xxxi. 3 ORIGIN OF ARTIODACTYLS 747 



hippopotamuses. Probably no members of this group developed the 

 ruminating habit, and they are sometimes called 'non ruminantia'. 

 The suborder Tylopoda is for the camels, and the third suborder, 

 Ruminantia, includes all the other modern forms of artiodactyl. 

 The earliest artiodactyls (Fig. 492), included in the Suiformes, were 



SUIFORMES RUMINANTIA 



Fig. 492. Chart of the evolution of the Artiodactyla. 



close to the ancestral stock of all placentals. In *Diacodexis from the 

 North American Lower Eocene there were tritubercular molars and 

 it was probably a small, running, omnivorous form, with four toes on 

 each foot. These animals could indeed almost equally well be classified 

 as insectivores or creodonts, and the only reason for placing them as 

 artiodactyls is that the talus had the typical pulley-like lower surface. 

 Later Eocene and early Oligocene forms developed a bunodont con- 

 dition, with sometimes six cusps in the upper molars, protocone, 

 paracone, metacone, hypocone, protoconule, and metaconule. In some 

 later forms these cusps show a selenodont condition. 



