xxxi. 2 CLASSIFICATION 745 



eyes, with a horizontal pupil, and long ears and an acute sense of 

 hearing. 



Artiodactyls have an elaborate system of scent-glands, on the head, 

 between the digits, in the inguinal region, and elsewhere, though not 

 usually around the anus. These glands are used for marking territory 

 and in the sexual and social life, which is often elaborately organized. 

 The colour of the coat and especially the form of the head and horns 

 also play an important part in the communication system between 

 individuals. 



The reproductive system remains rather close to the presumed 

 original eutherian condition. The uterus is bicornuate and in pigs the 

 placenta is of the diffuse epitheliochorial type. In ruminants there is 

 a cotyledonary placenta, but the contact between maternal and foetal 

 tissues is never very close (syndesmo-chorial) and the allantois is 

 usually large. 



2. Classification 



Superorder 5. Paraxonia 

 Order Artiodactyla 

 Suborder 1. Suiformes 



Infraorder 1. Palaeodonta. Pigs and peccaries. Eocene-Recent 

 *Diacodexis, Lower Eocene, N. America; *Homacodon, 

 Middle Eocene, N. America; *Entelodon, Lower Oligocene, 

 Holarctic; Sus, pigs, Lower Pliocene-Recent, Eurasia (then 

 world-wide); Phacochoerus, wart-hog, Pleistocene-Recent, 

 Africa; Dicotyles, peccary, Pleistocene-Recent, Central and 

 S. America; Potamochoerus, water-hog, Pleistocene-Recent, 

 Africa 

 Infraorder 2. Ancodonta. Hippopotamuses. Oligocene-Recent 

 * Anihr ac other ium, Oligocene-Pliocene; Hippopotamus, Plio- 

 cene-Recent, Eurasia, Africa 

 *Infraorder 3. Oreodonta. Eocene-Pliocene. N. America 

 *Merycoidodon (= *Oreodori), Oligocene; *Agriochoerus, 

 Oligocene-Miocene 

 Suborder 2. Tylopoda. Camels. Eocene-Recent 



*Protylopus, Eocene, N. America; *Poebrotherium, Oligocene, 

 N. America; *Proca?neIus, Miocene-Pliocene, N. America; 

 *Alticamehts, Miocene-Pliocene, N. America; Lama, 

 alpaca, Pleistocene-Recent, S. America; Camelus, camel, 

 dromedary, Pleistocene-Recent, Asia 



