MESOZOIC ERA 181 



armed with rows of pointed teeth, some of them 6 inches long. This enor- 

 mous engine of destruction was obviously well equipped to prey upon its 

 giant herbivorous contemporaries. 



The largest herbivorous dinosaurs belonged to a second division of the 

 Saurischia, the Sauropoda. These creatures departed from the character- 

 istics of their thecodont ancestors by returning to a four-footed or quad- 

 ripedal locomotion and modifying the conical teeth of their carnivorous 

 ancestors. Despite the return to quadripedal locomotion, however, the 

 forelegs of most of them remained shorter than the hind ones — a telltale 

 trace of their thecodont ancestry. The heads of sauropods were absurdly 

 small for animals of such great bulk. The teeth were reduced in size and 

 number. This relatively ineffectual dental armament suggests dependence 

 upon a soft type of water vegetation for food. Indeed, it is thought that 

 these giants spent much of their lives in lagoons and swamps. The nos- 

 trils of some of them were located high up on the head, seemingly to 



FIG. 9.7. Bronfosaurus, one of the largest dinosaurs. (Restoration by Charles R. Knight; 

 courtesy of the American Museum of Natural History.) 



make breathing possible while the mouth was engaged in underwater feed- 

 ing. Also, the bulk was so great that it is difficult to see how the legs 

 could have furnished adequate support, for protracted periods of time, 

 without the aid of buoyancy provided by surrounding water. The weight 

 of an animal varies in proportion to the cube of its length, while the 



