosaurs—so very different that we have not yet
-quite finished conjecturing as to the habits of the living animals. As
-already suggested in the popular name, the most striking characteristic
-of the typical plesiosaurs, the one which suggested to Buckland his
-frequently quoted simile, is the ofttimes enormously long neck,
-proportionately longer than that of any other known creatures of the
-past or present. In other truly aquatic animals the neck is actually
-shortened in the acquirement of a fish-like shape, and the number of
-bones composing it reduced. In the Sauropterygia the neck is usually
-longer than any truly land animals ever possessed, the longest-necked
-forms having as many as seventy-six vertebrae in the cervical region.
-The elongation of the neck among mammals is always due to an increase
-in the length of the individual bones, never to an increase in the
-number from seven, with but a single exception—a South American sloth
-<span class="pagenum" id="Page_78">[Pg 78]</span>
-which has nine cervical vertebrae. The long neck of birds is due both
-to an increase in the length of the individual vertebrae and to an
-increase in their number, to as many as twenty-one. But the elongation
-of the neck among plesiosaurs was very variable indeed; sometimes it
-was ten or twelve times the length of the head, at other times it was
-even shorter than the head. And the number of bones composing it was
-also extremely variable, scarcely any two species having the same,
-the known extremes being seventy-six and thirteen. In <i>Elasmosaurus
-platyurus</i>, for instance, the longest-necked plesiosaur known, the
-head was two feet in length, the neck twenty-three, the body nine,
-and the tail about seven; on the other hand, in the shortest-necked
-plesiosaur known, <i>Brachauchenius Lucasi</i>, the head was two and
-one-half feet in length, the neck less than two feet, and the body
-about five; the length of the tail is unknown.</p>
-
-<div id="FIG_32" class="figcenter">
-  <img  src="images/fig32.jpg" alt="" width="600" height="225" />
-  <p class="center space-below2"><span class="smcap">Fig. 32.</span>—Skeleton
-    of <i>Trinacromerum osborni</i>, a Cretaceous plesiosaur,<br /> as mounted in
-    the University of Kansas Museum.</p>
-</div>
-
-<p>Not only was the number of vertebrae so extraordinarily increased in
-many plesiosaurs, but in the longest necks the vertebrae themselves, as
-in birds, were more or less elongated, especially the posterior ones,
-which may be six or seven times the length of the anterior ones. Not
-only was the neck of such great length in many plesiosaurs, but it also
-tapered very much toward the head.</p>
-
-<p>The vertebrae are always biconcave, but the cavities are shallow,
-saucer-like, sometimes almost flat at each end, and very different from
-the conical fish-like cavities of ichthyosaurian vertebrae.
-<span class="pagenum" id="Page_79">[Pg 79]</span></p>
-
-<div id="FIG_33" class="figcenter">
-  <img  src="images/fig33.jpg" alt="" width="600" height="388" />
-  <p class="blockquot space-below2">
-        <span class="smcap">Fig. 33.</span>—Restoration of <i>Elasmosaurus
-        platyurus</i>, an Upper Cretaceous plesiosaur.</p>
-</div>
-
-<p><span class="pagenum" id="Page_80">[Pg 80]</span>
-Often the vertebrae are short throughout the vertebral column;
-sometimes the posterior cervicals and the dorsals are elongated and
-very robust. The trunk or body proper was never much elongated in the
-plesiosaurs, having only from twenty-five to thirty vertebrae. The
-tail was always shorter than the trunk, and it tapered rapidly to the
-extremity; in some specimens it has been observed to turn up slightly
-near the extremity, as though for the support of a small terminal fin.</p>
-
-<div id="FIG_34" class="figcenter">
-  <img  src="images/fig34.jpg" alt="" width="600" height="293" />
-  <p class="blockquot space-below2">
-   <span class="smcap">Fig. 34.</span>—Cervical vertebrae, from the side
-   and behind, and dorsal vertebra from in front of <i>Polycotylus</i>,
-   a Cretaceous plesiosaur: <i>az</i>, anterior zygapophysis; <i>pz</i>,
-   posterior zygapophysis, <i>r</i>, <i>r</i>, <i>r</i>, cervical ribs;
-   <i>d</i>, articulation of dorsal rib.</p>
-</div>
-
-<p>The ribs in the cervical region are short, but so locked together
-posteriorly as not to permit much lateral motion. They are sometimes
-double-headed in the neck, sometimes single-headed, but both heads
-when present articulate or are attached to the body of the vertebrae,
-distinguishing them at once from those of other animals, except the
-ichthyosaurs. In the dorsal region the ribs are attached high on the
-arch to the extremity of the stout transverse processes by a single
-head, very much as they are in some cetaceans, and quite unlike the
-condition in any other known reptile. They end freely below, having
-no attachment to a breast bone or other bony parts. Because of their
-shape and position as frequently found, the body in life must have been
-flattened from above downward, and broad; indeed, this shape is quite
-<span class="pagenum" id="Page_81">[Pg 81]</span>
-certain because of the very broad expanse of the coracoids, between the
-articulations of the front legs.</p>
-
-<div id="FIG_35" class="figcenter">
-  <img  src="images/fig35.jpg" alt="" width="400" height="455" />
-  <p class="blockquot space-below2">
-   <span class="smcap">Fig. 35.</span>—Pectoral girdle of
-   <i>Trinacromerum</i> from above: <i>ic</i>, interclavicle; <i>cl</i>,
-   clavicle; <i>sc</i>, scapula; <i>c</i>, coracoid.</p>
-</div>
-
-<p>The shoulder-girdle or pectoral arch is strangely unlike that of any
-other reptiles. There is no breast bone, since the breast bone is a
-comparatively late development in reptiles, not appearing, probably,
-until after the plesiosaurs had begun their existence. Taking the place
-<span class="pagenum" id="Page_82">[Pg 82]</span>
-of the sternum, the very large and broad coracoidsjoin each other in
-the middle, forming a sort of subdermal armor on the under side of
-the body in front. In some of the largest plesiosaurs these two bones
-measured together about six feet in length by four in width. Though
-so very large they are thick only in front between the articulations
-of the forelegs. The shoulder-blades are much reduced in size and
-are extraordinarily modified. The blade proper, that is, that part
-extending backward and upward, is narrow and small, affording but
-little surface for the attachment of muscles. On the inner side,
-extending toward the middle in front of the coracoids, there is another
-projection, often broad and large, to which was attached the clavicles
-when present, and often this projection met its mate of the opposite
-scapula in the middle in front of the coracoids in a broad union. The
-clavicles or collar-bones are small and thin, and sometimes absent;
-they also are united in the middle posteriorly with the coracoids when
-the scapula did not intervene. And the interclavicle also is sometimes
-wanting. Altogether the pectoral bones form a very large, broad, and
-concave trough inclosing the whole of the under side of the anterior
-part of the body. This extensive surface must have furnished attachment
-to stout and strong muscles controlling the downward and inward motion
-of the paddles.</p>
-
-<p>There is a well-developed sacrum of three vertebrae for the support
-of the pelvis or hip bones. The reason for its persistence in animals
-so thoroughly adapted for life in the water will be understood later.
-The ilium is slender; it was attached to the sides of the sacrum by
-ligaments, only, not forming a firm union, but strong nevertheless.
-The pubes and ischia, the other bones of the pelvis on the under side
-of the body, like the corresponding bones of the pectoral girdle, were
-enormously enlarged, forming great flat, bony plates.</p>
-
-<p>Besides these large bony plates of the shoulder and pelvic girdles,
-the short abdominal region was inclosed by numerous series of strong
-ventral ribs, that is, overlapping rod-like bones on each side,
-connected with a central piece. It will be seen that the whole under
-side of the body, from the base of the neck to the base of the tail,
-was well protected by bones, rigid and unyielding in front and behind,
-<span class="pagenum" id="Page_83">[Pg 83]</span>
-flexible for a short space below the abdomen; this surface, however, was
-not flat like the under shell of a turtle, but rounded from side to side.</p>
-
-<div id="FIG_36" class="figcenter">
-  <img  src="images/fig36.jpg" alt="" width="350" height="463" />
-  <p class="blockquot space-below2">
-    <span class="smcap">Fig. 36.</span>—Pelvic girdle from above of
-    <i>Trinacromerum osborni</i>, an Upper Cretaceous plesiosaur: <i>p</i>,
-    pubis; <i>is</i>, ischium; <i>il</i>, ilium.</p>
-</div>
-
-<p>Many of the characteristics of the limbs of the plesiosaurs are
-peculiar to themselves; others they had in common with other aquatic
-<span class="pagenum" id="Page_84">[Pg 84]</span>
-reptiles and mammals. The paddles resemble those of the ichthyosaurs
-more nearly than those of any other reptile, and it was doubtless this
-superficial resemblance which so long deceived the early anatomists
-as to the affinities of the two orders. Unlike all other aquatic
-animals, however, the plesiosaurs have the hind limbs nearly or quite
-as large as the front ones, and they doubtless were equally effective
-in function. The humerus and femur are always elongate, though broad
-and massive. In no other aquatic animals, save the marine turtles,
-do we find these bones relatively so long and strong; they are very
-short in the cetaceans, the sirenians, the ichthyosaurs, mosasaurs,
-thalattosaurs, and the marine crocodiles, in front at least. The strong
-muscular rugosities of the plesiosaurian bones are very suggestive of
-powerful swimming muscles.</p>
-
-<div id="FIG_37" class="figcenter">
-  <img  src="images/fig37.jpg" alt="" width="500" height="363" />
-  <p class="center space-below2">
-    <span class="smcap">Fig. 37.</span>—Pelvic girdle of <i>Elasmosaurus</i>:<br />
-    <i>p</i>, pubis; <i>is</i>, ischium; <i>il</i>, ilium.</p>
-</div>
-
-<div id="FIG_38" class="figcenter">
-  <img  src="images/fig38.jpg" alt="" width="500" height="568" />
-  <p class="blockquot space-below2">
-   <span class="smcap">Fig. 38.</span>—Paddles of Plesiosaurs: <i>A</i>,
-   right hind paddle of <i>Thaumatosaurus</i>, after Fraas; <i>B</i>,
-   right hind paddle of <i>Trinacromerum</i>; <i>C</i>, right front paddle
-   of same individual; <i>f</i>, femur; <i>fb</i>, fibula; <i>t</i>,
-   tibia; <i>h</i>, humerus; <i>r</i>, radius; <i>u</i>, ulna.</p>
-</div>
-
-<p>The bones of the forearms and legs, the wrists and ankles are all
-polygonal platelets of bones, closely articulating with each other. The
-finger and toe bones have a more elongated, hour-glass shape than those
-<span class="pagenum" id="Page_85">[Pg 85]</span>
-of the ichthyosaurs, resembling more nearly those of the mosasaurs,
-indicating a greater flexibility than the ichthyosaurs possessed. The
-ichthyosaur paddles must have been quite like the fins of fishes in
-function, while doubtless those of the plesiosaurs were capable of a
-more varied use, as indeed was required of them. Their articulation
-with the trunk was more of a ball-and-socket joint than in the other
-reptiles, showing possibility of considerable rotation on the long
-axis, and an antero-posterior propelling action. The paddles were
-certainly more powerful than those of any other aquatic air-breathing
-animals. There were no additional digits, all plesiosaurs having
-neither more nor less than five in each hand and foot. Hyperphalangy
-<span class="pagenum" id="Page_86">[Pg 86]</span>
-was sometimes carried to an excessive degree, some digits of some
-species having as many as twenty-four bones, a larger number than has
-been observed in any other air-breathing vertebrate.</p>
-
-<div id="FIG_39" class="figcenter">
-  <img  src="images/fig39.jpg" alt="" width="450" height="558" />
-  <p class="blockquot space-below2">
-    <span class="smcap">Fig. 39.</span>—Pectoral girdle (in part) and front
-    paddles of <i>Elasmosaurus</i> (after Riggs): <i>sc</i>, scapula;
-    <i>h</i>, humerus; <i>cor</i>, coracoid; <i>r</i>, radius; <i>u</i>, ulna.</p>
-</div>
-
-<p>In <a href="#FIG_38">Fig. 38 on p. 85</a> are shown two paddles, the front and
-hind paddles of a single individual of a very specialized plesiosaur from the Upper
-Cretaceous of Kansas (<i>Trinacromerum</i>). The long arm and thigh
-<span class="pagenum" id="Page_87">[Pg 87]</span>
-bones are followed by remarkably short and broad bones in place of
-the elongated forearm and leg bones of the land reptiles. Not only
-are these bones much broader than they are long, but there have been
-developed additional bones back of them in the same row—new bones
-which have no counterpart in any terrestrial reptiles. In the first of
-the three figures is shown a hind paddle of one of the earliest known
-plesiosaurs, <i>Thaumatosaurus</i>, from the lower part of the Jurassic
-of Germany. It will be seen here that the tibia and fibula are much
-more elongated than in <i>Trinacromerum</i>, and much more like the leg
-bones of land reptiles. A still more primitive stage in the evolution
-of the swimming paddle of the plesiosaurs will be seen in <a href="#FIG_48">Fig. 48
-on p. 99</a>, the possibly ancestral, amphibious nothosaur. Here the tibia and
-fibula, while relatively very much shorter than in any land reptile,
-still have, together with all the other bones of the leg, a terrestrial
-or amphibious type. In <a href="#FIG_39">Fig. 39</a> is seen the front paddles
-of the long-necked <i>Elasmosaurus</i>, which, though one of the latest of all
-plesiosaurs in geological history, has the structure of its paddles
-somewhat intermediate between that of the earlier <i>Plesiosaurus</i>
-and the later <i>Trinacromerum</i>.</p>
-
-<div id="FIG_40" class="figcenter">
-  <img  src="images/fig40.jpg" alt="" width="500" height="239" />
-  <p class="blockquot space-below2">
-    <span class="smcap">Fig. 40.</span>—Skull of <i>Elasmosaurus</i> from the
-    side: <i>pm</i>, premaxilla; <i>m</i>, maxilla; <i>po</i>, postorbital;
-    <i>j</i>, jugal.</p>
-</div>
-
-<p>The skull of the long-necked plesiosaurs is surprisingly small in
-comparison with the remainder of the skeleton, often very snake-like
-in shape, though very un-snake-like in structure. The short-necked
-plesiosaurs had often a relatively larger skull, in <i>Pliosaurus</i>,
-for instance, more than five feet long, sometimes rather broad and
-short, sometimes remarkably long and slender. The external nostrils
-were situated far back, very near the eyes, and were very small. The
-eyes, of considerable size, though by no means so large as those of
-the ichthyosaurs, were directed laterally, and were provided with a
-ring of bony sclerotic plates—rather small and weak ones, however. The
-quadrate bones—bones peculiar to the reptiles and birds—to which the
-lower jaws are articulated, are, as in the ichthyosaurs and crocodiles,
-<span class="pagenum" id="Page_88">[Pg 88]</span>
-rigidly fixed and immovable. The lower jaws, always rather slender, are
-firmly united in front, sometimes for a long distance, as in the modern
-gavials. The teeth of the broad-headed plesiosaurs are long, slender,
-pointed, and recurved, of a murderously cruel shape; they are deeply
-implanted in sockets, and number from twenty to thirty on each jaw
-above and below. There are no teeth on the bones of the palate, such
-as the mosasaurs possessed. The slender-jawed, gavial-like plesiosaurs
-have more numerous, but smaller teeth. The surface of the skull on each
-side behind, for the attachment of the muscles closing the mandibles,
-is of great extent; in some this surface is increased by a high, thin
-crest in the middle, as in strongly carnivorous animals, all of which
-give conclusive evidence of the powerful muscles used in biting and
-seizing. There is but one temporal opening on each side, as in the
-ichthyosaurs and the mosasaurs, whereas the crocodiles, thalattosaurs,
-phytosaurs, etc., have two. The brain cavity of all plesiosaurs is
-small, though the cavities of the internal ears, the semicircular
-canals at least, are large. The semicircular canals in vertebrates have
-little or nothing to do with the function of hearing; they serve rather
-for equilibration, for the co-ordination of muscular movement; possibly
-we may infer from their large size in the plesiosaurs that they were
-not at all clumsy in their movements. There is a large opening for
-the pineal body, the so-called eye in the roof of the brain cavity,
-though its possession does not necessarily imply the possession of a
-functional organ.</p>
-
-<div id="FIG_41" class="figcenter">
-  <img  src="images/fig41.jpg" alt="" width="600" height="181" />
-  <p class="blockquot space-below2">
-    <span class="smcap">Fig. 41.</span>—Skull of <i>Trinacromerum</i>
-    from the side: <i>ang</i>, angular; <i>d</i>, dentary; <i>pm</i>,
-    premaxilla; <i>po</i>, postorbital; <i>j</i>, jugal; <i>sur</i>,
-    surangular.</p>
-</div>
-
-<p>The Plesiosauria included some of the largest aquatic reptiles that
-have ever existed, equaled, perhaps, though not exceeded, by some of
-<span class="pagenum" id="Page_89">[Pg 89]</span>
-the extinct crocodiles. The largest known are probably those of the
-Kansas chalk, or the Jurassic of Wyoming, which probably reached a
-length of nearly or quite fifty feet, of which the neck formed about
-one-half. Some of them had paddles more than six feet in length. The
-head of the largest was about five feet in length, or about the size
-of that of the largest known ichthyosaurs and mosasaurs. The smallest
-known adult plesiosaurs were nearly ten feet in length. The teeth of
-the largest and most carnivorous plesiosaurs sometimes measure four
-inches in length.</p>
-
-<div id="FIG_42" class="figcenter">
-  <img  src="images/fig42.jpg" alt="" width="600" height="342" />
-  <p class="center space-below2">
-   <span class="smcap">Fig. 42.</span>—Restoration of <i>Trinacromerum</i>,<br />
-   a Cretaceous plesiosaur;<br /> length about ten feet.</p>
-</div>
-
-<p>As is the case with both the ichthyosaurs and mosasaurs, skeletons
-of plesiosaurs have been discovered with nearly all their bones in
-their relative positions, and with impressions of skin and outlines of
-body made before decomposition. Though our knowledge of the external
-appearance of the plesiosaurs when alive is perhaps not as full as we
-could wish, it is sufficient to give us a fairly good conception of
-what the animals really were. The skin was smooth and bare, without
-scales or plates of any kind, and Dames has described a terminal or
-nearly terminal fleshy dilatation of the tail, forming a sort of caudal
-fin, which may have aided as a steering apparatus. Mounted skeletons
-are preserved in a few museums, notably the British Museum, the
-American Museum of New York City, and the museum of the University of
-<span class="pagenum" id="Page_90">[Pg 90]</span>
-Kansas. Many nearly complete skeletons, however, preserved as they were
-found in the matrix, are shown in various museums.</p>
-
-<p>With these, principal facts regarding the structure, size, and external
-form of these animals we may venture to draw certain conclusions, or at
-least to offer certain conjectures as to their habits in life.</p>
-
-<p>Because of the rigid structure of the jaws, united in front and
-incapable of any lateral movement posteriorly, quite as are the jaws
-of crocodiles, we are sure that prey of any considerable size could
-not have been swallowed whole. The crocodiles tear away portions of
-the flesh of their victims by quick, powerful jerks, and it is very
-probable that the flat-headed plesiosaurs tore their food apart in
-the same manner. In these kinds the teeth are much larger and more
-irregular in size than are those of the long-snouted plesiosaurs, and
-their use was certainly as much for tearing as for seizing. There are
-the same differences between the size of the head and the size of the
-teeth among the various plesiosaurs that there are among the modern
-crocodiles and gavials. While the crocodiles seize and destroy even
-larger prey, drowning and tearing their victims to pieces, the gavials
-are more exclusively fish-eating, for which their small, sharp, and
-more numerous teeth especially fit them. Their food, of small size,
-is swallowed entire, and they are comparatively harmless, so far as
-animals of considerable size are concerned.</p>
-
-<p>The long neck, the thickset body, and short, stout tail are not at
-all what we should expect to find in quick-swimming animals. We may
-therefore assume that the motions of the plesiosaurs through the
-water were more turtle-like than fish-like. The tail, even though
-provided with a terminal, fin-like dilatation, was of little use in
-the propulsion of the body, since the range of its movements was
-restricted; it possibly served in a measure as a steering organ, a
-rudder. The large, freely movable paddles must have been effective
-organs of locomotion, and this function accounts for the relatively
-large size of the posterior pair, and the firm union of the pelvis with
-the vertebral column through the sacrum. With the hind limbs used as
-oar-like organs, a firmer union with the skeleton was required than the
-<span class="pagenum" id="Page_91">[Pg 91]</span>
-soft yielding flesh would permit. At the same time this union was
-ligamentous only, not bony and unyielding, since the limbs were never
-used to support the body upon the ground; and it is of interest to
-observe that the ilia are directed, not upward and forward, but upward
-and backward to the sternum, precisely the position that would be
-expected with the force or thrust coming from behind, and not below
-the yielding ligaments. Were the tail longer and more powerful, the
-hind limbs would have been smaller and weaker, of use chiefly in
-equilibration, involving the loss of any connection with the vertebral
-column and the disappearance of the sacrum. It is of interest, finally,
-to observe that many of the slender-jawed plesiosaurs had a relatively
-short neck; they were doubtless more distinctively fish-eating in
-habit, and possessed greater speed. That the limbs of plesiosaurs
-were powerful propelling organs is also conclusively proved by their
-structure. Quite unlike all those animals whose locomotion in the water
-is chiefly effected by the tail, the humeri and femora, the upper
-arm and thigh bones were elongated, and not shortened. They form the
-rigid and stout handles of oars whose blades are the thinner, flexible
-forearm, wrist, and fingers, or the corresponding foreleg, ankle,
-and toes. No other purely aquatic reptiles, save the turtles, which
-likewise are of the oar-propelled type, have elongated arm and thigh bones.</p>
-
-<p>Textbook illustrations of the plesiosaurs usually depict the necks,
-like those of the swans, freely curved, and a popular scientific
-article in one of our chief magazines a few years ago depicted one
-of them with the neck coiled like the body of a snake. One noted
-paleontologist, indeed, not many years ago described the plesiosaurs as
-resting on the bottom in shallow waters with the neck uplifted above
-the surface viewing the waterscape! And when we consider the fact that
-some species of the elasmosaurs had a neck not less than twenty feet in
-length, such a flexible use of it would not seem improbable. But the
-plesiosaurs did not and could not use the neck in such ways. They swam
-with the neck and head, however long, directed in front, and freedom
-of movement was restricted almost wholly to the anterior part. The
-posterior part of the neck was thick and heavy, and could not have been
-moved upward or downward to any considerable extent and not very much
-<span class="pagenum" id="Page_92">[Pg 92]</span>
-laterally. From all of which it seems evident that the plesiosaurs
-caught their prey by downward and lateral motions of their neck, rather
-than by quick swimming.</p>
-
-<div id="FIG_43" class="figcenter">
-  <img  src="images/fig43.jpg" alt="" width="450" height="514" />
-  <p class="center space-below2">
-     <span class="smcap">Fig. 43.</span>—Gastroliths and bones of an
-     undetermined plesiosaur from the Lower Cretaceous of Kansas.</p>
-</div>
-
-<p>About thirty years ago, the late Professor Seeley, a well-known English
-paleontologist who devoted much attention to the study of these
-reptiles, found with the remains of a medium-sized plesiosaur nearly a
-<span class="pagenum" id="Page_93">[Pg 93]</span>
-peck of smoothly polished, rounded, and siliceous pebbles. He believed
-that their occurrence with the skeleton was not accidental, but that
-they had been intentionally swallowed by the animal when alive, and
-formed at its death a part of its stomach contents. Even earlier than
-this the same habit had been noticed. Nearly at the same time that
-Seeley mentioned the peculiar discovery he had made the present writer
-found several specimens of plesiosaurs in the chalk of western Kansas
-with which similar pebbles were associated, an account of which was
-given soon afterward by the late Professor Mudge. Since then numerous
-like discoveries have made it certain that the plesiosaurs usually,
-if not always, swallowed such pebbles in considerable quantities, for
-what purpose we do not yet feel sure; one can only hazard a guess. The
-small size of the pebbles, or gastroliths, as they have been called,
-a half-inch or less in diameter, found with skeletons of large size,
-indicate much more complete digestion of the hard parts of their food
-than is the case with many other reptiles; no solid substance of size
-could have passed out of the plesiosaur stomach, and such is the case
-with the modern crocodiles, which have a like habit of swallowing
-pebbles. That the plesiosaurs picked up these siliceous pebbles,
-sometimes weighing a half-pound, accidentally with their food is highly
-improbable; they surely had something to do with their food habits. It
-is not at all unreasonable to suppose that the plesiosaurs, because of
-their comparative sluggishness, fed upon anything of an animal nature,
-whether living or dead, which came in their way; that carrion, squids,
-crustaceans, and fishes were all equally acceptable; they were probably
-largely scavengers of the old oceans. Barnum Brown found among the
-stomach contents of a plesiosaur fragments of fish and pterodactyl
-bones, and cephalopod shells. Gallinaceous birds, most of which have
-the same pebble-swallowing habit, have a thick-walled muscular stomach
-or gizzard, in which the pebbles serve as an aid in the trituration of
-food. Modern crocodiles, with the same pebble-swallowing habit, have a
-thick-walled muscular stomach, gizzard-like, though of course not as
-large as in birds; and the same habit has been noted by Des Longchamps
-in the ancient teleosaur crocodiles.</p>
-
-<p>It is hardly possible yet to decide whether or not the plesiosaurs were
-<span class="pagenum" id="Page_94">[Pg 94]</span>
-denizens of the open oceans for the most part, far from land. That many
-of them were rovers is quite certain. With the skeleton of a large
-plesiosaur found some years ago in western Kansas, there were many
-siliceous pebbles which could have come only from the shores of the
-old Cretaceous seas about the Black Hills, hundreds of miles distant.
-Some of the pebbles are red quartzite, quite identical with that of
-the bowlders brought to Kansas millions of years later by the glacial
-drift from outcroppings near the northern line of Iowa. The bones of
-plesiosaurs are often found in deposits believed to be of deep-water
-origin. But they are also found in Kansas associated with the remains
-of small turtles, flying reptiles, and birds which could only have
-lived near the shores. Indeed, their remains have often been found with
-those of strictly fresh-water animals which had been brought down by the
-floods to the seas. Their wide but rather sparse distribution in all
-kinds of marine sediments would rather indicate that they were at home
-far out in the tempestuous ocean or near the shores in protected bays,
-though probably they preferred the shallow water littoral regions. One
-conclusion is quite justified: they were not gregarious, as were the
-ichthyosaurs.</p>
-
-<p>It is not certain that the plesiosaurs were viviparous, though there
-are good reasons for the belief that they were. Remains of two embryos
-were found years ago in England associated in such a way that it is
-reasonable to suppose they were unhatched young, though embryos have
-never yet been found associated with skeletons of adults, as have those
-of ichthyosaurs in numerous instances. Bones of young, often quite
-young, plesiosaurs, are frequently found in shallow water deposits, and
-if the young were actually born alive they must have swum freely in the
-open waters while yet of very tender age. Rather singularly, however,
-the remains of these young plesiosaurs always occur as isolated bones.</p>
-
-<p>In geological range the plesiosaurs were very persistent, extending
-through nearly all the Mesozoic. They began their career as fully
-evolved plesiosaurs, so far as we now know, near the close of the
-Triassic period, and reached their culmination in the Upper Cretaceous,
-but survived to the close of that period. In the beginning of their
-career they were associated with the marine crocodiles and the
-ichthyosaurs, but outlived them to find companions and probably enemies
-<span class="pagenum" id="Page_95">[Pg 95]</span>
-in the huge and voracious mosasaurs of the later Cretaceous times. At
-no time do they appear to have been especially numerous, nor does it
-seem probable that they were ever a dominant type of marine vertebrate
-life, though their remains occur everywhere that marine deposits of
-the Jura and Cretaceous are known. Indeed, it may be said with almost
-certainty that rocks of these ages and of that character everywhere in
-the world contain fossil plesiosaurs. Their bones have been made known
-from Europe, Asia, Africa, Australia, and North and South America.
-From North America thirty or more species have been described from
-New Jersey, Alabama, Mississippi, Texas, Arkansas, Kansas, Nebraska,
-Colorado, New Mexico, Wyoming, North and South Dakota, California, etc.</p>
-
-<p>The cause of their final extinction no one knows, nor can we
-conjecture much about it with assurance. That climatic conditions
-became unfavorable for them is highly improbable, considering
-their cosmopolitan habits; they were not discriminating in their
-environments. After successfully withstanding their fiercest foes, the
-ichthyosaurs, crocodiles, and mosasaurs, and large carnivorous fishes,
-it does not seem probable that they would succumb to lesser enemies,
-though it may be that they were finally attacked successfully, not
-in the fulness of their strength as adults, but while young, by more
-insidious enemies. More probably after their long life of millions of
-years they had grown old, as everything grows old, and had become so
-fixed and unplastic in their structure and habits that even slight
-causes were at last their undoing. When we shall have bridged over
-that still imperfectly known transition period between the great Age
-of Reptiles and the greater Age of Mammals we shall have learned
-more definitely some of the causes of the extraordinary revolution
-in vertebrate life that then occurred. The plesiosaurs went out
-with nearly all of their kind, the mosasaurs, the pterodactyls, the
-dinosaurs; and, so far as we now know, their places in the sea, land,
-and air were not immediately taken by any other creatures.
-<span class="pagenum" id="Page_96">[Pg 96]</span></p>
-
-<div id="FIG_44" class="figcenter">
-  <img  src="images/fig44.jpg" alt="" width="600" height="403" />
-  <p class="center space-below2">
-   <span class="smcap">Fig. 44.</span>—<i>Nothosaurus</i>;<br /> restoration after
-   E. Fraas;<br /> landscape by Dorothy Williston.</p>
-</div>
-
-<p><span class="pagenum" id="Page_97">[Pg 97]</span></p>
-
-<h3>NOTHOSAURIA</h3>
-
-<p>A few years after the discovery of the plesiosaurs by Conybeare, the
-remains of animals of allied kinds were found in the Triassic rocks of
-Bavaria. At first they were supposed to be those of true plesiosaurs,
-and even the astute Cuvier was not very clear about them. Cuvier was
-the first to call attention to them, expressing the opinion that
-some of the fossils were of previously unknown animals allied to the
-crocodiles, lizards, and plesiosaurs. It was von Meyer, however, who
-first introduced a nothosaur to the scientific world under the name
-<i>Conchiosaurus</i>. A year later Count George of Münster described
-other forms under the name <i>Nothosaurus</i>, meaning “false lizard.”
-Count von Münster was a most zealous collector of the fossils of the
-Triassic deposits of Bavaria, amassing, after thirty years of active
-and enthusiastic labor, a very large amount of material, which, at
-his death, was purchased by the King of Bavaria and placed in the
-hands of von Meyer for study. Von Meyer was to Germany what Owen was
-to England, a man of deep learning, having an extensive knowledge of
-comparative anatomy, and being thorough and critical in his work. His
-descriptions and illustrations of these rich collections made by von
-Münster are masterpieces of scientific thoroughness. He recognized in
-<i>Nothosaurus</i> and other allied forms from the Bavarian Triassic
-a distinct group of semiaquatic reptiles allied to the plesiosaurs,
-and his conclusions have never been gainsaid. In more recent years
-additional remains of these animals from Bavaria and other places in
-Europe have been described, but none are known from other parts of the
-earth, or from other than Triassic rocks. Altogether about ten genera
-and about twice as many species have been described, probably all
-belonging in one family, and all by common consent now classified with
-the Sauropterygia.</p>
-
-<div id="FIG_45" class="figcenter">
-  <img  src="images/fig45.jpg" alt="" width="600" height="200" />
-  <p class="center space-below2">
-<span class="smcap">Fig. 45.</span>—Head and neck of <i>Nothosaurus</i>;<br />
-photograph of specimen in the Senckenberg Museum,<br /> from Dr. Dreverman.</p>
-</div>
-
-<p><span class="pagenum" id="Page_98">[Pg 98]</span></p>
-
-<div class="figcontainer">
-  <div class="figsub">
-   <img id="FIG_46" src="images/fig46.jpg" alt="" width="300" height="257" />
-   <p class="center"><span class="smcap">Fig. 46.</span>—Pectoral
-      girdle<br /> of <i>Nothosaurus</i>, from<br /> photograph by E. Fraas:<br />
-       <i>icl</i>, interclavicle; <i>cl</i>, clavicle;<br /> <i>sc</i>,
-      scapula; <i>cor</i>, coracoid.</p>
-  </div>
-  <div class="figsub">
-    <p class="space-below2">&nbsp;</p>
-    <img id="FIG_47" src="images/fig47.jpg" alt="" width="200" height="133" />
-   <p class="center"><span class="smcap">Fig. 47.</span>—Pelvic bones of<br />
-      <i>Nothosaurus</i>: <i>il</i>, ilium;<br />
-      <i>ac</i>, acetabulum; <i>p</i>, pubis;<br />
-      <i>is</i>, ischium.<br /> (After Andrews.)</p>
-   </div>
-</div>
-
-<p>The Nothosauria were much smaller reptiles than the plesiosaurs, none
-of them perhaps exceeding the size of the smallest known plesiosaurs.
-They were semiaquatic in habit, with many curious resemblances to
-other semiaquatic reptiles of a later time known, as the dolichosaurs.
-The neck is more or less elongated, having about twenty vertebrae in
-the longest-necked forms; the body is moderately long, and broad,
-and the tail is relatively short. The vertebrae and ribs are quite
-like those of the plesiosaurs, that is, the vertebrae are gently
-concave at each end, and the dorsal ribs are attached by a single
-head to the transverse process high up on the arch; the cervical ribs
-are double-headed, precisely like those of the older plesiosaurs,
-one of the characters which insistently proves the relationships of
-the two groups. The bones of the shoulders (<a href="#FIG_46">Fig. 46</a>) also
-have many resemblances to the extraordinary ones of the plesiosaurs, though
-they are much less specialized. There was no sternum; the coracoids
-are large, though very much smaller than those of the plesiosaurs.
-The collar-bones are large and strong, joining each other in front of
-the coracoids and firmly united with the shoulder-blades at the outer
-extremity. Four vertebrae are united to form a sacrum, and their union
-<span class="pagenum" id="Page_99">[Pg 99]</span>
-with the hip bones (<a href="#FIG_47">Fig. 47</a>) was much firmer than was the
-case with the plesiosaurs. The limbs are elongated, but it will be observed in the
-figures (<a href="#FIG_48">Fig. 48</a>) that the radius and ulna, tibia and fibula,
-that is, the bones of the forearm and of the leg proper, are relatively very
-short as compared with the humerus and femur, a sure indication of
-the beginning of aquatic habits. The toes and fingers were doubtless
-webbed, and there was no increase in the numbers of bones in the
-digits, so conspicuous in the plesiosaurs. The external nostrils
-are large, but are not situated so far back near the eyes as in
-the plesiosaurs. There is a large pineal opening in the top of the
-skull, as in the plesiosaurs, but no sclerotic or bony plates have
-been observed in the eyes. They had ventral ribs like those of the
-plesiosaurs.</p>
-
-<div id="FIG_48" class="figcenter">
-  <img  src="images/fig48.jpg" alt="" width="600" height="340" />
-  <p class="blockquot space-below2">
-   <span class="smcap">Fig. 48.</span>—Legs of <i>Lariosaurus balsami</i>,
-   an Upper Triassic nothosaur: <i>h</i>, humerus; <i>r</i>, radius;
-   <i>u</i>, ulna; <i>i</i>, intermedium; <i>ue</i>, ulnare; <i>f</i>,
-   femur; <i>fi</i>, fibula; <i>t</i>, tibia; <i>a</i>, astragalus;
-   <i>c</i>, calcaneum. (After Abel.)</p>
-</div>
-
-<p>No impressions of scales or bony plates have ever been found with the
-remains of the nothosaurs, and it is the belief that the skin was
-bare. A good idea of their general appearance will be gained from the
-accompanying restoration adapted from that of Professor Fraas (<a href="#FIG_44">Fig. 44</a>)
-and the restoration of the less highly specialized <i>Lariosaurus</i>,
-made from a very complete skeleton in the Frankfort museum (<a href="#FIG_49">Fig. 49</a>).</p>
-
-<p>It has been thought that these nothosaurs, so intermediate in
-structure between the true plesiosaurs and land reptiles, were the
-actual ancestors, but this is rather doubtful. It is probable that
-they were only very closely akin to the real ancestors, since in some
-ways they had become specialized too much, and, as we have already
-explained, highly specialized characters or organs can never go back to
-their earlier condition. The nothosaurs do prove beyond all possibility
-of doubt that the plesiosaurs were at least the descendants of animals
-closely allied to them, so closely, indeed, that it is doubtful whether
-we could distinguish external differences were all of them actually
-living at the present time.
-<span class="pagenum" id="Page_100">[Pg 100]</span></p>
-
-<div id="FIG_49" class="figcenter">
-  <img  src="images/fig49.jpg" alt="" width="600" height="242" />
-  <p class="center space-below2">
-   <span class="smcap">Fig. 49.</span>—<i>Lariosaurus balsami</i>.</p>
-</div>
-
-<p><span class="pagenum" id="Page_101">[Pg 101]</span>
-We have repeatedly seen that all aquatic animals have some or all the
-bones of the limbs shortened, and it is of interest to observe that the
-early plesiosaurs had longer forearm and foreleg bones than the later
-ones, just as we have seen was the case with the early ichthyosaurs.
-It would seem probable that all the early plesiosaurs had long necks,
-though some of the late ones in Cretaceous times had relatively short
-necks, shorter even than the known nothosaurs possessed.</p>
-
-<p>The nothosaurs doubtless lived about the shores of the ancient seas,
-spending much of their time in the water, leaving it perhaps when hard
-pressed by their enemies, as do some modern reptiles, or to rear their
-young. The teeth of the nothosaurs are long and slender in front,
-shorter behind. The animals must therefore have been carnivorous in
-habit, feeding probably upon such fishes as they could catch, and the
-various invertebrates which live in shallow water. The structure of the
-jaws and their attachments are quite as in the plesiosaurs, proving
-that they could not have swallowed large objects; but the skull is
-broader and flatter than that of most plesiosaurs, indicating habits
-not unlike those of the modern alligators and crocodiles.</p>
-
-<p>Some time we shall doubtless find remains of nothosaurs or nearly
-allied animals elsewhere than in Europe, but probably not from later
-deposits than the Triassic. So far as we now know, their geological
-range and geographical distribution were much restricted; they
-evidently wholly died out shortly after the plesiosaurs appeared.</p>
-<hr class="chap x-ebookmaker-drop" />
-
-<div class="chapter">
-<p><span class="pagenum" id="Page_102">[Pg 102]</span></p>
-<h2 class="nobreak" id="CHAPTER_VII">CHAPTER VII<br />
-<span class="h_subtitle">&nbsp;<br />ANOMODONTIA</span></h2>
-</div>
-
-<p class="f120"><b>LYSTROSAURUS</b></p>
-
-<p>Over a large area of South Africa, chiefly along the Orange River and
-its tributaries, there is an extensive series of deposits many hundreds
-of feet in thickness, usually called the Karoo beds, which, for more
-than fifty years, have been widely famous among scientific men for
-the many and remarkable vertebrate fossils which they have yielded.
-These deposits seem to represent the whole of the vast interval of
-time from the Carboniferous to the Jurassic, that is, the whole of
-the Permian and Triassic, though not many fossils have been found
-in the lowermost strata. Among the fossils of the lower strata are
-those of the strange creatures described in the following pages as
-<i>Mesosaurus</i>. From the deposits representing the Upper Permian
-and the Triassic the fossils that have been obtained are both abundant
-and diverse. Unfortunately, however, of the scores of forms that have
-been discovered few are known completely, and still fewer are known
-sufficiently well to enable us to picture the living animals.</p>
-
-<p>From the Upper Permian Karoo rocks two orders of reptiles have been
-recognized, the Cotylosauria, represented by more specialized forms
-than those from the Lower Permian of North America; and the order or
-group called by Broom the Therapsida. While the forms of this latter
-group have certain definite structural relationships with each other,
-they show so great a diversity among themselves that, when they shall
-be better known, it will be found necessary perhaps to separate them
-into several distinct orders.</p>
-
-<p>At least five groups of the Therapsida are now recognized by Broom,
-the Dromasauria, Dinocephalia, Anomodontia, Therocephalia, and
-Theriodontia. Of all these the members of the last-mentioned group have
-<span class="pagenum" id="Page_103">[Pg 103]</span>
-attracted the greatest interest among geologists and naturalists,
-because of their intimate relationships to the mammals—so intimate,
-indeed, that they seem almost to bridge over the interval between the
-two classes. From higher Karoo beds primitive representatives of the
-more crocodilian types have been discovered, forms which seem to be the
-beginning of that order described on later pages as the Parasuchia.</p>
-
-<p>It would lead us too far astray to mention even, let alone describe,
-the many forms of reptiles that have been discovered in the Karoo beds;
-nor indeed is it possible for anyone who has not attentively studied
-their remains to get a very clear conception of many of them, so
-incompletely have they been made known.</p>
-
-<p>Doubtless from among all these diverse forms there have been not a few
-which sought wider opportunities in the water, but, if so, we have
-as yet very little knowledge of them. One form only, so far as the
-writer is aware, has been credited with aquatic habits, a remarkable
-reptile belonging to the group originally called by Sir Richard Owen,
-the Anomodontia, a word meaning “lawless teeth,” and to the genus
-<i>Lystrosaurus</i>, also described by the same noted paleontologist.
