File:Image from page 100 of "Water reptiles of the past and present" (1914) (14586297750).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: -ing for the pineal body, the so-called eye in the roof of the braincavity, though its possession does not necessarily imply the pos-session of a functional organ. The Plesiosauria included some of the largest aquatic reptilesthat have ever existed, equaled, perhaps, though not exceeded,by some of the extinct crocodiles. The largest known are probably SAUROPTERYGIA 89 those of the Kansas chalk, or the Jurassic of Wyoming, whichprobably reached a length of nearly or quite fifty feet, of which theneck formed about one-half. Some of them had paddles more thansix feet in length. The head of the largest was about five feet inlength, or about the size of that of the largest known ichthyosaursand mosasaurs. The smallest known adult plesiosaurs were nearlyten feet in length. The teeth of the largest and most carnivorousplesiosaurs sometimes measure four inches in length. As is the case with both the ichthyosaurs and mosasaurs,skeletons of plesiosaurs have been discovered with nearly all their

Text Appearing After Image: Fig. 42.—Restoration of Trinacromerum, a Cretaceous plesiosaur; length aboutten feet. bones in their relative positions, and with impressions of skin andoutlines of body made before decomposition. Though our knowl-edge of the external appearance of the plesiosaurs when alive isperhaps not as full as we could wish, it is sufficient to give us a fairlygood conception of what the animals really were. The skin wassmooth and bare, without scales or plates of any kind, and Dameshas described a terminal or nearly terminal fleshy dilatation of thetail, forming a sort of caudal fin, which may have aided as a steeringapparatus. Mounted skeletons are preserved in a few museums,notably the British Museum, the American Museum of New YorkCity, and the museum of the University of Kansas. Many nearly QO WATER REPTILES OF THE PAST AND PRESENT complete skeletons, however, preserved as they were found in thematrix, are shown in various museums. With these principal facts regarding the structure, size,

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