With the beginning of the Cenozoic the record of the reptiles becomes relatively scanty in America. In the warm waters of the old Eocene lakes and rivers of Wyoming lived countless crocodiles, true crocodiles of modern aspect and of large size. But, as the climate of North America grew progressively colder, the crocodiles retreated to the south, till, in the Oligocene, the scanty remains of the last crocodiles are found in the American Tertiary. On the other hand, as the open lands appeared toward the close of the Eocene, and in the Oligocene and Miocene, the land tortoises throve and grew greatly in size. In the Bad Lands of South Dakota one may see their remains in almost incredible numbers. And in equally great numbers are these land tortoises, in shape much like the common box tortoise of today, but vastly larger, found in the rocks of the late Miocene or early Pliocene age in western Kansas. And these are the last records of the big tortoises in North America; their descendants are perhaps yet living in the Galapagos Islands. The history of the lizards and snakes, the only other reptiles found in the Cenozoic rocks of America, is very brief. A few specimens from the Lower Eocene of Wyoming; a few skinks and amphisbaenas from the Oligocene Bad Lands of South Dakota, and some bones of a python-like snake in the early Eocene of Wyoming are about all that we know of the Squamata in the Tertiary. Doubtless snakes and lizards were just as abundant then as now, though but few were preserved, for they are and always have been distinctly terrestrial animals, that only by accident fell into places where they could be fossilized. The author has collected reptile bones from nearly all of the horizons here mentioned and believes that the list is complete. CHAPTER V ADAPTATION OF LAND REPTILES TO LIFE IN THE WATER