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.