748 ARTIODACTYLS xxxi. 4 



4. Pigs and hippopotamuses 



The pigs have remained essentially in this Eocene condition; 

 Simpson recognizes this by classifying them with the Eocene forms 

 in one infraorder Palaeodonta, distinct from the amphibious Anco- 

 donta (hippopotamuses and anthracotheres) and the *Oreodonta. 



Fig. 493. Above, skull of the oreodont *Merycoidodon (after Scott); below, skeleton of 

 *Entelodon. (After Woodward, Palaeontology y Cambridge University Press.) 



Close relatives of the pigs are found from the Eocene, with bunodont 

 molars. Several lines can be recognized, including the entelodonts, 

 giant pigs of the Oligocene, over 5 ft high and 12 ft long and of gravi- 

 portal structure (Fig. 493). The modern pigs (Fig. 494) show a nearly 

 complete dentition, with persistently growing canine tusks, used for 

 defence and for digging roots. The orbit is continuous with the tem- 

 poral fossa. There are no horns. There are four toes, but only two 

 reach the ground. The brain is small. They mostly live in marshy, 

 forest conditions and are omnivorous, digging with the long snout for 

 food detected by smell. The neck muscles are very large. Pigs live 