-A restoration of the skeleton of <i>Lystrosaurus</i> has recently
-been published by Watson. This restoration the writer has reproduced
-in the present pages, though he has taken the liberty of making some
-minor changes, to accord better with what he believes must have been
-the position of the shoulder-blades and the hind legs. And he would
-also suggest that the tail in life did not turn down so much at its
-extremity as depicted by Watson.</p>
-
-<p>Both Broom and Watson believe that this animal was a powerful swimmer,
-and thoroughly aquatic in habit. To the present writer, however, this
-does not seem so evident. He is rather inclined to believe that the
-creature was chiefly terrestrial in habit, living probably in marshy
-regions, and perhaps seeking its food in shallow waters and in the mud.
-Aside from the position of the nostrils, which it will be observed are
-rather close to the eyes, a position so characteristic of many swimming
-reptiles and mammals, there is but little indication of aquatic
-adaptations elsewhere in the skeleton.
-<span class="pagenum" id="Page_104">[Pg 104]</span></p>
-
-<div id="FIG_50" class="figcenter">
-  <img  src="images/fig50.jpg" alt="" width="600" height="298" />
-  <p class="center space-below2">
-    <span class="smcap">Fig. 50.</span>—Skeleton of <i>Lystrosaurus</i>,<br />
-    as restored by Watson, slightly modified.</p>
-</div>
-
-<p><span class="pagenum" id="Page_105">[Pg 105]</span>
-The skull is of most extraordinary form. The face is turned downward,
-leaving the nostrils high up, in front of the eyes. The jaws were
-doubtless covered with a horny shield, like that of the turtles, having
-a cutting edge. There is a single pair of elongated canine teeth,
-possibly a sexual character. The lower jaws are heavy and stout, and
-Watson has said that the animal doubtless had the ability to open its
-mouth very widely. The quadrate, the bone with which the lower jaws
-articulate, is firmly fixed to the skull, and there is a single opening
-on the side of the skull posteriorly, a character common to all the Therapsida.</p>
-
-<p>The vertebrae are stout, and they have stout spines. The tail is
-remarkably short, stout, and stumpy; it could have been of no use
-whatever in the water for propulsion or even for steering. The front
-legs are short and stout; the forearm bones are short, suggesting
-either swimming or digging habits, and the foot is short and broad.
-The pelvis or hip bones are massive and were very firmly connected
-with the backbone by the aid of six vertebrae, a very unusual number
-in reptiles. The hind legs, as figured, show no indications whatever
-of aquatic adaptation, unless possibly the very slight shortening of
-the shin may be so construed. Watson believes that the bones of the
-pelvis, indicate, aside from its strong union with the backbones,
-strong swimming powers, but of this again the present writer is very
-skeptical. The very strong ischia and the flatness of the pelvis are
-both characters found among American Permian reptiles, which do not
-show otherwise the slightest indications of water habits.</p>
-
-<p>If then <i>Lystrosaurus</i> was a powerful swimmer, as has been
-maintained, it is very evident that the hind legs must have been used
-as the seals or sea-otters use them, to propel and to guide; but
-they in nowise resemble the legs of these swimming mammals. It seems
-altogether more reasonable to suppose that <i>Lystrosaurus</i> lived in
-the marshes, feeding upon vegetable food obtained by aid of its strong
-jaws and tusks—if the tusks were possessed by both sexes; and that the
-position of the nostrils may be ascribed to causes like those which
-brought about their recession in the Phytosauria, and not to strictly
-aquatic habits. Possibly the animal had habits somewhat similar to
-<span class="pagenum" id="Page_106">[Pg 106]</span>
-those of the hippopotamus; that it was an expert swimmer appears,
-to the present writer, improbable. The powerful front legs may be
-indicative of digging habits; the animal may have used them as an aid
-to its powerful jaws and tusks in uprooting marsh and water plants.
-However, <i>Lystrosaurus</i>, whatever may have been its habits, was a
-curious reptile. It was about three feet in length, massive in all its
-structure, and doubtless of slow and sluggish gait.</p>
-<hr class="chap x-ebookmaker-drop" />
-
-<div class="chapter">
-<p><span class="pagenum" id="Page_107">[Pg 107]</span></p>
-<h2 class="nobreak" id="CHAPTER_VIII">CHAPTER VIII<br />
-<span class="h_subtitle">&nbsp;<br />ICHTHYOSAURIA</span></h2>
-</div>
-
-<p>Early in the eighteenth century a curious work in the Latin language
-was published by a famous physician and naturalist—a professor in the
-University of Altorf by the name of Scheuchzer—entitled <i>Querulae
-Piscium</i>, or “Complaints of the Fishes.” The work was illustrated by
-many expensively engraved figures of various fossil remains, including
-one of some vertebrae which the author referred to as “the accursed
-race destroyed by the flood”! The history of the finding of these
-famous bones is recorded by Cuvier as follows:</p>
-
-<p class="blockquot">Scheuchzer, while walking one day with his friend
-Langhans in the vicinity of Altorf, a village and university of
-Nuremburg, went to the vicinity of the gallows to make some researches.
-Langhans, who had entered the inclosure of the gallows, found a piece
-of limestone containing eight dorsal vertebrae, of a black color
-and shining. Seized, says Scheuchzer, with a panic terror, Langhans
-threw the fragment of limestone beyond the wall of the inclosure, and
-Scheuchzer, picking it up, preserved two of the vertebrae which he
-believed to be human, and which he figured in his book, <i>Piscium Querulae</i>.</p>
-
-<p>About the same time another observer by the name of Baier discovered
-other and similar vertebrae in the vicinity of Altorf which he
-described and figured as those of a fish; and there was much earnest
-contention between Scheuchzer and Baier, as also between their friends,
-as to their supposed nature. Scheuchzer’s figure was often cited as
-indubitable evidence of the destruction of mankind by a universal
-flood, and it was not until nearly a century later that Cuvier showed
-that the bones were really those of a marine reptile.
-<span class="pagenum" id="Page_108">[Pg 108]</span></p>
-
-<div id="FIG_51" class="figcenter">
-  <img  src="images/fig51.jpg" alt="" width="400" height="499" />
-  <p class="center space-below2">
-    <span class="smcap">Fig. 51.</span>—Restoration of <i>Ichthyosaurus</i><br />
-    with young, by Charles R. Knight.<br /> (By permission of the<br /> American Museum
-    of Natural History.)</p>
-</div>
-
-<p>It must be recollected, in extenuation of so extraordinary a blunder
-on the part of so learned a man as was Scheuchzer, who, as a physician
-and professor, one would think ought to have been able to distinguish
-between vertebrae so different as are those of an ichthyosaur and a
-man, that, during all of the eighteenth century and well into the
-nineteenth, the belief was prevalent that all fossils were the relics
-of animals and plants that had perished in the great biblical flood.
-The science of geology was yet in its infancy, and there was no known
-record, other than the biblical one, of any great inundation of the
-<span class="pagenum" id="Page_109">[Pg 109]</span>
-earth’s surface which might account for the remains of sea-animals
-in rocks remote from the seas. This belief, so long held by even
-the wisest and most learned of scholars, so long welcomed by the
-theologians as proof of the literal accuracy of the Bible, was one of
-which Scheuchzer was quite convinced. His <i>Piscium Querulae</i> was
-largely a fantastic discussion of the supposed great world-catastrophe,
-the Noachian Deluge, by which the fishes had been destroyed and long
-imprisoned in the rocks through no sin of their own.</p>
-
-<p>It was the same author who, in a subsequent work, described and figured
-the fossil skeleton of a large salamander which he believed to be that
-of a child destroyed in the flood, and which he called “Homo diluvii
-testis.” In this specimen, which was discovered in the Tertiary rocks
-of Oeningen, and which is still preserved among the historically
-as well as scientifically famous fossils of the museum at Haarlem
-under the name <i>Andrias Scheuchzeri</i>, Scheuchzer thought that
-he detected, not only the skeleton of a child, but even its brain,
-liver, muscles, etc.! His engraving of this “Witness of the Flood,” the
-“sorrowful skeleton of an old sinner drowned in the Flood,” as also
-that of the ichthyosaur vertebrae of Altorf, were afterward printed in
-the famous “Copper Bible” as positive proof of the literal accuracy of
-the biblical record.</p>
-
-<p>Earlier than the publication of these figures by Baier and Scheuchzer,
-at the very close of the seventeenth century, a Welsh naturalist
-by the name of Lluyd, in a large and beautifully illustrated work,
-figured—perhaps for the first time—remains of ichthyosaurs, which he
-believed to be those of fishes. But Lluyd accounted for these and all
-other fossil remains by a very different theory from that of Scheuchzer
-and the theologians—a theory which at one time had many adherents
-among scholars. He believed that the spawn of fishes or the eggs of
-other creatures had been carried up from the seas and lands in moist
-vapors into the clouds, whence they had descended in rain, penetrating
-the earth to give origin to the fossils; in other words, he believed
-that all fossils grew in the earth from germs of the living animals
-that inhabited the land and seas. Certainly the old philosophers were
-hard driven to make facts agree with theories!
-<span class="pagenum" id="Page_110">[Pg 110]</span></p>
-
-<p>Remains of ichthyosaurs, abundant as they were and are in many deposits
-in England and Germany, attracted very little attention from the
-naturalists of the eighteenth century after the time of Scheuchzer and
-Baier, and nothing more was written about them until 1814, when Sir
-Everard Home, an English comparative anatomist, in an extensive series
-of large and finely illustrated, though rather discursive, works,
-described and figured a number of good specimens. To the animal the
-remains of which he rather vaguely and imperfectly described, he gave
-in 1819 the name <i>Proteosaurus</i>, in the belief that it was allied
-to the living <i>Proteus</i>, a salamander.</p>
-
-<p>In 1821 the curator of mineralogy of the British Museum—Koenig by
-name—after a more critical study of other remains, reached the
-conclusion that these animals were intermediate between the fishes and
-the reptiles, and gave to them the generic name <i>Ichthyosaurus</i>,
-meaning fish-reptile, a name by which the chief forms have ever since
-been known. Within the next few years many specimens of ichthyosaurs
-were carefully and fully described by Conybeare, Cuvier, Owen, and
-others of England, France, and Germany, making very clear all the
-more important details of their skeletal structure. Blaineville, in
-1835, thought that the ichthyosaurs constituted a distinct class of
-vertebrates equivalent to all other reptiles, the birds, and the
-mammals, which he called Ichthyosauria, the first appearance in
-literature of the name by which the order is properly known. Five years
-later, however, the famous English anatomist and paleontologist, the
-late Sir Richard Owen, united the ichthyosaurs with the plesiosaurs as
-a single order of reptiles, to which he gave the name Enaliosauria,
-meaning sea-reptiles, a name which has long been current in textbooks
-and general works on natural history. Moreover, Owen rather arbitrarily
-changed Blaineville’s name Ichthyosauria to Ichthyopterygia, a name
-which is often, though incorrectly, used to designate this order of
-reptiles. These briefly given and perhaps dry details will make clear
-how necessary is that rule of priority upon which naturalists so often
-insist. When anyone may change the names of organisms at will there
-will be no stability and no uniformity, because there is no one to
-<span class="pagenum" id="Page_111">[Pg 111]</span>
-decide, and the prestige of a great name, like that of Owen, will carry
-authority till someone else with greater authority appears. Whether or
-not the name <i>Proteosaurus</i>, first given to any member of this
-order, should take precedence over the later <i>Ichthyosaurus</i>
-is still in doubt, since Home gave no specific name to his species,
-and the very particular purists of modern times have decided that a
-genus is not named unless the species is also! We moderns sometimes
-are inclined to impose very stringent conditions upon the older
-naturalists; let us hope that we shall be treated more leniently by the
-future naturalists!</p>
-
-<p>It will lead us too far astray to follow in detail the history of
-the further discoveries of the ichthyosaurs during the early part
-of the nineteenth century. It may briefly be said, only, that no
-other group of extinct backboned animals excited more interest among
-scientific men. One incident will suffice. More than sixty years ago,
-an interesting deduction as to the living form of the ichthyosaurs was
-made by Sir Richard Owen. He observed that many of the known skeletons,
-as they were found in their rocky matrix, had a remarkable dislocation
-of the vertebrae at a certain place near the end of the tail, and,
-although such an appendage was quite unknown in other reptiles either
-living or extinct, concluded that the living animals had a terminal,
-horizontal, fleshy fin, very much like that of the whales and
-sirenians. Sure enough, discoveries made forty years later disclosed
-impressions in the rocks, not only of a large caudal fin, but also of
-a dorsal fin, as well as outlines of the flesh-covered paddles. The
-dislocation of the vertebrae at the place where the fleshy fin joined
-the more slender tail was due to the action of currents of water, or
-simple gravitation, upon a thin vertical fin and not, as Owen supposed,
-to the twisting of the terminal part as it fell to a horizontal
-position after partial decomposition of the soft parts.</p>
-
-<p>About twenty-five years ago, Professor E. Fraas, the present director
-of the Stuttgart Museum, described and figured very fully, not only
-specimens showing impressions of the fins and paddles, but also others
-of well-preserved and very complete skeletons of different species of
-ichthyosaurs from the Jurassic deposits of Würtemberg, in which remains
-<span class="pagenum" id="Page_112">[Pg 112]</span>
-of these animals occur in great profusion. His researches, and those of
-several authors since then, supplementing and confirming or disproving
-those of the many observers made during the preceding seventy years,
-have finally determined almost perfectly the complete structure of
-the more typical ichthyosaurs, enabling us to infer not a little as
-to their habits and distribution in the old Jurassic oceans. Within
-the past few years the discoveries of Professor J. C. Merriam of
-California have likewise added greatly to our knowledge of the earlier
-ichthyosaurs. It may now truthfully be said that of no group of extinct
-reptiles do we have a more complete and satisfactory knowledge than of
-the ichthyosaurs.</p>
-
-<div id="FIG_52" class="figcenter">
-  <img  src="images/fig52.jpg" alt="" width="600" height="203" />
-  <p class="center space-below2">
-    <span class="smcap">Fig. 52.</span>—<i>Ichthyosaurus quadricissus.</i><br />
-    Photograph of specimen in Senckenberg museum,<br /> from Dr. Dreverman.</p>
-</div>
-
-<p>Nevertheless we have yet very much more to learn about the order
-Ichthyosauria as a whole—whence they came and how they originated;
-what their nearest kin were among other reptiles; and especially, more
-about the connecting links between them and terrestrial reptiles. They
-have, as an order, so isolated a position, are so widely separated from
-all other reptiles in structure, that they have long been a puzzle to
-paleontologists. Like the whales and other cetaceans among mammals,
-we know the ichthyosaurs well in the plenitude of their power and the
-fulness of their development, but have yet only an imperfect knowledge
-of their earlier history, and none whatever of their earliest. However,
-as will be seen farther on, the recent discoveries by Merriam have
-shed much light on some of the stages of their evolution. So nearly
-perfectly were all the later ichthyosaurs adapted to their life in the
-water that it was believed by nearly all paleontologists until about a
-<span class="pagenum" id="Page_113">[Pg 113]</span>
-score of years ago that they had descended directly from fishes. But
-this belief has been quite abandoned by all, not only because the
-recent discoveries of the earlier ichthyosaurs have demonstrated a
-positive increase in the aquatic adaptations of the later forms, but
-also because a double origin of any type of animal life is quite out of
-accord with all known facts and principles of paleontology. It is quite
-possible for animals, in becoming adapted to peculiar environmental and
-<span class="pagenum" id="Page_114">[Pg 114]</span>
-food conditions, to acquire certain resemblances to other animals,
-but quite impossible for them to acquire their actual structure. The
-ichthyosaurs are true reptiles, and all reptiles must have had a common
-origin.</p>
-
-<div id="FIG_53" class="figcenter">
-  <img  src="images/fig53a.jpg" alt="" width="600" height="215" />
-  <img  src="images/fig53b.jpg" alt="" width="600" height="183" />
-  <img  src="images/fig53c.jpg" alt="" width="600" height="172" />
-  <p class="blockquot space-below2">
-   <span class="smcap">Fig. 53.</span>—<i>Baptanodon (Ophthalmosaurus).</i>
-   Skull from the side, from above, and from below (after Gilmore):
-   <i>ang</i>, angular; <i>bs</i>, basisphenoid; <i>d</i>, dentary;
-   <i>fr</i>, frontal; <i>j</i>, jugal; <i>la</i>, lacrimal; <i>mx</i>,
-   maxilla; <i>na</i>, nasal; <i>oc</i>, occipital condyle; <i>p</i>,
-   palatine; <i>pa</i>, parietal; <i>pm</i>, premaxilla; <i>po</i>,
-   postorbital; <i>ps</i>, parasphenoid; <i>pt</i>, pterygoid; <i>pf</i>,
-   prefrontal; <i>sa</i>, surangular; <i>sp</i>, splenial; <i>sq</i>,
-   squamosal; <i>st</i>, supratemporal; <i>q</i>, quadrate; <i>qj</i>,
-   quadratojugal.</p>
-</div>
-
-<div id="FIG_54" class="figcenter">
-  <img  src="images/fig54.jpg" alt="" width="500" height="462" />
-  <p class="blockquot space-below2">
-   <span class="smcap">Fig. 54.</span>—Occiput of <i>Baptanodon
-   (Ophthalmosaurus)</i>: <i>pa</i>, parietal; <i>soc</i>, supraoccipital;
-   <i>sq</i>, squamosal; <i>exoc</i>, exoccipital; <i>op.o</i>,
-   paroccipital; <i>sta</i>, stapes; <i>st</i>, supratemporal; <i>qu</i>,
-   quadrate; <i>qj</i>, quadratojugal; <i>pt</i>, pterygoid; <i>bs</i>,
-   basisphenoid; <i>sag</i>, surangular; <i>ag</i>, angular; <i>art</i>,
-   articular; <i>pra</i>, prearticular. (After Gilmore.)</p>
-</div>
-
-<p>We are sometimes in doubt, however, as to whether characters resembling
-those of other animals are really acquired as adaptations to peculiar
-environments, that is, parallel, convergent, or homo-plastic
-characters, or whether they are due to heredity from remote ancestors.
-The reptilian characters of the ichthyosaurs, however, are so emphatic
-that they can only be ascribed to heredity. Ichthyosaurs are as truly
-reptilian as crocodiles or snakes, notwithstanding their fish-like form
-and habits. The ichthyosaur ancestors were once truly land reptiles—of
-that we are as sure as we well can be. Some have thought that those
-ancestors were the primitive Rhynchocephalia, but most are now
-convinced that they were among the most primitive of reptiles, a branch
-probably from the cotylosaurs or cotylosaurian ancestors. Probably of
-all the extinct forms that we know the Proganosauria come the nearest;
-indeed it is not impossible that they may have been the actual forbears
-of the ichthyosaurs.</p>
-
-<p>The ichthyosaurs varied in length from two to thirty feet, but the
-different species, especially all the later ones, resembled each other
-pretty closely in shape; the beak was more slender in some than in
-others, and the shapes of the fins and paddles varied not a little, as
-we shall see. The jaws were long and slender, provided with numerous
-rather small but sharp and recurved teeth, especially well fitted for
-<span class="pagenum" id="Page_115">[Pg 115]</span>
-the seizure and retention of slippery prey. The teeth were inserted,
-not in separate sockets, as are those of the crocodiles and many other
-reptiles, but in long, deep grooves, and were easily lost, indeed so
-easily lost that one late American form was originally described as
-edentulous, and it was not till a number of years had elapsed that
-the teeth were found. The nostrils were small, and situated far back
-on the sides of the face, near the eyes. The eyes were very large,
-not only in proportion to the size of the skull, but, in the largest
-species, actually attaining in some, perhaps, the size of a human head.
-The eyeball was surrounded in front by an extraordinarily large and
-strong ring of ossifications in the sclerotic membrane, giving not only
-protection to the eye under the varying pressure of the water, but
-also greater control over vision. The neck was very short, so short,
-in fact, that no construction was visible in the living animal between
-the head and body; it was capable of only slight movement. The trunk
-was elongated and relatively slender, sometimes with more than fifty
-vertebrae in it. The tail also was long and flattened, ending in all
-the later species in a large fleshy fin, resembling the caudal fin of
-many fishes in shape and doubtless also in function. There was also a
-large dorsal fin, supported by hardened or calcified sinews, in shape
-like the dorsal fin of most fishes and many cetaceans. This character
-is absolutely unique among reptiles, so far as is known, and was one of
-the extreme specializations of water life. The hind limbs were smaller,
-often much smaller than the fore ones, and both were quite fin-like in
-life, or rather flipper-like, though not at all fin-like in structure.
-The skin was smooth and bare. In brief, to quote Fraas’s words:.</p>
-
-<p class="blockquot">The general aspect of the ichthyosaurs was very
-dolphin-like. The body was everywhere naked and probably dark in
-color. The head was produced in front into a long, slender snout, and
-was closely joined to the body posteriorly without indications of a
-neck. The body itself was cylindrical, expanded in front by the large
-thorax and abdomen, but rapidly diminishing into the long, slender,
-and strong tail. Close behind the head were the front paddles, which
-in some species were broad and shovel-like, in others elongated and
-pointed. The hind paddles were smaller than the front ones, sometimes
-greatly reduced in size, their function replaced by that of the very
-broad tail.</p>
-
-<p>From the foregoing descriptions and the restoration shown in <a href="#FIG_51">Fig. 51</a>,
-<span class="pagenum" id="Page_116">[Pg 116]</span>
-we see how very fish-like, or rather dolphin-like, these animals were
-in the external form—so fish-like that the name <i>Ichthyosaurus</i>
-is not misleading, though Koenig gave it in the mistaken belief that
-they were really allied to the fishes. When to these external features
-certain other fish-like details of the skeleton are added, we do not
-wonder that the early observers were so long in doubt about them. A
-more careful examination of the skeleton will, however, disclose so
-many truly reptilian characters that their external appearance and
-habits lose all significance.</p>
-
-<p>The vertebrae are deeply biconcave and fish-like, it is true, but a
-consideration of the reasons therefor will convince us that any other
-kind of vertebrae would be more remarkable. At the time when the
-ichthyosaurs must have originated, at the time when the first known
-ichthyosaurs appeared in geological history indeed, all reptiles had
-biconcave vertebrae, and for the most part at least deeply biconcave
-ones. The vertebrae remained fish-like throughout all their history,
-perpetuating their type until most other reptiles had developed a
-firmer one, because such vertebrae were best adapted for the quick,
-pliant movements of the spinal column so necessary for the well-being
-of the animals in the water. In the modern dolphins, animals in shape,
-size, and habits most wonderfully allied to what these old reptiles
-must have been, the small, flat-ended vertebrae are widely separated by
-disks of flexible cartilage.</p>
-
-<p>Not only were their vertebrae fish-like in form, but there are other
-characters in the spinal column of a primitive or generalized nature.
-As in all aquatic animals, the articulating processes between the
-vertebrae are either weak or wanting in the posterior part of the
-column. And they were not only small, but were situated, in many,
-high up, very remarkably resembling the peculiar arrangement of the
-articulations in the dolphins.</p>
-
-<p>There is no sacrum, that is, there were no united vertebrae posteriorly
-for the attachment and support of the pelvis, as no such support was
-needed. In only one other group of aquatic reptiles was the sacrum
-lost, though it has wholly disappeared in the cetaceans and sirenians
-among mammals. The chevron bones of the tail, usually bony arches on
-the under side of the tail for the protection of the blood-vessels, in
-crawling reptiles, were very imperfectly developed in the later forms,
-though normal in shape in the early ones. The ribs are numerous, long,
-<span class="pagenum" id="Page_117">[Pg 117]</span>
-and slender, very much resembling those of the fish-eating dolphins.
-They usually had, however, two attachments to the body of the vertebra
-and none to the arch, differing in this respect from all other animals.</p>
-
-<p>Of the shoulder bones, the scapula or shoulder-blade, as usual among
-water animals, is short and broad. In the place of a sternum the
-coracoids joined each other broadly in the middle, just as they did
-in the oldest known land reptiles. And there were clavicles and an
-interclavicle. Below the abdomen behind were numerous slender bones
-called ventral ribs. The pelvis is very weak, and was suspended
-below the spinal column in the fleshy walls of the abdomen. The hind
-legs were so small that little support was necessary for them, and,
-because they were not used either for the support of the body or for
-propulsion, they did not require a firm union with the skeleton.
-Doubtless had the ichthyosaurs continued to the present time, they
-would have lost entirely the hind legs, as have the cetaceans.</p>
-
-<div id="FIG_55" class="figcenter">
-  <img  src="images/fig55.jpg" alt="" width="600" height="276" />
-  <p class="blockquot space-below2">
-    <span class="smcap">Fig. 55.</span>—Pectoral girdle of <i>Baptanodon
-   (Ophthalmosaurus)</i>, an American Upper Jurassic ichthyosaur. (After Gilmore.)</p>
-</div>
-
-<p>It is in the limbs that most extraordinary differences from all other
-animals are seen. So great are these differences that it has been a
-puzzle to naturalists to understand how they could have arisen. In no
-other animals above the fishes, that is, in no other reptiles, in no
-amphibians, birds, or mammals, are there ever more than five fingers or
-five toes, the number with which air-breathing animals began. Fingers
-and toes may be lost and often are lost in all groups of life, until
-a single one in each limb may remain, as in the domestic horse. An
-increase of fingers and toes, however, seems to be an impossibility in
-<span class="pagenum" id="Page_118">[Pg 118]</span>
-evolution, and doubtless of real fingers and toes it is an equal
-impossibility. All naturalists are now agreed that a specialized
-character can never revert to a generalized condition, or rather to a
-generalized structure, that an organ once functionally lost can never
-be regained by descendants. A character once lost is lost forever;
-horses of the future can never have more than one finger or one toe in
-each limb.</p>
-
-<div class="figcontainer">
-  <div class="figsub">
-   <p class="space-below2">&nbsp;</p>
-   <img id="FIG_56" src="images/fig56.jpg" alt="" width="200" height="359" />
-   <p class="center"><span class="smcap">Fig. 56.</span>—Front paddle<br />
-      of <i>Ophthalmosaurus</i><br /> (after Andrews):<br />
-      <i>h</i>, humerus; <i>r</i>, radius; <i>u</i>,<br />
-       ulna; <i>p</i>, pisiform; <i>re</i>, radiale;<br />
-      <i>int</i>, intermedium; <i>ue</i>, ulnare.</p>
-  </div>
-  <div class="figsub">
-    <p class="space-below2">&nbsp;</p>
-    <img id="FIG_57" src="images/fig57.jpg" alt="" width="125" height="355" />
-   <p class="center"><span class="smcap">
-     Fig. 57.</span>—Front<br />
-     paddle of <i>Merriamia</i>,<br />
-     a Triassic ichthyosaur.<br />
-      (After Merriam.)<br />
-     Explanations as in<br /> Fig. 56.</p>
-   </div>
-</div>
-
-<p>And there was an increase in the ichthyosaurs, in some not only of
-the number of digits in each limb, but in all of the number of bones
-in each digit, a character found also in the unrelated mosasaurs and
-plesiosaurs. This increase in finger and toe bones, or hyperphalangy
-as it is called, is one of the most peculiar of all the adaptations to
-water life, changing the feet and hands from the ordinary walking type
-to the fish-like swimming type. The bones beyond the humerus and femur
-<span class="pagenum" id="Page_119">[Pg 119]</span>
-in the ichthyosaurs were so increased in number and so changed in form
-and relations that they bear little resemblance to the corresponding
-bones of other reptiles. They are merely polygonal platelets of bone,
-articulating on all sides and fitting closely together, permitting
-flexibility, but not much else.</p>
-
-<p>It is now believed that the increase, not only of additional
-digits, sometimes to as many as ten in each hand and foot, but
-of the finger and toe bones as well, was the result of a sort of
-vegetative reproduction. The margins and ends of the flippers were
-doubtless hardened by cartilage or fibrous material, and because of
-the action of the limbs this cartilagenous material broke up into
-nodules each of which took on ossification finally. Among the whales,
-where hyperphalangy also occurs, though to a less extent, it has
-been thought that the increase in number has been due simply to the
-ossification of the parts of each bone normally present, that is, to
-the epiphyses, which became separated from the shaft of each bone. But
-this explanation will hardly suffice for the fingers and toes of the
-plesiosaurs and ichthyosaurs, for there are altogether too many such
-ossifications; and besides, the bones in these animals, as in most
-reptiles, did not have epiphyses, or terminal separate ossifications of
-the bones of the skeleton.</p>
-
-<p>It will be observed from the figures that the arm and thigh bones of
-<i>Ichthyosaurus</i> are very much shortened—a striking adaptation to
-water life, so conspicuously seen in the modern whales and dolphins
-as well as in the mosasaurs, thalattosaurs, etc. So characteristic
-indeed is this shortening that, were every other bone of the skeleton
-of an ichthyosaur unknown save the humerus or femur, it would be quite
-certain from these alone that the animal was thoroughly aquatic in habit.</p>
-
-<p>About sixty years ago a rather aberrant form of ichthyosaur, now known
-as <i>Mixosaurus</i>, was discovered in rocks of Triassic age, that
-is, of much greater age than any ichthyosaurs previously found, in
-which not only the forearm but also the lower leg bones were longer,
-resembling more the corresponding bones of land animals. It was from
-the examination of specimens in 1887 of these mixosaurs that the
-late Professor Baur became convinced that the ichthyosaurs were the
-<span class="pagenum" id="Page_120">[Pg 120]</span>
-descendants of land reptiles, and not directly of the fishes as they
-were universally thought to have been at that time. As Professor Baur
-very pertinently said, if the ichthyosaurs were descended from the
-fishes directly, the earliest forms should be more nearly like the
-fishes than the later ones, whereas just the opposite was the real
-fact. The arguments which he gave in support of his contention were so
-convincing that they found immediate acceptance among all naturalists.
-Fortunately within the past fifteen years many other remains of early
-ichthyosaurs from the Triassic rocks of California have been brought
-to light by Professor Merriam, remains which throw a flood of light
-upon the early, though not the earliest, history of these strange
-reptiles. He has recognized among the forms he has discovered, not
-only new species, but several new genera, and perhaps new families
-of ichthyosaurs. His studies have demonstrated so well the stages of
-evolution between the early ichthyosaurs and the later ones in their
-progressive adaptation to water life that it will be of interest to
-summarize them here.</p>
-
-<p>In the early ichthyosaurs locomotion was largely by the aid of the
-limbs; in the later ones almost exclusively by the aid of the caudal
-fin. In the former the paddles were larger and the bones longer, more
-like those of land animals; in the latter they were relatively smaller
-and shorter, and more fin-like. In the digits of the early forms the
-finger and toe bones were more elongated and fewer in number. The hind
-limbs were nearly as large as the front ones in the Triassic, often
-very much smaller in the later ichthyosaurs; and the increased number
-of digits occurs only in the later forms.</p>
-
-<p>In the Triassic ichthyosaurs, all classed in the family Mixosauridae,
-the pelvis was larger and more firmly connected with the body than in
-the later forms.</p>
-
-<p>The skull of the early forms was relatively shorter, as compared with
-the trunk, the jaws shorter as compared with the head, the eyes were
-relatively small, the teeth in some less numerous, and set in distinct
-sockets like those of land reptiles; the vertebrae were relatively
-longer and less fish-like, and their articulations more like those of
-land reptiles.</p>
-
-<p>The distal part of the tail was not bent downward so sharply, that is,
-<span class="pagenum" id="Page_121">[Pg 121]</span>
-the terminal fin was smaller, or the tail may have been simply
-flattened near its end and not really fin-like. The scapula was longer
-and less fan-like in shape.</p>
-
-<p>And all these are remarkable evidences of an increased adaptation
-to water life in the more recent ichthyosaurs over the older ones.
-Were someone now so fortunate as to find ichthyosaurs in late Permian
-rocks, we should doubtless have the nearly complete chain between the
-most highly specialized type of water reptiles and their terrestrial
-ancestors.</p>
-
-<div id="FIG_58" class="figcenter">
-  <img  src="images/fig58.jpg" alt="" width="600" height="292" />
-  <p class="blockquot space-below2">
-    <span class="smcap">Fig. 58.</span>—Caudal fin of <i>Ichthyosaurus</i>,
-    after Baur (left figure); caudal fin of <i>Mixosaurus</i>, after Wiman
-    (right figure).</p>
-</div>
-
-<p>From the structure of the skeleton alone the early observers were
-justified in inferring much concerning the shape and habits of the
-living ichthyosaurs. Later discoveries have added so many definite
-facts that, at the present time, we know more about their habits
-than we do of any other extinct reptiles. In various places in
-England and Germany, especially in Würtemberg, the remains of
-ichthyosaurs are found in extraordinary abundance and perfection, not
-only whole skeletons lying in the positions which they had assumed
-after the decomposition of their bodies, but also often the actual
-remains, carbonized, of the skin, muscles, and ligaments, as well as
-delicate impressions of external parts. Many of these skeletons are
-obtained from the numerous stone quarries, where they are a sort of
-“by-product,” the sums received for them adding not a little to the
-income of the quarrymen. So many are obtained in this and other ways
-<span class="pagenum" id="Page_122">[Pg 122]</span>
-that specimens of ichthyosaurs are perhaps more frequently seen in the
-museums of the world than those of any other extinct backboned animal.
-Fairly complete skeletons may now be purchased of dealers in such
-things for from fifty to seventy-five dollars. As may be supposed, the
-best and most complete collections of these fossil remains are those of
-the British Museum in London and the museum in Stuttgart. From a study
-of those of the last-mentioned museum Professor Fraas has learned many
-interesting facts and reached many interesting conclusions regarding
-the life-habits of the ichthyosaurs. In the accompanying figure (<a href="#FIG_59">Fig. 59</a>)
-is shown a photographic reproduction of a very complete specimen,
-in which not only is the outline of the whole body shown, but also much
-of the carbonized remains of the muscles and skin has been detected.</p>
-
-<div id="FIG_59" class="figcenter">
-  <img  src="images/fig59.jpg" alt="" width="600" height="182" />
-  <p class="blockquot space-below2">
-    <span class="smcap">Fig. 59.</span>—<i>Ichthyosaurus quadricissus.</i>
-    (From a photograph from B. Hauff, Paleontologisches Atelier, Holzmaden.)</p>
-</div>
-
-<p>The attachment of the paddles to the body was broad antero-posteriorly,
-proving conclusively that they could not have been much used in
-propulsion, either in the water or upon land, since such use would
-require a fore-and-aft movement, and a consequent twisting or rotation
-of the whole arm or leg, which, because of the broad attachment, must
-have been very difficult, if not impossible.</p>
-
-<p>Microscopic examination of the remains of skin preserved disclosed
-an abundance of dark pigment, indicating, Professor Fraas believes,
-that the skin was dark colored above. Doubtless, also, the under
-side, as in nearly all swimming animals of the present time, was of a
-lighter color, because such coloration rendered the animals much less
-conspicuous in the water when seen either from above or below. That the
-<span class="pagenum" id="Page_123">[Pg 123]</span>
-skin was bare is proved by many impressions or molds of it that have
-been discovered in the rocks, in which many fine creases are seen,
-but nothing suggesting scales or bony plates, save on the front edge
-of the paddles, where impressions of overlapping scales have been
-observed. This is an interesting fact, bearing witness that their land
-ancestors had been covered everywhere with scales, much like those
-of existing lizards and other reptiles. Scales or bony plates were
-not only useless to the ichthyosaurs in the water, since they could
-afford no protection, but would have been detrimental in increasing the
-resistance in swimming.</p>
-
-<p>That the ichthyosaurs were predaceous animals is of course evident
-from their teeth, adapted for the seizure and retention of slippery
-prey, but not for tearing or comminuting. The fossilized remains of
-food found between the ribs of some specimens, in the place where the
-stomach was, together with fossil excrement, called coprolites, usually
-attributed to these animals, prove that they fed largely upon fishes,
-squids, belemnites, and probably other invertebrates. One ichthyosaur
-specimen preserved in the Stuttgart Museum has preserved in its stomach
-contents a mass composed of the remains of more than two hundred
-belemnites.</p>
-
-<p>Most interesting of all is the fact that, not very rarely, embryonic
-skeletons of ichthyosaurs have been found associated with the remains
-of adult animals, in such positions that they must have been inclosed
-within the body cavity at the death of the animals. As many as seven
-such embryonic skeletons have been observed with a single specimen. At
-first it was supposed that these skeletons were of small ichthyosaurs
-which had been swallowed whole as food, since it is not at all likely
-that these predaceous reptiles were discriminative in their choice
-of food when hungry. It is not improbable that in some cases this is
-the true explanation of the smaller skeletons within the larger ones,
-but it cannot be true of all, since wherever the small skeletons are
-identifiable they have been found to belong to the same species as the
-adult, and it would be absurd to suppose an ichthyosaur bent upon its
-prey would be at all likely to select as many as seven young animals,
-all of the same size and all of its own species. Furthermore, some
-of these young skeletons have been found in such positions as would
-indicate that they were inclosed within their egg-covering at the time
-<span class="pagenum" id="Page_124">[Pg 124]</span>
-of their death. Some of these embryos measure as much as twenty inches
-in length.</p>
-
-<p>Because the ichthyosaurs were born alive, and because so many of their
-skeletons are found with their various parts in orderly relation
-to each other, it is inferred with much probability that they were
-inhabitants, in large part at least, if not exclusively, of the open
-and deeper oceans. Had they been oviparous they must necessarily have
-laid their eggs upon the beaches, since no reptiles of the present
-time lay eggs in the water, and we have no other indications that
-the reptiles of the past have ever done so. And such habits would
-necessitate the periodical return to land. Had they been denizens of
-shallow waters, like the mosasaurs and plesiosaurs for the most part,
-their skeletons must surely have been disturbed by the currents and
-tides, as also by predaceous fishes, breaking up or displacing them or
-carrying away their bones. In shallow waters, also, the decomposing
-bodies would have been more liable to despoliation by the many
-scavengers of the seas.</p>
-
-<p>The ichthyosaurs must have been quite helpless upon land, their limbs
-being of little more use for locomotion than are the fins of fishes.
-Breathing air as they did, they were of course not suffocated when
-exposed, unless, as is the case with the whales, the feeble attachment
-of the ribs prevented the action of the respiratory muscles. If
-accidentally thrown upon the beaches, they doubtless were able to
-return to their home element more easily than the fishes can, by
-flopping, wriggling, and turning. As we have seen, the food consisted
-in part, perhaps the larger part, of small invertebrates, and because
-the bones of the lower jaws were closely united, permitting little or
-none of that expansion so characteristic of the snakes, all their prey
-must have been of relatively small size. In habit the ichthyosaurs were
-doubtless, like the dolphins and gavials, inoffensive and harmless,
-so far as animals of larger size were concerned. The abundance of
-their remains often found in restricted localities, while deposits of
-like age and character not far distant may be almost free from them,
-suggests that in all probability the ichthyosaurs, or the later ones at
-least, were more or less gregarious in habit as are the sea-mammals.
-<span class="pagenum" id="Page_125">[Pg 125]</span>
-They probably lived in schools, as do the porpoises, each species
-keeping to its restricted locality and not wandering far.</p>
-
-<p>The ichthyosaurs began their existence, so far as we now know, about
-the middle of Triassic times and continued to near the middle of
-Upper Cretaceous, when they disappeared forever from geological
-history. As we have seen, however, the earliest forms that we know
-were true ichthyosaurs in all respects, though more primitive than
-the later ones, indicating a long previous existence of which we yet
-have no knowledge. Their remains have been found widely distributed
-in Triassic rocks of Europe, Spitsbergen, Australia, and North
-America. During the Jurassic period they lived in great numbers and
-variety throughout the region that is now Europe. In North America
-the only marine rocks of this period that we know of have yielded
-numerous remains. These American ichthyosaurs were, however, among
-the most specialized of all ichthyosaurs—the culmination of their
-development. They were originally named <i>Sauranodon</i> in the belief
-that they were toothless, but in recent years their teeth, small
-and numerous, have been discovered. And the genus seems also to be
-identical with one previously named from the Jurassic of Europe called
-<i>Ophthalmosaurus</i>. The last known remains of ichthyosaurs have
-recently been found in the Benton Cretaceous of Wyoming. Scanty remains
-of ichthyosaurs are also known from Australia and New Zealand. Why the
-ichthyosaurs should have gone out of existence before the plesiosaurs
-and mosasaurs did, one cannot say; possibly their stock had grown old
-and feeble.</p>
-
-<hr class="chap x-ebookmaker-drop" />
-
-<div class="chapter">
-<p><span class="pagenum" id="Page_126">[Pg 126]</span></p>
-<h2 class="nobreak" id="CHAPTER_IX">CHAPTER IX<br />
-<span class="h_subtitle">&nbsp;<br />PROGANOSAURIA</span></h2>
-</div>
-
-<p class="f120"><b>MESOSAURUS</b></p>
-
-<p>There is some doubt whether those little creatures of Paleozoic times,
-to which some years ago the late Professor Baur gave the ordinal
-name Proganosauria, are really entitled to so much distinction among
-reptiles. The question of their rank has been much disputed for the
-past twenty years without any positive conclusion. Nor were they wholly
-aquatic in habit, though they did possess many aquatic adaptations.
