HERBIVOROUS DINOSAURS 



221 



when they encountered in all parts of the world the new en- 

 vironmental conditions of advancing Cretaceous time. 



The Iguanodontia 



Contemporaneous with the culminating period of the evo- 

 lution of the Sauropoda is the world-wide appearance of an 





J 



Fig. 99. Primitive Iguaxodont Camptosaurus from the Upper Jurassic of 



Wyoming. 

 This swift bipedal form was contemporary with the giant sauropod Apatosaunis and the 

 lighter-bodied Diplodocus. These iguanodonts were defenseless and dependent wholly 

 on alertness and speed, or perhaps on resort to the water, for escape from their enemies. 

 They were the prey of AUosaiirus (see Fig. 91). Mounted specimen in the American 

 Museum of Natural History. 



entirely different stock of bipedal herbivorous dinosaurs in 

 which the pelvis is bird-like (Ornithischia, Seeley). These 

 animals may be traced back (von Huene) to the Triassic 

 Naosaurus. The front of the jaws at an early stage lost the 

 teeth and developed a horny sheath or beak like that of the 

 birds, within which a new bone (predentary) evolves, giving to 

 this order the name Predentata. Entirely defenseless at this 

 stage {Camptosaurus), these relatively small, bipedal types 



