212 



THE ORIGIN AND EVOLUTION OF LIFE 



sauria was not known. It has since been discovered that 

 many of the ancient dinosaurs, especially those of carnivorous 

 habit, were bird-footed and adapted in structure for rapid, 

 cursorial locomotion; the body was completely raised above 



Fig. 90. North America ix Uppkr Triassic (,.\'i:\v\rkj Timk. 



The period of the primitive bipedal dinosaurs, with semi-arid, cool to warm climate, and 

 a prevailing flora of cycads and conifers. Remains of amphibians, primitive crocodiles, 

 and dinosaurs are found in the reddish continental deposits. Detail from the globe 

 model in the American Museum by Chester A. Reeds and George Robertson, after 

 Schuchert. 



the ground, the forward part being balanced with the aid of 

 the long tail. This primitive type of body structure is com- 

 mon to all the dinosaurs, and is evidence that the group 

 underwent a long period of evolution under semi-arid conti- 

 nental conditions in late Permian and early Triassic time. 

 The reptilian group discovered in the Connecticut valley (Fig. 