-That they were skilful and fleet swimmers, and capable of rapid
-evolutions in the water is quite certain, and, as the oldest known
-water reptiles, they are of more than passing interest.</p>
-
-<div id="FIG_60" class="figcenter">
-  <img  src="images/fig60.jpg" alt="" width="450" height="541" />
-  <p class="center space-below2">
-    <span class="smcap">Fig. 60.</span>—<i>Mesosaurus</i>; life restoration,
-    after McGregor,<br /> the posture of hind leg slightly modified.</p>
-</div>
-
-<p>But two genera and three or four species of the group are known, and of
-them, even, our knowledge in some respects is not as complete as one
-could desire. The first description of any member of the group was by
-the late Professor Gervais of Paris in 1867. He had only the anterior
-part of a single skeleton, from the Karoo beds of South Africa, to
-which he gave the name <i>Mesosaurus</i>, a rather meaningless term
-signifying “middle” or “intermediate” saurian. Nothing more was learned
-about any form till 1885, when the late Professor Cope described a
-specimen from the supposed Carboniferous of Brazil, which he believed
-to be closely related to <i>Mesosaurus</i>, though he had only a
-very imperfect specimen. He called it <i>Stereosternum</i>, also a
-meaningless term, since none of the animals has a “solid sternum,”
-nor any sternum at all, in fact! A few years later, in 1888 and 1892,
-the late Professor Seeley of England studied a number of specimens of
-<i>Mesosaurus</i>, adding not a little to our knowledge of the animals.
-More recently Dr. Woodward of England and Professor Osborn of America
-have given us still further information concerning them, and within
-the past few years Dr. McGregor of Columbia University has figured
-and described excellent specimens of a new species from Brazil, which
-he calls <i>Mesosaurus brasiliensis</i>. Not only were Dr. McGregor’s
-<span class="pagenum" id="Page_127">[Pg 127]</span>
-discoveries of great interest as settling many doubtful points in their
-structure, but they were still more so from the fact that he found his
-species so nearly like that from Africa that he placed it in the same
-genus. Since the proganosaurs were purely fresh-water or terrestrial
-animals, one can only wonder how they crossed from Africa to America,
-<span class="pagenum" id="Page_128">[Pg 128]</span>
-or, what is more probable, how they migrated from America to Africa,
-across the broad Atlantic Ocean, so long ago. The geologists tell us
-that the Atlantic and Pacific, in the main, have always been oceans
-since the beginning of terrestrial life upon the earth. Possibly
-the tribe of proganosaurs migrated by the very circuitous route of
-Europe and North America, or Asia and the Northwest; but that is very
-improbable, since nothing whatever resembling them has ever been found
-in the Northern Hemisphere, and it is quite certain that in the many
-thousands of years it must have taken them to travel from southern
-Africa to South America many of the reptiles must have perished on
-the way and left their remains in the rocks. The only conclusion that
-seems probable is that there was a direct land communication in those
-olden times between Africa, or at least India, and South America across
-what is now the Atlantic Ocean. Of course this route will be very
-difficult to prove, since we can never get to the bottom of the ocean
-to hunt for fossil proganosaurs. Were this peculiar distribution of the
-<span class="pagenum" id="Page_129">[Pg 129]</span>
-proganosaurs an isolated example, one might perhaps ascribe our lack of
-knowledge of any fossil proganosaurs in the Northern Hemisphere to the
-meagerness of the fossil records, but there are many other examples of
-similar import among other early animals.</p>
-
-<div id="FIG_61" class="figcenter">
-  <img  src="images/fig61.jpg" alt="" width="600" height="178" />
-  <p class="center space-below2">
-     <span class="smcap">Fig. 61.</span>—<i>Mesosaurus</i>; restoration of
-     skeleton.<br /> (After McGregor)</p>
-</div>
-
-<p>The age of the South American proganosaurs is now believed to be lower
-or lowermost Permian, like that of the African <i>Mesosaurus</i>;
-possibly, however, the age first described to <i>Stereosternum</i>
-(Carboniferous) may be correct.</p>
-
-<p>The known skeletons are all small, none exceeding a few feet in length.
-The skull, as shown in the figure by Dr. McGregor, is elongate, and
-its teeth are extraordinarily so, and very slender. The external
-nostrils are situated close to the eyes; and no sclerotic bones have
-been discovered. There are small teeth in the bones of the palate.
-The neck is elongate, composed of ten or twelve vertebrae. The trunk
-also is long and slender, and the tail is not only long, but also
-much flattened or compressed. All these are very characteristic of
-water life. The limbs, however, show a much less complete adaptation
-for swimming—not much more so in fact than do those of the living
-Crocodilia. The upper arm and the thigh bones are relatively long,
-while those of the forearm and the leg are shorter than among
-terrestrial reptiles, the first indication of swimming habits to appear
-in crawling animals. The digits are not much elongated, and they
-have no additional finger bones, save perhaps in a lately discovered
-form in Africa, in which Dr. Broom reports supernumerary bones in
-the fifth or “little” toe.<a id="FNanchor_3" href="#Footnote_3" class="fnanchor">[3]</a>
-The fingers and toes have only blunt terminal bones, that is, they
-were not distinctly clawed, and they were probably connected with each
-other by a membrane, as in a frog’s foot. This webbing of the feet is
-probable, not only because of the positions in which the bones have
-been found, but also because of the great length of the “little” toe,
-which is the longest in the foot, a character quite abnormal for a
-land reptile and quite characteristic of certain aquatic mammals,
-like the seals and sea-otters. There is a strong sacrum of two
-vertebrae, however, the pelvis and hind legs being connected with the
-spinal column firmly, clearly proving that, like the crocodiles, the
-proganosaurs had by no means lost their land proclivities.
-<span class="pagenum" id="Page_130">[Pg 130]</span></p>
-
-<p>Their vertebrae, as would be expected in such old reptiles, are quite
-primitive in structure, that is, they are deeply concave in each end,
-probably being perforated for the remains of the notochord. The pelvis
-also is of the old-fashioned type, that is, without an opening or
-vacuity between the bones below. The shoulder bones are old fashioned
-too. The shoulder-blade, especially, shows a decided adaptation to
-water life in its short, fan-like shape, very much like those of the
-mosasaurs, ichthyosaurs, whales, etc. Just why swimming animals should
-have short and broad shoulder-blades has not yet been explained, but
-doubtless they afforded better attachment for those muscles used more
-especially in swimming. The ribs are remarkably flat and heavy, and
-were not very firmly attached to the vertebrae. Heavy ribs are unusual
-among free swimming animals, but do occur in the modern sirenians,
-which live on the bottoms of shallow bays, etc., feeding upon plants.
-We may perhaps infer from this peculiar structure of the ribs that
-the proganosaurs lived more on the bottoms of shallow waters, feeding
-upon such fishes or invertebrates as they could capture, coming to the
-surface to breathe from time to time. Possibly they sought the shores
-for safety from their enemies, as do the Galapagos lizards, figured
-on <a href="#FIG_66">p. 142</a>; and doubtless they laid and hatched their eggs
-on land. A character which suggests that the proganosaurs lived only in the
-shallow waters is the elongated neck, reminding one of those two other
-groups of swimming reptiles, the dolichosaur lizards and the nothosaurs
-of the Sauropterygia, the only known reptiles besides the plesiosaurs
-having an abnormal number of neck bones. Still more suggestive of
-shallow, fresh-water habits is the absence of eye bones, as in the
-modern crocodiles.</p>
-
-<p>The long snout, with the long and slender teeth, and the position
-of the external nostrils far back near the eyes, together with the
-flattened and long tail and the webbed feet, are sufficient proof of
-expert swimming habits. The legs still functioned more or less for the
-support and propulsion of the body on the land, and they probably were
-only of slight service in the water. The alligator swims sinuously with
-<span class="pagenum" id="Page_131">[Pg 131]</span>
-its front legs collapsed and extended by the side of the body; its hind
-legs are used more as propellers, with the knee flexed and the feet
-turned outward and expanded. The legs of the proganosaurs doubtless
-were used in the same way, as shown in the restoration, which has been
-modified from the original of Dr. McGregor in accordance with this
-probable use of the legs.</p>
-
-<p>There seems to be an incongruity between the posterior nostrils and the
-heavy flat ribs, the former suggesting free swimming and diving habits,
-the latter shallow water and bottom habits. Possibly the position of
-the nostrils has been the result of the great elongation of the face in
-front of the nostrils; and we know that their posterior position in the
-phytosaurs (<a href="#FIG_95">Figs. 95</a> and <a href="#FIG_96">96</a>)
-has not been due to swimming habits only.</p>
-
-<p>Nothing has been discovered to indicate the nature of the external
-covering of the body. Possibly, even probably, the skin was more or
-less covered by horny scales or plates, though it may have been quite
-bare, as in the salamanders.</p>
-
-<p>To which other reptiles the proganosaurs are nearest related has long
-been a subject of dispute, and still is. The more probable view,
-however, is that they were a very early branch of the most primitive
-stock of reptiles, the Cotylosauria, one that soon perished, leaving
-no descendants, unless possibly the ichthyosaurs were their progeny.
-Some writers have thought that they were the early ancestral stock of
-the plesiosaurs, and they are often classified with the Sauropterygia.
-Still others have believed that they were an early side-branch of the
-great group of Rhynchocephalia. And this doubt has been chiefly due
-to our imperfect knowledge of the bones of the cranium. As has been
-explained, very much stress in the classification of reptiles has been
-laid by students on the possession of one, two, or no openings on the
-side of the skull back of the eyes. And this part of the skull of the
-Proganosauria has not yet been satisfactorily made out. Dr. McGregor
-thought that there are two openings in the temporal region, allying the
-group with the Rhynchocephalia. Dr. Huene is more positive that there
-is but one, like that of the ichthyosaurs. In this state of indecision,
-the proganosaurs may be dignified by giving them an ordinal position by
-themselves.</p>
-
-<hr class="chap x-ebookmaker-drop" />
-
-<div class="chapter">
-<p><span class="pagenum" id="Page_132">[Pg 132]</span></p>
-<h2 class="nobreak" id="CHAPTER_X">CHAPTER X<br />
-<span class="h_subtitle">&nbsp;<br />PROTOROSAURIA</span></h2>
-</div>
-
-<h3>PROTOROSAURUS</h3>
-
-<p>The genus <i>Protorosaurus</i> is of peculiar interest, as one of the
-first, if not the first, known fossil reptiles, described by Spener as
-long ago as 1710 as a crocodile, from fragmentary remains found in 1706
-in the Permian deposits of Thuringia. Numerous other skeletons or parts
-of skeletons attracted the attention of naturalists of the eighteenth
-century, but were very imperfectly described. No name was given to the
-animal represented by the various specimens until 1840, when Herman
-von Meyer restudied all the known material and described it under the
-name <i>Protorosaurus speneri</i>. The position of the genus among
-reptiles always has been and yet is uncertain, for the reason that the
-structure of the skull, and especially the structure of the temporal
-region, has never been satisfactorily determined. Seeley, in 1887,
-described more fully the original specimen of Spener, now preserved in
-the museum of the College of Surgeons of London, and because of certain
-peculiarities which it showed proposed for its reception the order
-Protorosauria. He thought that he detected an upper temporal vacuity,
-like that of lizards, but was very uncertain about the structure of the
-lower part of the temporal region. The writer, who has examined this
-type specimen, must admit that the structure of the region here is very
-doubtful. Under the general assumption, however, that all old reptiles
-must be related to <i>Sphenodon</i>, the Protorosauria have generally
-been classified as a suborder of the Rhynchocephalia. It is merely
-another instance of the proclivity we all have to propose hypotheses,
-and then, speedily forgetting that they are hypotheses, to accept them
-as facts.</p>
-
-<p><i>Protorosaurus</i> was long supposed to be an aquatic reptile, but we
-now know that it was a strictly terrestrial one, probably with climbing
-habits; and the genus concerns us only by reason of its possible
-relationships to distinctly aquatic reptiles of a later age.
-<span class="pagenum" id="Page_133">[Pg 133]</span></p>
-
-<div id="FIG_62" class="figcenter">
-  <img  src="images/fig62.jpg" alt="" width="400" height="480" />
-  <p class="center space-below2">
-      <span class="smcap">Fig. 62.</span>—Life restoration of
-         <i>Araeoscelis</i>.</p>
-</div>
-
-<p>A few years ago the writer described a very slender, lizard-like
-reptile about two feet in length from the Permian of Texas under
-the name <i>Araeoscelis</i>, so named because of its slender legs.
-The structure of both the skull and the skeleton of this reptile
-is now quite satisfactorily known, so well known indeed that the
-accompanying restoration (<a href="#FIG_62">Fig. 62</a>) has little that is
-conjectural about it, at least so far as the form is concerned. The skull
-has a single, upper temporal opening, quite like that of lizards, but the
-quadrate is not loose below. And this is really what we should expect
-in the ancestral lizards; and everything else of the skeleton, except
-perhaps one character, is what would be expected. That one character
-is the elongation of the cervical vertebrae, which are about twice
-the length of the dorsal vertebrae following them. The cervical
-ribs are very slender bones, articulating by a single head with the
-centrum only. In these and other characters, so far as they are known,
-<i>Araeoscelis</i> seems to agree with <i>Protorosaurus</i>, and both
-have very hollow bones.
-<span class="pagenum" id="Page_134">[Pg 134]</span></p>
-
-<div id="FIG_63" class="figcenter">
-  <img  src="images/fig63.jpg" alt="" width="600" height="244" />
-  <p class="center space-below2">
-     <span class="smcap">Fig. 63.</span>—Skeleton of <i>Pleurosaurus</i>.<br />
-     (After Lortet)</p>
-</div>
-<p><span class="pagenum" id="Page_135">[Pg 135]</span></p>
-
-<h3>PLEUROSAURUS</h3>
-
-<p>We may for the present be justified in maintaining the order
-Protorosauria for those reptiles having a single, typically upper
-temporal opening on each side, with a fixed quadrate, not including
-the ichthyosaurs. It is not improbable, however, that when more is
-known of the ancestors of the lizards, the whole group will find its
-most natural place among the Squamata. This definition will include a
-peculiar aquatic reptile that has been known for many years, but which
-has been wrongly classed in the same family as <i>Sphenodon</i>, on
-the purely gratuitous assumption that it has two temporal openings
-on each side; we now know that it has but one. This reptile, known
-scientifically as <i>Pleurosaurus</i>, was described originally by H.
-von Meyer in 1843, but we are indebted to M. Lortet for a more precise
-knowledge of the animal, and for the figure (<a href="#FIG_63">Fig. 63</a>) which
-is here given of the skeleton. Not a few excellent skeletons are preserved in
-the museums at Lyons and Munich. The specimen here figured, as actually
-preserved, measures about three feet in length; a part of the tail is
-missing, which is known from other specimens to have been remarkably long.</p>
-
-<p>The figures show clearly some of the remarkable aquatic adaptations of
-the animal, especially the short neck, the very long and narrow body,
-and the extraordinarily long and flattened tail. The head is elongate
-triangular in shape, resembling very much that of the mosasaurs; and
-the external nostrils are likewise situated remotely from the end
-of the snout, as in the mosasaurs. The extremity of the snout has a
-beak-like projection. The teeth are much longer, more pointed, and more
-recurved than is the case with most land reptiles, indicating their use
-for the capture and retention of slippery, quick-moving prey.</p>
-
-<p>The single-headed ribs are short, proving that the body was slender and
-<span class="pagenum" id="Page_136">[Pg 136]</span>
-doubtless cylindrical, more like that of a snake. The tail was not
-only enormously elongated, but it was also compressed into a flat and
-effective propelling organ in the water. This flattening of the tail
-is apparent from the skeleton, with its elongated chevrons below and
-spines above, and it is also proved by the fortunate preservation
-of the extremity of the tail of one specimen, showing not only the
-impressions of the scales in the matrix, but also the outlines that the
-soft parts had in life. To quote from Lortet, in translation: “The tail
-was covered wholly with small scales, regularly hexagonal in shape,
-shining and nacreous, larger on the under side than above. The upper
-border of the tail was surmounted by a broad crest, extending to its
-extremity, and composed of large, oval scales.” The body doubtless was
-wholly covered with scales, though it is not probable that the caudal
-crest continued along the back.</p>
-
-<div id="FIG_64" class="figcenter">
-  <img  src="images/fig64.jpg" alt="" width="600" height="343" />
-  <p class="center space-below2">
-<span class="smcap">Fig. 64.</span>—Life restoration of <i>Pleurosaurus</i>.</p>
-</div>
-
-<p>The limbs begin to show an aquatic adaptation, though not very
-pronounced. They are much shorter and smaller than are those of
-land-crawling reptiles; and the bones of the second series, that is,
-the radius and ulna, tibia and fibula, are relatively short, the
-beginning of adaptation to water habits. It is very probable that the
-feet were webbed, though the fifth digit, as usual, is shorter than the
-<span class="pagenum" id="Page_137">[Pg 137]</span>
-fourth. Doubtless on land the creature moved about in a serpentine way,
-for it could not have progressed very rapidly by the aid of its legs
-alone. The hind legs are longer than the front legs, and they were
-connected firmly with the body by means of a sacrum. The number of
-vertebrae in the neck is only five. The number of dorsal vertebrae is
-forty-three, a larger number than is known in any other air-breathing
-vertebrate with legs.</p>
-
-<p>Upon the whole, these lizard-like, almost snake-like pleurosaurians
-present some very curious adaptations to water life. In water they were
-doubtless speedy, swimming in serpentine undulations, with the small
-legs for the most part folded against the body and only of occasional
-use. Doubtless, too, had the pleurosaurs lived longer in geological
-history, they would have become quite snake-or eel-like, just as have
-some modern salamanders.</p>
-
-<p>In all probability the pleurosaurs lived habitually in fresh-water,
-perhaps visiting the shores for refuge, or for the hatching of their
-young. That they were not on the way toward a terrestrial snake-like
-body is evident from the flattened tail, and especially the crest of
-scales above; the tail was like that of the sea-snakes of the present
-time. <i>Pleurosaurus</i>, then, affords the solitary instance among
-reptiles of aquatic adaptation by the diminution of both front and hind
-extremities and the acquisition of a snake-like body and snake-like habits.</p>
-
-<hr class="chap x-ebookmaker-drop" />
-
-<div class="chapter">
-<p><span class="pagenum" id="Page_138">[Pg 138]</span></p>
-<h2 class="nobreak" id="CHAPTER_XI">CHAPTER XI<br />
-<span class="h_subtitle">&nbsp;<br />SQUAMATA</span></h2>
-</div>
-
-<p>The order Squamata, so called because of the dermal covering of
-overlapping horny scales, comprises the great majority of living
-reptiles. Although the scaly covering is characteristic of nearly all
-the members of the order, the most essential differences distinguishing
-them from other reptiles are, as usual, found in the skeleton, and
-especially in the skull. The quadrate bone, that to which the lower
-jaw is articulated on each side, is not wedged in immovably between
-other bones of the skull, as in all other reptiles, but is, instead,
-freely articulated with the cranium in such a way that its lower end
-moves both backward and forward, as well as inward and outward. This
-freedom of movement has in the past been thought to be due to the
-loss of a lower temporal arch, a bony bar connecting the lower end
-of the quadrate with the hind end of the upper jaw, which is very
-characteristic, for instance, of the Rhynchocephalia. Indeed, because
-of the many primitive characters which the lizards possess, it has
-generally been supposed that the order was an early branch of the
-rhynchocephalian stem. But we are now quite sure that the lizards
-are as primitive as the Rhynchocephalia, and that their origin, as
-an independent branch of the reptilian stem, goes quite as far if
-not farther back—quite sure that the ancestors of the lizards never
-had a lower temporal arcade and two temporal vacuities, but that
-the looseness of the quadrate bone has been due to the gradual loss
-of a bone which covered the whole side of the skull until only the
-upper part of it was left. In other words, the ancestral skull of the
-Squamata must have been like that of <i>Araeoscelis</i>, more fully
-described under the Protorosauria, a group than which there is perhaps
-none more closely allied to the Squamata.</p>
-
-<p>The bones of the roof of the mouth of the Squamata—that is, of the
-<span class="pagenum" id="Page_139">[Pg 139]</span>
-palate—are narrow and long, and are not closely articulated, as in
-most other reptiles; they often bear teeth, a primitive character. The
-teeth of all living lizards and snakes are not inserted in sockets,
-as are those of the crocodiles, but are co-ossified to the margins or
-sides of the jaws or the bones of the palate. But this is probably not
-a primitive character; doubtless the teeth of the early lizards were
-inserted in sockets like those of most other reptiles. The shoulder
-bones are absent in many and vestigial in some others. When present
-and fully developed, they comprise the shoulder-blades or scapulae,
-a single coracoid on each side, the clavicles, and an interclavicle.
-The vertebrae, except in some lizards, are procoelous, that is, with
-the body concave in front and convex behind, a peculiar structure
-that was developed only in crawling animals. In addition to the usual
-articulations for the union of the vertebrae there are also, in some
-of the lizards and mosasaurs and all of the snakes, additional ones
-called the zygosphene and zygantrum, which will be best understood
-by reference to <a href="#FIG_12">Fig. 12, p. 28</a>. But little less characteristic
-than the loose articulation of the lower jaws, so unique in this order of
-reptiles, is the manner of attachment of the ribs. They are always
-single-headed, articulating only with the body or lower part of the
-vertebra. The single-headed ribs of the plesiosaurs articulate with
-a projection on each side of the arch of the vertebra; those of the
-turtles to the space between the adjacent vertebrae; nearly all other
-reptiles have double-headed ribs, articulating in various ways. This
-character, it is seen, though apparently a simple one, immediately
-distinguishes a lizard or a snake from all other animals, except the
-thalattosaurs and protorosaurs.</p>
-
-<p>There is much difference of opinion among naturalists as to the proper
-classification of the different groups of this order of reptiles.
-Usually it is divided into four suborders, the Lacertilia or lizards;
-the Dolichosauria or long-necked lizards of the past; the Mosasauria,
-or extinct swimming lizards; and the Serpentes or Ophidia, the snakes.
-It matters very little which classification one accepts so long as it
-is remembered that the first three groups are closely related to each other.
-<span class="pagenum" id="Page_140">[Pg 140]</span></p>
-
-<h3>LIZARDS</h3>
-
-<p>Popularly a lizard is any four-legged reptile covered with scales,
-but such a definition is not strictly correct, since some lizards are
-legless and some other four-legged reptiles are covered with horny
-scales, notably the tuatera or <i>Sphenodon</i> of New Zealand, a
-reptile long classed with lizards, but now known to belong to quite a
-different order. Bearing in mind those characters given as characters
-of the order, it will be necessary to mention only those distinguishing
-the lizards from the snakes.</p>
-
-<div id="FIG_65" class="figcenter">
-  <img  src="images/fig65.jpg" alt="" width="600" height="190" />
-  <p class="center space-below2">
-    <span class="smcap">Fig. 65.</span>—Iguana.<br /> (By permission
-    of the New York Zoölogical Society)</p>
-</div>
-
-<p>It is true that the great majority of lizards have four legs, while the
-snakes are always functionally legless, but there are some lizards,
-like the glass snakes and the amphisbaenas, or slow lizards, which
-are quite legless and there are some snakes which have small but
-functionless hind legs. As usual, more important differences are found
-in the skull. The brain-case in all snakes is surrounded on all sides
-by bone, for the better protection of the brain, with the head resting
-quite prone on the ground. The brain of the lizards, for the most part,
-is protected on the sides and in front by a simple membrane. Nearly all
-lizards have movable eyelids, while snakes do not; snakes have a single
-lung, and a protrusible tongue, which very few lizards possess; and
-the lower jaws in front are united in the snakes by a ligament only.
-Notwithstanding these differences, the snakes and lizards are closely
-<span class="pagenum" id="Page_141">[Pg 141]</span>
-related animals, and must have come from a common ancestry; among all
-reptiles the known geological history of the snakes is shortest.</p>
-
-<p>Lizards, on the other hand, have a very high antiquity, beginning,
-as we now know, at least as long ago as early Triassic times. They
-still have many primitive characters in their structure and are the
-least advanced type of reptiles now living, with the exception of the
-tuatera. Their remains are seldom found in the rocks, probably because
-they have always been so strictly terrestrial in habit, for the most
-part seldom frequenting even the vicinity of the water. The true
-lizards now living number about eighteen hundred kinds, classified into
-about twenty families, divided among four chief groups, of which the
-chameleons, the amphisbaenas, our common lizards, and the monitors are
-representatives.</p>
-
-<p>Most living lizards are inhabitants of warm climates, though some
-extend rather far north in the temperate zone. With the exception of
-New Zealand, and the polar and subpolar regions, lizards are found
-in all parts of the world. The great majority live only in high and
-dry places, though some are denizens of low and marshy places, a few
-even not being averse to the water. They are, for the most part, spry
-in their movements, some little ones scarcely six inches in length
-taxing a vigorous man’s speed to capture; and many are expert climbers
-of cliffs, trees, and even the ceilings of residences. Some, the
-remarkable little flying dragons of Ceylon, have an extraordinary
-development of the skin on the sides of the body, supported by the
-expanded ribs, forming a sort of parachute whereby the creatures
-can sail considerable distances through the air. Nearly all are
-carnivorous, feeding upon small mammals, birds, other reptiles, frogs,
-and insects; a few only are herbivorous, such as the iguanas, which are
-often used for human food. Nearly all lizards are oviparous, laying
-from two to thirty eggs. In size the great majority are small, less
-than a foot in length; but some, such as the monitors and iguanas,
-reach a length of from four to six feet, or even more, and certain
-extinct monitors of India are known to have attained a length of thirty
-feet. They are, for the most part, slender, graceful, prettily marked,
-and quite inoffensive creatures. A few are short, flat, or stumpy in
-<span class="pagenum" id="Page_142">[Pg 142]</span>
-shape, such as the so-called horned toad. One or two species only, the
-“Gila monsters,” are reputed to be venomous.</p>
-
-<div id="FIG_66" class="figcenter">
-  <img  src="images/fig66.jpg" alt="" width="500" height="437" />
-  <p class="center space-below2">
-    <span class="smcap">Fig. 66.</span>—<i>Amblyrhynchus cristatus</i>, the
-    Galapagos sea-lizard.<br /> (From Brehm)</p>
-</div>
-
-<p>There is but a single species of lizard now living which is in any true
-sense aquatic in habit, the well-known sea-lizard of the Galapagos
-Islands, scientifically known as <i>Amblyrhynchus cristatus</i>. It
-is a large lizard, with a short rounded head, a flat tail, and webbed
-feet. Its specific name is derived from the erect fringed crest along
-its back and tail. Its habits are best given in Darwin’s words:
-<span class="pagenum" id="Page_143">[Pg 143]</span></p>
-
-<p class="blockquot">It is extremely common on all the islands
-throughout the group, and lives exclusively on the rocky sea-beaches,
-being never found, at least I never saw one, even ten yards inshore.
-It is a hideous looking creature, of a dirty black color, stupid and
-sluggish in its movements. The usual length of a full grown one is
-about a yard, but there are some even four feet in length; a large one
-weighed twenty pounds. The tails are flattened sideways, and all four
-feet are partially webbed. They are occasionally seen some hundred
-yards from the shore swimming about. When in the water this lizard
-swims with perfect ease and quickness, by a serpentine movement of the
-body and flattened tail—the legs being motionless and closely collapsed
-to the sides. A seaman on board sank one, with a heavy weight attached
-to it, thinking thus to kill it directly; but when an hour afterward
-he drew up the line it was quite active. Their limbs and strong claws
-are admirably adapted for crawling over the rugged and fissured masses
-of lava, which everywhere forms the coast. The nature of this lizard’s
-food (seaweed) as well as the structure of the tail and feet, and
-the fact of its having been seen voluntarily swimming out at sea,
-absolutely proves its aquatic habits; yet there is in this respect one
-strange anomaly, namely, that when frightened it will not leave the
-island. Hence it is easy to drive these lizards down to any little
-point overhanging the sea, where they will sooner allow a person to
-catch hold of their tails than jump into the water. They do not seem
-to have any notion of biting; but when much frightened they squirt a
-drop of fluid from each nostril. I threw one several times as far as I
-could into a deep pool left by the retreating tide, but it invariably
-returned by a direct line to the spot where I stood. It swam near the
-bottom, with a very graceful and rapid movement, and occasionally aided
-itself over the uneven ground with its feet. As soon as it arrived
-near the edge, but still being under water, it tried to conceal itself
-under the tufts of seaweed, or it entered some crevice. I several times
-caught the same lizard by driving it to a point, and, though possessed
-of such perfect powers of diving and swimming, nothing could induce
-it to enter the water; and as often as I threw it in it returned in
-the manner described above. Perhaps this singular piece of apparent
-stupidity may be accounted for by the circumstance that this reptile
-has no enemies whatever on shore, whereas at sea it must often fall a
-prey to the numerous sharks.</p>
-
-<p>These lizards are of much interest as indicating one of the ways in
-which true land reptiles have become aquatic in their habits. Tempted
-by the abundance of food growing in shallow water a little beyond their
-reach, the reptiles ventured farther and farther to obtain it. The tail
-gradually became a propelling organ, though the lizard still retained
-in large measure its land habits and land feet, because of the dangers
-from its water enemies. It is not at all improbable that, in course
-of time, were these Galapagos lizards left unmolested, they would
-become fleeter swimmers by the development of a terminal caudal fin
-and paddle-like legs, thus competing with their aquatic enemies and no
-longer needing recourse to the land for protection. They also serve to
-indicate that long-tailed aquatic reptiles never used their legs to an
-appreciable extent as organs of propulsion in the water.
-<span class="pagenum" id="Page_144">[Pg 144]</span></p>
-
-<div id="FIG_67" class="figcenter">
-  <img  src="images/fig67.jpg" alt="" width="600" height="318" />
-  <p class="center space-below2">
-   <span class="smcap">Fig. 67.</span>—<i>Varanus</i>, Australian monitor lizard.<br />
-   (By permission of the New York Zoölogical Society.)</p>
-</div>
-
-<p><i>Flat-headed lizards.</i>—Among the living lizards there is one
-group, called the monitors, which have so many characters peculiar to
-themselves that they seem rightfully entitled to an isolated place
-among the lizards of the present time. The group includes about thirty
-species, all belonging in the one genus <i>Varanus</i>, and all living
-in India, Africa, and Australia. In size, some of the species of
-<i>Varanus</i> are the largest of all terrestrial lizards known in the
-past or present; in other ways also they have reached the maximum of
-specialization among lizards. The head is pointed, broad, and flat,
-and the body and tail are long. They have nine vertebrae in the neck,
-a larger number than is to be found in any other terrestrial lizard.
-Unlike other lizards they have a protrusible tongue like that of the
-snakes. All are carnivorous in habit, feeding upon small backboned
-animals, insects, and especially upon eggs, which they crush between
-their teeth while holding them aloft. Most species live wholly upon the
-land, and some are arboreal. Others, especially those of the Nile, live
-about water and are excellent swimmers. The terrestrial species have a
-round tail and small external nostrils, but the water species have the
-tail much flattened, and the nostrils have large cavities, which, when
-<span class="pagenum" id="Page_145">[Pg 145]</span>
-closed under water, are said to serve as reservoirs of air for
-respiration. Of one of these swimming species Annandale writes:</p>
-
-<p class="blockquot"><i>Varanus salvator</i> is common in Lower Siam
-where it is equally at home on land, in water, and among the branches
-of trees. The eggs are laid in hollow tree trunks. When in the water
-the lizard swims beneath the surface, the legs being closely applied to
-the sides, and the tail functioning both as oar and rudder.</p>
-
-<p>These lizards take to the water to escape from their land enemies and
-not for food, a habit also known among certain other lizards, and
-one precisely the reverse of that of the Galapagos lizards. It would
-seem very probable that animals of such carnivorous habits as are the
-monitors might easily learn to capture water animals for food and
-thus eventually become aquatic in habit. This inclination toward, and
-partial adaptation to, water habits in the monitors is of much interest
-because in all probability the instinct is one of long inheritance from
-those remote ancestors which gave origin to the truly aquatic members
-of the order. Though the known geological history of the monitors does
-not extend far back, they are so intimately allied in their anatomical
-structure to the aquatic and semiaquatic lizards of Cretaceous times
-that there could seem to be no doubt of the common ancestry.</p>
-
-<p><i>Dolichosaurs.</i>—About fifty years ago Professor Owen, the
-famous English paleontologist, described a peculiar semiaquatic
-lizard from the Cretaceous rocks of England to which he gave the name
-<i>Dolichosaurus</i>, in allusion to the slender form of the body. Just
-what relations these slender lizards have to modern lizards has long
-been a problem; some have thought that they were their progenitors, but
-there are very good reasons for doubting this. No modern lizards, save
-the monitors, have more than eight vertebrae in the neck, while these
-dolichosaurs had as many as seventeen, a remarkable specialization for
-aquatic life that could hardly have been lost by their descendants.
-For this reason the dolichosaurs have usually been considered as
-representing a distinct suborder. But they have many resemblances
-otherwise to the monitors. They were semiaquatic in habit, and never
-more than six feet in length. They are yet imperfectly known, and no
-restoration of any form has hitherto been attempted. Their peculiar
-<span class="pagenum" id="Page_146">[Pg 146]</span>
-interest lies in the elongation of the neck, quite like that of the
-wholly unrelated nothosaurs and proganosaurs, which have been described
-in the foregoing pages. Doubtless similar habits in each had like
-results, but just what these habits were in the slender lizards we do
-not yet know.</p>
-
-<p><i>Aigialosaurs.</i>—Within recent years a number of other lizards
-have been made known from the Lower Cretaceous rocks of Dalmatia which
-present most remarkable intermediate characters between the monitors,
-dolichosaurs, and the mosasaurs, the famous sea-lizards of Upper
-Cretaceous age. Some of these lizards had twelve or thirteen vertebrae
-in the neck, while others had but seven—an unusually short neck
-characteristic of the mosasaurs. These latter kinds, belonging to two
-or three genera, are included in a distinct group. They were long and
-slender, the head long and pointed. The teeth, conical and sharp, were
-attached in shallow pits, quite as in the mosasaurs. The lower jaws
-had a hinge just back of the teeth, as in the mosasaurs, of which the
-only trace in modern lizards is found among the monitors. Still more
-remarkable, though perhaps not so easily appreciated, is the shape of
-the quadrate bone, with a broad flaring rim for the ear cavity, quite
-unlike that of land lizards, but quite like that of the mosasaurs. In
-fact, the very peculiar skull is almost identical with that of the true
-sea-lizards. The body and tail also resemble those of the mosasaurs
-more than those of the monitors, but there is a firm attachment of the
-pelvis to the backbone, and the legs are long and lizard-like, though
-not as long as those of land lizards. The feet were webbed in life, and
-the toes have no claws, conclusively demonstrating their water habits.
-The vertebrae indeed have the same peculiar articulations, called
-zygosphenes, as in most of the mosasaurs. The largest aigialosaurs were
-about six feet in length, that is, of about the size of the smallest
-known mosasaurs.</p>
-
-<div id="FIG_68" class="figcenter">
-  <img  src="images/fig68.jpg" alt="" width="400" height="542" />
-  <p class="center space-below2">
-    <span class="smcap">Fig. 68.</span>—<i>Clidastes</i>, an American
-      mosasaur.<br /> Life restoration.</p>
-</div>
-
-<p>We have then in the aigialosaurs nearly every known intermediate
-character that we could wish for in a connecting link between the
-mosasaurs and the monitors, lizards that were equally at home on land
-or in the water, and there can be scarcely a doubt that they were
-<span class="pagenum" id="Page_147">[Pg 147]</span>
-either the direct ancestors or closely akin to the direct ancestors of
-the strictly marine mosasaurs; and scarcely a doubt that they were the
-descendants of the actual forbears of the modern monitors, which, as we
-have seen, have acquired partial aquatic habits in escaping from their
-<span class="pagenum" id="Page_148">[Pg 148]</span>
-enemies. The dolichosaurs we can now understand were a side branch
-from these semiaquatic aigialosaurs which, specializing in another
-direction, quickly came to grief, perhaps in competition with their
-more agile and skilful short-necked kin.</p>
-
-<p>Taking all these facts into consideration it seems best to unite
-the monitors, dolichosaurs, and aigialosaurs into one group of the
-Lacertilia, the Platynota, intermediate in place between the true land
-lizards and the truly aquatic mosasaurs.</p>
-
-<h3>MOSASAURS</h3>
-
-<p>At St. Pietersberg, a small mountain in the vicinity of Maestricht,
-Holland, there are immense subterranean stone quarries, which have
-been worked for more than a thousand years. The stone quarried from
-them is a sandy limestone of Upper Cretaceous age containing many
-well-preserved remains of extinct animals that have long been sought by
-collectors of fossils. In 1776 Major Drouin—an officer of a near-by
-garrison, one of much military importance in those days—secured from
-one of these quarries some bones of an extinct reptile, which, though
-of interest, afforded but little information concerning the structure
-and affinities of the animal to which they had once belonged. In 1780
-a very perfect skull, in excellent preservation, of the same kind of
-an animal was obtained from the same quarry by Dr. Hofmann, an army
-surgeon of the same garrison, whose interest in such things had been
-incited by Major Drouin’s collections. This specimen, so renowned in
-science, has had a remarkable and eventful human history, in part
-related by St. Faujas de Fond, a French commissary of the “Army of the
-North,” and one of the participants:</p>
-
-<p class="blockquot">In one of the great galleries or subterranean
-quarries in which the Cretaceous stone of St. Pieter’s Mount is worked,
-about five hundred paces from the entrance, and ninety feet below the
-surface, the quarrymen exposed part of the skull of a large animal in
-a block of stone which they were engaged in quarrying. On discovering
-it they suspended their work and went to inform Dr. Hofmann, surgeon to
-the forces at Maestricht, who for some years had been collecting the
-fossils from the quarry, remunerating the workmen liberally for the
-discovery and preservation of them. Dr. Hofmann, arriving at the spot,
-saw with extreme pleasure the indication of a magnificent specimen; he
-<span class="pagenum" id="Page_149">[Pg 149]</span>
-directed the operations of the men, so that they worked out the block
-without injury to the fossil, and he then, by degrees, cleared away the
-yielding matrix and exposed the extraordinary jaws and teeth, which
-have since been the subject of so many drawings, descriptions, and
-discussions. This fine specimen which Dr. Hofmann had transported with
-so much satisfaction to his collection, soon became, however, a source
-of much chagrin to him. Dr. Goddin, one of the canons of Maestricht,
-who owned the surface of the soil beneath which was the quarry whence
-the fossil was obtained, when the fame of the fossil reached his ears,
-pleaded certain feudal rights in support of his claim to it. Hofmann
-resisted and the canon went to law. The whole chapter supported their
-reverend brother, and the decree ultimately went against the poor
-surgeon, who lost both the specimen and his money, for he was made to
-pay the costs of the action. The canon, leaving all remorse to the
-judges who pronounced the iniquitous sentence, became the happy and
-contented possessor of this unique example of its kind.</p>
-
-<p class="blockquot no-indent">[Translation by Leidy.]</p>
-
-<p class="space-above2">But the canon was ultimately despoiled of his
-ill-gotten treasure. At the siege of Maestricht in 1795, the famous
-skull to which Hofmann had devoted so much anxious thought and labor,
-fell into the hands of the French and was carried off as one of the
-spoils of war. So widely celebrated had the specimen become during
-the fifteen years which had elapsed since its discovery, through the
-writings of several noted scientific men, that the French general
-commanded his artillerists to spare the house in which it was known to
-be. The canon, however, shrewdly suspecting that such an unexpected and
-extraordinary mark of favor was not for his own sake but rather for
-the sake of the famous fossil, had it removed and carefully hidden in
-a house in the city. After the capitulation of Maestricht the eagerly
-sought-for fossil was not to be found, and the offer of a reward of six
-hundred bottles of wine, so the story goes, was made for its recovery.
-So tempting was the offer that, ere long, it was brought in triumph to
-the house of St. Faujas de Fond, by a half-dozen grenadiers, whence it
-was later transferred to Paris, where it now is.</p>
-
-<p>We may well sympathize with Dr. Hofmann in the loss of his cherished
-specimen, since, had it not been for his zeal, money, and labor, it
-would never have escaped the usual fate of such things—complete
-destruction. But we must remember that St. Faujas de Fond, the recorder
-of this history, was a Frenchman, and somewhat interested in robbing
-the reverend canon of it; possibly there is another side of the story
-which has never been told.
-<span class="pagenum" id="Page_150">[Pg 150]</span></p>
-
-<p>After peace was declared, one has regretfully to add that the canon,
-not Dr. Hofmann, was reimbursed for it, or so it is said. Cuvier rather
-naïvely says that it was ceded to the Garden of Plants of Paris,
-perhaps in the way that many other things are ceded to the conqueror
-in time of war. The specimen is really a good one, even when compared
-with many found in recent years, and there is little wonder that the
-cupidity of St. Fond was incited by it. Casts of it are now or have
-been in nearly every noted museum of the world, and pictures of it
-illustrated nearly every textbook of geology published during the
-first three-quarters of the past century. It had been the subject of
-considerable controversy even before it came into the hands of Cuvier.
-Peter Camper figured and described the skull as that of a whale or
-“breathing fish”; while St. Fond himself later called it a crocodile.
