REPTILES 



369 



the same is true of the very different Chelone. These 

 are independent adaptations to marine life, recalling 

 the whales and the plesiosaurs. Gigantic land tor- 

 toises exist in the Galapagos Island and the islands of 

 the Indian Ocean, where they have been able to survive 

 on account of their isolation. In former geological 

 times similar great tortoises were found on continental 

 areas, for example, in Colorado and in Egypt. 



7. The Crocodilia, or crocodiles and alligators, were Crocodiles 

 formerly much more numerous than at present. They and aUi 

 superficially resemble gigantic lizards, but are' struc- 

 turally quite distinct. There are several living genera, 

 of which the most familiar are Crocodilus, the true 

 crocodiles, and Alligator, the alligator. The latter is 

 distinguished from the former by the broad, rounded 

 snout. The alligator of the southern United States 

 may be looked upon as a remnant of an old fauna, 

 since animals of this genus were formerly much more 



gators 



Photograph by E. R. Sanborn, N. Y. Zool. Soc. 

 FIG. 146. Senegal crocodile. 



