The Tetrapoda: Amphibia, Reptiles, Birds 613 



gradually increased in abundance during the Permian, and reached the 

 heights of their development during the Mesozoic, the great Age of 

 Reptiles. At the end of the Mesozoic, they were gradually being re- 

 placed by the up and coming mammals and birds; today the reptiles 

 though fairly abundant are only remnants. The largest living reptile 

 is but a pygmy in comparison to the giants of the Mesozoic. 



CROCODlLIA 

 CROCODILES' ALLIGATORS 



STCMOFRULING REPTILES 



Fig. 204. — The family tree of the ruling reptiles. ( From Romer: 

 Vertebrates. Copyright, 1941, The University of Chicago Press.) 



Man and the 



From the stem reptiles, the cotylosaurs, the many diverging rep- 

 tilian lines developed. The ichthyosaurs reverted to water and acquired 

 a fishlike form, complete with fins. The plesiosaurs developed enor- 

 mously elongated necks and paddlelike limbs, and apparently ranged in 

 the shallower parts of the ocean. The lizards and snakes, the turtles, 



