File:Image from page 170 of "Water reptiles of the past and present" (1914) (14586412268).jpg

Identifier: waterreptilesofp1914will Title: Water reptiles of the past and present Year: 1914 (1910s) Authors: Williston, Samuel Wendell, 1851-1918 Subjects: Aquatic reptiles Publisher: Chicago, Ill., The University of Chicago Press Contributing Library: Boston Public Library Digitizing Sponsor: Boston Public Library

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Text Appearing Before Image: Fig. 76.—Platecarpus; right front paddle:h, humerus; r, radius; u, ulna. SQUAMATA 159 the only ones among water reptiles that would be dangerous andoffensive to man, were they all living today. For a long time it was thought that the mosasaurs had nobreast bone, and that, in consequence, the front part of the thoraxwas expansible. Under this assumption the mosasaurs would havebeen much more snake-like in habit than they really were. Theloose construction of the jaws doubtless permitted the swallowingof prey of considerable size, and the inference was that they habitu-ally preyed upon animals of large size. A snake will often swallowa frog of larger diameter than its own body, the flexible jaws andloosely connected ribs permitting it to pass to the abdominalcavity. But the unyielding ring formed by the anterior ribs con-nected with the breast bone in the mosasaurs, as in other lizards,conclusively proves that large animals could not have been swal-

Text Appearing After Image: Fig. 77.—Platecarpus; pelvis, from below: p, pubis; il, ilium; is, ischium lowed whole by the mosasaurs. In several instances the fossilizedstomach contents, composed chiefly or wholly of fishes, have beenfound between the ribs of mosasaurs, and in none were the fishesmore than two or three feet in length, though the reptiles werefrom sixteen to twenty feet long. Possibly the largest mosasaursthose thirty or thirty-five feet in length, might have captured andswallowed fishes six or seven feet long, but in all probability theirusual prey was of smaller relative size. The very loose construction of the pelvic bones, those to whichthe hind legs are articulated, is an evidence of more completeadaptation to water life than was or is the case with any otherwater air-breathers except the ichthyosaurs and cetaceans. Thesacrum had entirely lost its function as a support to the pelvisand had disappeared, that is, the vertebrae composing it had become 160 WATER REPTILES OF THE PAST AND PRESENT

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