-Crocodile or alligator skeletons were rare in those days, and St. Fond
-made a special trip to the British Museum to study one. But it was
-really Adrian Camper, a son of Peter Camper, who deserves the credit,
-so often wrongly ascribed to Cuvier, for the recognition of the true
-nature of the fossil. He insisted that the animal was a lizard allied
-to the living monitors, an opinion which it will be seen has finally
-been proved to be correct within very recent years.</p>
-
-<p>In 1808 this famous skull, and all other known remains of a similar
-nature, came under the observation of Cuvier, the renowned French
-naturalist and paleontologist, who confirmed the views of Adrian
-Camper. He fully described and figured all the known parts of the
-skeleton that had later come to light, calling the animal the great
-lizard of the Meuse, the river near which Hofmann’s specimen was found.
-Conybeare, a well-known paleontologist of England, some years later
-formally christened it <i>Mosasaurus</i>, a transliteration of Cuvier’s
-phrase, from the Latin <i>Mosa</i>, for Meuse, and <i>saurus</i>, a
-lizard. For more than half a century Cuvier’s figure of the skull
-of the original specimen appeared in works on geology over the name
-<i>Mosasaurus hofmanni</i>, or <i>Mosasaurus camperi</i>. One could
-wish that the former name for the species might prevail, in recognition
-of the zealous doctor who was so shabbily treated in his possession of
-the specimen.
-<span class="pagenum" id="Page_151">[Pg 151]</span></p>
-
-<p class="space-below2">For some years the few specimens discovered
-by Drouin and Hofmann were all that were known of the mosasaurs. A
-few others of related forms were discovered in England, and some were
-reported from New Jersey by early explorers, but there was little
-published about the mosasaurs till 1843, when Dr. August Goldfuss,
-a noted German paleontologist, described and beautifully figured an
-excellent specimen from the United States. This specimen also had a
-rather eventful history. It was discovered early in the fourth decade
-by Major O’Fallen, an Indian agent, near the Great Bend of the Missouri
-River, whence it was transported by him to St. Louis and placed in his
-garden as a curiosity. It happened that Prince Maximilian of Wied,
-the famous naturalist, in his travels through the United States, saw
-the specimen and secured it, taking it to Germany on his return. He
-presented it to the Museum of Haarlem where Goldfuss saw and described
-it. Rather oddly, this specimen was of a species closely allied to the
-original one of Maestricht, a species which has since only rarely been
-found. It was called <i>Mosasaurus maximiliani</i> by Goldfuss, though
-some time previously, it has since been found, some fragments of the
-same species were described by Harlan, an American author, under the
-name <i>Ichthyosaurus missouriensis</i>. Goldfuss’ paper was strangely
-overlooked by subsequent writers, and it was not till the discovery of
-numerous remains of mosasaurs by Leidy, Cope, and Marsh in the chalk of
-western Kansas, nearly thirty years later, that much was added to the
-world’s knowledge of these strange reptiles.</p>
-
-<div id="FIG_69" class="figcenter">
-  <img  src="images/fig69.jpg" alt="" width="600" height="72" />
-  <p class="blockquot space-below2">
-    <span class="smcap">Fig. 69.</span>—Skeleton of <i>Plalecarpus</i> as
-    mounted in the Paleontological Exhibit. Walker Geological Museum,
-    University of Chicago.</p>
-</div>
-
-<p><span class="pagenum" id="Page_152">[Pg 152]</span>
-Perhaps nowhere in the world are the fossil remains of marine animals
-more abundantly and better preserved than in these famous chalk
-deposits of Kansas. The exposures are of great extent—hundreds of
-square miles—and the fossil treasures they contain seem inexhaustible.
-Long-continued explorations by collectors have brought to light
-thousands of specimens of these swimming lizards, some of them of
-extraordinary completeness and perfect preservation, so complete and
-so perfect that there is scarcely anything concerning the mosasaurs
-which one might hope to learn from their fossil remains that has not
-been yielded up by these many specimens. The complete structure and
-relations of all parts of the skeleton, impressions of the bodies made
-in the soft sediments before decomposition had occurred, the character
-of their food, the nature of the skin covering, and even some of the
-color markings of the living animals have all been determined with
-certainty. Not only from Kansas, but also from many other parts of the
-world, have remains of these animals been discovered, until now it may
-truthfully be said that no other group of extinct reptiles is better
-represented by known fossil remains than the mosasaurs. From England,
-Belgium, Russia, and France in Europe; from New Jersey, Georgia,
-Alabama, Mississippi, Texas, New Mexico, Colorado, Kansas, Nebraska,
-the Dakotas, Wyoming, and other places in the United States; from New
-Zealand and South America they have been obtained in greater or less
-abundance and perfection.</p>
-
-<div id="FIG_70" class="figleft">
-  <img  src="images/fig70.jpg" alt="" width="150" height="289" />
-  <p class="center">
-     <span class="smcap">Fig. 70.</span>—Tooth<br /> of <i>Tylosaurus</i>.</p>
-</div>
-
-<p>Their geological history is relatively brief, notwithstanding their
-wide distribution over the earth in such great numbers and diversity.
-The earliest are known from near the beginning of the Upper Cretaceous
-of New Zealand, whence it is believed by some that they migrated to
-other parts of the world, appearing in North America some time later.
-They reached their culmination in size, numbers, and variety very soon,
-and then disappeared forever before the close of Cretaceous time. The
-largest complete specimen of a mosasaur known measures a little more
-than thirty feet in length, but incomplete skeletons of others indicate
-a maximum length of about forty feet. The skulls of the largest species
-are about five feet long. The smallest known adult skeletons are
-<span class="pagenum" id="Page_153">[Pg 153]</span>
-scarcely eight feet in length. There are now known at the present time
-seven or eight genera of three distinct types, all belonging to one
-family, the Mosasauridae, including about twenty-five known species.
-While a few of the genera are widely distributed over the earth, the species
-are all of restricted range, indicating, perhaps, non-migratory habits.</p>
-
-<p>The adaptation of the mosasaurs to an aquatic life was very complete,
-though perhaps not so complete as was that of the ichthyosaurs. The
-skull is flattened, narrow, and more or less elongate, but large in
-proportion to the remainder of the skeleton—nearly one-sixth of the
-entire length; that relative size doubtless is indicative of very
-predaceous and pugnacious habits. The teeth in the typical forms are
-numerous, strong, and sharp, conical in shape, and recurved. Not
-only are there numerous teeth in both the upper and lower jaws, but
-there are also two rows of strong teeth implanted in the back part of
-the palate, upon bones called pterygoids, the use of which will be
-understood later. The teeth were inserted on large, tumid, bony bases,
-rather loosely attached in shallow pits or alveoli, unlike the teeth of
-all modern lizards. Such a mode of attachment of the teeth doubtless
-had some relation to the habits of the animals concerning which we
-are not quite clear. They were easily dislodged, and, in consequence,
-of very unequal size, some full grown, some small, and others just
-appearing above the surface of the gums in the living animals. The
-frequent loss of teeth and their constant and easy replacement by new
-ones is a peculiarity of predaceous reptiles, thereby insuring their
-best functional use.</p>
-
-<p>The external nostrils, of large size, were situated at a considerable
-distance back of the end of the snout, but not nearly so far back or so
-near the eyes as were the nostrils of the ichthyosaurs, plesiosaurs,
-<span class="pagenum" id="Page_154">[Pg 154]</span>
-and phytosaurs. Their size and position suggest a use like that of the
-modern aquatic monitors, as mentioned on a preceding page. The eyes
-were of moderate size, those of the less purely aquatic forms being
-directed more laterally than those of species of more distinctly diving
-habits. They were protected by a stout ring of bony plates, as were the
-eyes of all truly aquatic reptiles of the past. The ears, also, in most
-if not all mosasaurs, had a thick cartilaginous ear-drum in place of a
-simple membrane, evidently, as Dollo has shown, for better protection
-under undue pressure of the water in deep diving.</p>
-
-<div id="FIG_71" class="figcenter">
-  <img  src="images/fig71.jpg" alt="" width="600" height="136" />
-  <p class="blockquot space-below2">
-   <span class="smcap">Fig. 71.</span>—<i>Clidastes</i>, inner side of right
-   mandible: <i>ang</i>, angular; <i>art</i>, articular; <i>cor</i>,
-   coronoid; <i>pa</i>, prearticular; <i>sur</i>, surangular.</p>
-</div>
-
-<p>As in all other lizards, the bones with which the lower jaws
-articulate, the quadrates, were loosely attached at the upper end,
-permitting great freedom of movement in all directions, more even than
-the land lizards have. The lower jaws were long and powerful, armed
-with a single row of teeth on each side, from sixteen to eighteen
-in number. Just back of the teeth, a little beyond the middle, each
-mandible has a remarkable joint, quite unknown in land lizards, though
-a trace of it is found in the monitors, permitting much movement
-between the front and back parts, both laterally and vertically, though
-chiefly in the former direction. Furthermore, as in land snakes but not
-as in land lizards, the front ends of the two sides of the jaws were
-somewhat loosely attached to each other by ligaments. This looseness of
-the two sides of the jaws, not only in front but also behind, together
-with the joint in each, was of the greatest use in swallowing prey, as
-will be explained farther on.
-<span class="pagenum" id="Page_155">[Pg 155]</span></p>
-
-<div id="FIG_72" class="figcenter">
-  <img  src="images/fig72a.jpg" alt="" width="600" height="189" />
-  <img  src="images/fig72b.jpg" alt="" width="600" height="251" />
-  <img  src="images/fig72c.jpg" alt="" width="600" height="212" />
-  <p class="blockquot space-below2">
-   <span class="smcap">Fig. 72.</span>—Skulls of mosasaurs. Upper figure,
-   <i>Clidastes</i>, from the side; middle figure, <i>Platecarpus</i>,
-   from below; lower figure, <i>Tylosaurus</i>, from above: <i>an</i>,
-   angular; <i>bs</i>, basisphenoid; <i>c</i>, coronoid; <i>ep</i>,
-   epipterygoid; <i>fr</i>, frontal; <i>j</i>, jugal; <i>l</i>, lacrimal;
-   <i>m</i>, maxilla; <i>na</i>, nasal; <i>oc</i>, occipital condyle;
-   <i>pa</i>, parietal, palatine; <i>pm</i>, premaxilla; <i>pf</i>,
-   prefrontal; <i>pt</i>, pterygoid; <i>po</i>, postorbital; <i>q</i>,
-   quadrate; <i>sp</i>, splenial; <i>sq</i>, squamosal; <i>tr</i>,
-   transverse; <i>v</i>, vomer.</p>
-</div>
-
-<p>As in most other aquatic reptiles, the neck was short and strong, the
-vertebrae being less in number than in most other lizards. The trunk
-was long and slender, more especially so in the surface-swimming kinds,
-with from twenty-two to thirty-four vertebrae. The tail was long, no
-longer than the tail of some land lizards, but more powerful, and
-broader and flatter. It was expanded or dilated more or less toward
-the free end, that is, with the beginning of a terminal caudal fin,
-such as the more specialized ichthyosaurs and crocodiles possessed. The
-<span class="pagenum" id="Page_156">[Pg 156]</span>
-vertebrae were procoelous, that is, concave in front and convex behind,
-like those of most modern lizards and all modern snakes and crocodiles,
-but quite unlike the biconcave vertebrae of all other aquatic reptiles.
-This kind of articulation of the backbones gave greater firmness and
-strength to the spinal column, but decreased the flexibility, and its
-possession by these animals was doubtless due to their descent from
-land lizards which had already acquired it. The loss of flexibility,
-however, was partly compensated by the loss of the additional
-articulating surfaces of the tail.</p>
-
-<div id="FIG_73" class="figcenter">
-  <img  src="images/fig73.jpg" alt="" width="600" height="363" />
-  <p class="blockquot space-below2">
-   <span class="smcap">Fig. 73.</span>—<i>Platecarpus</i>; occipital view
-   of skull: <i>bo</i>, basioccipital; <i>eo</i>, exoccipital; <i>pf</i>,
-   postfrontal; <i>st</i>, stapes; <i>pt</i>, pterygoid; <i>q</i>, quadrate.</p>
-</div>
-
-<p>As in all other aquatic reptiles, it is in the limbs that the most
-striking characteristics of these water lizards or “sea-serpents” are
-found. The legs were so completely adapted to an aquatic mode of living
-that the animals must have been practically helpless upon land, able
-perhaps to move about in a serpentine way when accidentally stranded
-upon the beaches, but probably never seeking the land voluntarily.
-The front limbs, like those of all other swimming animals having a
-powerful propelling tail, were larger than the hind ones, though not
-very much so. The bones of the first two segments, that is, the arm,
-forearm, and thigh and leg bones, were all short and broad, resembling
-those of the ichthyosaurs more than those of any other reptiles, save
-perhaps the thalattosaurs, discussed below. The articular surfaces
-of all the limb bones, as in other aquatic animals, were restricted
-in extent, indicating limited motion between the joints, though
-doubtless having great flexibility. In the most specialized types,
-such as <i>Tylosaurus</i>, the wrist and ankle bones were almost
-wholly cartilaginous, just as they are in the water salamanders, and
-in whales and porpoises. This tendency of the ends of long bones, the
-wrists and ankles as well as other bones of the skeleton, to become
-more cartilaginous, or less well ossified, in animals purely aquatic in
-<span class="pagenum" id="Page_157">[Pg 157]</span>
-habit is a marked one. So much is this the case that paleontologists
-always suspect water habits in reptiles showing it, even though but few
-parts of the skeleton are known.</p>
-
-<div class="figcontainer">
-  <div class="figsub">
-   <img id="FIG_74" src="images/fig74.jpg" alt="" width="200" height="388" />
-   <p class="center"><span class="smcap">Fig. 74.</span>—<i>Clidastes</i>;<br />
-    left front paddle: <i>c</i>, coracoid;<br />
-    <i>h</i>, humerus; <i>r</i>, radius;<br />
-    <i>sc</i>, scapula; <i>u</i>, ulna.</p>
-  </div>
-  <div class="figsub">
-    <img id="FIG_75" src="images/fig75.jpg" alt="" width="180" height="368" />
-   <p class="center space-above2">
-    <span class="smcap">Fig. 75.</span>—<i>Tylosaurus</i>;<br />
-    left front paddle: <i>c</i>, coracoid;<br />
-    <i>sc</i>, scapula; <i>h</i>, humerus;<br />
-    <i>r</i>, radius; <i>u</i>, ulna.</p>
-   </div>
-</div>
-
-<p>Increase in the number of bones of the digits is a more or less
-conspicuous characteristic of all mosasaurs. In those forms in which
-the wrists and ankle bones had become cartilaginous in great part, as
-many as eleven phalanges have been observed in the longest toes, though
-in other forms, those with more completely ossified wrists and ankles,
-only two or three additional bones have been developed in the longest
-<span class="pagenum" id="Page_158">[Pg 158]</span>
-fingers and toes by aquatic habits. The pliability and flexibility of
-the fingers and toes were certainly very great, but they could not
-possibly have been flexed or bent so as to grasp or seize anything;
-and of course all vestiges of claws had disappeared. Many specimens
-have been found with all the bones of the limbs, that is, the “paddle
-bones,” in the positions they occupied when the animals died. Figures
-of three such specimens, made from photographs or careful drawings by
-the writer, are shown herewith (<a href="#FIG_74">Figs. 74-76</a>). In several such
-specimens very clear impressions of the smooth membranes between the fingers have
-been observed, and in one specimen preserved in the collections of the
-University of Kansas the outline of the fleshy parts connecting the
-paddle with the body has been preserved.</p>
-
-<div id="FIG_76" class="figcenter">
-  <img  src="images/fig76.jpg" alt="" width="600" height="326" />
-  <p class="blockquot space-below2">
-    <span class="smcap">Fig. 76.</span>—<i>Platecarpus</i>; right front
-    paddle: <i>h</i>, humerus; <i>r</i>, radius; <i>u</i>, ulna.</p>
-</div>
-
-<p>It will be seen by comparison of the figures of the mosasaur paddles
-with those of the ichthyosaurs and plesiosaurs that there was a wide
-difference in their structure, though all have the characteristic
-shortening of the limb bones and increase in the numbers of the
-finger and toebones, that is hyperphalangy. It is probable that these
-differences mean a more powerful and varied use of the limbs in the
-mosasaurs. It is certain that the mosasaurs were much more predaceous
-and pugnacious in their habits than were any other truly aquatic
-backboned air-breathing animals of the past or present. They were the
-<span class="pagenum" id="Page_159">[Pg 159]</span>
-“land sharks” of the ancient seas, and probably the only ones among
-water reptiles that would be dangerous and offensive to man, were they
-all living today.</p>
-
-<p>For a long time it was thought that the mosasaurs had no breast
-bone, and that, in consequence, the front part of the thorax was
-expansible. Under this assumption the mosasaurs would have been much
-more snake-like in habit than they really were. The loose construction
-of the jaws doubtless permitted the swallowing of prey of considerable
-size, and the inference was that they habitually preyed upon animals of
-large size. A snake will often swallow a frog of larger diameter than
-its own body, the flexible jaws and loosely connected ribs permitting
-it to pass to the abdominal cavity. But the unyielding ring formed by
-the anterior ribs connected with the breast bone in the mosasaurs, as
-in other lizards, conclusively proves that large animals could not
-have been swallowed whole by the mosasaurs. In several instances the
-fossilized stomach contents, composed chiefly or wholly of fishes, have
-been found between the ribs of mosasaurs, and in none were the fishes
-more than two or three feet in length, though the reptiles were from
-sixteen to twenty feet long. Possibly the largest mosasaurs, those
-thirty or thirty-five feet in length, might have captured and swallowed
-fishes six or seven feet long, but in all probability their usual prey
-was of smaller relative size.</p>
-
-<div id="FIG_77" class="figcenter">
-  <img  src="images/fig77.jpg" alt="" width="600" height="188" />
-  <p class="blockquot space-below2">
-    <span class="smcap">Fig. 77.</span>—<i>Platecarpus</i>; pelvis, from
-    below: <i>p</i>, pubis; <i>il</i>, ilium; <i>is</i>, ischium.</p>
-</div>
-
-<p>The very loose construction of the pelvic bones, those to which
-the hind legs are articulated, is an evidence of more complete
-adaptation to water life than was or is the case with any other water
-air-breathers except the ichthyosaurs and cetaceans. The sacrum
-had entirely lost its function as a support to the pelvis and had
-disappeared, that is, the vertebrae composing it had become quite like
-<span class="pagenum" id="Page_160">[Pg 160]</span>
-the adjacent ones, by the loss of the ribs connecting them with the
-ilium. The small pelvis was suspended loosely in the walls of the
-abdomen, or at the most was feebly connected with a single vertebra
-by ligaments. It was entirely useless as a support for the legs.
-The mosasaurs could not possibly have raised their bodies from the
-ground while on land. It is well known that the land lizards and the
-crocodiles raise their bodies free from the ground while running or
-walking; none drags its body over the surface.</p>
-
-<div id="FIG_78" class="figcenter">
-  <img  src="images/fig78.jpg" alt="" width="600" height="238" />
-  <p class="center space-below2">
-    <span class="smcap">Fig. 78.</span>—Photograph of carbonized remains of
-    scales of <i>Tylosaurus</i>.</p>
-</div>
-
-<p>In several instances complete or nearly complete skeletons of mosasaurs
-have been discovered with the different bones nearly all in the
-positions and relations they had after the decomposition of the flesh,
-together with the carbonized remains of the skin and impressions of
-the investing scales and membranes. The nature of the body covering is
-therefore known with certainty from nearly all parts of the body. The
-body everywhere, save on the membrane between the fingers and toes, and
-perhaps on the top of the skull, was covered with small overlapping
-scales, very much like those of the monitors. These scales, however,
-were small and smooth in comparison with the size of the animals, those
-of a mosasaur twenty feet in length being almost precisely the size of
-those of a monitor six feet long. The top of the skull seems to have
-been covered with horny plates, as in most lizards. In one instance
-parallel dark bars, obliquely placed, and of narrow width, formed by
-carbonized pigment, were observed by the writer. As has been stated, in
-<span class="pagenum" id="Page_161">[Pg 161]</span>
-some instances fish bones and fish scales have been observed among
-the fossilized stomach contents, and it is quite certain that the
-food of these creatures must have been composed chiefly of fishes,
-though of course it is not improbable that other small vertebrates,
-birds, pterodactyls, the young of plesiosaurs, and possibly small
-mammals, may occasionally have formed a part of their diet. That the
-mosasaurs were very pugnacious in life is conclusively proved by the
-many mutilations of their bones that have been observed, mutilations
-received during life and partly or wholly healed at the time of death.
-Bones of all vertebrates are repaired after injury by the growth of
-more or less spongy osseous material about the injured part, forming a
-sort of natural splint. This material is more or less entirely removed
-by absorption when it is no longer required for the support of the
-broken ends. Many such injured bones of the mosasaurs have been found;
-sometimes the bones of the hands and feet have grown together, and not
-infrequently the vertebrae have been found united by these osseous
-splints; occasionally even the skull itself, especially the jaws,
-attest extensive ante-mortem injuries. In a single instance the writer
-has observed the loss of a part of the tail, where it probably had been
-bitten off. It may be mentioned, however, that the bones of the tail
-had no such “breaking points” in the mosasaurs as have those of many
-land lizards, whereby a part or all may be lost as a result of even a
-trivial injury, and then regrown. Such a condition in an organ relied
-upon entirely for propulsion would have been immediately fatal to the
-existence of the mosasaurs. The large jaws and teeth are in themselves
-sufficient evidence of the fiercely carnivorous propensities of the
-mosasaurs. The constant renewal of the sharply pointed teeth, thereby
-preventing deterioration by use or accident, preserved, even in the
-oldest animals, the effectiveness of the youthful structure.</p>
-
-<p>We may now understand how the mosasaurs seized and swallowed their
-prey. Living constantly in the water, away from all firm objects, with
-small, short limbs quite incapable of holding struggling prey, and
-the body not sufficiently serpentine to hold it in its folds after
-the manner of snakes, the mosasaurs would have found it difficult or
-impossible to swallow fishes of even moderate size, were their jaws of
-<span class="pagenum" id="Page_162">[Pg 162]</span>
-the same construction as are those of the land lizards. If they preyed
-upon small animals only, or if they tore their prey to pieces after the
-manner of the alligators, there would have been no especial difficulty
-in deglutition. But it is certain that the animals which the mosasaurs
-devoured were not always small, and they must have been swallowed
-whole, since their teeth were not adapted, like those of the alligators
-and true crocodiles, for the rending of bodies. One who has watched a
-snake swallow a frog or another snake will appreciate the difficulties
-against which the mosasaurs contended in swallowing fishes a fifth or a
-sixth of the length of their own bodies. The ordinary snake, no matter
-where or how it seizes its prey, invariably swallows it head first. Its
-mandibles are even more loosely united in front than were those of the
-mosasaurs, and while there is no joint in the snake’s mandibles such
-as there is in the mosasaurs’, the loose union of the various bones of
-the mandibles serves the same purpose. The frog or lizard, while firmly
-held by the slender teeth, is slowly moved sideways by the alternate
-lateral action of the jaws till the head is reached. Many non-poisonous
-snakes, if they find it impracticable or impossible to reverse the
-position of their prey in this way, wrap the folds of their body about
-it, holding it firmly while they release their mouth-hold and seize
-it by the head. An amusing instance of these habits came under the
-observation of the writer not long ago, in Texas. A large “blue racer”
-(<i>Bascanion</i>), six feet four inches in length, caught an unusually
-large bullfrog by one hind leg, but in almost less time than it takes
-to relate, the head of the frog had entered the snake’s gullet and the
-mouth was closed over it, notwithstanding the vigorous muscular and
-vocal protests on the part of the frog. Wishing to secure the skull
-of the snake for his collection, the writer seized an ax standing
-conveniently by and cut the snake cleanly in two. The peristaltic
-action of the deglutitional muscles carried the frog slowly on about
-two feet farther to the ax-made orifice, from which it emerged, and,
-after a few croakings against such unkind usage, calmly hopped off into
-the near-by pool of water! Many poisonous snakes release their prey
-after killing it; other snakes may force their prey down the throat by
-pressing it against the ground.
-<span class="pagenum" id="Page_163">[Pg 163]</span></p>
-
-<p>Even small fishes could not possibly have been swallowed by the
-mosasaurs in any other way than head first, since the backwardly
-projecting, and often long, spines would have rendered any other
-procedure impossible. Even after the head had entered the gullet,
-deglutition could have been effectively completed only by the aid of
-some mechanism whereby the fish could have been pulled or pushed back
-into the constricting fauces. The strong teeth of the upper jaws and
-palate held firmly the struggling prey, while the loosely united jaws,
-bending laterally at the joint back of the middle, either alternately,
-or more probably in unison, steadily forced it far enough back to be
-seized by the muscles of the fauces.</p>
-
-<p>The shape of the mosasaurs, though slender, does not suggest
-extraordinary speed in the water; doubtless most of the fishes that
-lived in the seas with them could swim faster than they. Their prey
-was captured, for the most part at least, by sudden and quick lateral
-movements, for which their powerful and flexible paddles admirably
-adapted them.</p>
-
-<p>It is a rather remarkable fact that, among the thousands of specimens
-of mosasaurs which have been collected during the past forty years in
-both Europe and North America, there never has been found one of a
-very young animal. Of almost all other animals occurring abundantly
-as fossils some specimens are sure to be discovered of young and even
-embryonic individuals. It is quite certain that all such voracious
-monsters as were the mosasaurs did not die of old age. Some specimens,
-it is true, have been found that were evidently not full grown animals,
-but the observed differences in the size of the fossil bones are not
-great. All are of adult or nearly adult animals. If the mosasaurs were
-oviparous, as were the ichthyosaurs, and probably the plesiosaurs,
-and as are some living land lizards, the apparently entire absence of
-embryonic bones associated with often nearly complete skeletons of the
-mosasaurs is inexplicable; certainly <i>some</i> mosasaurs must have
-died a short time before the birth of their young. But embryos have
-never been discovered, though numerous skeletons inclosing fossilized
-stomach contents have been found. From this fact it would seem very
-<span class="pagenum" id="Page_164">[Pg 164]</span>
-probable that the mosasaurs were oviparous, as are most other lizards.
-But this, after all, may be a hasty inference.</p>
-
-<p>No known reptiles lay their eggs in the water. Perhaps there is some
-reason why the eggs of reptiles and birds, so different from those of
-fishes and amphibians, cannot hatch in water; and there is no good
-reason for supposing that the mosasaurs were exceptions to this rule.
-Unless carefully hidden or protected by the parent, the eggs or very
-young of the mosasaurs would have been subject to many and grave
-dangers. Fish eggs are usually small and produced in great numbers,
-thousands often being extruded from a single female. Among so many
-there is a greater probability that at least two will hatch and survive
-to maturity, reproducing their kind. It is unreasonable to suppose
-that the lizards of the past were more prolific of eggs than are their
-relatives now living; nor is it possible that their eggs could have
-been as small as are those of most fishes. Modern lizards seldom lay
-more than twenty-five or thirty eggs at a time; even the turtles, with
-their greater vicissitudes, seldom produce more than one hundred. The
-eggs of the mosasaurs were certainly large and few in number, and the
-young animals must have begun breathing air immediately after escaping
-from the shells. If the mosasaurs were oviparous they must have laid
-their eggs upon the shores and beaches, as do the sea-turtles and the
-Crocodilia. Nor is it at all probable that the female mosasaurs gave
-even that protection to their eggs or young that the crocodiles and
-turtles give. The young mosasaurs, perhaps reaching a foot in length,
-must have been left entirely to their own devices and their own fate at
-the very earliest stages of their independent careers.</p>
-
-<p>The waters in which the mosasaurs abounded swarmed with many kinds of
-predaceous fishes, to say nothing of the hordes of their own kinds, all
-carnivorous in the highest degree, to all of which the tender saurians
-must have been choice food. Possibly the shallow waters of the bays and
-estuaries may have afforded protection to the newly hatched reptiles.
-It would seem probable that the female mosasaurs went up the rivers
-for a shorter or longer distance to lay their eggs or give birth to
-their young, and that the young reptiles remained in such relatively
-<span class="pagenum" id="Page_165">[Pg 165]</span>
-protected places until of a sufficient size to cope with the fierce
-enemies of the open seas. We know practically nothing of the
-inhabitants of the lakes and rivers during all the time in which the
-mosasaurs existed; and this perhaps is the real reason why we have
-never yet found a specimen of a young mosasaur.</p>
-
-<div id="FIG_79" class="figcenter">
-  <img  src="images/fig79.jpg" alt="" width="600" height="329" />
-  <p class="center space-below2">
-    <span class="smcap">Fig. 79.</span>—Head of <i>Tylosaurus</i>.</p>
-</div>
-
-<p>We have seen that many skeletons of ichthyosaurs are found entire, and
-but little disturbed in position, suggesting, if not proving, that the
-animals as a rule lived and died far out in the deep seas, away from
-the disturbing effects of currents of water on their decaying bodies.
-Among the thousands collected, the great majority of the specimens
-of mosasaurs consist of a few bones or a part of the skeleton only.
-Moreover, nearly all specimens show the disturbing effects of currents
-of water; and the bones are usually associated with those of turtles,
-birds, and flying reptiles, which probably did not often venture far
-from the shores; all of which goes to prove that the mosasaurs in
-general lived in the comparatively shallow waters of the seas, and
-not far from the shores. That some were excellent divers, descending
-probably many fathoms deep in the water, is certain, because of the
-extraordinary protective structures of the eyes and ears.</p>
-
-<p>But the various kinds of mosasaurs differed not a little in their
-habits. Some, like <i>Mosasaurus</i> and <i>Clidastes</i>, were
-doubtless chiefly surface swimmers, as is evidenced by their better
-ossified bones, firmer articulation, and the presence of the additional
-<span class="pagenum" id="Page_166">[Pg 166]</span>
-zygosphenal articulations of the vertebrae, wanting in other forms,
-as also by the structure of their paddles. They had a relatively long
-body and short tail, the tail having a more pronounced distal expansion
-than in the case of other forms, and the eyes looking laterally, not
-at all upward. The feet, as shown in <a href="#FIG_74">Fig. 74</a>, were broad
-and short, with most of the wrist and ankle bones well ossified, and with but few
-extra bones in the digits. <i>Tylosaurus</i> (<a href="#FIG_79">Fig. 79</a>), on the
-other hand, had a more slender skull, the nostrils were situated farther
-back from the tip of the snout, the tail was longer and more powerful,
-and the feet were very highly specialized (<a href="#FIG_75">Fig. 75</a>). The wrist
-and the ankle were almost wholly cartilaginous, the fifth finger and fifth toe
-were much longer, and the number of phalanges was greatly increased.
-Moreover, the bones of the skeleton are more spongy, the joints are
-more cartilaginous, and the ears were better protected by a heavy coat
-of cartilage. In most of these respects the genus <i>Platecarpus</i>
-was intermediate between <i>Clidastes</i> and <i>Tylosaurus</i> (<a href="#FIG_76">Fig. 76</a>).</p>
-
-<p>Like nearly all other lizards, the mosasaurs had a pineal opening
-in the skull, but it is not at all probable that they possessed a
-functional pineal eye.</p>
-
-<p>Many and varied have been the opinions of scientific men regarding
-the relationships of these animals, as has been intimated. They were
-thought to be a kind of whale or breathing fish by Peter Camper;
-crocodiles, by St. Fond; and aquatic lizards, by Adrian Camper and
-Cuvier. The late Professor Cope thought they were more nearly related
-to the snakes than to the lizards, and that they might even have been
-the ancestral stock from which the snakes have descended. Because
-of this belief he gave to them the name Pythonomorpha, meaning
-python-like, and this name, really the first ever applied to them, is
-yet often used instead of Mosasauria. A more complete knowledge of
-the mosasaurs, however, and especially the recent discoveries of the
-semiaquatic connecting links, called the aigialosaurs and described
-on a preceding page, have set at rest all doubt as to their real
-affinities. They are real lizards, differing less from the living
-monitor land lizards than do the monitors from some other land lizards,
-especially the amphisbaenas and chameleons. And to Adrian Camper is due
-<span class="pagenum" id="Page_167">[Pg 167]</span>
-the credit for the recognition of their real relationship, though it
-required more than a century to prove that he was right.</p>
-
-<div id="FIG_80" class="figcenter">
-  <img  src="images/fig80.jpg" alt="" width="600" height="293" />
-  <p class="center space-below2">
-    <span class="smcap">Fig. 80.</span>—<i>Globidens alabamensis.</i><br />
-    Part of mandible, with teeth.<br /> (From Gilmore.)</p>
-</div>
-
-<p>Very recently, and since the foregoing was written, a remarkable new
-type of mosasaurs has been discovered in Alabama and Europe. Only
-fragmentary jaws, a few vertebrae, and some skull bones are known,
-so that it is impossible yet to decide how closely the new form is
-related to the true mosasaurs, but so far as the evidence goes the
-only distinguishable character is the teeth. These, instead of being
-elongated and pointed, are nearly spherical, as shown in <a href="#FIG_80">Fig. 80</a>.
-Such teeth could have been used only for crushing shell-fish, and not at all
-for the seizure and retention of slippery fishes. The genus, which was
-called <i>Globidens</i> by its discoverer, Mr. Gilmore, includes two
-known species, from Alabama and Europe, the latter recently described
-by Dollo. It has been suggested that this peculiar kind of dentition
-was a more primitive or intermediate one, a kind that the first
-mosasaurs had before they became fully adapted to the water; but this
-is doubtful, since <i>Globidens</i> comes from late Cretaceous, and
-must be one of the later types. If <i>Globidens</i> is a true mosasaur,
-and it seems to be one, its life-habits must have been remarkably
-different from those that have long been known. Possibly when the limbs
-and more of the skull are found, <i>Globidens</i> will prove to be of a
-distinctive type.
-<span class="pagenum" id="Page_168">[Pg 168]</span></p>
-
-<h3>SNAKES</h3>
-
-<p>The chief differences between snakes and lizards have already been
-given and need not be repeated, save very briefly. Snakes are always
-functionally legless, though some have vestiges of the hind pair;
-the brain-case is wholly bony; the upper temporal bar is wanting;
-the lower jaws are united in front by ligaments only, like those of
-the mosasaurs; the vertebrae are greatly increased in number, and
-always have the additional zygosphenal articulations like those of
-<i>Clidastes</i> and <i>Mosasaurus</i> and some lizards; there is but
-one lung, and the eyes are always without free eyelids. But these
-characters are really not very important, since every one of them is
-found in the lizards or mosasaurs, except the complete ossification of
-the brain-case, and even this is partly ossified in the mosasaurs. It
-is rather the presence of all these characters which distinguishes a
-snake from a lizard.</p>
-
-<p>The number of living snakes is nearly as great as that of the living
-lizards, and their distribution over the earth is very similar. Snakes
-are for the most part strictly terrestrial in habit. Some live more
-or less among trees, and some live in the water, though with but few
-exceptions all are fully capable of rapid progression upon land. They
-are almost invariably carnivorous in habit, swallowing their prey
-whole, and usually alive, as has been described. Some poison their prey
-or crush it to death before swallowing it. Some feed upon eggs which
-are swallowed whole and then crushed in their stomachs by projecting
-bones from the under side of the vertebrae developed for that purpose.
-In size snakes vary from a few inches in length to twenty-five or more
-feet, no known extinct forms being larger than the living anacondas
-and boas. In geological history the earliest remains known date from
-the latter part of the Cretaceous, and it is quite probable that they
-have a briefer history than that of the lizards of which they are the
-descendants. Venomous serpents are known only from comparatively recent
-geological times, and it is probable that venomosity is the latest and
-final specialization of importance in the reptilian class.
-<span class="pagenum" id="Page_169">[Pg 169]</span></p>
-
-<div id="FIG_81" class="figcenter">
-  <img  src="images/fig81.jpg" alt="" width="500" height="436" />
-  <p class="center space-below2">
-    <span class="smcap">Fig. 81.</span>—<i>Hydrus bicolor</i>; sea-snake.<br />
-    (From Brehm)</p>
-</div>
-
-<p>Of strictly aquatic snakes there is no known geological history, and it
-is improbable that there is any such history. There are a few snakes
-now living—very venomous ones, allied to the deadly cobras—which
-have become so completely adapted to life in the water that they are
-unable to exist or even move about on land. These are the well-known
-sea-snakes of the Indian Ocean and adjacent waters. Perhaps the most
-highly specialized and typical of these is the black-banded sea-snake,
-<i>Distina cyanocincta</i>, which reaches a length of four or five
-feet, and is a rapid and excellent swimmer. From the figure (<a href="#FIG_81">Fig. 81</a>)
-it is seen that the body is very much flattened from side to side, and
-lacks or has but a few vestiges of the transverse scales on the under
-side so characteristic of all other snakes, and which enable them to
-move about on land. So helpless are these snakes on land that it is
-said sailors will handle them carelessly, because of their inability to
-bite while out of water, though the bite is very venomous. They never
-come on land for any purpose whatever, and their young, unlike those of
-<span class="pagenum" id="Page_170">[Pg 170]</span>
-most other snakes, are born alive. There are a number of species of
-these sea-snakes, though comparatively little is known of their habits.
-They are of especial interest as another example of the ways in which
-air-breathing land vertebrates have become adapted to water life. The
-adaptation, however, was simple, for nearly all snakes swim freely in
-water by undulatory movements; it would require not much change to
-convert an ordinary water snake into one like these sea-snakes.</p>
-<hr class="chap x-ebookmaker-drop" />
-
-<div class="chapter">
-<p><span class="pagenum" id="Page_171">[Pg 171]</span></p>
-<h2 class="nobreak" id="CHAPTER_XII">CHAPTER XII<br />
-<span class="h_subtitle">&nbsp;<br />THALATTOSAURIA</span></h2>
-</div>
-
-<p>Millions of years before the first appearance of the mosasaurs in
-geological history, another group of reptiles showing many curious
-resemblances to them attempted a rather precarious existence in the
-water. Its members survived long enough to acquire many structural
-adaptations to a water life, long enough to become diversely modified,
-but not long enough, apparently, to wander far from their birthplace,
-not long enough to attain that security from their enemies and more
-ambitious competitors, the early ichthyosaurs and plesiosaurs, to
-insure them a long existence. They were only a partial success as water
-reptiles.</p>
-
-<p>It has been only within a few years that we have had any knowledge
-whatever of them, and that knowledge is still very incomplete, too
-incomplete to justify any attempt to picture them as living animals,
-even though we take the liberties that some of our illustrators
-of extinct animals feel warranted in assuming. The first known
-specimens of these “sea-reptiles”—for that is the meaning of the
-word Thalattosauria—were discovered and described by Professor J.
-C. Merriam less than ten years ago, and all our knowledge of these
-animals is due to the same author, who has studied attentively the
-known specimens, all of which are preserved in the museum of the
-University of California. The first discovered fragmentary specimens
-were confounded with those of early ichthyosaurs, from the Upper
-Triassic rocks of northern California with which they were associated.
-No specimen has yet been found that is even approximately complete;
-some parts of the skeleton are not yet known, even from fragmentary
-remains, and not till other and more complete specimens have been found
-will it be possible to determine the real form of the living animals or
-to decide what their nearest relationships with other reptiles were.
-Professor Merriam thinks that they were related most closely with the
-<span class="pagenum" id="Page_172">[Pg 172]</span>
-Rhynchocephalia (<a href="#Page_176">p. 176</a>) of which the <i>Sphenodon</i>,
-or tuatera, of New Zealand is the only living representative, but whose direct
-genealogical history runs back nearly or quite to the time in which the
-thalattosaurs lived. On the other hand, there are so many resemblances
-to the mosasaurs shown in the remains that have been discovered, that
-it is possible the thalattosaurs were only a short-lived branch of the
-primitive lizards, which we also know were in existence at the time
-when the thalattosaurs lived. However, even though they resembled the
-mosasaurs, there could have been no direct genealogical relationships
-between them, for it is quite certain that the thalattosaurs very soon
-went out of existence, leaving no descendants. But it matters little
-which were the land forbears of the thalattosaurs; they present such
-distinct adaptations to water life—characters all their own—that
-their ancestral kinship may well be left to the future researches of
-the curious paleontologist. For the present, at least, they may well be
-placed in an order of reptiles all their own, as Professor Merriam has
-proposed—the Thalattosauria.</p>
-
-<div id="FIG_82" class="figcenter">
-  <img  src="images/fig82.jpg" alt="" width="600" height="208" />
-  <p class="center space-below2">
-    <span class="smcap">Fig. 82.</span>—Skull of <i>Thalattosaurus</i>.<br />
-    (After Merriam)</p>
-</div>
-
-<p>No thalattosaurs were large animals. If they had the same proportions
-between the lengths of head, body, and tail as the mosasaurs, none
-exceeded seven feet in length, and they may have been even shorter,
-though probably not much. The figure of the skull, as restored by
-Professor Merriam, shows many striking aquatic adaptations, in the
-elongated, pointed muzzle, in the large external nostrils, situated
-far back toward the eyes, and in the well-ossified ring of bones
-surrounding the eyeball. There is a parietal opening in the roof of the
-skull, as in the modern lizards and tuatera; but it is not known for
-<span class="pagenum" id="Page_173">[Pg 173]</span>
-certainty whether there were two openings on each side in the roof of
-the skull, as in the modern tuatera. While this character may seem
-trivial, it is really one of the most important in the reptilian
-anatomy in determining the relationship and classification of reptiles.
