Water Reptiles of the Past and Present

by Samuel Wendell Williston

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.