270 



HISTORICAL GEOLOGY 



Elephant. It was a plant-eater and probably not as ferocious as 

 it looked. Good specimens have been found in the western in- 

 terior of the United States. Triceratops existed only during the 

 Cretaceous period. 



Theropods were carnivorous Dinosaurs, as proved by their 

 numerous sharp teeth set in comparatively large heads (see Fig. 



Fig. 171 



Theropods, Allosaurus agilis, of the Dinosaur division of Mesozoic Reptiles. 

 Restored by C. R. Knight, under the direction of H. F. Osborn. (Cour- 

 tesy of the American Museum of Natural History.) 



171). They were bipedal, that is they walked on two legs, the 

 front limbs having been very small and used only for grasping. 

 The toes were armed with sharp claws. The bipedal habit com- 

 bined with the long, ponderous tail gave them a sort of Kangaroo 

 aspect. The limb bones were hollow, thus suggesting a bird-like 

 structure. In fact before it was known that the numerous tracks 

 in the Newark sandstone of the Connecticut Valley were made by 

 creatures of this sort, they were called "Bird-tracks." Theropods 

 reached a length of fully 15 feet, and though much smaller than 

 many other Dinosaurs, they were probably the most ferocious of 

 all and more than likely preyed upon even the much larger plant- 