-The teeth are conical and pointed in the front end of the upper and
-lower jaws, but farther back they are rounded, rugose, and obtuse, and
-could have been used only for crushing hard objects, like mollusks,
-crustaceans, etc. (<a href="#FIG_82">Fig. 82</a>). And not only was there a row of
-such teeth on each jaw (only partly seen in the figure), but similar teeth covered
-a large part of the palate. And the lower jaws, it is seen, are rather massive.</p>
-
-<p>The vertebrae were, of course, of the more primitive kind, that is,
-with the ends concave, both in front and behind. It would have been
-strange indeed were they of any other kind, since reptiles with
-ball-and-socket joints to the vertebrae, that is, concave on one end
-and convex on the other, as in nearly all living reptiles, did not come
-into existence till long after the thalattosaurs had disappeared from
-geological history; and it is also a curious fact that such vertebrae
-appear to have originated only among animals crawling on land, so that
-they would not have been a character acquired by the thalattosaurs
-after descending into the water. It will be seen from the figure of
-a dorsal vertebra that the rib was attached by a single articular
-surface, almost exclusively to the body of the vertebra, quite like
-those of all lizards, snakes, and mosasaurs, and unlike those of
-other reptiles. This too may seem to be a trivial character to prove
-relationships with the lizards, but it is a curious fact that no two
-animals having different kinds of ribs are closely related to each
-other. Possibly, however, this looser mode of attachment of the ribs
-in the thalattosaurs was one of their peculiar adaptations to a water
-life, and may not have been derived from their land ancestors.</p>
-
-<div class="figcontainer">
-  <div class="figsub">
-   <img id="FIG_83" src="images/fig83.jpg" alt="" width="200" height="314" />
-   <p class="center">
-    <span class="smcap">Fig. 83.</span>—Dorsal vertebra<br />
-    of <i>Thalattosaurus</i>.<br /> (After Merriam.)</p>
-  </div>
-  <div class="figsub">
-    <img id="FIG_84" src="images/fig84.jpg" alt="" width="230" height="313" />
-   <p class="center">
-    <span class="smcap">Fig. 84.</span>—<i>Thalattosaurus</i>:<br />
-    bones of front extremity: <i>s</i>, scapula;<br />
-    <i>c</i>, coracoid; <i>h</i>, humerus;<br />
-    <i>r</i>, radius; <i>u</i>, ulna.<br /> (After Merriam.)</p>
-   </div>
-</div>
-
-<p>Of the limbs, only a few bones are known, but these are very
-instructive. The arm bones, as shown in <a href="#FIG_84">Fig. 84</a>, are strikingly like
-<span class="pagenum" id="Page_174">[Pg 174]</span>
-those of the mosasaurs, as will be seen by comparing the figure on <a href="#FIG_74">p. 157</a>.
-The humerus is a little more elongated than that of the mosasaurs,
-more nearly like the mosasaurian femur. The shoulder-blade and the
-coracoid are imperfectly ossified, as is seen from the figure—another
-characteristic of aquatic life. What the fingers and toes were like
-cannot be said; probably they were bound together by membrane, forming
-swimming paddles similar to those of the mosasaurs. Some of the bones
-referred to the pelvis are known, but it is not known whether they are
-united to the spinal column by a sacrum, as in land animals. Nor is
-anything certainly known of the hind leg or much of the tail. Since the
-front legs show marked aquatic adaptations, it is altogether certain
-that the hind legs will be found to be modified more or less, though
-not so much modified as the front legs, because, as we have seen, the
-front legs are always more specialized in aquatic animals than the
-hind ones, even as the hind legs are more specialized than the front
-ones in land animals. Possibly the hind legs will be found to be more
-like those of the Thalattosuchia, as shown on <a href="#FIG_110">p. 212</a>, that
-is, partly terrestrial in character. Doubtless the tail was long and flattened,
-possibly with a terminal fin-like dilation, though this is less probable.</p>
-
-<p>As regards the habits and food of the thalattosaurs, no better summary
-can be given than that of Professor Merriam, in his own words:</p>
-
-<div class="blockquot">
-<p>The remains of thalattosaurs are known only in purely marine
-deposits containing little or no material of terrestrial origin.
-They are associated with a fauna consisting of numerous forms, both
-vertebrate and invertebrate, which are not known to have existed
-away from marine areas. In the structure of the skeleton we find the
-abbreviated and broadened proximal segments of the limbs, the slender
-snout with prehensile terminal teeth, and the median superior nostrils,
-<span class="pagenum" id="Page_175">[Pg 175]</span>
-indicating a purely aquatic type. There can scarcely be room for
-doubt that the thalattosaurs as a group were typical marine forms.
-The larger and more specialized species comprised in the genus
-<i>Thalattosaurus</i> were strictly natatory. They may have visited the
-shore, but, like the plesiosaurs, were better fitted for swimming than
-for crawling. Of the smaller <i>Nectosaurus</i> we unfortunately do
-not know the limbs. They may have been considerably less specialized,
-and the animal to a correspondingly greater degree a shore-dweller.
-<i>Nectosaurus</i> is, however, found in the same deposits with other
-forms and appears to be as common as the others; so that it is safe to
-consider it as having passed the greater part of its life away from the
-shore.</p>
-
-<p>From what we know of the vertebral column of <i>Thalattosaurus</i>
-it appears that the animal had a relatively short neck and a long
-dorsal region, the proportions being nearly those in the vertebral
-column of some mosasaurs. Only the anterior portion of the caudal
-region is known. The slender, rounded neural spines with well-developed
-articulating processes seen here are not such as commonly appear
-in forms with a highly specialized sculling tail, and it is hardly
-probable that a caudal fin of large size was developed.</p>
-
-<p>The anterior limbs evidently formed paddles of moderate size.
-The posterior pair may have been larger, in compensation for lack
-of a strong sculling tail. It is, however, possible, that as in
-<i>Geosaurus</i> (of the thalattosuchian crocodiles) the hind limbs
-were not typically natatory, and the distal end of the tail was
-vertically expanded.</p>
-
-<p>No specimens have yet been found which are well enough preserved
-to show any remains of the stomach contents, and we have no definite
-evidence concerning the food of the thalattosaurs, more than is
-furnished by the general structure of the animal. The character of the
-paddles, the form of the skull, and the presence of slender prehensile
-teeth in the terminal portions of the jaws would indicate that they
-fed in part upon some swiftly moving prey which was caught by a quick
-snap of the jaws, deglutition being assisted by the curved teeth of the
-pterygoids. The heavy vomerine and posterior mandibular teeth may have
-been used for crushing the light shells of ammonites, which existed in
-vast numbers in the same seas.</p>
-</div>
-
-<hr class="chap x-ebookmaker-drop" />
-
-<div class="chapter">
-<p><span class="pagenum" id="Page_176">[Pg 176]</span></p>
-<h2 class="nobreak" id="CHAPTER_XIII">CHAPTER XIII</h2>
-</div>
-
-<h3>RHYNCHOCEPHALIA</h3>
-
-<p>In some of the small islands near the northeast coast of New Zealand
-certain small and peculiar, lizard-like reptiles, known as tuateras,
-have long been known. For many years they were supposed, even by
-scientific men, to be real lizards, so much do they resemble in
-external appearances and in habits the lizards of other parts of the
-earth. It was early observed, however, that they presented certain
-remarkable internal differences from the real lizards or Lacertilia,
-though it was not till about twenty-five years ago that the importance
-of these differences was recognized by the late Professor Cope, who
-separated them into a distinct order quite co-ordinate with the
-lizards, crocodiles, and turtles. These little reptiles, seldom
-reaching a length of two feet, have now become so scarce that the New
-Zealand government protects them by law from unnecessary destruction;
-nevertheless it will probably be only a short time before they become
-extinct, the end of a long genealogical line. No other living reptiles
-have retained more of the old-fashioned or primitive characters than
-this <i>Sphenodon</i> or <i>Hatteria</i>, as the animal is called,
-and because of them it is of peculiar interest to zoölogists, and
-especially paleontologists.</p>
-
-<p>The differences of these beaked lizards from the true lizards are
-especially noticeable in the skull, and more especially in the
-arrangement of the bones which give articulation to the lower jaws
-(<a href="#FIG_8">Fig. 8</a>). In the lizards and snakes the quadrate bone is
-loosely articulated at its upper end with the cranium, and has no inferior
-bar or arch connecting its lower end with the jugal and the back
-part of the upper jaw. <i>Sphenodon</i>, on the contrary, has the
-quadrate bone firmly fixed to its adjacent bones at both ends, and is
-quite immovable. The vertebrae are biconcave like those of all early
-reptiles, not concavo-convex as are the vertebrae of most other living
-reptiles. The intercentra or hypocentra, little wedge-shaped bones
-<span class="pagenum" id="Page_177">[Pg 177]</span>
-between the centra below, are more persistent in <i>Sphenodon</i> than
-in any other living land animals except the gecko lizards. Upon the
-whole the tuatera is the most old-fashioned of living reptiles, and in
-consequence it has nearly lost out in competition with new things.</p>
-
-<div id="FIG_85" class="figcenter">
-  <img  src="images/fig85.jpg" alt="" width="600" height="306" />
-  <p class="center space-below2">
-    <span class="smcap">Fig. 85.</span>—<i>Sphenodon punctatum</i>,
-    or tuatera.<br /> (From specimen in the Yale University museum.)</p>
-</div>
-
-<p>With these living tuateras we have nothing further to do, since they
-are land animals, living about the beaches of the New Zealand islands,
-and only occasionally venturing into the water, hiding from their
-enemies in the holes in the rocks. But, from some of their antecedents,
-from some of their direct forbears perhaps, there have gone off at
-different times various branches, whose descendants wandered into
-foreign lands or into foreign places, and lived and flourished for a
-brief time and then became extinct. Some of these went down into the
-water and became more or less aquatic in habit; some, indeed, changed
-their forms and habits so greatly that they are often, perhaps rightly,
-segregated into different orders. Whether or not they should be called
-Rhynchocephalia matters little, however. It is merely a matter of
-opinion as to how great the changes should be in order to entitle the
-offspring to a genealogical tree all its own. Of these branches there
-are two, whose relationships seem to be definite, the Choristodera and
-Thalattosauria, though there is more doubt about the latter than the
-former. A third group, that included <i>Pleurosaurus</i>, seems, from
-<span class="pagenum" id="Page_178">[Pg 178]</span>
-more recent discoveries, to belong to a different line of descent and
-has been described under the Protorosauria.</p>
-
-<p>In the direct line of ancestry there is no known form that was
-distinctly aquatic. The oldest known of these, perhaps, is that shown
-in <a href="#FIG_86">Fig. 86</a>, <i>Sapheosaurus</i> from the Jurassic of Solenhofen.
-Its resemblance to the modern tuatera is great, and doubtless its habits
-were very similar, though its rather long tail and rather short neck
-possibly indicate subaquatic habits.</p>
-
-<div id="FIG_86" class="figcenter">
-  <img  src="images/fig86.jpg" alt="" width="600" height="254" />
-  <p class="center space-below2">
-    <span class="smcap">Fig. 86.</span>—<i>Sapheosaurus</i>,<br />
-    an Upper Jurassic rhynchocephalian.<br />
-    (After Lortet.)</p>
-</div>
-
-<h3>CHORISTODERA</h3>
-
-<p>Among the many reptiles of the past which have sought a more congenial
-or a safer home in the water few have had a more interesting history,
-or a briefer one, than those to which the late Professor Cope gave
-the name Choristodera in 1876. Many students of repute consider the
-group an order, others a suborder of the Rhynchocephalia. The group,
-whether order or suborder, are interesting because of their long and
-devious migrations from western North America to Europe, or vice versa,
-through rivers and ponds; interesting also because of the persistence
-of certain old-fashioned traits that clung to them long after their
-disappearance in other animals. Perhaps these traits were among the
-causes of their merely moderate success as animals of the water, traits
-that led to their early dissolution. Like the proganosaurs, which they
-must have resembled in external appearance not a little, they wandered
-from their birthplace in the western continent, to perish in the
-eastern; and like them their span of existence was short.
-<span class="pagenum" id="Page_179">[Pg 179]</span></p>
-
-<p>Their history among mankind, too, is brief. The first known specimens,
-from western North America, were described by Professor Cope in 1876,
-under the name <i>Champsosaurus</i>. In the following year Professor
-Gervais of Paris made known another form from Rheims, which he called
-<i>Simoedosaurus</i>, so closely allied to the American that even
-yet they have not been sharply distinguished. Some years later these
-European specimens were more fully described by the well-known Belgian
-paleontologist, Dr. Dollo, but it has been only within the past few
-years that our knowledge of the animals has been made at all complete
-by the discovery and description of several excellent skeletons of
-<i>Champsosaurus</i> by Mr. Barnum Brown of New York.</p>
-
-<div id="FIG_87" class="figcenter">
-  <img  src="images/fig87.jpg" alt="" width="600" height="196" />
-  <p class="center space-below2">
-    <span class="smcap">Fig. 87.</span>—<i>Champsosaurus</i>; skeleton,<br />
-    as mounted in American Museum. (Brown.)</p>
-</div>
-
-<p>These semiaquatic reptiles never grew very large—not more than four
-or five feet in length; nor did they ever succeed in becoming fully
-at home in the water, certainly no more so than our modern alligators
-and crocodiles. They remained to the end of their comparatively brief
-existence essentially land animals, probably seeking their food in the
-<span class="pagenum" id="Page_180">[Pg 180]</span>
-water but fleeing to the land for protection and for the breeding of
-their young. Their chief water adaptations are seen in the elongate
-face and flattened swimming tail. Their legs remained essentially
-terrestrial, and could have been of but little use in the water for
-propulsion; the feet even were doubtfully webbed, or if so, not more
-than are those of the alligator. Singularly, like the proganosaurs,
-their ribs were heavy and stout, also suggesting bottom-crawling
-habits, like those of the living Galapagos lizards. The skull was
-lightly built, and the face was long and slender, like that of the
-gavials and proganosaurs; but, like those of the former and unlike
-those of the latter, the nostrils were situated at the extreme tip.
-The hind legs were firmly attached to the body by the sacrum; and no
-sclerotic bones of the eyes have been discovered. The neck was neither
-unusually long nor unusually short. The body was probably covered with
-horny scales.</p>
-
-<div id="FIG_88" class="figcenter">
-  <img  src="images/fig88.jpg" alt="" width="500" height="406" />
-  <p class="center space-below2">
-    <span class="smcap">Fig. 88.</span>—Restoration of <i>Champsosaurus</i>.</p>
-</div>
-<p><span class="pagenum" id="Page_181">[Pg 181]</span></p>
-<div id="FIG_89" class="figcenter">
-  <img  src="images/fig89.jpg" alt="" width="600" height="308" />
-  <p class="center space-below2">
-    <span class="smcap">Fig. 89.</span>—<i>Champsosaurus</i>; skull<br />
-    from above. (After Brown.)</p>
-</div>
-
-<p>To the student of paleontology these animals are of interest because of
-the retention of several primitive traits which had long disappeared in
-other known reptiles. While the vertebrae had ceased to be perforated
-by the notochord, as in the early reptiles, they were still shallowly
-<span class="pagenum" id="Page_182">[Pg 182]</span>
-biconcave. The first bone of the neck, the atlas, had changed but
-little from that of their very ancient forbears of Permian times, and
-the bones of the palate still retained numerous teeth scattered over
-it, like those of the same Paleozoic ancestors. Most primitive and
-old fashioned of all was the pelvis, which was so unlike that of all
-known contemporary or later reptiles that, were a paleontologist to
-see it without knowing whence it came, he would be almost sure to say
-that it belonged to a Paleozoic, or at least a Triassic, reptile, and
-not only to an early reptile but a very primitive one at that. This
-peculiarity consists in the absence of any opening between the ischium
-and pubis, which is characteristic of every living vertebrate with
-legs. And these and other old-fashioned characters could not possibly
-have been new developments; they must have existed in all the ancestors
-of the Choristodera from Paleozoic to early Tertiary times, though not
-a single other reptile is known to have possessed them, for the greater
-part of this time. Perhaps when Asia and northwestern America have
-been more thoroughly explored for vertebrate fossils, some of their
-ancestors which perished on their great migration from the western to
-the eastern continent in late Cretaceous times will be discovered.</p>
-
-<div class="figcontainer">
-  <div class="figsub">
-   <img id="FIG_90" src="images/fig90.jpg" alt="" width="300" height="213" />
-   <p class="center">
-    <span class="smcap">Fig. 90.</span>—Pectoral girdle of<br />
-    <i>Champsosaurus</i>.<br /> (After Brown.)</p>
-  </div>
-  <div class="figsub">
-    <p class="space-below2">&nbsp;</p>
-    <img id="FIG_91" src="images/fig91.jpg" alt="" width="200" height="126" />
-   <p class="center space-above2">
-    <span class="smcap">Fig. 91.</span>—<i>Champsosaurus</i>;<br />
-    pelvic bones.<br /> (After Brown.)</p>
-   </div>
-</div>
-
-<p>The choristoderans began their existence, so far as is now known, in
-North America in late Cretaceous times and died out in both Europe and
-North America in early Tertiary times. That is, they were one of the
-<span class="pagenum" id="Page_183">[Pg 183]</span>
-few branches of reptilian life which not only witnessed the extinction
-of the great dinosaurs and plesiosaurs, but the advent also of the
-early placental mammals. They lived millions of years after the
-proganosaurs became extinct, and, similar as they are in form, there
-is no relation between them. Moreover, in all probability they did not
-migrate to the eastern continent over the same route.</p>
-
-<p>The structure of the head and teeth of the Choristodera clearly
-indicates a fish-eating habit, or at least a diet of soft-bodied,
-free swimming invertebrates. The legs and ribs, as also the armor of
-ventral ribs, like those of the plesiosaurs, point very insistently
-toward a bottom-crawling habit while in the water.</p>
-<hr class="chap x-ebookmaker-drop" />
-
-<div class="chapter">
-<p><span class="pagenum" id="Page_184">[Pg 184]</span></p>
-<h2 class="nobreak" id="CHAPTER_XIV">CHAPTER XIV</h2>
-</div>
-
-<h3>PARASUCHIA</h3>
-
-<p>The first known specimen of the order of reptiles now generally
-known as the Parasuchia was found in Würtemberg, Germany, in 1826
-and very briefly and inadequately described<a id="FNanchor_4" href="#Footnote_4" class="fnanchor">[4]</a>
-two years later by Professor George Jaeger. The specimen was a sorry
-one, and was sadly misinterpreted by Jaeger. It consisted chiefly of
-casts of the alveoli or sockets of a number of teeth, more or less
-connected by corroded or decomposed portions of the jaws. He recognized
-the casts as teeth of a peculiar reptile, but mistook the roots for
-crowns, and, naturally concluding that such obtuse teeth would be
-of use only for the mastication of vegetable food—about the last
-kind of food to which the phytosaurs were addicted—called the animal
-<i>Phytosaurus</i>, meaning plant saurian. Because of differences he
-observed in the shapes of the teeth he thought that they belonged
-to two distinct species, which he called <i>cylindricodon</i> and
-<i>cubicodon</i>; but the differences were due simply to the different
-positions they held in the jaws.</p>
-
-<p>Fourteen years later Hermann von Meyer, the renowned German
-paleontologist, described and figured other remains of the same or an
-allied reptile under the name <i>Belodon plieningeri</i>. In subsequent
-papers during the next twenty-three years von Meyer very fully
-described and beautifully illustrated the skulls and other remains
-of this and other species, all of which he referred to the genus
-<span class="pagenum" id="Page_185">[Pg 185]</span>
-<i>Belodon</i>, the name by which for many years the animals were
-generally known in scientific literature. Von Meyer thought that he
-recognized in <i>Belodon kapfii</i>, the species most often figured in
-textbooks, the same animal that Jaeger had previously described.</p>
-
-<p>Von Meyer was not at all certain about the relationships of his
-<i>Belodon</i>, though he recognized its affinity with the crocodiles.
-It was Huxley who, in a famous paper on the evolution of the
-crocodiles, published in 1875, united <i>Belodon</i> and another genus
-from the Trias of Scotland, which he called <i>Stagonolepis</i>, with
-the Crocodilia as representatives of the suborder Parasuchia, one of
-the three into which he divided the order. Huxley admitted that the
-relationships between the Parasuchia and the Mesosuchia or Eusuchia,
-the other suborders which he proposed, were not as intimate as those
-between the latter two, which were separated solely on the structure of
-the palate and vertebrae, as has been explained in chap. xv. As early
-as 1869 the late Professor Cope recognized certain forms which had been
-previously described from Carolina as belonging to the group, calling
-them <i>Belodon</i>, but it was not until 1896 that E. Fraas separated
-<i>Belodon planirostris</i> of von Meyer as a member of a distinct
-genus, to which he gave the name <i>Mystriosuchus</i>.</p>
-
-<p>Here, as a part of the order Crocodilia, the phytosaurs remained till
-within very recent years, though there have been some mild protests
-against the association, especially by Marsh, Zittel, and Baur. The
-famous English paleontologist, Richard Owen, located the “Belodontia,”
-as the phytosaurs were often called, in his order Thecodontia, based
-chiefly upon the manner of the insertion of the teeth in sockets.
-But this has long since been shown to have little value in the
-classification of reptiles. Various authors have written about the
-phytosaurs in later years, notably Cope, Fraas, Huene, and Jaekel, but
-it was J. H. McGregor who first definitely separated the phytosaurs
-into a distinct order, in a careful revision of the American forms.
-He called the order Parasuchia, after Huxley, dividing into two
-suborders, the Phytosauria, after Jaeger, and the Aetosauria, a group
-which, for lack of a better place, had previously been classed with the
-Crocodilia, either as a member of the Parasuchia or as an independent
-suborder by Zittel (the Pseudosuchia). More recently Huene has shown
-<span class="pagenum" id="Page_186">[Pg 186]</span>
-that certain African reptiles from the Lower Trias had certain very
-definite characters entitling them to an independent position, for
-which he proposed the order Pelycosimia. Upon the whole, however,
-these characters seem to be primitive parasuchian, and the group may
-provisionally be placed in the order Parasuchia, as a third suborder,
-the Pelycosimia. The order Parasuchia, then, until we know much more
-about the latter two groups, may be conveniently divided into three
-suborders, the Phytosauria, Aetosauria or Pseudosuchia, and the
-Pelycosimia, all of Triassic age.</p>
-
-<p>McGregor was quite right in retaining for the suborder the name
-Phytosauria, suggested by Jaeger in 1828, inappropriate as the word is
-etymologically, but was hardly justified in substituting the generic
-name <i>Phytosaurus</i> for the long and well-known <i>Belodon</i>,
-because it is quite impossible to say that Jaeger’s very fragmentary
-specimen upon which he based the genus <i>Phytosaurus</i> really is the
-same as <i>Belodon</i>. Professor Fraas very kindly showed the writer
-the original type-specimen of Jaeger, now preserved in the Stuttgart
-Museum, and both are agreed that it is impossible to prove the identity
-of <i>Belodon</i> and <i>Phytosaurus</i> from the very fragmentary
-and imperfect specimen. It is quite as probable, for instance, that
-<i>Phytosaurus</i> and <i>Mystriosuchus</i> are identical as that
-<i>Phytosaurus</i> and <i>Belodon</i> are. Unfortunately, this is
-not the only case in vertebrate paleontology where the fragmentary
-specimens to which names have been given are inadequate to determine
-the species, or genus, or even the family to which they belong; there
-have been very many such instances. The pioneers in paleontology were
-often justified in naming small and obscure fragments of bones, or
-single bones. One would be justified even yet in giving a name to an
-indeterminable fragment of a bird bone from the Triassic formation,
-because the discovery of a bird of any kind in that formation would
-be very important for science, even if its precise kind might never
-be recognized from the specimen. Nevertheless, the custom is a very
-reprehensible one when indiscriminately followed. For these reasons
-the writer disagrees with McGregor in substituting the inappropriate
-name <i>Phytosaurus</i> for <i>Belodon</i>, the name by which the most
-typical forms were so long known.
-<span class="pagenum" id="Page_187">[Pg 187]</span></p>
-
-<p>The Aetosauria, which have long been known from a marvelous specimen
-found in Würtemberg many years ago and described by the elder Fraas,
-need not detain us long. They were relatively small reptiles about
-two feet long, almost completely incased in a bony armor, and purely
-terrestrial in habit. The skull even yet is not perfectly known, and
-it is possible that when it is the group may have to be dissociated
-from the phytosaurs. The nostrils were not posterior, and the skull is
-short. Other specimens of the same group have been described from the
-Upper Triassic rocks of Massachusetts.</p>
-
-<p>The Pelycosimia of Huene are very interesting as showing apparently
-primitive forms with which the true phytosaurs may have been intimately
-related ancestrally. They, too, have a rather short skull with the
-nostrils in front, and were not at all aquatic in habit. Not much is
-known about the single genus that is located in the group, aside from
-the skull and a few limb bones.</p>
-
-<h3>PHYTOSAURIA</h3>
-
-<p>The Phytosauria, so far as known, were all reptiles of considerable
-size, greatly resembling the crocodiles, and especially the gavials
-in form and habit, but differing very greatly in having the external
-nostrils situated far back near the eyes; in having no false palate
-so characteristic of the Crocodilia; in having a more primitive
-shoulder-girdle, consisting of a short coracoid, interclavicle, and
-clavicles; and in having the ordinary type of pelvis, that is, with the
-pubis entering into the acetabular articulation for the femur. They
-were all, like the crocodiles, covered more or less by a bony armor;
-there are two openings on each side of the temporal region; there
-is no pineal opening; the vertebrae are gently biconcave, precisely
-like those of the early or mesosuchian crocodiles; there is always
-an opening of considerable size, called the preorbital foramen, in
-front of the eyes, as in some crocodiles, many dinosaurs, and most
-pterodactyls; there is also an opening through the back part of the
-mandibles as in crocodiles; and the double-headed ribs are attached
-exclusively to the transverse process of the arch, precisely as in the
-crocodiles, dinosaurs, and pterodactyls. From all these it is evident
-<span class="pagenum" id="Page_188">[Pg 188]</span>
-that the phytosaurs are related most nearly to the crocodiles and
-dinosaurs, and are probably an early branch of the stem from which
-they, the pterodactyls and the birds, arose, a branch that persisted
-<span class="pagenum" id="Page_189">[Pg 189]</span>
-only a short time, geologically speaking, and went entirely out of
-existence at the close of Triassic times, leaving no descendants
-behind. Nevertheless, in this comparatively brief life-span they
-developed not a few distinctive forms and became widely distributed
-over the earth. Their remains are known from the Upper Trias of
-Germany, England, and Scotland, India, South Africa, and from
-Massachusetts, North and South Carolina, and many places in the Rocky
-Mountains. No true phytosaurs are yet known from South America, but in
-<span class="pagenum" id="Page_190">[Pg 190]</span>
-all probability they will be discovered there when the Triassic
-deposits of that continent have been better explored for fossils. In
-the Rocky Mountains, especially, their remains are widely scattered,
-they have been found in many localities in Wyoming, Colorado, Oklahoma,
-Utah, and New Mexico. Though for the most part their known remains
-from these localities are yet fragmentary, not less than four distinct
-genera have been described from these regions: “<i>Belodon</i>,”
-<i>Angistorhinus</i>, <i>Paleorhinus</i>, and <i>Episcoposaurus</i>.
-From the Carolinas and Massachusetts a single genus, though described
-under numerous names, has been made known, originally called by Emmons
-<i>Rutiodon</i> (<i>Rhytidodon</i>). And from Europe and India at
-least as many more different genera are known. All these genera are,
-however, so closely allied that they are placed in the single family
-Belodontidae.</p>
-
-<div id="FIG_92" class="figcenter">
-  <img  src="images/fig92.jpg" alt="" width="600" height="428" />
-  <p class="center space-below2">
-    <span class="smcap">Fig. 92.</span>—Restoration of <i>Mystriosuchus</i>,<br />
-    an Upper Triassic phytosaur.</p>
-</div>
-<div id="FIG_93" class="figcenter">
-  <img  src="images/fig93.jpg" alt="" width="600" height="302" />
-  <p class="blockquot space-below2">
-    <span class="smcap">Fig. 93.</span>—Skull of <i>Mystriosuchus</i>, a
-    phytosaur: <i>pm</i>, premaxilla; <i>m</i>, maxilla; <i>na</i>, nasal;
-    <i>f</i>, frontal; <i>p</i>, prefrontal; <i>l</i>, lacrimal; <i>pf</i>,
-    postfrontal; <i>po</i>, postorbital; <i>pa</i>, parietal; <i>sg</i>,
-    squamosal; <i>qj</i>, quadratojugal; <i>pl</i>, palatine; <i>t</i>,
-    transverse; <i>in</i>, internal nares; <i>en</i>, external nares;
-    <i>pt</i>, pterygoid; <i>bs</i>, basisphenoid; <i>eo</i>, exoccipital.
-    (After McGregor.)</p>
-</div>
-
-<div class="figcontainer">
-  <div class="figsub">
-   <p class="space-below2">&nbsp;</p>
-   <img id="FIG_94" src="images/fig94.jpg" alt="" width="250" height="321" />
-   <p class="center">
-     <span class="smcap">Fig. 94.</span>—Dorsal vertebrae<br />
-     of phytosaur: <i>az</i>, anterior zygapophysis;<br />
-     <i>pz</i>, posterior zygapophysis; <i>d</i>,<br />
-     <i>c</i>, articulations of rib.</p>
-  </div>
-  <div class="figsub">
-    <img id="FIG_95" src="images/fig95.jpg" alt="" width="250" height="379" />
-   <p class="center">
-    <span class="smcap">Fig. 95.</span>—Scapula and<br />
-    coracoid of <i>Rutiodon carolinensis</i>,<br />
-    an American phytosaur.<br /> (After McGregor.)</p>
-   </div>
-</div>
-<p><span class="pagenum" id="Page_191">[Pg 191]</span></p>
-
-<div id="FIG_96" class="figcenter">
-  <img  src="images/fig96.jpg" alt="" width="500" height="187" />
-  <p class="center space-below2">
-   <span class="smcap">Fig. 96.</span>—<i>Belodon</i>; restoration of head,<br />
-   from above.</p>
-</div>
-<div id="FIG_97" class="figcenter">
-  <img  src="images/fig97.jpg" alt="" width="600" height="149" />
-  <p class="center space-below2">
-    <span class="smcap">Fig. 97.</span>—<i>Mystriosuchus</i>: restoration of
-    head,<br /> from above.</p>
-</div>
-
-<p>In <i>Belodon</i> (<a href="#FIG_96">Fig. 96</a>), the earliest known and most
-typical genus, perhaps, the moderately elongated face has a high crest reaching nearly
-to its front end, and this type is known both from Europe and from New
-Mexico. Others have the face long and slender, even longer and more
-<span class="pagenum" id="Page_192">[Pg 192]</span>
-slender than in the ancient teleosaur crocodiles or the modern gavials.
-In some forms the teeth are cylindrical and slender throughout, and
-there may be as many as fifty on each jaw, or two hundred in all; while
-in others only the anterior teeth are cylindrical and the posterior
-teeth are flattened and serrate along their cutting edges. In the body
-not very great differences have been observed. Some are more slender
-than others, and there are minor differences in the shapes and sizes
-and numbers of the bony scutes along the back and on the throat.</p>
-
-<p>But they are all alike in their essential characters, a very long
-beak with numerous teeth; the foremost ones on the expanded, more
-or less spoon-shaped front extremity, are more or less, sometimes
-greatly, elongated. The jaws may be likened to a long and slender
-pair of tongs with nipping teeth at the front end. The strong, long,
-and flattened tail is sufficient evidence that the phytosaurs were
-excellent swimmers, but, aside from that and the posterior location of
-the external nostrils, directly over the internal, few other aquatic
-adaptations are observed in the skeleton. There are no sclerotic bony
-plates about the eyes, or at least none have so far been discovered,
-although among the numerous known specimens they would confidently be
-expected were they really present in the skeleton; and the presence of
-bony armor negatives markedly aquatic habits.</p>
-
-<p>Doubtless on the whole the habits of the phytosaurs were not very
-unlike those of the modern gavials, which they so strongly resemble
-in form, size, and general characters. But they differ very greatly
-from the gavials in the extreme posterior position of the nostrils,
-and in the greatly elongated teeth of the front end of the beak,
-teeth which must have had some especial and peculiar use. Nor is the
-position of the nares to be accounted for satisfactorily by reference
-to aquatic habits. It has been suggested that the creatures used the
-very long and slender beak in prodding and probing in the sand and
-mud for soft-bodied invertebrates, worms and the like, for which the
-teeth would be especially fitted; and that the posterior position of
-the nostrils may be in part, perhaps wholly, accounted for by this
-habit, which permitted the reptiles to breathe without extricating the
-beak from the mud or shallow waters. That the animals were wholly and
-<span class="pagenum" id="Page_193">[Pg 193]</span>
-intensely carnivorous in habit is attested by their teeth; although
-they are called “plant saurians,” they never had anything to do with
-plants in the way of food. Unfortunately so far no specimens have
-ever been found showing the remains of stomach contents, nor have any
-been found showing impressions of the form of the body or of any of
-its parts. Until such specimens are found, as they doubtless will be
-eventually, one can be less sure of the precise details in their life
-reconstructions. However, the skeleton is now known nearly completely,
-and this suffices to give a very approximately correct idea of what the
-animals were like when alive.</p>
-<hr class="chap x-ebookmaker-drop" />
-
-<div class="chapter">
-<p><span class="pagenum" id="Page_194">[Pg 194]</span></p>
-<h2 class="nobreak" id="CHAPTER_XV">CHAPTER XV<br />
-<span class="h_subtitle">&nbsp;<br />CROCODILIA</span></h2>
-</div>
-
-<p>The order of reptiles to which the name Crocodilia is technically
-applied comprises less than twenty-five living species, popularly
-known as crocodiles, alligators, caimans, and gavials. They are often
-of great size, ugly and repulsive in appearance, cruel and vicious
-in habit, wholly carnivorous, and denizens, almost exclusively, of
-fresh-water lakes or rivers in tropical and subtropical regions; a few
-only venture into the sea near the shores. They are all excellent and
-powerful swimmers, but are by no means exclusively aquatic in habit,
-many of them spending a large part of the time on the shores; and they
-invariably seek the land for the deposition and hatching of their eggs.
-In size they are the largest of living reptiles, some of the existing
-species reaching a length of twenty-five feet, while some extinct
-species were probably fully twice that length.</p>
-
-<p>The geological history of the crocodiles is a very ancient one,
-reaching back at least as far as the early Jurassic and probably to
-the Triassic. The culmination of the order, at least so far as size,
-variety, and numbers are concerned, was doubtless before the close of
-the Mesozoic. The early crocodiles, however, were of a more generalized
-structure in some respects, though specialized in others, because of
-which naturalists in the past have usually divided the order into three
-or four chief subdivisions, or suborders, two of which, the Mesosuchia
-and the Thalattosuchia, became extinct before or during Cretaceous
-time. The third suborder, the Parasuchia of many textbooks, has now
-been unanimously separated by paleontologists from the Crocodilia as an
-independent order. The fourth suborder of the textbooks, the Eusuchia,
-a word meaning <i>true</i> crocodiles, appeared in geological history,
-so far as we yet know, shortly before the extinction of the Mesosuchia,
-and is best known from the forms now living, all of which belong to it.
-<span class="pagenum" id="Page_195">[Pg 195]</span>
-Although the modern crocodiles can hardly be called, as a group, purely
-aquatic reptiles, we shall find it of interest, because of their
-intimate relation to the older and more strictly marine forms, to speak
-of them somewhat in detail.</p>
-
-<h3>MODERN CROCODILES,<br /> EUSUCHIA</h3>
-
-<p>The crocodiles of the present—and we use the word in the technical
-sense of Crocodilia—because of their general resemblance to the
-lizards, or true “saurians,” were classed with them by the older
-naturalists, whence comes the popular name alligator, a corruption
-of the Spanish <i>el lagarto</i>, or “the lizard,” given to some of
-the South American forms by early explorers. But this resemblance
-is a superficial one only, as was early recognized by comparative
-anatomists. The crocodiles, indeed, are only remotely related to the lizards.</p>
-
-<div id="FIG_98" class="figcenter">
-  <img  src="images/fig98.jpg" alt="" width="600" height="286" />
-  <p class="center space-below2">
-    <span class="smcap">Fig. 98.</span>—Senegal crocodile.<br />
-    (By permission of the New York Zoölogical Society.)</p>
-</div>
-
-<p>The head or cranium is flattened and broad, the facial part or snout
-sometimes greatly elongated and slender, and the external nostrils are
-always situated at the front end. The bones of the upper surface of
-the cranium and face have many pit-like depressions. The neck is short
-and stout, and but little movable. The body is somewhat depressed and
-flattened, not cylindrical and slender, as in the more typical water
-reptiles. The tail is much elongated and compressed, forming a powerful
-<span class="pagenum" id="Page_196">[Pg 196]</span>
-means of propulsion in swimming, its breadth being increased by a
-vertical row of horny plates above. The limbs are of the ordinary
-elongated type—ambulatory rather than swimming legs—and are not of
-much use for propelling the body in the water; the front legs indeed
-are usually held close to the body while the animal is swimming. The
-toes, however, are partially connected by webs, to a slight extent only
-in the alligators and crocodiles, but much more so in the long-snouted
-gavials. The feet have five toes in front and four behind; and the loss
-of the fifth toe can only be ascribed to terrestrial habits. The body
-is covered more or less with horny scutes or scales, beneath which are
-several rows of thickened, pitted, bony plates on the dorsal side, and
-sometimes also on the under side, forming a more or less extensive
-bony armor. The eyes have movable lids, as in most lizards, and the
-ear-opening is small.</p>
-
-<p>But the external appearance of these reptiles is not sufficient to
-distinguish them widely from other groups, and we must resort to
-the internal structure, especially that of the skeleton, for the
-more essential differential characters. The most crucial of these,
-the one which more than any other determines their relationships,
-consists in the position and shape of the bone with which the lower
-jaw articulates, the quadrate bone, so characteristic of reptiles. As
-in the plesiosaurian and ichthyosaurian skulls, it is firmly united
-with the adjoining bones, not articulating freely with them, as in the
-lizards and snakes. But this fixed relation of the bones is very unlike
-that of the plesiosaurs, ichthyosaurs, and turtles, in that it is held
-in place by <i>two</i> bony bars or arches, the upper extending forward
-to unite with the bones at the back part of the orbit, the lower, with
-the hind extremity of the upper jaw. The lower jaws are rigidly united
-in front, sometimes for a long distance; they have, almost always,
-a hole or opening through the hinder part, known in but few other
-reptiles. The bones of the palate are all firmly united, forming a
-nearly complete roof, very unlike the condition in the mosasaurs and
-lizards. The palate also is very peculiar in the development of a plate
-of bone below the nasal chambers, forming a complete bony canal on each
-side through which the respiratory air passes far back to the internal
-<span class="pagenum" id="Page_197">[Pg 197]</span>
-opening of the nostrils above the pharynx, and not, as in other
-reptiles—save the immediate ancestors of the mammals—entering the
-mouth at the front end. This peculiar arrangement of the air-passages,
-so like that of ourselves, has much to do with the water habits of the
-crocodiles, as we shall see.</p>
-
-<p>The teeth are conical in shape, and are always restricted to the edges
-of the jaws, above and below. They are inserted deeply and firmly in
-sockets, and are replaced frequently by new ones growing beneath them,
-pushing the older ones out as their usefulness becomes impaired by
-injury or by use. In some species there are as many as thirty teeth in
-each side of the jaws, above and below, although the broad-headed kinds
-have a smaller number.</p>
-
-<div class="figcontainer">
-  <div class="figsub">
-   <img id="FIG_99" src="images/fig99.jpg" alt="" width="250" height="485" />
-   <p class="center"><span class="smcap">Fig. 99.</span></p>
-  </div>
-  <div class="figsub">
-    <img id="FIG_100" src="images/fig100.jpg" alt="" width="250" height="489" />
-   <p class="center"><span class="smcap">Fig. 100.</span></p>
-   </div>
-<p class="center"><span class="smcap">Fig. 99.</span>—Skull of
-<i>Alligator mississippiensis</i>, from below.</p>
-
-<p class="blockquot no-indent"><span class="smcap">Fig. 100.</span>—The
-same, from above: <i>bo</i>, basioccipital; <i>bs</i>, basisphenoid;
-<i>f</i>, frontal; <i>j</i>, jugal; <i>l</i>, lacrimal; <i>m</i>,
-maxilla; <i>n</i>, nasal; <i>p</i>, parietal; <i>pa</i>, palatine;
-<i>pm</i>, premaxilla; <i>pf</i>, prefrontal; <i>pr</i>, postfrontal;
-<i>pt</i>, pterygoid; <i>q</i>, quadrate; <i>qj</i>, quadratojugal;
-<i>tr</i>, transverse.</p>
-</div>
-
-<p>The neck is short, as has been stated, but it always includes in living
-forms nine vertebrae, a number probably slightly in excess of that of
-<span class="pagenum" id="Page_198">[Pg 198]</span>
-their terrestrial forbears. By the peculiar mode of attachment of
-the short “hatchet-shaped” ribs, much lateral movement of the neck
-is prohibited, nor is any very great vertical movement possible. The
-vertebrae of the whole column, save the atlas, the second sacral, and
-the first caudal—which is a very remarkable anomaly—are concave in
-front and convex behind, agreeing in this respect with those of all
-other living reptiles, save the turtles, the tuatera, and some lizards.
