xxxi. 6 



OREODONTS 



751 



pigs. There were four functional digits in each foot, and a complete 

 tooth row, including molars whose cusps were selenodont and in some 

 later forms quite high-crowned. Although Eocene intermediate forms 

 have not been found, it may be presumed that the oreodonts arose 

 from a basal palaeodont ancestor. They pursued an independent 

 evolution in North America parallel in some ways to that of the rumin- 

 ants in the Old World. Unlike the latter, they were at a disadvantage 

 in the changed conditions of the Pliocene and then died out. 



Jr 



Fig. 498. Llama, Lama. (From photographs.) 



* 'Agriochoerus and its relatives were oreodonts that acquired claws 

 and therefore represent a parallel to ancylopod perissodactyls, with 

 which they were for a long time confused. It has been guessed by some 

 that the claws were used for digging roots, by others that they were 

 for climbing. 



6. Camels 



All other artiodactyls chew the cud and are often included in a 

 single group Ruminantia. However, the camels have been a separate 

 stock since the Eocene and are so distinct from the remainder that it 

 is convenient to keep them in a separate suborder Tylopoda. They 

 have been common animals since the late Eocene, flourishing especi- 

 ally in North America, although, like the horses, they died out there 

 very recently and survive today only as remnants, which migrated 

 from North America in the Pleistocene, the camels to the Old World 

 and the llamas to South America. The bactrian camel of the Gobi 

 Desert in central Asia is perhaps a wild form, all others being com- 

 mensals of man. The llamas (Fig. 498), though similar in basic 

 structure to the camels, differ in the smaller size, long hair, and lack 



