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 these 

 open places for the better and more abundant food found therein, 

 so also the lowland tortoises found better food and fewer enemies 

 there, for they are all strictly herbivorous in habit. The mammals 

 became more conspicuous to their enemies when they went into 

 the open, and it was only by the development of speed, more sober 

 coloration, and perhaps greater cunning that they found safety 

 from them. The tortoises were handicapped by low intelligence, 

 and they could not develop speed, for they were not constructed to 



Fig. ii8. — Tesludo sumeirei, a giant upland tortoise. (From Hay, after Roth- 

 schild.) 



that end. But they did find protection in their bony shell, which 

 became thicker, higher, and more convex, and with smaller open- 

 ings. To quote Dr. Hay: "We may suppose that it would be 

 much more difficult for a carnivorous animal to effect an entrance 

 into such a shell than into one depressed, and whose borders may 

 be spanned by the jaws of their enemies." Perhaps also the highly 

 arched form of the shell gave greater capacity for the lungs, and 

 the tortoises in general, it is said, do have better lung capacity 

 than the more aquatic or lowland types of turtles. Possibly, also, 

 the heavier shell lessened the evaporation of the body fluids, and 

 made the tortoises less dependent upon the vicinity of water. 