-The ribs of the neck have their two heads attached, one to the body of
-the vertebra, the other to the arch, but those of the dorsal region,
-though double-headed, have both become attached to the transverse
-projection of the arch, a seemingly trivial character, but one which
-immediately distinguishes all crocodiles from all other water reptiles,
-and from all terrestrial reptiles, indeed, save the Parasuchia,
-Pterosauria, and Dinosauria. The pelvis is firmly attached to the
-spinal column by two sacral vertebrae.</p>
-
-<div id="FIG_101" class="figcenter">
-  <img  src="images/fig101.jpg" alt="" width="600" height="242" />
-  <p class="blockquot space-below2">
-    <span class="smcap">Fig. 101.</span>—Vertebrae of gavial from the
-    side (cervical), and from in front (dorsal): <i>az</i>, anterior
-    zygapophysis; <i>pz</i>, posterior zygapophysis; <i>d</i>, diapophysis;
-    <i>r</i>, cervical rib; <i>c</i>, articulation for head; <i>t</i>, for
-    tubercle of dorsal rib.</p>
-</div>
-
-<p>The collar-bones, or clavicles, are wanting in crocodiles; there is
-a slender interclavicle; and the shoulder-blade and coracoid are well
-developed (<a href="#FIG_102">Fig. 102</a>). The bones of the pelvis are loosely
-united with each other as they are in most reptiles (<a href="#FIG_104">Fig. 104</a>).
-The pubes, the anterior bones below, unlike those of all other reptiles, do not help
-to form the acetabulum or socket for the articulation of the thigh
-bone, nor do they articulate with each other. This single character
-sharply distinguishes a crocodile from all other reptiles, living or
-<span class="pagenum" id="Page_199">[Pg 199]</span>
-extinct, and is almost the only character that separates the order from
-the dinosaurs, aside from the peculiar structure of the nasal passages
-in the skull. On the under side of the body, connected with the front
-end of the pubes, there are seven or eight pairs of abdominal ribs,
-corresponding to the plastron of the turtles and similar to those of
-the ichthyosaurs and plesiosaurs. The mosasaurs have no such ribs.</p>
-
-<div class="figcontainer">
-  <div class="figsub">
-   <img id="FIG_102" src="images/fig102.jpg" alt="" width="270" height="502" />
-   <p class="center"><span class="smcap">Fig. 102.</span></p>
-  </div>
-  <div class="figsub">
-    <img id="FIG_103" src="images/fig103.jpg" alt="" width="210" height="504" />
-   <p class="center"><span class="smcap">Fig. 103.</span></p>
-   </div>
-  <p class="blockquot no-indent"><span class="smcap">Fig. 102.</span>—Scapula (<i>sc</i>) and
-         coracoid (<i>cor</i>) of gavial.</p>
-
-  <p class="blockquot no-indent"><span class="smcap">Fig. 103.</span>—Front
-   foot of crocodile: <i>u</i>, ulna; <i>r</i>, radius; <i>re</i>,
-   radiale; <i>ue</i>, ulnare; <i>p</i>, pisiform.</p>
-</div>
-
-<p class="space-above2">Furthermore, the crocodiles differ from all
-other living reptiles in having a four-chambered heart, like that
-of birds and mammals, that is, a heart with two auricles and two
-ventricles. This more perfect structure of the circulatory organs does
-not, however, insure at all times a complete separation of the pure or
-arterial blood from the impure or venous blood, since the blood may be
-more or less intermixed outside of the heart by a connection between
-<span class="pagenum" id="Page_200">[Pg 200]</span>
-the venous and the arterial systems. Whether these imperfectly
-developed organs, so suggestive of a higher and more perfect mode of
-respiration, are the vestiges of what were once among some reptiles
-functional structures, or whether they are rudiments of a higher
-organization, developing independently in these creatures, cannot
-be positively determined, but it seems very probable that, far back
-in geological times, some reptiles, especially the pterodactyls and
-dinosaurs, had their respiratory and circulatory systems more like
-those of the birds and mammals of today. Unfortunately, however, if
-such was the case, we may never be able to prove it, although proof
-would not be impossible; stranger things than fossil hearts have been
-found by paleontologists!</p>
-
-<p>The stomach, moreover, in the crocodiles is fashioned somewhat after
-that of the birds, with an imperfect division into crop and gizzard.
-Some crocodiles of today have the habit of swallowing hard pebbles,
-as do many birds. There is an old myth that the crocodile of the Nile
-swallows a pebble on each of its birthdays, thus giving reliable
-information as to its age by the number found in its gizzard at
-its death! And this habit has been suggested for some of the most
-ancient crocodiles, the teleosaurs, by the recurring presence of
-siliceous pebbles found with the remains of their skeletons. And we
-have seen this pebble-swallowing habit was also characteristic of the
-plesiosaurs, with whose remains “stomach-stones,” or gastroliths, as
-they have been called, are often found.</p>
-
-<div id="FIG_104" class="figcenter">
-  <img  src="images/fig104.jpg" alt="" width="400" height="314" />
-  <p class="center space-below2">
-   <span class="smcap">Fig. 104.</span>—Pelvis of crocodile: <i>il</i>,
-   ilium; <i>is</i>, ischium; <i>pu</i>, pubis.</p>
-</div>
-
-<p>All of these various characters of the skeleton and fleshy parts are
-pretty conclusive evidence that the crocodiles, ugly creatures that
-they are, today enjoy the highest rank among cold-blooded animals. They
-are perhaps in some respects of not so high a type of reptiles as were
-some of the extinct reptiles, but that they have survived so long, so
-many millions of years, is pretty good evidence of endurance, to say
-the least.
-<span class="pagenum" id="Page_201">[Pg 201]</span></p>
-
-<p>Living crocodiles belong to three distinct groups or families: the
-true crocodiles and alligators; the long-snouted crocodiles or Borneo
-gavials; and the true gavials of India. Members of the first of these
-families are really only subaquatic, or amphibious in habit; they move
-about on land with entire freedom, and often seek their food there.
-Certain marked aquatic characters they do possess, in the skull and
-tail, as we shall see. They are indigenous to southern China, India,
-Africa, Madagascar, the southern part of the United States, Central
-America, and the northern part of South America. The members of this
-family are distinguished by the more or less broad and flat head, the
-possession of comparatively few teeth of large size, and by having the
-toes less completely webbed. The crocodiles proper differ from the
-caimans and alligators especially in the arrangement of the teeth.
-During later geological times, that is, during early Tertiary times,
-the geographical range of the Crocodilidae was much more extended
-than it is at present, the remains of many often very large species,
-being found in the lake deposits of the northwestern parts of the
-United States, Great Britain, Germany, France, etc. Yet earlier, in
-the late Cretaceous rocks of the United States, in Texas, and Wyoming
-especially, there have been found rather scanty remains of a gigantic
-crocodile which must have been nearly fifty feet in length when living.</p>
-
-<p>The second family, the Tomistomidae, or long-snouted crocodiles,
-comprises but two living species, both restricted at the present time
-to Borneo. These crocodiles have a moderately slender snout, because
-of which they are sometimes called gavials, though it is not nearly so
-slender as that of the true Gangetic gavial. This family is probably
-older than either of the other living ones, and is the only one known
-with certainty to have lived during much of the Cretaceous times,
-several species of considerable size having been found in New Jersey
-and Europe. Their feet are better webbed than are those of the true
-crocodiles and alligators, the front feet partly, the hind feet wholly
-so. In general structure they seem to be the most primitive of the
-living Crocodilia, and may have been the ancestors of all modern forms.
-<span class="pagenum" id="Page_202">[Pg 202]</span></p>
-
-<div id="FIG_105" class="figcenter">
-  <img  src="images/fig105.jpg" alt="" width="600" height="367" />
-  <p class="center space-below2">
-   <span class="smcap">Fig. 105.</span>—Gavial.<br />
-   (By permission of the New York Zoological Society)</p>
-</div>
-
-<p><span class="pagenum" id="Page_203">[Pg 203]</span>
-The third family, the Gavialidae, also comprises but two living
-species, both restricted in habitat to the rivers of India. Of these
-the famed gavial of the Ganges is the better known and the more highly
-specialized. The skull of this species has an exceedingly long and
-slender snout; the teeth are numerous, small, and slender; and the feet
-are more fully webbed than are those of other members of the order. In
-habits the gavials are more distinctly aquatic than are the crocodiles
-and alligators. They feed almost exclusively upon small fishes, for
-the seizure and retention of which their small and sharply pointed
-teeth are admirably adapted. The hind feet are relatively long, a
-character that will be better understood when comparison is made with
-those of the Thalattosuchia. Although attaining a large size, fully
-twenty-five feet in length, they are comparatively harmless animals,
-never attacking human beings or other large animals, as do some of the
-crocodiles proper. The gavials have lived a long time in the Indian
-regions, the Gangetic gavial itself having been found in deposits
-of Pleiocene age, perhaps the oldest known of all living species of
-air-breathing vertebrates. Some of the extinct gavials of the same
-region attained a length of nearly or quite fifty feet, possibly the
-longest, if not the largest, of all swimming reptiles of ancient or
-modern times. Extinct gavials have been reported from South America,
-but are not yet fully known.</p>
-
-<p>While the fish-eating gavials swallow their prey whole, the crocodiles,
-caimans, and alligators prey upon all living animals that come within
-their reach, whether large or small, and they will often leave the
-water to seize their intended victims, such as pigs, sheep, birds, or
-even human beings. Their teeth, as has been already stated, are much
-larger, longer, and more irregular in size than those of the gavials.
-Their victims are often drawn under the water and drowned, the peculiar
-posterior position of the internal nostrils permitting the animals to
-breathe with the mouth and to firmly hold their prey under water, while
-the extremity of the snout and the external nostrils are above the surface.</p>
-
-<p>As the firm, unyielding bony palate, the fixed position and
-articulation of the lower jaws, and their rigid attachment to each
-other in front do not permit creatures of large size to enter the gullet
-<span class="pagenum" id="Page_204">[Pg 204]</span>
-whole, the crocodiles and alligators must tear their food to pieces,
-which they do by quick, strong jerks from side to side, aided by the
-powerful tail; or they may twist off a limb or some other part of their
-victims by a rapid rotation of the whole body, two assisting in this
-operation, rotating in opposite directions.</p>
-
-<p>Living crocodiles lay from twenty to sixty eggs, according to the
-species; these eggs are sometimes the size of a goose egg, and are
-covered with a hard shell. They are laid either in a deep excavation
-in the sand and covered over by the parent; or under leaves and straw.
-The female remains on guard until the eggs are hatched, of which she
-is apprized, it is said, by a peculiar noise uttered by the partly
-imprisoned young. She thereupon reopens the nest, and guides her
-liberated infants to the water, where she leaves them to their fate.
-Whether this remarkable habit is one that has been acquired in recent
-times or not is uncertain, but because it has been observed in a
-number of unrelated forms, it is probable that the instinct is of long
-inheritance, and may account for certain peculiarities of structure in
-some of the ancient members of the order. Doubtless the habit arose
-because of the unprotected places in which the eggs are necessarily
-laid on the shores and beaches, and because the eggs are comparatively
-so few in number. The sea-turtles likewise lay their eggs in hollows
-scooped out of the sand of the beaches, but the parents give no further
-care to their eggs, nor to their newly hatched offspring, a neglect
-which is compensated for by the much larger number of eggs they lay,
-because of which the chances are much greater that a few will survive the
-more numerous vicissitudes to which the eggs and young turtles are exposed.</p>
-
-<h3>ANCIENT CROCODILES,<br /> MESOSUCHIA</h3>
-
-<p>The name Mesosuchia, meaning “middle crocodiles,” by which the ancient
-members of the Crocodilia have generally been known, was given by
-Huxley in the belief that they were intermediate between the “true”
-or modern crocodiles and an ancient group which he united with the
-order under the name “Parasuchia.” A fuller and better knowledge of
-the members of this last group has proved very conclusively that they
-are really less allied to the crocodiles than are some other orders of
-reptiles, the dinosaurs for instance, and should be properly classed by
-<span class="pagenum" id="Page_205">[Pg 205]</span>
-themselves as a distinct order. And, more recently, it has also become
-quite apparent that the old crocodiles should not be separated so
-widely from the modern ones as Huxley proposed; that the differences
-distinguishing them from the recent members of the order are really
-not of more than family importance. We thus have left but two chief
-divisions of the Crocodilia, the Eusuchia and Thalattosuchia; and the
-latter group even, by some authors, perhaps rightly, are included under
-the true crocodiles as a family only.</p>
-
-<div id="FIG_106" class="figcenter">
-  <img  src="images/fig106.jpg" alt="" width="600" height="168" />
-  <p class="center space-below2">
-   <span class="smcap">Fig. 106.</span>—<i>Teleosaurus</i>;
-   skull, from above.</p>
-</div>
-
-<p>These older crocodiles, the Mesosuchia of Huxley, comprise a
-considerable number of extinct forms which lived as far back as the
-early part of the Jurassic, and continued nearly to, if not actually
-into, Cenozoic time, that is, to the Eocene. They differ from all
-living forms, chiefly in having, not concavo-convex but biconcave
-backbones, that is, the more primitive vertebrae with which all
-reptiles began. Nor was the internal opening of the nasal passages so
-far back in the mouth as in the later forms. In other respects they did
-not differ very greatly from some of those now living. All the earliest
-kinds that we know of—the teleosaurs—had a long, slender snout,
-resembling very much that of the modern gavials. And they were, for the
-most part, incased in a more complete bony armor, on both the dorsal
-<span class="pagenum" id="Page_206">[Pg 206]</span>
-and the ventral sides; and the front legs were smaller than those of
-the gavials even. The resemblance of the living teleosaurs to the
-modern gavials must have been very great, although the heavier bony
-armor indicates a less exclusively aquatic life. They probably lived
-more in the shallow waters of the seas near the shores.</p>
-
-<p>Near the close of the Jurassic appeared for the first time, so far as
-we now know, broad-headed mesosuchian crocodiles, forms having less
-numerous and stronger teeth, and resembling closely modern alligators.
-It has been believed that these broad-headed kinds were of later origin
-than the more slender-nosed teleosaurs, but a moment’s consideration
-will make it evident how improbable such an evolution must be. The
-crocodiles must have descended from strictly terrestrial reptiles, and
-no terrestrial reptiles have a slender nose. That they should have
-acquired a slender face in adaptation to water habits and then returned
-to the more primitive land type with a broad face and less strictly
-aquatic habits is contrary to all our experience in paleontology. From
-this it is altogether probable that broad-faced crocodiles of later
-times must have been the descendants of broad-faced kinds that were
-in existence during all the Jurassic times, but of which we as yet
-have no knowledge. These broad-faced Jurassic crocodiles were, for the
-most part, small creatures, much smaller than the teleosaurs even, and
-smaller than any species of crocodiles now living. Their remains are
-known only from fresh-water or shore deposits, and are, for the most
-part, associated with those of land and fresh-water animals. About the
-time of their first known appearance in geological history, the small
-mammals and birds had also become more or less abundant, and it was
-suggested by Owen that these land animals had something to do with the
-development of the ancient amphibious crocodiles. Perhaps this was the
-case with respect to their greater abundance and development, and with
-certain peculiarities of their structure, but that the gavial-like
-teleosaurs should have come back to the land and reverted to a more
-primitive form seems quite improbable.</p>
-
-<p>During Cretaceous times, especially in America, numerous forms of
-these old mesosuchian crocodiles were doubtless in existence, both
-slender-nosed and broad-nosed, and some of them must have been of
-<span class="pagenum" id="Page_207">[Pg 207]</span>
-considerable size, though none known was as large as some of the
-late crocodiles. This type, with biconcave vertebrae, continued to
-live on, in both North and South America, to the latter part of
-Cretaceous times, and it is even possible that some continued on
-into the Tertiary. But long before the close of the Cretaceous, the
-modern kind appeared, those with concavo-convex vertebrae, and more
-posterior internal nostrils. The earliest are known from New Jersey
-(<i>Thoracosaurus</i>, <i>Holops</i>), so like the Borneo gavials
-of today that they are properly classified in the same family, the
-Tomistomidae or Gavialidae. If all the later, procoelian type, that
-is, those with concavo-convex vertebrae, originated from a single form
-when the amphicoelian or mesosuchian type became extinct, Huxley’s
-classification into the Mesosuchia and Eusuchia would perhaps be
-proper, but we have much reason to suppose that the change in the kinds
-of vertebra and in the position of the nostrils was only incidental,
-and may have occurred in more than one line of descent, that is, it
-may have occurred in the broad-headed kinds of the Jurassic to the
-broad-headed crocodiles of today, as also in the gavial-like forms of
-the Cretaceous to the gavials of the present. And this is the reason
-why naturalists no longer recognize the classification of Huxley,
-which, partly perhaps because of the prestige of his name, has so long
-been accepted in our chief works on natural history.</p>
-
-<h3>MARINE CROCODILES,<br /> THALATTOSUCHIA</h3>
-
-<p>While the ancient crocodiles of which we have spoken resembled the
-modern ones so closely in form of body and probably in habits, there
-were certain others of the old Jurassic seas which departed so widely
-both in structure and in habits, from their associates that they are by
-some authors given a place wholly by themselves as a distinct group.
-This has been called by Professor Fraas the Thalattosuchia, a word
-meaning “sea-crocodiles.” They were a very early side-branch from the
-great genealogical tree of the Crocodilia, a branch which departed so
-widely from their associates in adapting themselves to a peculiar and
-aberrant mode of existence that they cannot be considered as typical
-crocodiles, although so closely related to them in other respects that
-<span class="pagenum" id="Page_208">[Pg 208]</span>
-therecannot be the least doubt regarding their ancestry. None of the
-crocodiles which we have considered, whether ancient or modern, can
-truthfully be called purely aquatic. They never ceased to use their
-limbs for locomotion on land, more or less of the time, or for the
-support of the body; and many of them have subsisted, in part at least,
-on land animals. How easy it may have been for some of them to become
-almost wholly emancipated from land habits we may easily conjecture.
-The gavials, as we have seen, are more at home in the water than upon
-land; their food is chiefly found in the water; but, so long as their
-habits restrict them chiefly to fresh-water, or to the vicinity of the
-<span class="pagenum" id="Page_209">[Pg 209]</span>
-shores, their limbs continue to be used as much for crawling as for
-swimming. Were the gavials to be driven out to sea by the stress of
-fresh-water conditions or attracted thereto by a greater abundance of
-more easily obtainable or better food, so far from land that they no
-longer would have much use for their legs for the support or propulsion
-of their bodies, in the course of time they would doubtless change to
-a more purely aquatic type. And in that change there would be material
-modifications of their structure: their limbs would become better
-adapted to movements in the water; the skin would become smoother,
-and the bony and horny scales would be lost, since they would be not
-only useless in the water, but actually detrimental to the well-being
-of the animals; and the tail would develop into a more powerful organ
-of propulsion, as a means of increasing their speed in obtaining food
-or in escaping their enemies, such as the sharks. In fact, we can
-only imagine that in the transformation precisely those modifications
-would occur which we actually find in these old sea-crocodiles,
-the Thalattosuchia. And they are of especial interest to us here
-because nowhere do we find a better example of Nature in the act of
-transforming a terrestrial or subterrestrial animal into a truly
-aquatic one.</p>
-
-<div id="FIG_107" class="figcenter">
-  <img  src="images/fig107.jpg" alt="" width="600" height="463" />
-  <p class="center space-below2">
-   <span class="smcap">Fig. 107.</span>—<i>Geosaurus</i>, an Upper Jurassic
-   thalattosuchian crocodile, drawn from restoration and figures by Fraas.</p>
-</div>
-
-<p>The group comprises only a few forms, so far as known. All were of
-modest size among extinct reptiles, from ten to twenty feet in length,
-and all are from the Upper Jurassic deposits of Europe. They did
-not exist very long, probably because they found it impossible to
-discard old habits and old structures entirely and become absolutely
-<span class="pagenum" id="Page_210">[Pg 210]</span>
-emancipated from the land; their breeding habits possibly were
-too deeply impressed into their structure readily to change, as
-did those of other sea-reptiles. Some of their remarkable aquatic
-adaptations have long been known, but only within a dozen years has
-our knowledge of them become at all complete. Three or four genera
-have been described, but only a few forms are well known, of which
-<i>Geosaurus</i> may be taken as most typical. To this we shall confine
-our descriptions.</p>
-
-<div id="FIG_108" class="figcenter">
-  <img  src="images/fig108.jpg" alt="" width="600" height="347" />
-  <p class="center space-below2">
-    <span class="smcap">Fig. 108.</span>—<i>Geosaurus</i>; skull from side
-     and from above.<br /> (After Fraas.)</p>
-</div>
-
-<p>The skull of <i>Geosaurus</i> is rather small in comparison with
-the length of the body, smaller proportionally than in any living
-crocodile, but not much smaller than that of the teleosaurs. The snout
-is long and slender, much like that of the teleosaurs and gavials, but
-the bones of the whole upper surface are quite smooth, not roughened
-and pitted like those of modern forms. The skull of <i>Dakosaurus</i>,
-another genus of thalattosuchians, is much less elongate than
-that of <i>Geosaurus</i>, but has the other characteristics of
-<i>Geosaurus</i>. The eyes are provided with a stout ring of sclerotic
-bones, with a pupillary opening of less than one inch. We have seen
-that all other strictly aquatic reptiles have similar eye bones, but
-no other crocodiles have them. The internal openings of the nostrils
-are large and long, but they are not situated far back, as in the
-modern crocodiles, not even so far back as in the early teleosaurs.
-They had no need of the peculiar breathing apparatus of the amphibious
-crocodiles, since all their prey must have been water-breathing
-creatures. Their eyes were directed laterally, not more or less upward,
-as in their nearest relatives. Nearly all other crocodiles have an
-<span class="pagenum" id="Page_211">[Pg 211]</span>
-opening through the hind end of the lower jaw, but the thalattosuchians
-did not. The teeth were about as numerous as in the modern gavials, but
-they projected freely only a short distance above the gums in life, and
-they were very slender and sharply pointed, excellently well adapted
-for catching smooth and slippery fishes. Their vertebrae, like those
-of all other reptiles of their time, were biconcave. Those of the neck
-resembled those of the teleosaurs, save that there were only seven,
-fewer than is the case with any other members of the order. In becoming
-adapted to their peculiar mode of life these crocodiles lost two
-vertebrae from the neck. All modern crocodiles have two ribs attached
-to the first vertebra; the thalattosaurs had but one, another evidence
-of primitive characters. While the number of vertebrae in the neck was
-reduced, in the back it was increased to eighteen; all other crocodiles
-have but fifteen or sixteen. The trunk was long, another adaptation to
-water life. There were two firmly united vertebrae in the sacrum, as in
-the modern forms. The reason for the persistence of this terrestrial
-character we shall see later.</p>
-
-<div id="FIG_109" class="figcenter">
-  <img  src="images/fig109.jpg" alt="" width="600" height="326" />
-  <p class="center space-below2">
-<span class="smcap">Fig. 109.</span>—Tail, scapula (<i>sc</i>), and
-coracoid (<i>c</i>) of <i>Geosaurus</i>.<br /> (After Fraas.)</p>
-</div>
-
-<p>The tail was very long and strong, nearly as long as all the remainder
-of the body, and relatively much longer than in other crocodiles. It is
-of interest to observe that the head, neck, body, and tail had almost
-the same relative proportions as those of the great sea-lizards, the
-<span class="pagenum" id="Page_212">[Pg 212]</span>
-mosasaurs. The terminal bones of the tail are very peculiar, and very
-different from the corresponding bones of other crocodiles. While the
-spines of the tail bones along the anterior part are only moderately
-stout and long, and are directed obliquely backward, near the terminal
-part they become suddenly much broader and are directed upward, and, a
-little farther along, obliquely forward. The chevron bones on the under
-side also here become broader and longer. The end of the tail curves
-markedly downward to end in a slender point. It will be remembered that
-a similar downward curvature of the end of the tail observed in nearly
-all specimens of ichthyosaurs induced in Owen the belief that the
-animals had a fleshy terminal fin, a belief which later discoveries of
-the carbonized remains of the flesh confirmed. The peculiar structures
-observed in various specimens of these sea-crocodiles, even though no
-impressions or remains of the fleshy parts have been discovered, is
-quite conclusive evidence that these animals also had a broad, fleshy,
-terminal fin. No other explanation of the structure is possible.</p>
-
-<div id="FIG_110" class="figcenter">
-  <img  src="images/fig110.jpg" alt="" width="600" height="289" />
-  <p class="center space-below2">
-   <span class="smcap">Fig. 110.</span>—<i>Geosaurus.</i> Elongate hind leg,
-   and paddle-like front leg.<br /> (After Fraas.)</p>
-</div>
-
-<p>The ribs are not at all stout and are not much curved. They are
-directed posteriorly in the known specimens preserved in the matrix in
-<span class="pagenum" id="Page_213">[Pg 213]</span>
-such a way as to indicate a slender thorax and abdomen, not the broad
-body of the modern crocodiles. The abdominal ribs, that is, those
-protecting the region on the under side of the body between the breast
-bone and the pelvis, are strongly developed in <i>Geosaurus</i>.
-The sternum, always present in other crocodiles, is wanting in
-<i>Geosaurus</i>. The shoulder-blades and coracoids, often changed
-in shape in water reptiles, are not unlike those of the amphibious
-crocodiles, but are smaller and flatter.</p>
-
-<p>The fore limbs, to use Professor Fraas’s words, “are among the most
-interesting of all the peculiarities of <i>Geosaurus</i>,” and show
-very clearly that these animals were excellent swimmers. The humerus is
-remarkably short and broad; the two bones of the forearm, the radius
-and ulna, are broad, rounded, or angular plates, not long bones, as
-in other crocodiles; the wrist bones also are broad and plate-like.
-The three bones of the thumb, that is of the digit which received
-most strongly the impact of the water in swimming, are also broad and
-flat. All of these bones are marvelously aquatic in type, as will be
-evident from a comparison of them with the corresponding bones of the
-ichthyosaurs and mosasaurs. The bones of the other fingers, however,
-were not much changed from the ordinary crocodilian form, as a further
-comparison of them with the fingers of a land crocodile will show.
-Furthermore the whole limb or paddle was very small in comparison with
-the hind leg, and it was attached very near to the head. The relative
-proportions of the front and hind limbs in the geosaurs, gavials, and
-alligators are instructive as showing the progressive decrease in size
-of the front legs from the subaquatic, through the semiaquatic, to
-the almost purely aquatic type. The hind legs, strangely enough, were
-not very different in size and structure from those of the gavials or
-teleosaurs. The thigh bone is long and slender, though the bones of the
-leg and ankle are somewhat shortened and flattened, as are also those
-of the first toe. There were no claws on the hind feet, a distinctly
-aquatic adaptation, and the toes were certainly webbed. The pelvis,
-while not especially stout, is of good size, and was firmly attached to
-the sacrum.
-<span class="pagenum" id="Page_214">[Pg 214]</span></p>
-
-<p>Perhaps all these characters may best be summed up in the words of
-Professor Fraas, as translated:</p>
-
-<p class="blockquot">We recognize in <i>Geosaurus</i> an unusually
-slenderly built crocodile, in appearance very different from all true
-crocodiles. The smooth, rounded skull, with its greatly elongated and
-slender snout, and the deep-lying, small eyes, reminds one most of
-the ichthyosaurs. The skull merges into the slender, elongated trunk
-without a visible neck, and the body was provided neither above nor
-below with horny or bony armor, but was, probably, as in the whales,
-covered with a smooth, soft skin. The anterior extremities, attached
-far forward, are developed as paddles, and served rather as organs of
-equilibration than as a means of propulsion, which was the function of
-the elongated hind legs and the extraordinarily strong and powerful
-tail, which supported at its end a large fin. The entire impression
-given of the animal is that of an excellent swimmer, with all the
-peculiar aquatic adaptations. In the skeleton, however, all the
-characters of the original crocodiles are preserved. Most remarkable
-are the laterally placed eyes, protected by the stout sclerotic bones,
-and the overhanging bones of the orbits. So, too, the large temporal
-openings of the skull, doubtless due to the absence of the bony plates
-in the integument, give to the animal a strangely abnormal appearance
-for a crocodile.</p>
-
-<p>We have observed that all the truly aquatic air-breathing animals,
-save the plesiosaurs, have either lost the hind legs or else have them
-greatly reduced in size, and the disproportionately large size of these
-members in <i>Geosaurus</i> seems inexplicable. But an explanation is
-not, I think, hard to find. In the adaptation to water life the first
-to become modified for the control of the body are the front legs.
-The hind legs never have any really important use when the tail is a
-powerful propeller. The hind legs of the geosaurs are still essentially
-legs and not paddles, and they were doubtless used either occasionally
-for propulsion on land, or perhaps for pushing the body about on
-the bottom of shallow waters. And the presence of a well-developed
-ventral armor of bony ribs possibly also indicates more or less of the
-terrestrial crawling habit. As soon as the hind legs cease to be used
-for crawling they take on only a feeble use for the equilibration of
-the body, and speedily become small, until finally they disappear.
-That the hind legs of these creatures were of some use in the water
-is certain, because of the modifications in their structure, and
-especially because of the loss of the claws; but that they were of
-<span class="pagenum" id="Page_215">[Pg 215]</span>
-important use as propellers is hardly probable. We may therefore infer
-that the thalattosuchians, while distinctively sea-reptiles, had not
-entirely lost their land habits. Moreover, it is highly probable that
-their egg-laying habits, which would hardly change with a greater
-adaptation to water life, compelled the animals recurrently to visit
-the shores. To have finally lost their hind legs they must have become
-viviparous in habit, since it seems to be impossible for any true
-air-breathers to be hatched in water. Perhaps this insurmountable habit
-was the final cause of their extinction in competition with the truly
-viviparous aquatic flesh-eaters. The thalattosuchians had but a brief
-existence in geological history, during the latter part of the Jurassic
-period only, so far as certainly known, nor did they become widely
-dispersed over the earth; they are known from Europe, possibly from Brazil.</p>
-
-<hr class="chap x-ebookmaker-drop" />
-
-<div class="chapter">
-<p><span class="pagenum" id="Page_216">[Pg 216]</span></p>
-<h2 class="nobreak" id="CHAPTER_XVI">CHAPTER XVI</h2>
-</div>
-
-<h3>CHELONIA</h3>
-
-<p>No order of reptiles of the past or present is more sharply and
-unequivocally distinguished from all others than the Chelonia or
-Testudinata. No order has had a more uniformly continuous and
-uneventful history. None now in existence has had a longer known
-history, and of none is the origin more obscure. The first known
-members of the order, in Triassic times, were turtles in all respects,
-as well or nearly as well adapted for their peculiar mode of life as
-are those now living, and were they now living they would attract no
-especial attention from the ordinary observer and but little from the
-naturalist. From time to time some have gone after better things,
-and have come to grief, but the main line has remained with fewer
-improvements, fewer evolutional changes, than any other group of higher
-vertebrates. The turtles seem very early to have adapted themselves
-so well to their peculiar mode of life, to have intrenched themselves
-so thoroughly in their own province, that no other creatures have
-been able to overcome them, or to drive them from it. The remains of
-no other air-breathing vertebrates are so omnipresent in the rocks
-as those of the turtles; they may be expected wherever fossils of
-air-breathing animals are found, though unfortunately often only in
-scattered and broken fragments. The loose union of their skeletal bones
-and their general habits of life in shallow waters left their bodies as
-food for scavengers, or for dismemberment by the tides and currents.</p>
-
-<p>Relationships with other reptiles they really have none. Some have
-thought that the plesiosaurs were their first cousins, others the
-Placodontia, an indeterminate group of extinct reptiles usually placed
-with the Anomodontia. But their relationship with neither of these is
-closer than with the crocodiles, dinosaurs, or pterodactyls. They are
-<span class="pagenum" id="Page_217">[Pg 217]</span>
-the only reptiles that we know, besides the cotylosaurs, which have no
-holes in the temporal roof of the skull, and as the cotylosaurs were
-the most primitive and the oldest of reptiles, this fact incontestably
-proves that the turtles had a very ancient origin, though we know
-them no farther back than the later Triassic. They are the only order
-of reptiles of which not a single member is known to have teeth, or
-even vestiges of them. Until recently only a single specimen has been
-known from the Trias, and of that only the casts of the shell; but
-the shell was as fully developed and as complete as that of a modern
-alligator snapper, which it resembled much in form and in size. And
-doubtless the habits of this ancient <i>Proganochelys</i> were similar
-to those of the alligator snapper. The early cotylosaurian reptiles
-were all littoral-or marsh-loving animals, and more or less aquatic,
-and doubtless the early turtles continued in the same environments
-and with the same habits after acquiring a shell for protection and
-losing their teeth, which for some inexplicable reason they seemed no
-longer to need. Until near the close of the Jurassic period probably
-all turtles were amphibious animals of the marshes, spending much,
-perhaps the larger part, of the time in the water, good swimmers, and
-yet good crawlers. With the beginning of the Cretaceous, however, some
-of them became ambitious for new and untried modes of life. Various
-ones went down into the sea and became marine animals, reaching the
-zenith of their prosperity and the maximum of size before the close
-of the period, but continuing in diminished size and numbers to the
-present time, if we may consider the leather-back turtle as really
-their descendant. Others in the Cretaceous took to the rivers and
-ponds, and became almost as thoroughly aquatic in their thin shape
-and soft covering; and their lineal descendants still continue in the
-rivers of the Northern Hemisphere. Still others, in the Age of Mammals,
-took to the upland, and competed with the mammals in the open places
-and prairies, reaching their maximum in Miocene-Pliocene times, when
-for some unknown reason the giants among them were driven from the
-mainlands to continue a precarious existence to the present time in
-some of the larger islands.
-<span class="pagenum" id="Page_218">[Pg 218]</span></p>
-
-<div class="figcontainer">
-  <div class="figsub">
-   <img id="FIG_111" src="images/fig111.jpg" alt="" width="300" height="388" />
-   <p class="center"><span class="smcap">Fig. 111</span></p>
-  </div>
-  <div class="figsub">
-    <img id="FIG_112" src="images/fig112.jpg" alt="" width="300" height="364" />
-   <p class="center"><span class="smcap">Fig. 112</span></p>
-   </div>
-  <p class="center"><span class="smcap">Figs.</span> 111 and 112.—<i>Graptemys.</i>
-         (From Hay.)</p>
-  <p class="blockquot no-indent">
-    <span class="smcap">Fig. 111.</span>—Carapace: <i>cp1</i>, <i>cp2</i>, etc., costal
-    plates; <i>cs1</i>, <i>cs2</i>, etc., costal scutes, horny; <i>n1</i>,
-    <i>n2</i>, etc., neural bones; <i>nup</i>, nuchal bone; <i>nus</i>,
-    nuchal scute; <i>py</i>, pygal bone; <i>spy</i>, suprapygal; <i>spy 2</i>,
-    second suprapygal, or postneural; <i>vs1</i>, <i>vs2</i>, etc.,
-    vertebral scutes; 1, 2, 3-12 on right side, marginal scutes; 1, 2, 3-12
-    on left side, peripheral bones.</p>
-
-  <p class="blockquot no-indent">
-    <span class="smcap">Fig. 112.</span>—Plastron: <i>ab</i>, abdominal scutes; <i>an</i>,
-    anal scutes; <i>ent</i>, entoplastron (interclavicle); <i>epi</i>,
-    epiplastron (clavicle); <i>fem</i>, femoral scute; <i>g</i>, gular
-    scute; <i>hum</i>, humeral scute; <i>hyo</i>, hypoplastron bone;
-    <i>hypo</i>, hypoplastron; <i>in</i>, inguinal scute; <i>py</i>, pygal
-    bone; <i>xiph</i>, xiphiplastron.</p>
-</div>
-
-<p>Were there no turtles living we should look upon the fossil forms
-as among the strangest of all vertebrate animals—animals which
-had developed the strange habit of concealing themselves inside of
-their ribs, for that is literally what the turtles do. The box or
-shell of an ordinary turtle is composed of the backbones and ribs,
-to which are soldered a shell of bony skin plates above, with the
-clavicles, interclavicle, and ventral ribs below. Except in the strange
-leather-back turtle described farther on, these plates form definite
-series. Ten of them cover the spines of the dorsal vertebrae, in the
-mid-line, one over each, of which the turtles have the smallest number
-of any known reptiles. There are eight on each side over the ribs,
-united by suture with each other and with the middle series; and, in
-<span class="pagenum" id="Page_219">[Pg 219]</span>
-addition, there are twenty-six bones surrounding them and attached to
-them. All these bones compose what is called the carapace, which forms
-a complete roof in the more terrestrial types, more or less imperfect,
-with vacuities between the bones in the marine forms. On the under
-side, in addition to the clavicles and the interclavicle, there are
-three pairs of enlarged ventral ribs that go to form the plastron,
-solid and complete in land turtles, with openings in the water forms.
-And in the land forms the plastron is more or less firmly united with
-the carapace.</p>
-
-<div id="FIG_113" class="figcenter">
-  <img  src="images/fig113.jpg" alt="" width="400" height="358" />
-  <p class="center space-below2">
-    <span class="smcap">Fig. 113.</span>—<i>Toxochelys</i>;<br /> coracoid and scapula.</p>
-</div>
-
-<p>In the skeleton contained within the box thus formed is the very
-peculiar pectoral girdle, composed of scapula and coracoid, the scapula
-so peculiar that the controversy as to its homologies is not yet quite
-settled. Most authors, until recently, have believed that its peculiar
-shape (<a href="#FIG_113">Fig. 113</a>) is due to the co-ossification of the
-procoracoid with the scapula instead of as usual its loss or union with the true
-coracoid, so called. We are now pretty sure that this is not true,
-since in reality there is no such bone as the procoracoid, the bone
-so called being the real or true coracoid; and because, in the second
-place, the long anterior projection called the procoracoid is really
-only an outgrowth of the scapula itself and not a fused, separate bone.
-Hence the bone is properly called the scapula-proscapula, and not the
-scapula procoracoid, as it usually has been. The coracoids are elongate
-and flattened and without the usual supracoracoid foramen, so generally
-present in reptiles. The only other reptiles having a similar structure
-of the scapula are the plesiosaurs, and it has been because of this
-<span class="pagenum" id="Page_220">[Pg 220]</span>
-apparent resemblance that some good paleontologists have thought the
-turtles and plesiosaurs were allied. The sacrum is composed of two
-vertebrae only, and the pelvis of the usual three bones, the ilium, the
-ischium, and the pubis, all covered over by the shell.</p>
-
-<div id="FIG_114" class="figcenter">
-  <img  src="images/fig114.jpg" alt="" width="400" height="504" />
-  <p class="center space-below2">
-   <span class="smcap">Fig. 114.</span>—Pelvis of <i>Chelone</i>, from below:<br />
-   <i>pu</i>, pubis: <i>is</i>, ischium; <i>il</i>, ilium (in acetabulum).</p>
-</div>
-
-<p>In every known turtle the neck is composed invariably of eight
-vertebrae, but they are peculiar in many respects. In the earliest
-known turtles the neck vertebrae were, as would be supposed, biconcave,
-but they soon became very variable in all; in each neck some are
-biconcave, some biconvex, some opisthocoelous, and some procoelous. And
-Dr. Hay tells us that the neck has increased in length in the later forms.</p>
-
-<p>The skull also is very peculiar in that it has some very primitive
-characters and others very aberrant. The temporal roof, as has been
-said, has no holes through it, though it is often reduced by the
-emargination of the borders, whether from below or behind, until in
-some the whole temporal region is exposed, and not at all covered over.
