172 STUDIES FOR STUDENTS 



Fossil forms of the group are found in the Eocene of Europe 

 and North America, but the greatest development of the family- 

 came from the Pliocene to Recent. The origin of the Siddae is 

 not at all well known, but there seems to be little doubt that 

 they are the specialized branch of some carnivorous stem. 



AchcE?iodon, from the Bridger Eocene, has very strong canines 

 and the cheek teeth are similar in many respects to those of the 

 primitive Camivora. 



Elotherium, from the Oligocene of Europe and the United 

 States, White River, is one of the ancestral forms. The head is 

 long, the posterior teeth are multitubercular, the premolars are 

 conical, and the canines and incisors are long and well fitted for 

 grasping. The limbs were peculiarly long, and altogether the 

 animal seems to have been a rather vicious type of carnivorous 

 hog that had the running powers of a deer. 



Platygonns, from the Pliocene and the Pleistocene of the 

 United States, was a very small form that seems to have been the 

 direct ancestor of the peccary. 



Sics, the true hog, appeared in Europe and Asia, in the Upper 

 Miocene and has continued ever since. There is no native 

 member of the genus in the Americas. 



Hippopotamidae . — The Hippopotamus is not known earlier than 

 the Pliocene, and occurs in deposits of that age in England and 

 in India. The existing forms are confined in Africa. 



Oreodontidae . — This is an extinct group that is confined to the 

 Miocene and the lower Pliocene of the United States. It is 

 primitive in all of its characters ; the dentition is complete and 

 the fore limb has five digits ; the metapodials are not united. 

 One peculiar thing is that the anterior lower premolar tooth 

 passed forward and acted as the canine, while the canine assumed 

 the aspect and the function of an incisor. The sense of hearing 

 was very acute, the bulla of the ear reaches, in some of the later 

 forms a very large size. The animals were all small, never 

 reaching a size larger than that of a Newfoundland dog, and in 

 most cases were much smaller. From the manner of the occur- 

 rence of their remains it seems that they lived near the banks 



