54° 



HISTORICAL GEOLOGY 



Carnivorous Dinosaurs. — The most striking features of the car- 

 nivorous dinosaurs were the bipedal habit and the disparity in size 

 between the fore and 

 hind limbs, a char- 

 acter which increased 

 as the race became 

 older, until in later 

 forms (Tyranno- 

 saurus, Fig. 503) the 

 arms are so absurdly 

 small that it is diffi- 

 cult to conjecture 

 their use. As the 

 fore limbs decreased 

 in size and gradually 

 relinquished their 

 function, although 

 never entirely aban- 

 doning it, the hind 

 legs, in addition to 

 their duty of support- 

 ing the weight of the body, had to assume a grasping function as 

 well, and the claws became, in consequence, great talons, differing 

 thus markedly from those of an earlier type (Anchisaurus). This 

 grasping function, however, was perhaps trans- 

 ferred to the teeth quite as much as to the hind 

 limbs. The earlier forms probably walked on 

 all fours, but as the fore limbs became smaller, 

 they stalked about on their hind legs, or pos- 

 sibly leaped about in kangaroo fashion with the 

 forward part of the body lifted from the ground 

 and balanced by the powerfully developed tail. 

 A second group (Compsognathus, Fig. 504) 



differed from the above 

 in being lighter in 

 build, with the fore 

 limb developed for 

 grasping its prey. 

 The skull is very light and bird-like in some genera (Anchisaurus) ; 

 and, although quite large in others (Tyrannosaurus), it is always 



Fig. 503. — Skull of Tyrannosaurus, a. gigantic car- 

 nivorous dinosaur. The skull is four and a half feet 

 long and the animal was sixteen feet high when standing. 

 (After Prof. H. F. Osborn.) 



Fig. 504. — A bird-like carnivorous dinosaur, Comp- 

 sognathus, about two feet long. (After Abel.) 



