NORTH AMERICA AND THEIR VERTEBRATE FAUNA. 129 



body. The head was short, with large eyes and large auditory openings 

 which were covered by a tympanic membrane. The limbs were proportion- 

 ately long ; the humerus of Dissorophus is nearly as long as the skull and the 

 femur fully as long or longer; the wrists, ankles, and feet were well formed 

 and strong, but rather broad, the tarsal and carpal bones being rather disk- 

 like, and without strong articular surfaces, as compared with the same ele- 

 ments in Eryops. The tail was short. The large eyes, well-developed audi- 

 tory sense, and proportionately long limbs show that these animals were 



Fig. 16. — Restoration of Dissorhorphus muUicinclus Cope. About one-fifth natural size. 



probably more alert than most of the amphibians of their time, and capable 

 of rapid and sustained motion. It was probably just this alertness and 

 ability to get around which brought them into the danger from predatory 

 reptiles, and made armor necessary. 



Cacops. — ^Williston has remarked upon the frog-like appearance of the 

 Cacops skeleton, especially shown in the large head and pectoral region, the 

 short neck and tail, and the posterior limbs longer than the anterior. He has 



Fig. 17. — Restoration of Cacops aspidephorous Williston. About one-fourth natural size. 



also shown that the toes were without claws, and suggests that the feet were 

 webbed, and that the animal was a good swimmer. The presence of armor 

 is no objection to the assumption that the animals were largely aquatic, 

 but the high development of the senses of sight and hearing, the evident 

 agility, and the location of the armor on the back, suggest that the animals 

 frequently sought the shore, and even ranged freely upon the land. In the 

 water the attack would be at least as much from below as from above, and 

 the dorsal armor would have no special value, but on the land such small 

 creatures would be most likely to be seized from above, where even the begin- 



