MESOZOIC ERA: THE AGE OF REPTILES 541 



relatively delicate. The skeleton is very light, as would be expected 

 of animals of their habits, and the limb bones are hollow. An 

 improvement in the teeth is noticeable from period to period ; those 

 of the earliest (Anchisaurus), although plainly for eating flesh, are 

 not the perfect instruments possessed by those of later date (Allo- 

 saurus, Fig. 505), which are long and somewhat flattened, with ser- 

 rated edges. It is not known that the carnivorous dinosaurs were 

 especially ornamented ; one genus (Ceratosaurus), however, pos- 

 sessed a horn on the nose, and a row of small bones embedded in the 



Fig. 505. — Restoration of Allosaurus, a carnivorous dinosaur. The small size 

 of the fore limbs as compared with the hind is striking. (Restoration by C. R. Knight, 

 under the direction of Professor Osborn. Copyright, American Museum of Natural 

 History.) 



skin down the middle of the back, but aside from this, ornamentation 

 was rare. They varied greatly in size, from animals as small as a cat 

 to the largest carnivorous land animals that ever lived. Tyran- 

 nosaurus was 40 feet long, with teeth projecting from two to six inches 

 from the jaw. It is possible that this last was developed to prey 

 upon the great armored dinosaurs (p. 545) which attained their 

 greatest size and most perfect protection in the Upper Cretaceous, 

 shortly before the extinction of the race. 



The carnivorous dinosaurs are the earliest known, beginning in 

 the Triassic and living throughout the whole of the Mesozoic. 



Unarmored Quadrupedal Dinosaurs (Sauropoda). — These were 

 the largest animals of the time. A study of the skeleton and restora- 



