Image from page 239 of "Water reptiles of the past and present" (1914) (14586618467)

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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of the Cenozoic, that is, with the great development of themammals, and reached the maximum of their development in theMiocene; and they have been on the decline ever since. In theNorthern Hemisphere, at least, the slowly cooling climate through-out the Eocene, and a decided decrease in moisture, brought about 228 WATER REPTILES OF THE PAST AND PRESENT the prairies and prairie plants before its close. Just as the horses,rhinoceroses, camels, and other herbivorous mammals took to theseopen places for the better and more abundant food found therein,so also the lowland tortoises found better food and fewer enemiesthere, for they are all strictly herbivorous in habit. The mammalsbecame more conspicuous to their enemies when they went intothe open, and it was only by the development of speed, more sobercoloration, and perhaps greater cunning that they found safetyfrom them. The tortoises were handicapped by low intelligence,and they could not develop speed, for they were not constructed to
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Fig. 118.-schild.) -Testudo sumeirei, a giant upland tortoise. (From Hay, after Roth- that end. But they did find protection in their bony shell, whichbecame thicker, higher, and more convex, and with smaller open-ings. To quote Dr. Hay: We may suppose that it would bemuch more difficult for a carnivorous animal to effect an entranceinto such a shell than into one depressed, and whose borders maybe spanned by the jaws of their enemies. Perhaps also the highlyarched form of the shell gave greater capacity for the lungs, andthe tortoises in general, it is said, do have better lung capacitythan the more aquatic or lowland types of turtles. Possibly, also,the heavier shell lessened the evaporation of the body fluids, andmade the tortoises less dependent upon the vicinity of water. CHELONIA 229 Certain it is that the common box tortoise, of like form and habits,occurs not rarely on the arid plains, far from water. The neck and legs became fully retractile within the shell;the digits were s