File:Image from page 66 of "Water reptiles of the past and present" (1914) (14792860633).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: ame, and a few bones of an ancient crocodileare known. Immediately overlying the Baptanodon beds, the Morrison beds,of from two hundred to four hundred feet in thickness, probablyof Uppermost Jurassic and Lowermost Cretaceous age, have yieldedan exceedingly rich vertebrate fauna, consisting chiefly of dinosaurs.Discovered first in the vicinity of Morrison, Colorado, in 1877,hundreds of tons of bones have been collected from these beds for THE AGE OF REPTILES 55 various museums. The dinosaurs include many genera of all threesuborders, varying in size from that of a cat to some of the largestknown land animals. Of other reptiles a very few jaws of a truerhynchocephalian, a fragment of a wing bone of a pterodactyl,numerous turtles, and crocodiles, only, are known. The beds arepredominantly black-clay shales, intercalated with sandstones, andall are of fresh-water origin. From beds definitely known as Lower Cretaceous (Trinity)in Oklahoma, a few bones of a sauropod dinosaur are known, and

Text Appearing After Image: Fig. 30.—Restoration of Casea, a theromorph reptile from the Permian of Texas,about four feet long. from nearly corresponding rocks in southern Kansas, plesiosaurs,crocodiles, turtles, and carnivorous dinosaurs are known fromsparse remains. Doubtless the Potomac beds of Virginia, whichhave yielded bones of various dinosaurs, are also of LowerCretaceous age. With the exception of a single vertebra of doubtful affinitiesand the cast of a turtle-shell no vertebrate fossils have everbeen discovered in the extensive sandstones of Dakota age, thelowermost of the Upper Cretaceous. From the next horizon abovethe Dakota, the Benton Cretaceous, chiefly marine limestones, at 56 WATER REPTILES OF THE PAST AND PRESENT least three genera of plesiosaurs are known from Kansas, Texas,and Arkansas, with two or three more from the limestone shalesof Wyoming. A few specimens of armored dinosaurs, two generaof ancient crocodiles, nearly the last of their kind, some marineturtles, and a few vertebrae of

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