Water Reptiles of the Past and Present

by Samuel Wendell Williston

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.

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.