-There is no parietal foramen, so constantly present in all the early
-reptiles and in the lizards and the tuatera of modern times. There
-are no teeth or vestiges of teeth, but the jaws have usually a horny
-cutting edge, which seems to be quite as serviceable; in the river
-turtle the lips are fleshy. There is no transverse or transpalatine
-bone. There is a single vomer only, not paired as in other reptiles,
-whence comes the doubtful theory that the vomers of other reptiles are
-not the real vomers originally so named in mammals, and hence often
-<span class="pagenum" id="Page_221">[Pg 221]</span>
-called prevomers. The vomer of the turtles under this theory is
-believed to be the real homologue of the mammalian bone. The palate is
-always slightly, sometimes nearly wholly, underfloored, as in mammals,
-carrying the internal nostrils far back in the mouth. In the occipital
-region of the skull there is a separate bone on each side called the
-paroccipital or opisthotic, which has been indistinguishably fused with
-the exoccipital in all other reptiles except the ichthyosaurs since
-Triassic times.</p>
-
-<div class="figcontainer">
-  <div class="figsub">
-   <img id="FIG_115" src="images/fig115.jpg" alt="" width="300" height="436" />
-   <p class="center"><span class="smcap">Fig. 115</span></p>
-  </div>
-  <div class="figsub">
-    <img id="FIG_116" src="images/fig116.jpg" alt="" width="300" height="447" />
-   <p class="center"><span class="smcap">Fig. 116</span></p>
-   </div>
-  <p class="center"><span class="smcap">Figs.</span> 115 and 116.—<i>Trachemys.</i>
-         (From Hay.)</p>
-  <p class="blockquot no-indent">
-   <span class="smcap">Fig. 115.</span>—Skull from above: <i>fr</i>, frontal; <i>ju</i>,
-   jugal; <i>pa</i>, parietal; <i>paoc</i>, paroccipital; <i>pfr</i>,
-   prefrontal; <i>pof</i>, postfrontal; <i>pro</i>, proötic; <i>qu</i>,
-   quadrate; <i>sq</i>, squamosal; <i>soc</i>, supraoccipital.</p>
-
-  <p class="blockquot no-indent">
-   <span class="smcap">Fig. 116.</span>—Skull from below: <i>alv</i>, alveolar surface
-   of maxilla; <i>boc</i>, basioccipital; <i>bap</i>, basisphenoid;
-   <i>exoc</i>, exoccipital; <i>mx</i>, maxilla; <i>pal</i>, palatine;
-   <i>paoc</i>, paroccipital; <i>pmx</i>, premaxilla; <i>pro</i>, proötic;
-   <i>pt</i>, pterygoid; <i>qu</i>, quadrate; <i>qj</i>, quadratojugal;
-   <i>sq</i>, squamosal; <i>vom</i>, vomer.</p>
-</div>
-
-<p class="space-above2">In the feet the numbers of phalanges—that is,
-the bones of the free digits—are like those of mammals, that is, two
-in the first and three in each of the other four digits. The land
-tortoises have lost some of these, while the river turtles have either
-gained one or two in the fourth finger and fourth toe, or else have
-<span class="pagenum" id="Page_222">[Pg 222]</span>
-enjoyed an uninterrupted descent from the primitive reptiles which
-normally possessed that number. All other reptiles, save those
-phylogenetically allied to the primitive mammals, that is, the
-Theriodontia and their allies, have normally the phalangeal formula 2,
-3, 4, 5, 4. It was partly because of this similarity of the numbers
-of toe bones that the turtles have been classed in the great group of
-reptiles that includes the ancestors of the mammals; that is, under
-this theory, the turtles would enjoy a nearer relationship to the
-mammals and to man himself than any other living reptiles! But this
-classification has been shown to be quite artificial.</p>
-
-<div id="FIG_117" class="figcenter">
-  <img  src="images/fig117a.jpg" alt="" width="600" height="217" />
-  <img  src="images/fig117b.jpg" alt="" width="600" height="140" />
-  <p class="blockquot space-below2">
-    <span class="smcap">Fig. 117.</span>—Limbs of <i>Colpochelys</i>, a
-    recent sea-turtle: <i>H</i>, humerus; <i>R</i>, radius; <i>U</i>, ulna;
-    <i>r</i>, radiale; <i>i</i>, intermedium; <i>u</i>, ulnare; <i>p</i>,
-    pisiform; <i>c</i>, centrale; <i>T</i>, tibia; <i>F</i>, fibula;
-    <i>a</i>, astragalus; <i>m</i>, fifth metatarsal. (From Wieland.)</p>
-</div>
-
-<p>From what has been said, it will be surmised that the Chelonia
-represent in themselves one of the primary subdivisions of the class
-Reptilia, and that, unlike most others, the order has enjoyed a most
-remarkable longevity. And doubtless they are one of the primary
-branches of the reptilian stock, which has remained distinct since
-Permian times at least, if not since Carboniferous, isolated and
-remarkably homogeneous, giving off no branches which departed far from
-the main stock, and on the whole leading a singularly placid existence
-for ten or more million years.</p>
-
-<p>In most textbooks the order Chelonia is divided into three suborders,
-the Pleurodira, the Cryptodira, and the Trionychoidea.
-<span class="pagenum" id="Page_223">[Pg 223]</span>
-In recent years, however, the earlier members of the older group
-of Pleurodira have been separated into a fourth suborder, the
-Amphichelydia, a group characterized by some not very important
-differences in the plastron and skull, and including those forms in
-which the cervical vertebrae are amphicoelous. This group continued to
-Eocene times before it became extinct, and consisted of archaic forms
-which persisted after all the other suborders had come into existence.
-The Cryptodira, especially characterized by the manner in which they
-withdraw the head and neck within the shell by an <b>S</b>-like
-vertical flexure, are known from the Lower Jurassic and are still the
-dominant group of today, with more than one hundred and forty living
-species. The Pleurodira in the narrower sense are first known from
-their remains in the Upper Cretaceous of North America and are still
-represented by about forty species, living in the Southern Hemisphere.
-They are distinguished from the other groups by the manner in which
-they withdraw the neck and head into the shell, by a horizontal,
-sidewise flexure. The third suborder, the Trionychoidea, also began
-in Cretaceous times, so far as we know, and are represented by about
-seventy living species, chiefly in the Northern Hemisphere. They are
-especially characterized by the absence of bony marginal plates and the
-soft epidermis.</p>
-
-<p>With the exception of the land tortoises, all turtles from the
-beginning of their career as an order to the present time have been
-more or less at home in the water. In some, like the marine forms, the
-adaptation to aquatic life has produced marked changes in structure: in
-the loss of the horny dermal shields and in the loss of bone tissue; in
-the flattening of the shell, and in the development of the front legs
-into swimming flippers, with a loss of the claws. In the absence of a
-guiding tail, which is always small in the marine turtles, propulsion
-must of course be wholly by the aid of the limbs. As oar propellers the
-marine turtles show some of the peculiar characters of the plesiosaurs.
-With a like short and broad body, a more or less elongated and
-flexible neck, there could be no sinuosity of the body in swimming.
-As an oar-like organ the humerus became flattened, and its muscular
-attachments, as in the plesiosaurs, descended far down the shaft,
-<span class="pagenum" id="Page_224">[Pg 224]</span>
-giving greater mechanical advantage. Unlike all other aquatic
-vertebrates, the turtles never developed real hyperphalangy. Only in
-the river turtles is there a possibility of an increase in the bones of
-the fourth digit.</p>
-
-<p>To discuss in general the structure and habits of the living chelonians
-would extend this chapter to an undue length, and would add nothing
-to the many excellent works on natural history accessible to the
-student. We have therefore contented ourselves with a brief outline of
-the geological history of the order, with especial reference to their
-aquatic habits.</p>
-
-<h3>SIDE-NECKED TURTLES.<br /> PLEURODIRA</h3>
-
-<p>The suborder of Chelonia, generally known as the snake-necked or
-side-necked turtles or tortoises, comprises about forty living
-species, confined to South America, Africa save the northernmost part,
-Madagascar, New Guinea, and Australia. In Australia they are the only
-members of the order known—another instance of the peculiar isolation
-of the fauna of that region. In the past they lived in North America
-during Upper Cretaceous times, the earliest known forms of the group
-in its restricted sense, of which seven species are described by Hay.
-In Eocene times they are also known from Europe and Asia, from both of
-which regions they have long since disappeared.</p>
-
-<p>The Pleurodira, as the term indicates, are easily distinguished from
-all other turtles by the way in which they withdraw the head within
-the shell. Instead of withdrawing it by an <b>S</b>-shaped flexure of
-the neck between the shoulder-blades, as do other turtles, these bend
-the neck laterally in a horizontal plane, bringing the head within the
-margins of the shell in front of one or the other foreleg; and the
-margins of the shell are produced here in an eave-like fashion for the
-greater protection of the head. In the structure of the shell, which
-is always fully developed into a box, these turtles do not differ
-very much from the Cryptodira, though there may be some extra bones
-in the plastron, as also in the skull. The nasal bones are always,
-the lacrimals sometimes, well developed; the latter never, the former
-rarely, found in other groups. The lower jaws articulate a little
-differently, and the external ear is always fully surrounded by bone.
-<span class="pagenum" id="Page_225">[Pg 225]</span>
-Very characteristic is the bony union of the pelvis with the plastron
-below, which never occurs in other turtles, unless it be the
-Amphichelydia.</p>
-
-<p>The side-necked turtles are all of fresh-water habit, similar to that
-of the fresh-water tortoises spoken of farther on. The neck is often
-very long and snake-like, which accounts for one of the names given
-to these turtles; because it is withdrawn into the shell sidewise, it
-has more distinctively ball-and-socket joints between the vertebrae,
-with distinct transverse processes for the attachment of the necessary
-side-moving muscles. The feet in all are more or less webbed and armed
-with strong claws.</p>
-
-<p>The largest and perhaps the best known of all living side-necked
-turtles is the giant Amazon turtle of South America, which sometimes
-has a shell nearly three feet in length. Its feet are broadly webbed,
-and the shell is rather flat in the adult; it is an excellent swimmer
-in the waters of the Orinoco and Amazon. Six or seven species of
-the genus to which it belongs are known, all of them South American
-except one that lives in Madagascar and one fossil found in the Eocene
-of India. This remarkable distribution is but one more of the many
-instances known in zoölogy and paleontology that seem to prove an early
-land connection between India and South America. Had the migration
-between the two continents occurred by way of Asia and Bering straits,
-as did that of hosts of mammals, one would certainly expect to find
-some evidence of it in the North American Tertiary rocks, which, so
-far, is lacking.</p>
-
-<h3>CRYPTODIRA</h3>
-
-<p>The chief families of the Cryptodira turtles are the Chelydridae,
-or snappers; the Emydidae, or marsh tortoises; the Testudinidae, or
-land tortoises; the Chelonidae, or sea-turtles; the Protostegidae, or
-ancient sea-turtles; and the Dermochelydidae, or leather-backs. Other
-doubtful or smaller groups, both living and extinct, may be omitted, or
-incidentally mentioned.</p>
-
-<h3>SNAPPING TURTLES</h3>
-
-<p>The family of snapping turtles, the Chelydridae, are of interest
-because of their peculiar geographical distribution at the present time.
-<span class="pagenum" id="Page_226">[Pg 226]</span>
-Only four species are known, three of them from North America, the
-fourth from New Guinea. The family is one of the most primitive of
-living turtles, though no members of it are known with certainty from
-earlier rocks than the Oligocene. In all probability, also, they have
-retained, more than have any other group of turtles, unless it be some
-of the fresh-water tortoises, the primitive habits of the earlier or
-earliest turtles, though of course there have been modifications, both
-in structure and in habits. The three species of the United States
-include two of the snapping turtles proper and the alligator turtles of
-the southern states, which sometimes reach a length of three feet. All
-the species are largely aquatic in habit, powerful and active swimmers,
-with webbed feet and strong claws, and both on the land and in the
-water they are bold and fierce. They have a relatively large head and
-very strong jaws. Agassiz saw one bite off a piece of a plank an inch
-in thickness, and they can usually be raised from the ground by any
-object which they seize. The carapace and plastron are much reduced,
-and are rather loosely united. The shell is not large enough for the
-complete withdrawal of the head and legs within it, and the tail is
-unusually large and strong. The common snapping turtle, <i>Chelydra
-serpentina</i>, is found from Canada to Ecuador, and its remains have
-been found with those of the mammoth and mastodon in Pleistocene
-deposits; and related species of the same genus have been reported from
-the Miocene of England.</p>
-
-<h3>FRESH-WATER OR MARSH TORTOISES</h3>
-
-<p>The family of turtles or tortoises (Emydidae) represented at the
-present time by the common terrapin, painted tortoise, and box tortoise
-of the United States, and commonly called fresh-water turtles or
-tortoises, comprises the largest group of living chelonians—nearly a
-third of all existing members of the order. They are widely distributed
-over all parts of the earth except Australia, and are of very varied
-habits. Some are almost exclusively aquatic; others, like the painted
-tortoise, are partially so, while others, especially the common box
-tortoise, are almost as exclusively terrestrial as the true land
-tortoises, dying even, if forced to live long in water.
-<span class="pagenum" id="Page_227">[Pg 227]</span></p>
-
-<p>The shell in the more aquatic forms is depressed or flattened, but
-in the terrestrial kinds may be as highly arched as in the true land
-tortoises. The feet are adapted primarily for walking, but nearly
-always have the toes webbed, and the digits are longer than are those
-of the land tortoises. Only the two or three middle toes have claws.
-Some species have developed hinges in the plastron, whereby they may be
-completely closed up after the head and legs are withdrawn within the
-shell. Most of the species are carnivorous in habit, but a few, like
-the box tortoise, are strictly vegetarian.</p>
-
-<p>Geologically the fresh-water tortoises have a not very ancient history,
-going back no farther than do the land tortoises, that is, to the
-beginning of the Cenozoic or Age of Mammals. Fully fifty species
-are known from the Tertiary rocks of North America, or more than
-three-fourths as many as are now living upon the earth.</p>
-
-<p>The family at most can be said to be only amphibious in habit, and has
-no striking aquatic adaptations, since the shell is well developed and
-is covered with horny shields. The flattened shell of the more aquatic
-forms is characteristic, as is also the greater degree of webbing
-between the toes.</p>
-
-<h3>LAND TORTOISES</h3>
-
-<p>Perhaps the last of the more noteworthy specializations of
-the Chelonia, and indeed among the last of the more important
-specializations of the Reptilia, are the upland tortoises, of which
-the common “gopher” of the southern states is almost the only remnant
-in North America. They formed a part of the great hegira of forest and
-marsh animals to the open prairies, away from the lowlands and water
-which the turtles had inhabited almost exclusively for millions of years.</p>
-
-<div id="FIG_118" class="figcenter">
-  <img  src="images/fig118.jpg" alt="" width="600" height="324" />
-  <p class="center space-below2">
-    <span class="smcap">Fig. 118.</span>—<i>Testudo sumeirei</i>, a giant
-    upland tortoise.<br /> (From Hay, after Rothschild.)</p>
-</div>
-
-<p>They began their career, Dr. Hay thinks, at about the beginning of
-the Cenozoic, that is, with the great development of the mammals, and
-reached the maximum of their development in the Miocene; and they
-have been on the decline ever since. In the Northern Hemisphere, at
-least, the slowly cooling climate throughout the Eocene, and a decided
-<span class="pagenum" id="Page_228">[Pg 228]</span>
-decrease in moisture, brought about the prairies and prairie plants
-before its close. Just as the horses, rhinoceroses, camels, and other
-herbivorous mammals took to these open places for the better and more
-abundant food found therein, so also the lowland tortoises found better
-food and fewer enemies there, for they are all strictly herbivorous in
-habit. The mammals became more conspicuous to their enemies when they
-went into the open, and it was only by the development of speed, more
-sober coloration, and perhaps greater cunning that they found safety
-from them. The tortoises were handicapped by low intelligence, and they
-could not develop speed, for they were not constructed to that end. But
-they did find protection in their bony shell, which became thicker,
-higher, and more convex, and with smaller openings. To quote Dr. Hay:
-“We may suppose that it would be much more difficult for a carnivorous
-animal to effect an entrance into such a shell than into one depressed,
-and whose borders may be spanned by the jaws of their enemies.” Perhaps
-also the highly arched form of the shell gave greater capacity for the
-lungs, and the tortoises in general, it is said, do have better lung
-capacity than the more aquatic or lowland types of turtles. Possibly,
-also, the heavier shell lessened the evaporation of the body fluids,
-and made the tortoises less dependent upon the vicinity of water.
-<span class="pagenum" id="Page_229">[Pg 229]</span>
-Certain it is that the common box tortoise, of like form and habits,
-occurs not rarely on the arid plains, far from water.</p>
-
-<p>The neck and legs became fully retractile within the shell; the digits
-were shortened up, without a vestige of webbing membrane between them;
-the phalanges were reduced in number to two in each toe, and nearly all
-the toes have well formed claws. The feet are placed squarely upon the
-ground, and the body is elevated in walking. They can swim, when by accident
-they are thrown into the water, only as any terrestrial mammal can.</p>
-
-<p>About forty species of land tortoises are known throughout the world
-at the present time, though North America, the probable original home
-of the tribe, has but three, all small. The larger species are all now
-denizens of islands, especially the Galapagos Islands, where the giant
-tortoises have long been famous. And many of our living forms have
-changed but little since Eocene times. In the Oligocene and Miocene
-they inhabited western North America in enormous numbers. In the Bad
-Lands of South Dakota one can often see the remains of a dozen or more
-of these giant tortoises at one time, specimens varying from one to
-three feet in length of shell. In river deposits, those of the late
-Miocene or early Pliocene, the writer has seen areas of an acre or more
-literally strewn with their remains, as though droves of them had been
-overwhelmed and perished together. About fifty species of these land
-tortoises are known from the American Tertiary, thirty-two of them
-belonging to the modern genus <i>Testudo</i>, which comprises the giant
-tortoises of the Galapagos. The largest known species of the group is
-one of <i>Testudo</i> from the Pliocene of India, which had a shell six
-feet in length. Why the larger species became extinct in Pliocene times
-on the mainland to survive only in the islands is not known; possibly
-their carnivorous enemies became too cunning and too numerous.</p>
-
-<h3>SEA-TURTLES.<br /> CHELONIDAE</h3>
-
-<p>The sea-turtles, or Chelonidae comprise five or six living species,
-inhabitants for the most part of tropical and subtropical oceans, of
-which the green or edible turtle (<i>Chelone</i>), the hawksbill turtle
-<span class="pagenum" id="Page_230">[Pg 230]</span>
-(<i>Caretta</i>), and the loggerhead (<i>Eretmochelys</i> [<a href="#FIG_119">Fig. 119</a>])
-are the best known. They are all thoroughly aquatic in habit, and
-of large size, from three to five feet in length. The carapace is
-heart-shaped, and reduced, that is, with large openings between the
-ribs; the plastron also is reduced and loosely united to the carapace.
-The neck is short and the head is not retractile within the shell. The
-temporal region of the skull is roofed over. The four legs form large
-and powerful flippers, and the hind legs are relatively small. The
-body is flattened and the tail is small. The aquatic characters of the
-limbs are seen especially in the broad and strong humerus, with the
-radial crest for the attachment of powerful muscles situated far down
-on the shaft; in the relative shortness of the radius and ulna, and
-the large size of the latter bone; in the flattened carpal bones; and
-in the great elongation of the digits and the absence of all but one
-or two of the claws. Unlike the leather-back turtle and the Cretaceous
-sea-turtles, the carapace and plastron are completely covered with
-horny shields, from which indeed the tortoise shell of commerce is
-derived. Except the green turtle, all members of the family are carnivorous.</p>
-
-<div id="FIG_119" class="figcenter">
-  <img  src="images/fig119.jpg" alt="" width="600" height="374" />
-  <p class="center space-below2">
-   <span class="smcap">Fig. 119.</span>—<i>Eretmochelys</i>, loggerhead
-   turtle.<br /> (By permission of the New York Zoölogical Society.)</p>
-</div>
-
-<p><span class="pagenum" id="Page_231">[Pg 231]</span>
-Extinct members of the family are known from scanty remains in Cenozoic
-and late Cretaceous rocks. From the earlier Cretaceous deposits of the
-plains more primitive allied forms occur, often classed in distinct
-families of which <i>Toxochelys</i> (<a href="#FIG_120">Fig. 120</a>) and <i>Desmatochelys</i>
-are the more noteworthy. The latter genus, especially, might well
-have been an ancestor of all the modern forms. About three feet in
-length, it had all the essential characteristics of the sea-turtles,
-in its thin form, roofed-over skull, reduced carapace, loose plastron,
-and flipper-like limbs. The single known specimen, preserved in the
-museum of the University of Kansas, came from the lower rocks of
-the Upper Cretaceous of Nebraska. Yet earlier, at the close of the
-Jurassic, there were shore turtles of considerable size that had begun
-to develop a fondness for the open seas; to acquire a depressed form
-and lightened shell, the limbs still retaining, however, more of the
-terrestrial or crawling form. They are grouped as a separate family,
-the Thalassemydae, and include the first of the Chelonia to depart from
-the marsh and fresh-water habits which for long ages, perhaps, had
-limited the activities and evolution of the turtles.</p>
-
-<div id="FIG_120" class="figcenter">
-  <img  src="images/fig120.jpg" alt="" width="500" height="425" />
-  <p class="center space-below2">
-   <span class="smcap">Fig. 120.</span>—Carapace of <i>Toxochelys bauri</i>,<br />
-   an Upper Cretaceous sea-turtle: <i>ep</i>, epineural.<br /> (After Wieland.)</p>
-</div>
-
-<h3>ANCIENT SEA-TURTLES.<br /> PROTOSTEGIDAE</h3>
-
-<p><span class="pagenum" id="Page_232">[Pg 232]</span></p>
-
-<div id="FIG_121" class="figcenter">
-  <img  src="images/fig121.jpg" alt="" width="600" height="274" />
-  <p class="blockquot space-below2">
-<span class="smcap">Fig. 121.</span>—<i>Toxochelys latiremis</i>; front leg: <i>hum</i>,
-humerus; <i>rad</i>, radius; <i>ul</i>, ulna; <i>int</i>, intermedium; <i>uln</i>, ulnare;
-<i>p</i>, pisiform; <i>cen</i>, centrale. (From Wieland.)</p>
-</div>
-
-<div id="FIG_122" class="figcenter">
-  <img  src="images/fig122.jpg" alt="" width="500" height="334" />
-  <p class="center space-below2">
-    <span class="smcap">Fig. 122.</span>—<i>Desmatochelys lowii</i>;<br />
-    skull from above and below.</p>
-</div>
-
-<p>Forty-four years ago the late Professor E. D. Cope, one of the
-greatest naturalists America has ever produced, in almost the earliest
-exploration of the great Cretaceous fossil deposits of western Kansas,
-discovered and collected a remarkable specimen of one of the most
-extraordinary turtles that is known even yet. By an error somewhat
-natural for those times, when the theory of evolution was just
-<span class="pagenum" id="Page_233">[Pg 233]</span>
-beginning to attain acceptance by naturalists, he thought that the
-specimen, notwithstanding its monstrous size, represented a very
-primitive kind of turtle, and gave to it the name <i>Protostega
-gigas</i>, meaning gigantic first roof! The late Professor George
-Baur, to whom paleontology owes so much, showed that, far from being
-a primitive turtle, <i>Protostega</i> was really one of the most
-specialized types of the order. Professor Cope’s account of the discovery
-of the specimen is of so much interest that it may be quoted here:</p>
-
-<p>“In the very young tortoise or turtle the ribs are separate, as in
-other animals. As they grow older they begin to expand at the upper
-side of the upper end, and with increased age the expansion extends
-throughout the length. The ribs first come in contact where the process
-commences, and in the land tortoise they are united at the end. In the
-sea-turtles the union ceases a little above the ends. The fragments
-of the <i>Protostega</i> were seen by one of the men projecting from
-a ledge of a low bluff. After several square feet of rock had been
-removed, we cleared up the floor and found ourselves well repaid. Many
-long, slender pieces of two inches in width lay upon the ledge. They
-were evidently ribs, with the usual heads, but behind each head was
-a plate-like the flattened bowl of a huge spoon, placed crosswise.
-Beneath these stretched two broad plates, two feet in width, and no
-thicker than binder’s board. The edges were fingered and the surface
-was hard and smooth. All this was quite new, among fully grown animals.
-Some bones of a large paddle were recognized, and a leg bone. The
-shoulder-blade of a huge tortoise came next, and further examination
-showed that we had stumbled on the burial place of the largest species
-of sea-turtle yet known. But the ribs were those of an ordinary turtle
-just hatched, and the great plates represented the bony deposit in the
-skin, which, commencing independently in modern turtles, unite with
-each other at an early day. But it was incredible that the largest
-of known turtles should be but just hatched, and for this and other
-reasons it has been concluded that this ‘ancient mariner’ is one of
-those forms, not uncommon in old days, whose incompleteness in some
-respects points to the truth of the belief that animals have assumed
-their modern perfection by a process of growth from more simple beginnings.”
-<span class="pagenum" id="Page_234">[Pg 234]</span></p>
-
-<p>Later studies by Doctors G. Baur, E. C. Case, O. P. Hay, and especially
-G. R. Wieland, of the abundant and excellent material, preserved in the
-museums of Yale and Kansas universities and the Carnegie Institution,
-and especially the discovery by Wieland in 1895 of an allied and
-yet larger form which he called <i>Archelon</i>, have determined
-practically every detail of the structure of this remarkable group of
-sea-turtles. A surprisingly complete specimen of <i>Archelon</i> is
-mounted in the museum of Yale University.</p>
-
-<div id="FIG_123" class="figcenter">
-  <img  src="images/fig123.jpg" alt="" width="500" height="430" />
-  <p class="blockquot space-below2">
-   <span class="smcap">Fig. 123.</span>—<i>Archelon ischyros</i>; skeleton
-   from above: <i>n</i>, nuchal, <i>r</i>, <i>r</i>, <i>r</i>, ribs;
-   <i>m</i>, <i>m</i>, peripheral bones; <i>h</i>, humerus; <i>r</i>,
-   radius; <i>u</i>, ulna; <i>t</i>, tibia; <i>fi</i>, fibula. (From Wieland.)</p>
-</div>
-
-<p>About a half-dozen species and two genera of the family have so far
-been described, all coming from the Upper Cretaceous deposit of Kansas
-and South Dakota, the genus <i>Archelon</i> from later rocks than those
-which have yielded <i>Protostega</i>.</p>
-
-<p>The general form and structure of <i>Archelon</i> will best be
-understood from the accompanying figures after Wieland (<a href="#FIG_123">Figs. 123</a>,
-<a href="#FIG_124">124</a>, <a href="#FIG_125">125</a>)
-and the restoration of the living animal as interpreted by the
-<span class="pagenum" id="Page_235">[Pg 235]</span>
-writer (<a href="#FIG_126">Fig. 126</a>). If the leather-back turtle, described
-farther on, is really the descendant of these or allied turtles, as many
-authors believe, it of course represents the very highest aquatic
-specialization of all Chelonians. If, on the other hand, as some
-believe, the leather-back is the end of a long and independent line
-of descent, then <i>Archelon</i> represents the highest aquatic
-specialization of all other turtles.</p>
-
-<p>In size, at least, <i>Archelon</i> attained the maximum of the order,
-reaching a length of more than twelve feet, and a weight of more than
-three tons. Except that the shell was not heart-shaped or elongated as
-in all modern sea-turtles, but nearly circular in outline, it had all
-the aquatic adaptations of the sea-turtle in a yet higher degree.</p>
-
-<div id="FIG_124" class="figcenter">
-  <img  src="images/fig124.jpg" alt="" width="500" height="435" />
-  <p class="blockquot space-below2">
-   <span class="smcap">Fig. 124.</span>—<i>Archelon</i> from below, without
-   plastron: <i>h</i>, humerus; <i>r</i>, radius; <i>u</i>, ulna;
-   <i>sc</i>, scapula; <i>c</i>, coracoid; <i>p</i>, pubis; <i>i</i>,
-   ischium. (From Wieland.)</p>
-</div>
-
-<p><span class="pagenum" id="Page_236">[Pg 236]</span></p>
-
-<div id="FIG_125" class="figcenter">
-  <img  src="images/fig125.jpg" alt="" width="500" height="441" />
-  <p class="blockquot space-below2">
-   <span class="smcap">Fig. 125.</span>—<i>Archelon</i>; skeleton from
-   below: <i>hp</i>, hyoplastron; <i>hpp</i>, hypoplastron. (From Wieland.)</p>
-</div>
-
-<p>The shell was depressed; the dermal plates covering the ribs had almost
-entirely disappeared, remnants only of their upper ends remaining; the
-skull (<a href="#FIG_127">Fig. 127</a>) had the temporal region wholly roofed over;
-the neck was short and not retractile. The front legs were strong flippers,
-the humerus was long and stout, with the crest for the attachment
-of muscles far down on the shaft; the digits were greatly elongated
-and clawless, etc. The plastron only was less reduced than in the
-case of the modern sea-turtles. No traces of horny shields have been
-discovered. As to the nature of the covering and the general appearance
-of the turtle when alive, Dr. Wieland has kindly given the writer his
-views, as follows:</p>
-
-<p>“After direct study or fairly close examination of all the fossil
-material of importance thus far collected representing the
-Protostegidae, it seems certain that in all the members of the group
-an external leathery layer was well developed. In no instance is there
-the slightest trace of horny shield sulci, or grooves; though it seems
-probable that there was some gradation toward a thin and perhaps even
-slightly horny hide. In <i>Archelon ischyros</i> the reduced condition
-<span class="pagenum" id="Page_237">[Pg 237]</span>
-of the carapace and the presence of the continuous row of large,
-median, supraneural elements render it quite certain that there was a
-development of leathery hide comparable to that of <i>Dermochelys</i>.
-The same may be said of <i>Protostega gigas</i>. But <i>Archelon
-Marshii</i> had a less reduced carapace, and the leathery skin was
-probably less well developed; and <i>Protostega Copei</i>, in which no
-<span class="pagenum" id="Page_238">[Pg 238]</span>
-trace of supraneurals remains, must have made some approach to the
-horn-shield condition. A more distinct suggestion of transition from
-the leathery to the horny shield covering may be seen in the very
-different contemporary Cretaceous form, <i>Toxochelys Bauri</i>,
-where ossified epi-or supraneurals occupy quite exactly the nodal
-relation of the five vertebral horn shields of later turtles, like
-<i>Lytoloma</i>, though there are not the slightest traces of sulci.</p>
-
-<div id="FIG_126" class="figcenter">
-  <img  src="images/fig126.jpg" alt="" width="600" height="371" />
-  <p class="center space-below2">
-   <span class="smcap">Fig. 126.</span>—<i>Archelon ischyros</i>,
-   a gigantic sea-turtle<br /> from the Upper Cretaceous of South Dakota.</p>
-</div>
-
-<div id="FIG_127" class="figcenter">
-  <img  src="images/fig127.jpg" alt="" width="500" height="279" />
-  <p class="blockquot space-below2">
-    <span class="smcap">Fig. 127.</span>—Skull of <i>Archelon ischyros</i>:
-    <i>pa</i>, parietal; <i>f</i>, frontal; <i>pm</i>, premaxilla;
-    <i>pf</i>, prefrontal; <i>ptf</i>, postfrontal; <i>m</i>, maxilla;
-    <i>j</i>, jugal; <i>qj</i>, quadratojugal; <i>sur</i>, surangular;
-    <i>d</i>, dentary; <i>an</i>, angular. (After Wieland.)</p>
-</div>
-
-<p>“From a purely anatomical standpoint I have suggested that
-<i>Archelon</i> had seven dorsal keels corresponding to those of
-<i>Dermochelys</i>. There is much excellent reason for regarding
-dermogene ossification as essentially double-layered throughout the
-Reptilia.</p>
-
-<p>“In any restoration of <i>Archelon ischyros</i> only the mid-line
-should be accentuated as a series of rather sharp supraneural crests.
-These are shown to have been present by the characteristic groove-like
-median pits with radiating striae, which are such a prominent feature
-of epineurals. It is reasonable to believe that the pits mark the
-attachment of horny crests developed in the leathery hide. Such were
-<span class="pagenum" id="Page_239">[Pg 239]</span>
-doubtless projected, more or less keel-like, to a height of one or
-two inches, and thus gave to the mid-line of the carapace, when
-seen laterally, a distinctly sinuous outline not unlike that of
-<i>Toxochelys</i>.”</p>
-
-<p>As regards the habits of these ancient sea-turtles, we may offer
-tolerably certain conjectures. In the opinion of the writer, the less
-reduced plastron indicates a bottom-feeding habit, a view that is
-strengthened by the more rounded form of the shell, like that of the
-river turtle. All in all it would seem that <i>Protostega</i> and
-<i>Archelon</i> lived habitually on the soft bottoms of the shallower
-seas, feeding upon the hordes of large shell-fish, for which their
-powerful parrot-like beak was admirably adapted. That the species
-of <i>Protostega</i> did not commonly frequent the deeper oceans is
-indicated by the general absence of their remains in the deeper water
-deposits. The writer, in a long collecting experience, always found
-their remains associated with those of the smaller <i>Toxochelys</i>,
-toothed birds, pterodactyls, and the smaller mosasaurs.</p>
-
-<p>Perhaps no one can speak more authoritatively as to the habits of these
-gigantic sea-turtles of the Cretaceous than Dr. Wieland:</p>
-
-<p>“With regard to the general habits and appearance of <i>Archelon</i>
-much might doubtless be said if the present-day sea-turtles were more
-familiar objects. Dr. Hay thought that <i>Archelon ischyros</i> was a
-clumsy or even a sluggish, mainly littoral animal, moving slowly about
-the bottom of quiet inlets in quest of shell-fish; I, on the contrary,
-much struck by the powerful flippers, and especially by the flattening
-of the humerus, with its low radial crest and obviously strong
-musculature, have held that unusual swimming power and adaptation to a
-strictly marine life were indicated. Perhaps, as usual where experts
-differ, it is probable that both views are in part correct, and that
-<i>Archelon</i> was only a moderately good swimmer. It may be noted
-that, notwithstanding the almost circular body, the femoral notch, that
-for the hind leg, lies far back, so that it is not necessary, on the
-score of bulk, to assume slowness of motion, or the inability to pursue
-a sea-going life. Furthermore, it is now known that the development of
-the digits fell little short of that seen in <i>Colpochelys</i>
-(<a href="#FIG_117">Fig. 117</a>) or <i>Eretmochelys</i>, truly marine turtles.</p>
-
-<p>“Therefore, while there can be no doubt that <i>Archelon</i> was
-strictly carnivorous in habit, and well able to navigate the open seas,
-<span class="pagenum" id="Page_240">[Pg 240]</span>
-it is not likely that it fed on other than relatively slow-moving
-prey. Lydekker looked upon the broad mandibles and broad palate
-of <i>Lytoloma</i> as specializations for a mussel diet; and very
-similarly in <i>Archelon</i>, while the decurved beak would easily
-transform him into a most formidable enemy, the heavy premaxillaries
-and vomer, and the flat but deep lower jaw, suggest an adept crusher of
-crustaceans. The presence of vast quantities of <i>Nautilus dekayi</i>,
-which I found accompanying one of the specimens, was doubtless
-accidental, but it plainly suggests that this cephalopod was one of the
-teeming sources of food in the <i>Archelon</i> environment.</p>
-
-<p>“The huge bulk of the mature <i>Archelon</i> might account for the
-shearing off and loss of the flippers of younger forms caught between
-the shells of the ‘elder boatmen of the Cretaceous seas,’ as Cope has
-called them, during any sudden rush while herding on the shores. But
-probably the young turtles did not much frequent the shores at either
-egg-laying or other times. Whence it is much more likely that it was
-a mosasaur or some of the gigantic fishes like <i>Portheus</i> which
-bit off the right hind flipper in the type-specimen of <i>Archelon
-ischyros</i>, well above the heel, as I have described it. That this
-happened rather early in life is shown by the arrested growth of the
-right femur and remaining portions of the tibia and fibula, which are
-all uniformly 10 per cent smaller than the corresponding bones of the
-left flipper.”</p>
-
-<p>While there were many small fishes in the Niobrara seas which the
-Protostegas inhabited, the most striking thing in the fauna is the
-great abundance of molluscal shells, especially <i>Ostrea congesta</i>.
-And with them were great hordes of larger pelycypod mollusks, some of
-them of enormous size. Some of the largest reach a diameter of nearly
-four feet, with shells so thin that one can hardly understand how they
-could have supported such large, oyster-like creatures. One can imagine
-that such shell-fish might have afforded an almost inexhaustible source
-of food for the large turtles; and several times the writer has found
-remains of <i>Protostega</i> associated with such shells. From all of
-which evidence it seems very probable indeed that Dr. Wieland is right
-in imputing to these gigantic turtles a shell-feeding habit, a habit
-<span class="pagenum" id="Page_241">[Pg 241]</span>
-which required neither speed nor great prowess; and perhaps the
-formidable beak was used more in social quarrels than for food-getting.
-That these marine turtles departed from the usual reptilian habit of
-laying their eggs upon land is improbable. The tortoise shell turtles
-of the Bahamas lay three or four hundred eggs in a hollow scooped out
-in the sand and then leave the young to their own devices; certainly
-many a one is gobbled up by birds of prey or other enemies on their way
-to the water. Perhaps the young <i>Archelon</i> lost its hind leg in
-some such mishap.</p>
-
-<h3>LEATHER-BACK MARINE TURTLES</h3>
-
-<p>The most remarkable member of the Chelonia now living is <i>Dermochelys
-coriacea</i> (<a href="#FIG_128">Fig. 128</a>), the great leathery or leather-back
-turtle of the warmer parts of the Atlantic, Indian, and Pacific oceans,
-the sole member of the family Dermochelydidae. It is the largest of
-all living turtles and the most thoroughly aquatic of all, whether
-living or extinct. It sometimes reaches a length of six feet, or
-half that of the largest known extinct forms, and weighs a thousand
-or more pounds. Agassiz saw a specimen that he said weighed a ton.
-Unlike other turtles, it has a carapace quite peculiar to itself,
-composed of a layer of thin, irregularly polygonal bones forming a
-mosaic, completely hidden in the thick skin, and entirely free from
-the skeletal bones beneath them. The larger of these skin bones form
-seven rows above, which appear in the living animal as sharp keels
-running the whole length of the shell. On the under side there are five
-rows of smaller-sized bones, under which there are vestiges of bones
-representing the normal plastron of turtles. The limbs are powerful,
-flattened paddles, not unlike those of <i>Eretmochelys</i>, but wholly
-destitute of claws. The front paddles are much larger than the hind
-ones; the humerus is long and flattened, and the digits are elongated.
-The leather-back is a powerful and effective swimmer, going long
-distances. Its habits are not well known; its food is chiefly fish,
-crustaceans, and mollusks.</p>
-
-<div id="FIG_128" class="figcenter">
-  <img  src="images/fig128.jpg" alt="" width="600" height="447" />
-  <p class="center space-below2">
-    <span class="smcap">Fig. 128.</span>—<i>Dermochelys coriacea.</i><br />
-    (From Brehm.)</p>
-</div>
-
-<p>So very different is the structure of its shell that some excellent
-naturalists regard <i>Dermochelys</i> as the equivalent in rank of all
-other turtles combined, the sole representative of the suborder Athecae,
-<span class="pagenum" id="Page_242">[Pg 242]</span>
-as distinguished from the Thecophora. Dr. Hay, whose authority on
-fossil turtles is of the highest, believes that its line of ancestry
-has been distinct from that of all other turtles from Triassic times
-at least. Others believe that the leather-back is merely a highly
-specialized form derived from the ordinary shelled type, a descendant
-of some of the marine turtles of Cretaceous times. In support of the
-primitive ancestry of the leather-back Dr. Hay offers the following:</p>
-
-<p>“The writer holds the view that the earliest turtles possessed
-practically two kinds of shell, one purely dermal, consisting probably
-of a mosaic of small bones arranged in at least twelve longitudinal
-zones. Each zone probably consisted of a row of larger bones bordered
-on each side by smaller bones. Each of these bones was covered by a
-horny scute. The nearest approach to such a dermal shell is in our
-days seen in <i>Dermochelys</i>. Beneath the skin there seems to have
-existed a carapace more or less complete, which consisted of a nuchal,
-<span class="pagenum" id="Page_243">[Pg 243]</span>
-a median row of neurals, eight pairs of costals, a pygal, probably one
-or more supraneurals, and about eleven peripherals on each side. To
-what extent the neurals and the costal plates had become anchylosed to
-the neural spines and the ribs respectively, it is now impossible to
-determine. Nor can we say to what extent the various elements of the
-carapace had become connected with one another. There was a subdermal
-plastron which was composed of at least eleven bones.</p>
-
-<p>“According to the author’s view, as time went on the external,
-mosaic-like shell disappeared in most turtles, while a more efficient
-armor was developed out of the subdermal elements. In the ancestors of
-<i>Dermochelys</i>, however, the dermal armor was retained, while the
-more deeply seated one disappeared, with the exception of the nuchal bone.”</p>
-
-<p>Such a hypothesis as the foregoing satisfactorily explains the
-extraordinary mosaic shell of the leather-back, and is perhaps an
-acceptable explanation of the rather strange fact that the horny
-shields of turtles do not correspond with the bones below them, as
-might be expected. Unfortunately this hypothesis lacks sufficient
-proof. About the only evidence that is offered in its support is the
-existence of a row of bones along the middle line in the Cretaceous
-<i>Toxochelys</i>, and notably in <i>Archelon</i>, both aquatic forms.
-It is urged that these bones, the epineurals of Wieland, are really
-the remains of an external layer that persisted in these turtles.
-However, they might have been new ossifications, such as we know did
-occur in not a few of the land tortoises later over the tail and limbs.
-Aside from <i>Proganochelys</i> in the vast interval of time from the
-Triassic to the Eocene no other evidence of such an external dermal
-layer has been discovered. The chief argument against such divergent
-ancestry of the turtles in two chief lines of descent is the fact that
-in its other structure <i>Dermochelys</i> shows great resemblance to
-other sea-turtles of the Cretaceous times—so much resemblance that it
-seems impossible that the ancestors of the leather-back should have
-paralleled them in almost everything except the shell.</p>
-
-<p>On the other hand, those who disagree with this view believe that the
-modern leather-back is the descendant of such Cretaceous marine turtles
-as <i>Protostega</i> or <i>Archelon</i>, some of which had lost nearly
-<span class="pagenum" id="Page_244">[Pg 244]</span>
-all of the costal plates and had the neurals and marginals reduced.
-It is urged that some of these early marine forms, after they had
-practically lost the ordinary bones of the carapace, for some reason
-or other found a bony shell again necessary for their welfare.
