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. 32.—Skeleton of Trinacromerum osbomi, a Cretaceous plesiosaur, as mountedin the University of Kansas Museum. chenius Lucasi, the head was two and one-half feet in length, theneck less than two feet, and the body about five; the length of thetail is unknown. Not only was the number of vertebrae so extraordinarilyincreased in many plesiosaurs, but in the longest necks the verte-brae themselves, as in birds, were more or less elongated, especiallythe posterior ones, which may be six or seven times the length ofthe anterior ones. Not only was the neck of such great lengthin many plesiosaurs, but it also tapered very much toward thehead. The vertebrae are always biconcave, but the cavities are shallow,saucer-like, sometimes almost flat at each end, and very differentfrom the conical fish-like cavities of ichthyosaurian vertebrae. SA UROPTERYGIA

Text Appearing After Image: 8o WATER REPTILES OF THE PAST AND PRESENT Often the vertebrae are short throughout the vertebral column;sometimes the posterior cervicals and the dorsals are elongatedand very robust. The trunk or body proper was never muchelongated in the plesiosaurs, having only from twenty-five to thirtyvertebrae. The tail was always shorter than the trunk, and ittapered rapidly to the extremity; in some specimens it has beenobserved to turn up slightly near the extremity, as though for thesupport of a small terminal fin. The ribs in the cervical region are short, but so locked togetherposteriorly as not to permit much lateral motion. They are

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