120 



ANIMAL BIOLOGY 



C. Reptiles 



Apparently descended from primitive Amphibians, the Reptiles 

 met new and more favorable land conditions with progressive 

 structural and physiological features: for example, they skipped 

 metamorphosis and so started out from the egg with functional 

 lungs and on four feet. So the Reptiles very soon, geologically 

 speaking, became the dominant Vertebrates on the Earth, flourish- 

 ing both in number of individuals and variety of species adapted 



Fig. 79. — Reptiles of the past. A, a Dinosaur, Branchiosaurus (length 

 about 80 feet); B, a Pterodactyl, Rhamphorhynchus. (From Lull.) 



to all sorts of land and swamp conditions, and even, secondarily, 

 to aquatic and aerial life. Probably the best known representa- 

 tives of the extinct population of the Age of Reptiles are some of 

 the giant Dinosaurs. (Figs. 79, 232.) 



Although the supremacy of the Reptiles eventually passed to 

 the Mammals, there are still some five thousand species living 

 to-day. These are arranged in three chief orders : the Testudinata, 

 Crocodilia, and Squamata, represented by the Turtles and 

 Tortoises, the Crocodiles and Alligators, and the Lizards and 

 Snakes, respectively. 



1. Turtles and Tortoises 



Typically encased in a shell composed of bony plates firmly 

 fixed to the backbone and to the ribs, the Turtles and Tortoises 



