478 



AN INTRODUCTION TO ZOOLOGY 



the Ornithischia, in which the girdle approaches more closely that 

 of the birds. The Order Crocodilia Crocodiles, Alligators, and 

 Ga vials probably arose from the Saurischia in Mid Triassic times, 

 but their remains are not found until the early layers of the 



FIG. 171. 'Restoration of the sauropod dinosaur, Diplodocus, based upon the 

 mounted specimen in the Carnegie Museum. Length, 87 feet. Coman- 

 chian, Wyoming. After Lull, from Schuchert's "Historical Geology." 



Comanchian, when they are fully differentiated and resemble 

 modern forms. Undoubted Saurischian Dinosaurs appear in the 

 Upper Trias, and -continue on until the end of the Cretaceous. 

 They become specialised along two lines, the one herbivorous and 



FIG. 172. Restoration of Brachiosaurus, the most ponderous sauropod. 

 Length, about 80 feet. Comanchian, North America and East Africa. 

 Modified from Matthew. 



the other carnivorous. The herbivorous forms reached their zenith 

 in the Comanchian times, when they were represented by three 

 gigantic forms, Diplodocus, Brontosaurus, and Brachiosaurus, 

 undoubtedly the largest land animals of which we have any know- 

 ledge. They were about 87 feet, 66 feet, and 80 feet long respectively, 