-Possibly they had become littoral in habit; possibly they again became
-subject to new and dangerous enemies in their unprotected condition,
-notwithstanding their great size; perhaps the zeuglodons were among
-their enemies. Now, as we have seen, an animal never takes a back
-track and recovers a thing it has once lost. It was impossible for the
-ancestors of the leather-back again to acquire an orthodox shell, and
-they forthwith proceeded to acquire quite another kind that would serve
-the same purpose.</p>
-
-<p>Possibly the truth lies between the variant views, in the theory
-recently expressed by Versluys: “The shell of tortoises and turtles is
-formed by a combination of two layers of dermal ossifications, a thecal
-layer and a more superficial epithecal layer, the latter generally
-represented by the marginals only. The leather-back is a member of the
-Cryptodira, and is allied to the other marine turtles. The problem of
-the origin of the aberrant shell of the leather-back seems to find its
-solution in the hypothesis that it is a secondary proliferation of the
-marginals and such other epithecal elements as were present in its
-thecophorous ancestors.”</p>
-
-<p>In other words, Versluys believes that Hay’s and Wieland’s views of the
-primitive double layer of exoskeletal bones is essentially correct, but
-that <i>Dermochelys</i> was derived from later forms in which some of
-them, only, as in <i>Archelon</i>, had remained. Baur’s contention that
-“<i>Dermochelys</i> is not the least, but the most specialized marine
-turtle” seems to have been fully justified.</p>
-
-<h3>RIVER TURTLES.<br /> TRIONYCHOIDEA</h3>
-
-<p>No reptile is more familiar or more exasperating to the river fisherman
-than the turtle, variously known as the river, soft-shelled, or mud
-turtle. It lives, often in great numbers, in most of the rivers, ponds,
-and bayous of the interior east of the Rocky Mountains, and especially
-in those of sluggish current and muddy bottoms. It is voraciously
-carnivorous in habit, feeding upon the smaller fish, mussels, and such
-other living food as it can capture. With its long, sinuous neck and
-<span class="pagenum" id="Page_245">[Pg 245]</span>
-snake-like head, and soft, mottled skin, it is repulsive enough to most
-persons, but is especially annoying to the fisherman, since it devours
-with impunity his bait so long as he feeds it, and can seldom be caught
-on the hook because of its hard and bony mouth, in which only by good
-luck will the hook catch. And the luckless string of fish that the
-fisherman leaves in the water may be almost completely devoured in a
-few hours by these fiercely predaceous feeders. However, if so annoying
-while seeking for better game, it in part makes up for the annoyance it
-causes by furnishing in its own body a not unpalatable food for those
-who like to eat reptiles.</p>
-
-<div id="FIG_129" class="figcenter">
-  <img  src="images/fig129.jpg" alt="" width="500" height="400" />
-  <p class="center space-below2">
-    <span class="smcap">Fig. 129.</span>—<i>Trionyx</i>, river turtle.<br />
-    (By permission of the New York Zoölogical Society.)</p>
-</div>
-
-<p>The river turtles will be readily recognized from the accompanying
-illustration (<a href="#FIG_129">Fig. 129</a>). They are very flat, covered with
-a soft, smooth skin, with a long, sinuous neck and a small, snake-like
-and vicious-looking head which has a protuberant snout with the
-external nasal orifice at its end. Their feet are webbed and somewhat
-<span class="pagenum" id="Page_246">[Pg 246]</span>
-paddle-like, but always with three stout claws—whence comes the name
-of the group—on the anterior digits, which are used for burrowing in
-the mud and excavating holes for their eggs. These turtles burrow more
-or less in the mud, with the long neck free, lying in wait for their
-prey, and coming to the surface from time to time to breathe. As the
-shape of the body and the paddle-like feet would suggest, they are
-active swimmers and purely aquatic in habit, never leaving the water
-unless compelled to. They bury their hard-shelled eggs on the shores
-only a few feet from the water, and leave them to their fate. If the
-pools in which they live dry up, they burrow deeply in the mud and
-await the rains and floods. In captivity they feed upon all kinds of
-food, vegetable as well as animal, and are active and aggressive.</p>
-
-<div id="FIG_130" class="figcenter">
-  <img  src="images/fig130.jpg" alt="" width="500" height="302" />
-  <p class="center space-below2">
-    <span class="smcap">Fig. 130.</span>—<i>Aspideretes</i>, a trionychoid
-    turtle<br /> from the Basal Eocene of New Mexico;<br /> skull from above.
-    (From Hay.)</p>
-</div>
-
-<p>Because of certain peculiarities, they are usually classed in a
-separate suborder all their own, the Trionychoidea, especially
-distinguished from the Cryptodira, which in general they resemble in
-most respects, aside from the absence of the usual horny dermal plates,
-in the lack of a marginal row of bony plates around the carapace—not a
-very important distinction. Less than thirty living species are known,
-all of them exclusively, or chiefly of fresh-water habit. Six species
-are known from North America; the remainder inhabit Africa, south of
-the Sahara Desert, southern India, and most of the East Indian islands;
-none is known from Australia. No species lives in South America and
-none is known to have lived there in past times. During Eocene,
-Oligocene, and Miocene times these fresh-water turtles lived in the
-region of Europe in great numbers, but for some inexplicable reason
-they became extinct there and never returned. Nearly seventy species of
-the Trionychoidea, belonging in two families, are described by Dr. Hay
-from the Tertiary rocks of North America, more than twice the number now
-<span class="pagenum" id="Page_247">[Pg 247]</span>
-living throughout the world. Some of these were of relatively large
-size, measuring fully two feet in the length of the shell. And in some
-places they must have been very abundant. The writer has seen, in the
-Bad Lands of the Continental Divide, their weathered-out remains so
-numerous that they might be raked into windrows miles in length along
-the sloping bluffs, all in small fragments, for their bones, like those
-of most turtles, are only loosely united by sutures and readily drop
-apart before fossilization. Their shells may be readily distinguished
-from those of all other turtles by the granulated, pitted, or
-sculptured exterior surface, that was covered by the skin in life;
-other turtles have the surface smooth below the horny shields, the
-margins of which are marked on the bones by grooves or sulci; the few
-marine turtles of the past that were probably covered with a soft skin
-instead o£ horny shields had the shell smooth and much less completely
-ossified.</p>
-
-<div id="FIG_131" class="figcenter">
-  <img  src="images/fig131.jpg" alt="" width="600" height="154" />
-  <p class="center space-below2">
-   <span class="smcap">Fig. 131.</span>—<i>Aspideretes</i>, a trionychoid
-   turtle<br /> from the Eocene of New Mexico;<br /> front leg. (From Hay.)</p>
-</div>
-
-<p>As to the origin of the soft-shelled turtles there has been not a
-little difference of opinion. The earliest ones known in geological
-history date back only to about the middle of the Cretaceous; perhaps
-they branched off from the horny-shelled turtles somewhat earlier, but
-probably not much. There are some, however, who think that this group
-of turtles was very primitive, perhaps the most primitive, but the
-writer agrees with Dr. Hay in rejecting this view. Unlike those of all
-other turtles, the fourth digit in front and hind feet has one or two
-more phalanges than have other turtles. We have seen that the oldest
-known reptiles had the digital formula 2, 3, 4, 5, 3 or 4. Most other
-<span class="pagenum" id="Page_248">[Pg 248]</span>
-turtles have the same numbers of bones in the digits that mammals have,
-that is, two phalanges in the thumb and big toe and three in each of
-the other digits. The river turtles have a larger number in the fourth
-digit, either four or five. It seems to be a law that evolution is
-irreversible, and if so could the river turtles have been descended
-from forms with a less number of phalanges? But, the skeleton of the
-Trionychoidea resembles the more specialized turtles in so many ways
-that one can hardly believe they were all accidental or parallel.</p>
-
-<p>We may then assume that at about the time that the ordinary marsh
-turtles took to the sea to become marine, others took advantage of
-the fresh-water ponds and rivers, and in doing so, like the marine
-turtles, lost their horny epidermal shields, and became thinner in
-shape, thereby reducing the resistance to the water. Instead, however,
-of reducing the costal plates over the ribs, they retained them intact
-and complete for some reason or other, but lost instead the marginal
-row of bones, unlike the marine turtles which retained them even after
-they had lost nearly all of the costal plates. Possibly also they
-regained additional bones in the fourth digit, a sort of hyperphalangy
-like that of the more strictly aquatic reptiles. Or, possibly, they may
-have descended from some branch of the turtles which had not yet lost
-these bones, retaining them because they were still serviceable for
-swimming. We know nothing yet about the structure of the feet of the
-early turtles, and it is possible that not all had acquired the reduced
-phalangeal formula.</p>
-
-<p>In the development of aquatic habits the river turtles do not show
-the same degree of specialization in the limbs that the strictly
-marine forms do. The humerus (<a href="#FIG_131">Fig. 131</a>) is a slender bone,
-with the tuberosities for the attachment of the muscles situated near the
-proximal end. The radius and ulna are relatively short, and the foot is
-long. The hind legs, as would be supposed, are less highly specialized
-as swimming paddles, and are relatively smaller. Nevertheless the
-Trionychoidea present an interesting type of adaptation to water
-habits, both in body and in limbs.</p>
-<hr class="chap x-ebookmaker-drop" />
-
-<div class="chapter">
-<p><span class="pagenum" id="Page_249">[Pg 249]</span></p>
-<h2 class="nobreak" id="INDEX">INDEX</h2>
-</div>
-
-<ul class="index">
-<li class="isub1">Adaptation to aquatic life, <a href="#Page_59">59</a>.</li>
-<li class="isub1">Aetosauria, <a href="#Page_187">187</a>.</li>
-<li class="isub1">Aigialosaurs, <a href="#Page_146">146</a>.</li>
-<li class="isub1">Alligator, <a href="#FIG_99"><i>197</i></a>.</li>
-<li class="isub1">Amblyrhynchus, <a href="#FIG_66"><i>142</i></a>.</li>
-<li class="isub1">Andrews, C. W., <a href="#Page_75">75</a>.</li>
-<li class="isub1">Angistorhinus, <a href="#Page_190">190</a>.</li>
-<li class="isub1">Anomodontia, <a href="#Page_102">102</a>.</li>
-<li class="isub1">Aquatic reptiles, adaptation of, <a href="#Page_59">59</a>.</li>
-<li class="isub1">Araeoscelis, <a href="#FIG_62"><i>133</i></a>, <a href="#Page_138">138</a>.</li>
-<li class="isub1">Archelon, <a href="#Page_234">234</a>, <a href="#FIG_125"><i>236</i></a>,
-                  <a href="#FIG_127"><i>238</i></a>, <a href="#Page_239">239</a>.</li>
-<li class="isub1">Archosauria, <a href="#Page_33">33</a>.</li>
-<li class="isub1">Aspideretes, <a href="#FIG_130"><i>246</i></a>, <a href="#FIG_131"><i>247</i></a>.</li>
-
-<li class="isub1 ifrst">Baptanodon, <a href="#FIG_53"><i>113</i></a>, <a href="#FIG_54"><i>114</i></a>,
-                     <a href="#FIG_55"><i>117</i></a>.</li>
-<li class="isub1">Baur, George, <a href="#Page_119">119</a>, <a href="#Page_120">120</a>, <a href="#Page_185">185</a>, <a href="#Page_234">234</a>.</li>
-<li class="isub1">Belodon, <a href="#Page_185">185</a>, <a href="#Page_189">189</a>,
-                     <a href="#FIG_96"><i>191</i></a>.</li>
-<li class="isub1">Belodontia, <a href="#Page_185">185</a>.</li>
-<li class="isub1">Bêche, De la, <a href="#Page_73">73</a>.</li>
-<li class="isub1">Bogalobou, <a href="#Page_75">75</a>.</li>
-<li class="isub1">Broom, Robert, <a href="#Page_5">5</a>, <a href="#Page_102">102</a>, <a href="#Page_103">103</a>, <a href="#Page_129">129</a>.</li>
-<li class="isub1">Brown, Barnum, <a href="#Page_93">93</a>, <a href="#Page_179">179</a>.</li>
-<li class="isub1">Buckland, Dean, <a href="#Page_75">75</a>, <a href="#Page_77">77</a>.</li>
-
-<li class="isub1 ifrst">Cacops, <a href="#FIG_18"><i>35</i></a>.</li>
-<li class="isub1">Camper, Adrian, <a href="#Page_149">149</a>, <a href="#Page_166">166</a>.</li>
-<li class="isub1">Camper, Peter, <a href="#Page_149">149</a>, <a href="#Page_166">166</a>.</li>
-<li class="isub1">Captorhinus, <a href="#FIG_26"><i>49</i></a>.</li>
-<li class="isub1">Caretta, <a href="#Page_230">230</a>.</li>
-<li class="isub1">Carpus, <a href="#Page_38">38</a>.</li>
-<li class="isub1">Casea, <a href="#FIG_30"><i>55</i></a>.</li>
-<li class="isub1">Case, E. C., <a href="#Page_234">234</a>.</li>
-<li class="isub1">Champsosaurus, <a href="#FIG_87"><i>179</i></a>, <a href="#FIG_88"><i>180</i></a>,
-       <a href="#FIG_89"><i>181</i></a>, <a href="#FIG_90"><i>182</i></a>.</li>
-<li class="isub1">Chelone, <a href="#FIG_114"><i>220</i></a>, <a href="#Page_229">229</a>.</li>
-<li class="isub1">Chevrons, <a href="#Page_32">32</a>.</li>
-<li class="isub1">Choristodera, <a href="#Page_178">178</a>.</li>
-<li class="isub1">Classification of reptiles, <a href="#Page_13">13</a>.</li>
-<li class="isub1">Clavicles, <a href="#Page_37">37</a>.</li>
-<li class="isub1">Cleithrum, <a href="#Page_36">36</a>.</li>
-<li class="isub1">Clidastes, <a href="#FIG_68"><i>147</i></a>, <a href="#FIG_71"><i>154</i></a>,
-     <a href="#FIG_72"><i>155</i></a>, <a href="#FIG_74"><i>157</i></a>, <a href="#Page_166">166</a>.</li>
-<li class="isub1">Collection of fossils, <a href="#Page_10">10</a>.</li>
-<li class="isub1">Colpochelys, <a href="#FIG_117"><i>222</i></a>.</li>
-<li class="isub1">Conybeare, Rev., <a href="#Page_73">73</a>, <a href="#Page_110">110</a>, <a href="#Page_149">149</a>.</li>
-<li class="isub1">Cope, E. D., <a href="#Page_126">126</a>, <a href="#Page_176">176</a>, <a href="#Page_178">178</a>, <a href="#Page_185">185</a>, <a href="#Page_231">231</a>, <a href="#Page_233">233</a>.</li>
-<li class="isub1">Coracoid, <a href="#Page_36">36</a>.</li>
-<li class="isub1">Cotylosauria, <a href="#Page_16">16</a>.</li>
-<li class="isub1">Cryptodira, <a href="#Page_226">226</a>.</li>
-<li class="isub1">Cretaceous of Kansas, <a href="#FIG_1"><i>8</i></a>.</li>
-<li class="isub1">Crocodiles,</li>
-<li class="isub3">ancient, <a href="#Page_204">204</a>;</li>
-<li class="isub3">marine, <a href="#Page_207">207</a>;</li>
-<li class="isub3">modern, <a href="#Page_195">195</a>.</li>
-<li class="isub1">Crocodilia, <a href="#Page_15">15</a>, <a href="#Page_194">194</a>.</li>
-<li class="isub1">Crocodilus, <a href="#FIG_98"><i>195</i></a>.</li>
-<li class="isub1">Cuvier, Georges, <a href="#Page_73">73</a>, <a href="#Page_97">97</a>, <a href="#Page_107">107</a>, <a href="#Page_110">110</a>, <a href="#Page_149">149</a>.</li>
-
-<li class="isub1 ifrst">Darwin, Charles, <a href="#Page_142">142</a>.</li>
-<li class="isub1">De Fond, St. Faujas, <a href="#Page_148">148</a>.</li>
-<li class="isub1">Dermochelys, <a href="#Page_241">241</a>, <a href="#FIG_128"><i>242</i></a>.</li>
-<li class="isub1">Desmatochelys, <a href="#Page_231">231</a>, <a href="#FIG_122"><i>232</i></a>.</li>
-<li class="isub1">Dimetrodon, <a href="#FIG_19"><i>36</i></a>, <a href="#FIG_28"><i>51</i></a>.</li>
-<li class="isub1">Dinosauria, <a href="#Page_18">18</a>.</li>
-<li class="isub1">Dolichosaurs, <a href="#Page_145">145</a>.</li>
-<li class="isub1">Dolichobrachium, <a href="#Page_54">54</a>.</li>
-<li class="isub1">Dollo, Louis, <a href="#Page_167">167</a>, <a href="#Page_179">179</a>.</li>
-
-<li class="isub1 ifrst">Edaphosaurus, <a href="#FIG_7"><i>23</i></a>.</li>
-<li class="isub1">Elasmosaurus, <a href="#FIG_33"><i>79</i></a>, <a href="#FIG_37"><i>84</i></a>,
-         <a href="#FIG_39"><i>86</i></a>, <a href="#FIG_40"><i>87</i></a>.</li>
-<li class="isub1">Enaliosauria, <a href="#Page_75">75</a>.</li>
-<li class="isub1">Eosauravus, <a href="#Page_52">52</a>.</li>
-<li class="isub1">Episcoposaurus, <a href="#Page_190">190</a>.</li>
-<li class="isub1">Eretmochelys, <a href="#FIG_119"><i>230</i></a>.</li>
-<li class="isub1">Eryops, <a href="#FIG_14"><i>31</i></a>, <a href="#FIG_24"><i>47</i></a>.</li>
-<li class="isub1">Eusuchia, <a href="#Page_195">195</a>.</li>
-<li class="isub1">Exoskeleton, <a href="#Page_43">43</a>.</li>
-<li class="isub1">Extinct reptiles of North America, <a href="#Page_52">52</a>.</li>
-
-<li class="isub1 ifrst">Femur, <a href="#Page_41">41</a>.</li>
-<li class="isub1">Fibula, <a href="#Page_41">41</a>.</li>
-<li class="isub1">Foot, <a href="#Page_42">42</a>.</li>
-<li class="isub1">Fraas, Eberhard, <a href="#Page_74">74</a>, <a href="#Page_75">75</a>, <a href="#Page_99">99</a>, <a href="#Page_111">111</a>, <a href="#Page_115">115</a>, <a href="#Page_185">185</a>, <a href="#Page_213">213</a>.</li>
-
-<li class="isub1 ifrst">Gastroliths, <a href="#FIG_43"><i>92</i></a>, <a href="#Page_200">200</a>.</li>
-<li class="isub1">Gavial, Borneo, <a href="#Page_201">201</a>;</li>
-<li class="isub3">Gangetic, <a href="#FIG_101"><i>198</i></a>, <a href="#FIG_102"><i>199</i></a>,
-                <a href="#FIG_105"><i>202</i></a>.</li>
-<li class="isub1">Gavialidae, <a href="#Page_203">203</a>.</li>
-<li class="isub1">Geological Ages, <a href="#Page_46">46</a>.</li>
-<li class="isub1">Geosaurus, <a href="#FIG_107"><i>208</i></a>, <a href="#FIG_108"><i>210</i></a>,
-            <a href="#FIG_109"><i>211</i></a>, <a href="#FIG_110"><i>212</i></a>,
-            <a href="#Page_214">214</a>.</li>
-<li class="isub1">Gervais, Professor, <a href="#Page_126">126</a>.</li>
-<li class="isub1">Gilmore, Charles, <a href="#Page_113">113</a>, <a href="#Page_167">167</a>.</li>
-<li class="isub1">Globidens, <a href="#FIG_80"><i>167</i></a>.</li>
-<li class="isub1">Goldfuss, August, <a href="#Page_151">151</a>.</li>
-<li class="isub1">Graptemys, <a href="#FIG_111"><i>218</i></a>.</li>
-
-<li class="isub1 ifrst">Hadrosaurus, <a href="#Page_56">56</a>.</li>
-<li class="isub1">Hand, <a href="#Page_38">38</a>.</li>
-<li class="isub1">Hauff, B., <a href="#Page_122">122</a>.</li>
-<li class="isub1">Hay, Oliver P., <a href="#Page_220">220</a>, <a href="#Page_227">227</a>, <a href="#Page_228">228</a>, <a href="#Page_234">234</a>, <a href="#Page_242">242</a>.</li>
-<li class="isub1">Hofmann, Dr., <a href="#Page_148">148</a>.</li>
-<li class="isub1">Holops, <a href="#Page_207">207</a>.</li>
-<li class="isub1">Home, Everard, <a href="#Page_110">110</a>.</li>
-<li class="isub1">Homo diluvii testis, <a href="#Page_108">108</a>.</li>
-<li class="isub1">Huene, Friedrich von, <a href="#Page_131">131</a>, <a href="#Page_185">185</a>.</li>
-<li class="isub1">Humerus, <a href="#Page_38">38</a>.</li>
-<li class="isub1">Huxley, Thomas, <a href="#Page_185">185</a>, <a href="#Page_207">207</a>.</li>
-<li class="isub1">Hydrus, <a href="#FIG_81"><i>169</i></a>.</li>
-<li class="isub1">Hyperphalangy, <a href="#Page_118">118</a>.</li>
-<li class="isub1">Hypocentrum, <a href="#Page_36">36</a>.
-       <span class="pagenum" id="Page_250">[Pg 250]</span></li>
-
-<li class="isub1 ifrst">Ichthyosauria, <a href="#Page_17">17</a>, <a href="#Page_107">107</a>.</li>
-<li class="isub1">Ichthyosaurus, <a href="#FIG_51"><i>108</i></a>,
-       <a href="#FIG_52"><i>112</i></a>, <a href="#Page_119">119</a>, <a href="#Page_121">121</a>,
-       <a href="#FIG_59"><i>122</i></a>.</li>
-<li class="isub1">Iguana, <a href="#FIG_65"><i>140</i></a>.</li>
-<li class="isub1">Ilium, <a href="#Page_39">39</a>.</li>
-<li class="isub1">Interclavicle, <a href="#Page_37">37</a>.</li>
-<li class="isub1">Intercentrum, <a href="#Page_30">30</a>.</li>
-<li class="isub1">Ischium, <a href="#Page_39">39</a>.</li>
-
-<li class="isub1 ifrst">Jaeger, George, <a href="#Page_184">184</a>.</li>
-<li class="isub1">Jaekel, <a href="#Page_185">185</a>.</li>
-
-<li class="isub1 ifrst">Karoo beds, <a href="#Page_102">102</a>.</li>
-<li class="isub1">Koenig, <a href="#Page_110">110</a>.</li>
-
-<li class="isub1 ifrst">Labidosaurus, <a href="#FIG_6"><i>22</i></a>, <a href="#FIG_10"><i>26</i></a>,
-       <a href="#FIG_27"><i>50</i></a>.</li>
-<li class="isub1">Laecertilia, <a href="#Page_140">140</a>.</li>
-<li class="isub1">Lariosaurus, <a href="#FIG_48"><i>99</i></a>, <a href="#FIG_49"><i>100</i></a>.</li>
-<li class="isub1">Leather-back turtles, <a href="#Page_241">241</a>.</li>
-<li class="isub1">Leidy, Joseph, <a href="#Page_151">151</a>.</li>
-<li class="isub1">Limnoscelis, <a href="#FIG_3"><i>20</i></a>, <a href="#FIG_24"><i>47</i></a>.</li>
-<li class="isub1">Lizards, <a href="#Page_140">140</a>;</li>
-<li class="isub3">flat-headed, <a href="#Page_144">144</a>;</li>
-<li class="isub3">Galapagos, <a href="#Page_142">142</a>.</li>
-<li class="isub1">Lull, Richard, <a href="#Page_54">54</a>.</li>
-<li class="isub1">Lystrosaurus, <a href="#Page_103">103</a>, <a href="#FIG_50"><i>104</i></a>.</li>
-<li class="isub1">Lortet, M., <a href="#Page_135">135</a>.</li>
-
-<li class="isub1 ifrst">McGregor, J. H., <a href="#Page_126">126</a>, <a href="#Page_129">129</a>, <a href="#Page_131">131</a>, <a href="#Page_185">185</a>, <a href="#Page_186">186</a>, <a href="#Page_189">189</a>.</li>
-<li class="isub1">Mandible, <a href="#Page_25">25</a>.</li>
-<li class="isub1">Mantell, Dr., <a href="#Page_75">75</a>.</li>
-<li class="isub1">Marsh, O. C., <a href="#Page_54">54</a>, <a href="#Page_185">185</a>.</li>
-<li class="isub1">Merriam, J. C., <a href="#Page_112">112</a>, <a href="#Page_120">120</a>, <a href="#Page_171">171</a>, <a href="#Page_174">174</a>.</li>
-<li class="isub1">Merriamia, <a href="#FIG_57"><i>118</i></a>.</li>
-<li class="isub1">Mesosaurus, <a href="#Page_126">126</a>, <a href="#FIG_60"><i>127</i></a>,
-       <a href="#FIG_61"><i>128</i></a>.</li>
-<li class="isub1">Mesosuchia, <a href="#Page_185">185</a>, <a href="#Page_204">204</a>.</li>
-<li class="isub1">Meyer, Hermann von, <a href="#Page_75">75</a>, <a href="#Page_87">87</a>, <a href="#Page_132">132</a>, <a href="#Page_134">134</a>, <a href="#Page_184">184</a>.</li>
-<li class="isub1">Mixosaurus, <a href="#Page_119">119</a>.</li>
-<li class="isub1">Monitor lizards, <a href="#Page_144">144</a>.</li>
-<li class="isub1">Mosasauria, <a href="#Page_148">148</a>, <a href="#Page_166">166</a>.</li>
-<li class="isub1">Mosasaurus, <a href="#Page_148">148</a>;</li>
-<li class="isub3">hofmanni, <a href="#Page_149">149</a>;</li>
-<li class="isub3">maximiliani, <a href="#Page_151">151</a>.</li>
-<li class="isub1">Münster, Georg von, <a href="#Page_97">97</a>.</li>
-<li class="isub1">Mudge, B. F., <a href="#Page_93">93</a>.</li>
-<li class="isub1">Mystriosuchus, <a href="#Page_185">185</a>, <a href="#FIG_92"><i>188</i></a>,
-    <a href="#FIG_93"><i>189</i></a>, <a href="#FIG_97"><i>191</i></a>.</li>
-
-<li class="isub1 ifrst">Nares, <a href="#Page_23">23</a>.</li>
-<li class="isub1">Nectosaurus, <a href="#Page_175">175</a>.</li>
-<li class="isub1">Nothosauria, <a href="#Page_95">95</a>.</li>
-<li class="isub1">Nothosaurus, <a href="#FIG_44"><i>96</i></a>, <a href="#FIG_45"><i>97</i></a>,
-         <a href="#FIG_46"><i>98</i></a>.</li>
-
-<li class="isub1 ifrst">O’Fallen, Major, <a href="#Page_151">151</a>.</li>
-<li class="isub1">Ophiacodon, <a href="#FIG_13"><i>30</i></a>, <a href="#FIG_15"><i>32</i></a>,
-       <a href="#FIG_20"><i>37</i></a>, <a href="#FIG_21"><i>38</i></a>,
-       <a href="#FIG_22"><i>40</i></a>, <a href="#FIG_23"><i>42</i></a>.</li>
-<li class="isub1">Ophidia, <a href="#Page_168">168</a>.</li>
-<li class="isub1">Ophthalmosaurus, <a href="#FIG_56"><i>118</i></a>, <a href="#Page_125">125.</a></li>
-<li class="isub1">Orders of reptiles, <a href="#Page_16">16</a>.</li>
-<li class="isub1">Osborn, H. F., <a href="#Page_126">126</a>.</li>
-<li class="isub1">Ostodolepis, <a href="#FIG_17"><i>33</i></a>.</li>
-<li class="isub1">Owen, Richard, <a href="#Page_75">75</a>, <a href="#Page_103">103</a>, <a href="#Page_110">110</a>, <a href="#Page_111">111</a>, <a href="#Page_185">185</a>.</li>
-
-<li class="isub1 ifrst">Paleorhinus, <a href="#Page_190">190</a>.</li>
-<li class="isub1">Paliguana, <a href="#Page_5">5</a>.</li>
-<li class="isub1">Parasuchia, <a href="#Page_18">18</a>, <a href="#Page_184">184</a>.</li>
-<li class="isub1">Parietal foramen, <a href="#Page_23">23</a>.</li>
-<li class="isub1">Pectoral girdle, <a href="#Page_34">34</a>.</li>
-<li class="isub1">Pelvic girdle, <a href="#Page_39">39</a>.</li>
-<li class="isub1">Pelvis, <a href="#Page_39">39</a>.</li>
-<li class="isub1">Pelycosauria, <a href="#Page_186">186</a>.</li>
-<li class="isub1">Pelycosimia, <a href="#Page_187">187</a>.</li>
-<li class="isub1">Phytosauria, <a href="#Page_18">18</a>, <a href="#Page_187">187</a>.</li>
-<li class="isub1">Phytosaurus, <a href="#Page_186">186</a>, <a href="#Page_187">187</a>.</li>
-<li class="isub1">Pineal foramen, <a href="#Page_23">23</a>.</li>
-<li class="isub1">Platecarpus, <a href="#FIG_69"><i>151</i></a>, <a href="#FIG_72"><i>155</i></a>, <a href="#FIG_73"><i>156</i></a>,
-      <a href="#FIG_76"><i>158</i></a>, <a href="#FIG_77"><i>159</i></a>, <a href="#Page_166">166</a>.</li>
-<li class="isub1">Platynota, <a href="#Page_148">148</a>.</li>
-<li class="isub1">Plesiosauria, <a href="#Page_77">77</a>.</li>
-<li class="isub1">Plesiosaurus, <a href="#FIG_31"><i>74</i></a>.</li>
-<li class="isub1">Pleurodira, <a href="#Page_224">224</a>.</li>
-<li class="isub1">Pleurosaurus, <a href="#FIG_63"><i>134</i></a>, <a href="#FIG_64"><i>136</i></a>, <a href="#Page_177">177</a>.</li>
-<li class="isub1">Polycotylus, <a href="#Page_80">80</a>.</li>
-<li class="isub1">Proatlas, <a href="#Page_32">32</a>.</li>
-<li class="isub1">Proganochelys, <a href="#Page_217">217</a>.</li>
-<li class="isub1">Proganosauria, <a href="#Page_17">17</a>.</li>
-<li class="isub1">Proteosaurus, <a href="#Page_110">110</a>.</li>
-<li class="isub1">Protorosauria, <a href="#Page_17">17</a>, <a href="#Page_132">132</a>.</li>
-<li class="isub1">Protorosaurus, <a href="#Page_132">132</a>.</li>
-<li class="isub1">Protostega, <a href="#Page_233">233</a>, <a href="#Page_234">234</a>.</li>
-<li class="isub1">Protostegidae, <a href="#Page_231">231</a>.</li>
-<li class="isub1">Pseudosuchia, <a href="#Page_185">185</a>.</li>
-<li class="isub1">Pterosauria, <a href="#Page_18">18</a>.</li>
-<li class="isub1">Pubis, <a href="#Page_39">39</a>.</li>
-<li class="isub1">Pythonomorpha (Mosasauria), <a href="#Page_166">166</a>.</li>
-
-<li class="isub1 ifrst">Range of Reptilia, <a href="#FIG_23A"><i>45</i></a>.</li>
-<li class="isub1">Rhachitomous vertebrae, <a href="#Page_17">17</a>.</li>
-<li class="isub1">Rhynchocephalia, <a href="#Page_17">17</a>, <a href="#Page_176">176</a>.</li>
-<li class="isub1">Rhytidodon, <a href="#Page_190">190</a>.</li>
-<li class="isub1">Ribs, <a href="#Page_33">33</a>.</li>
-<li class="isub1">River turtles, <a href="#Page_244">244</a>.</li>
-<li class="isub1">Rutiodon, <a href="#FIG_95"><i>190</i></a>.</li>
-
-<li class="isub1 ifrst">Sacrum, <a href="#Page_32">32</a>.</li>
-<li class="isub1">Sapheosaurus, <a href="#FIG_86"><i>178</i></a>.</li>
-<li class="isub1">Sauranodon (Baptanodon), <a href="#Page_125">125</a>.</li>
-<li class="isub1">Sauropterygia, <a href="#Page_17">17</a>, <a href="#Page_73">73</a>.</li>
-<li class="isub1">Scheuchzer, <a href="#Page_107">107</a>.</li>
-<li class="isub1">Seeley, H. G., <a href="#Page_75">75</a>, <a href="#Page_126">126</a>, <a href="#Page_132">132</a>.</li>
-<li class="isub1">Seymouria, <a href="#FIG_4"><i>21</i></a>, <a href="#FIG_25"><i>48</i></a>.</li>
-<li class="isub1">Shoulder-girdle, <a href="#Page_34">34</a>.</li>
-<li class="isub1">Simoedosaurus, <a href="#Page_179">179</a>.</li>
-<li class="isub1">Skeleton of reptiles, <a href="#Page_19">19</a>.</li>
-<li class="isub1">Skull of reptiles, <a href="#Page_21">21</a>.</li>
-<li class="isub1">Snakes, <a href="#Page_168">168</a>.</li>
-<li class="isub1">Spener, <a href="#Page_132">132</a>.</li>
-<li class="isub1">Sphenodon, <a href="#FIG_8"><i>24</i></a>, <a href="#Page_132">132</a>,
-                   <a href="#FIG_85"><i>176</i></a>.</li>
-<li class="isub1">Squamata, <a href="#Page_17">17</a>, <a href="#Page_138">138</a>.</li>
-<li class="isub1">Stegocephalia, <a href="#Page_48">48</a>.</li>
-<li class="isub1">Stereosternum, <a href="#Page_126">126</a>.</li>
-<li class="isub1">Sternum, <a href="#Page_37">37</a>.</li>
-<li class="isub1">Stomach-stones, <a href="#Page_200">200</a>.
-       <span class="pagenum" id="Page_251">[Pg 251]</span></li>
-
-<li class="isub1 ifrst">Tarsus, <a href="#Page_42">42</a>.</li>
-<li class="isub1">Teeth, <a href="#Page_21">21</a>, <a href="#Page_25">25</a>.</li>
-<li class="isub1">Teleosaurus, <a href="#FIG_106"><i>205</i></a>.</li>
-<li class="isub1">Temporal openings, <a href="#Page_23">23</a>.</li>
-<li class="isub1">Testudo, <a href="#FIG_118"><i>228</i></a>.</li>
-<li class="isub1">Thalattosauria, <a href="#Page_17">17</a>, <a href="#Page_171">171</a>.</li>
-<li class="isub1">Thalattosaurus, <a href="#FIG_82"><i>172</i></a>, <a href="#FIG_83"><i>173</i></a>,
-                 <a href="#FIG_84"><i>174</i></a>.</li>
-<li class="isub1">Thalattosuchia, <a href="#Page_207">207</a>.</li>
-<li class="isub1">Therapsida, <a href="#Page_16">16</a>.</li>
-<li class="isub1">Theromorpha, <a href="#Page_16">16</a>.</li>
-<li class="isub1">Thaumatosaurus, <a href="#FIG_31"><i>74</i></a>.</li>
-<li class="isub1">Thoracosaurus, <a href="#Page_207">207</a>.</li>
-<li class="isub1">Tibia, <a href="#Page_41">41</a>.</li>
-<li class="isub1">Tomistomidae, <a href="#Page_201">201</a>.</li>
-<li class="isub1">Tortoises, <a href="#Page_216">216</a>;</li>
-<li class="isub3">fresh-water, <a href="#Page_226">226</a>;</li>
-<li class="isub3">land, <a href="#Page_227">227</a>;</li>
-<li class="isub3">marsh, <a href="#Page_226">226</a>.</li>
-<li class="isub1">Toxochelys, <a href="#FIG_113"><i>219</i></a>, <a href="#FIG_120"><i>231</i></a>,
-              <a href="#FIG_121"><i>232</i></a>.</li>
-<li class="isub1">Trachemys, <a href="#FIG_115"><i>221</i></a>.</li>
-<li class="isub1">Trimerorhachis, <a href="#FIG_9"><i>25</i></a>.</li>
-<li class="isub1">Trinacromerum, <a href="#FIG_32"><i>77</i></a>, <a href="#FIG_35"><i>81</i></a>,
-             <a href="#FIG_36"><i>83</i></a>, <a href="#FIG_38"><i>85</i></a>,
-             <a href="#FIG_41"><i>88</i></a>, <a href="#FIG_42"><i>89</i></a>.</li>
-<li class="isub1">Trionychoidea, <a href="#Page_244">244</a>.</li>
-<li class="isub1">Trionyx, <a href="#FIG_129"><i>245</i></a>.</li>
-<li class="isub1">Tuatera, <a href="#Page_176">176</a>. <i>See</i> Sphenodon.</li>
-<li class="isub1">Turtles, <a href="#Page_216">216</a>;</li>
-<li class="isub3">river, <a href="#Page_244">244</a>;</li>
-<li class="isub3">sea, <a href="#Page_229">229</a>;</li>
-<li class="isub3">ancient sea, <a href="#Page_231">231</a>;</li>
-<li class="isub3">side-necked, <a href="#Page_224">224</a>.</li>
-<li class="isub1">Tylosaurus, <a href="#FIG_70"><i>153</i></a>, <a href="#FIG_72"><i>155</i></a>,
-             <a href="#FIG_75"><i>157</i></a>, <a href="#FIG_78"><i>160</i></a>,
-             <a href="#FIG_79"><i>165</i></a>, <a href="#Page_166">166</a>.</li>
-
-<li class="isub1 ifrst">Varanus, <a href="#FIG_67"><i>144</i></a>.</li>
-<li class="isub1">Varanops, <a href="#FIG_29"><i>53</i></a>.</li>
-<li class="isub1">Ventral ribs, <a href="#Page_34">34</a>.</li>
-<li class="isub1">Vertebrae, <a href="#Page_28">28</a>;</li>
-<li class="isub3">notochordal, <a href="#Page_29">29</a>;</li>
-<li class="isub3">rhachitomous, <a href="#Page_31">31</a>.</li>
-<li class="isub1">Versluys, <a href="#Page_244">244</a>.</li>
-
-<li class="isub1 ifrst">Watson, D. M. S., <a href="#Page_103">103</a>.</li>
-<li class="isub1">Wieland, G. R., <a href="#Page_234">234</a>, <a href="#Page_236">236</a>, <a href="#Page_239">239</a>, <a href="#Page_243">243</a>.</li>
-<li class="isub1">Woodward, A. S., <a href="#Page_126">126</a>.</li>
-
-<li class="isub1 ifrst">Zittel, Carl von, <a href="#Page_185">185</a>.</li>
-</ul>
-
-<div class="footnotes">
-<p class="f150 u"><b>Footnotes:</b></p>
-
-<div class="footnote"><p class="no-indent">
-<a id="Footnote_1" href="#FNanchor_1" class="label">[1]</a>
-Paired maxillae, premaxillae, nasals, prefrontals, lacrimals,
-frontals, parietals, dermosupraoccipitals, tabularia, supratemporals,
-intertemporals, squamosals, jugals, quadratojugals, postorbitals,
-postfrontals, quadrates, exoccipitals, paroccipitals, vomers,
-palatines, pterygoids, sphenomaxillae, stapes, transverse, alisphenoids
-or orbitosphenoids, epipterygoids, articulars, prearticulars, angulars,
-surangulars, coronoids, splenials, dentaries, one supraoccipital, one
-basioccipital, one basisphenoid, one ethmoid.</p></div>
-
-<div class="footnote"><p class="no-indent">
-<a id="Footnote_2" href="#FNanchor_2" class="label">[2]</a></p>
-
-<div class="poetry-container">
-  <div class="poetry"><div class="stanza">
-    <div class="verse indent0">Are God and Nature then at strife,</div>
-    <div class="verse indent0">That Nature lends such evil dreams?</div>
-    <div class="verse indent0">So careful of the type she seems</div>
-    <div class="verse indent0">So careless of the single life.—<i>In Memoriam</i>, lv.</div>
-  </div></div>
-</div>
-</div>
-
-<div class="footnote"><p class="no-indent">
-<a id="Footnote_3" href="#FNanchor_3" class="label">[3]</a>
-An additional phalange has also been observed in the fifth
-toe of a South American species.</p></div>
-
-<div class="footnote"><p class="no-indent">
-<a id="Footnote_4" href="#FNanchor_4" class="label">[4]</a>
-“The author showed drawings and some specimens of two hitherto unknown
-reptiles from the white, coarse-grained sandstone, of which one in the
-form of the skull resembles the gavial, but is distinguished by the
-cylindrical form of the lateral teeth of the jaws; he therefore calls
-it provisionally <i>cylindricodon</i>, and a second species or genus,
-of which, however, so far only fragments of the jaws have been found,
-because of the four-cornered form of the teeth, <i>cubicodon</i>, while
-at the same time for the genus or family, to which the remains of these
-animals have belonged, he proposes the name <i>Phytosaurus</i>, since
-the teeth seem to be more adapted to a vegetable diet, even though they
-have not been worn away, as in <i>Iguanodon</i>.”—<i>Isis</i> (1828),
-p. 441 (translation).</p></div>
-</div>
-
-<div class="transnote bbox space-above2">
-<p class="f120 space-above1">Transcriber’s Notes:</p>
-<hr class="r5" />
-<p class="indent">The cover image was created by the transcriber, and is in the public domain.</p>
-<p class="indent">The illustrations have been moved so that they do not break up
-                  paragraphs and so that they are close to the text they illustrate.</p>
-<p class="indent">Typographical and punctuation errors have been silently corrected.</p>
-</div>
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