Samuel Wendell Williston.

Water reptiles of the past and present online

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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 AGE OF REPTILES 53

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




Fig. 20. — Restoration of Varanops, a theromorph reptile from the Permian of
Texas; about four feet long.

Upper Triassic age of Nevada and northern California have yielded
numerous remains of primitive ichthyosaurs, the only known re-
mains 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.

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.



54 WATER REPTILES OF THE PAST AND PRESENT

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 anomo-
donts, 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 dis-
covered 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 Con-
necticut 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 Wyo-
ming, 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



THE AGE OF REPTILES



55



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




Fig. 30. — Restoration of Casea, a theromorph reptile from the Permian of Texas,
about four feet long.

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.

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



56 WATER REPTILES OF THE PAST AND PRESENT

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 Nio-
brara 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 dino-
saurs, 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



THE AGE OF REPTILES 57

western Texas and New Mexico, have come many marvelous speci-
mens 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 speciali-
zations 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 ryhnchocephalians 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 Eo-
cene, 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



58 WATER REPTILES OF THE PAST AND PRESENT

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 Wyo-
ming are about all that we know of the Squamata in the Tertiary.
Doubtless snakes and lizards were - just as abandunt 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 con-
tinuously 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 pre-
vent 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 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, 1 the first law of life

1 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 Mcmoriam, lv.

59



60 WATER REPTILES OF THE PAST AND PRESENT

is not the preservation of self, but the prosperity of the race. What-
ever 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.

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 Jand.
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 amphib-
ians, 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 oppor-
tunities, 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 surround-
ings, they must, so far as possible, acquire like forms and like



ADAPTATION OF LAND REPTILES TO LIFE IN WATER 61

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 acquire-
ment of great size, for that has been the invariable end of water
air-breathers of long duration — specializations which finally pre-
vented 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



62 WATER REPTILES OF THE PAST AND PRESENT

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 sys-
tem, 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 "whale-
bone." 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, exclu-
sively 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.



ADAPTATION OF LAND REPTILES TO LIFE IN WATER 63

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 con-
siderable 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 func-
tionally 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 pre-
cisely 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



64 WATER REPTILES OF THE PAST AND PRESENT

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 Choristo-
dera, described farther on, are exceptions, since their nostrils are
at the extremity of the snout. Both of these types, however, not-
withstanding 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 nos-
trils 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 verte-
brae that could be called cervical. It happens that most of the
earliest reptiles, as we know them, were more or less amphibious in


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Online LibrarySamuel Wendell WillistonWater reptiles of the past and present → online text (page 5 of 19)