Water Reptiles of the Past and Present

by Samuel Wendell Williston

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.

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.

Fig. 45.—Head and neck of Nothosaurus;
photograph of specimen in the Senckenberg Museum,
from Dr. Dreverman.