ELEPHANTS, HORSES, AND CAMELS 



169 



velopmcnt of two incisors into enormous tusks, used in fighting 

 and digging. 



Elephant Phylogeny. Remote Ancestors and Divergent Forms. 

 The earliest fossils of proV)oscidean ancestors an^ found in th(^ upper 

 Eocene deposits of Africa. They belong to the genus Moeritherium, 

 which is characterized by the elongation of incisors in both jaws, 

 enlargement and recession of the nasal openings in the skull, forma- 

 tion of air cells at the back of the skull, and transversely ridged 

 molars, although it shows little further resemblance to the Probos- 

 cidea (Fig. 94). It is 

 supposed to have existed 

 until some time in the 

 Oligocene, when it be- 

 came extinct. 



The Oligocene also 

 produced the genus Pal- 

 aeomastodon (Fig. 95), 

 of which fossil remains 

 are found in Africa and 

 Asia. The members of 

 Palaeomastodon show a 

 marked advance in the development of the characters mentioned, 

 and were probably descendants of Moeritherium. The molars are 

 little more advanced, but the incisors of the upper jaw are well 

 developed tusks, and the skull is higher, with a greater develop- 

 ment of cancellated bone. 



In the Miocene another probable descendant of Moeritherium 

 appeared in Europe, existing until the Pliocene, when it became 

 extinct. This genus, Dinotherium, displays a peculiar develop- 

 ment of deflected lower jaw and tusks, while the tusks of the 

 upper jaw appear to have been lacking. The size of these animals 

 was about that of the mastodons. While they show evidences of 

 the development of a proboscis, and are in general well advanced 

 over Moeritherium, they gave rise to no existing forms. 



The Miocene, however, saw the rise of three other genera which 

 appear in Europe, Asia, Africa and North America. The first, 

 Trilophodon, is supposed to have descended directly from Palaeo- 

 mastodon. Its distribution includ(\s the four continents men- 

 tioned and it persisted "until the extinction of the mastodon in 

 post-Glacial time." Aside from the elongation of the lower jaw, 



Fig. 95. — Head of Palaeomastodon, restored by 

 Lull. (From Lull.) 



