Water Reptiles of the Past and Present

by Samuel Wendell Williston

The distal part of the tail was not bent downward so sharply, that is, the terminal fin was smaller, or the tail may have been simply flattened near its end and not really fin-like. The scapula was longer and less fan-like in shape.

And all these are remarkable evidences of an increased adaptation to water life in the more recent ichthyosaurs over the older ones. Were someone now so fortunate as to find ichthyosaurs in late Permian rocks, we should doubtless have the nearly complete chain between the most highly specialized type of water reptiles and their terrestrial ancestors.

Fig. 58.—Caudal fin of Ichthyosaurus, after Baur (left figure); caudal fin of Mixosaurus, after Wiman (right figure).

From the structure of the skeleton alone the early observers were justified in inferring much concerning the shape and habits of the living ichthyosaurs. Later discoveries have added so many definite facts that, at the present time, we know more about their habits than we do of any other extinct reptiles. In various places in England and Germany, especially in Würtemberg, the remains of ichthyosaurs are found in extraordinary abundance and perfection, not only whole skeletons lying in the positions which they had assumed after the decomposition of their bodies, but also often the actual remains, carbonized, of the skin, muscles, and ligaments, as well as delicate impressions of external parts. Many of these skeletons are obtained from the numerous stone quarries, where they are a sort of “by-product,” the sums received for them adding not a little to the income of the quarrymen. So many are obtained in this and other ways that specimens of ichthyosaurs are perhaps more frequently seen in the museums of the world than those of any other extinct backboned animal. Fairly complete skeletons may now be purchased of dealers in such things for from fifty to seventy-five dollars. As may be supposed, the best and most complete collections of these fossil remains are those of the British Museum in London and the museum in Stuttgart. From a study of those of the last-mentioned museum Professor Fraas has learned many interesting facts and reached many interesting conclusions regarding the life-habits of the ichthyosaurs. In the accompanying figure ([Fig. 59]) is shown a photographic reproduction of a very complete specimen, in which not only is the outline of the whole body shown, but also much of the carbonized remains of the muscles and skin has been detected.

Fig. 59.—Ichthyosaurus quadricissus. (From a photograph from B. Hauff, Paleontologisches Atelier, Holzmaden.)

The attachment of the paddles to the body was broad antero-posteriorly, proving conclusively that they could not have been much used in propulsion, either in the water or upon land, since such use would require a fore-and-aft movement, and a consequent twisting or rotation of the whole arm or leg, which, because of the broad attachment, must have been very difficult, if not impossible.

Microscopic examination of the remains of skin preserved disclosed an abundance of dark pigment, indicating, Professor Fraas believes, that the skin was dark colored above. Doubtless, also, the under side, as in nearly all swimming animals of the present time, was of a lighter color, because such coloration rendered the animals much less conspicuous in the water when seen either from above or below. That the skin was bare is proved by many impressions or molds of it that have been discovered in the rocks, in which many fine creases are seen, but nothing suggesting scales or bony plates, save on the front edge of the paddles, where impressions of overlapping scales have been observed. This is an interesting fact, bearing witness that their land ancestors had been covered everywhere with scales, much like those of existing lizards and other reptiles. Scales or bony plates were not only useless to the ichthyosaurs in the water, since they could afford no protection, but would have been detrimental in increasing the resistance in swimming.

That the ichthyosaurs were predaceous animals is of course evident from their teeth, adapted for the seizure and retention of slippery prey, but not for tearing or comminuting. The fossilized remains of food found between the ribs of some specimens, in the place where the stomach was, together with fossil excrement, called coprolites, usually attributed to these animals, prove that they fed largely upon fishes, squids, belemnites, and probably other invertebrates. One ichthyosaur specimen preserved in the Stuttgart Museum has preserved in its stomach contents a mass composed of the remains of more than two hundred belemnites.