ir. VERTEBRATA: ilAMAIALIA, PROBOSCIL'IA. 



643 



the prong horn, which sheds its horns, and Hoploceras montanus* the 

 Rocl^y mountain sheep. 



Section III. TYLOPODA, stomach without manyplies, no frontal 

 horns, diffuse placenta. Camelus, the camels of the 01<1 World; C. drome- 

 darius, one hump; C. hactrianus, two humps. Auchenia lama, A. alpaca 

 of South America. 



Paleontology of the Ungulata. 



Extensive paleontological material, especially from the tertiary rocks 

 of our western states, has cleared up many lines of ungulate descent 

 and has rendered it probable that the COXDYLARTHKA of the eocene, 

 with five-toed plantigrade feet, well-developed ulna and fibula, and an 

 omnivorous dentition, formed the stock from which descended the artio- 

 dactyles and perissodaotyles, and possibly carnivores and primates as well, 

 the ungulate line extending through the Amblypoda. From one gi-oup of 

 these (the Phenacodontid.e) the lines of rhinoceros and tapir have come, 

 and in an almost complete series we know the ancestry of the horse. 

 Ilijramtherium (Eohip-pus) and Oroliippiis of the eocene had the fore feet 

 four-toed (fig. 066, 1) ; PaUeotheriuni and 3Iesohippiis (.') of the lower 



VTV^ 7. 



'^' 



1, Orohtppys 

 •'*, Prutokippns 



Fig. 666.— Evolution of fore foot of horse. (From Wiedersheim.) 

 (eocene): ^, Memhipjyus (lower miocene); 3, Miohippus (niiocene); 

 (upper pliocene); 5, Plii:hippus (pleistocene); «, Equus. 



miocene and 3Iio7iippus of the later miocene were three-toed, while Mk/-}/- 

 hippiis and Hipparion {PlioMppus, 4) of the pliocene were near the horse 

 ill tooth structure. The single-toed horses appeared in the pleistocene 

 with Pliohippus (.5) and then Equtcs itself (6-). It is a peculi;ir fact tliat 

 the horse entirely died out in America, although the chief part of its his- 

 tory was enacted here. 



The AMBLY'PODA, mentioned above, were semi-plantigrade peuta- 

 dactyle forms, appearing in the lowest eocene, and reacliing, in Uinfa- 

 tlieriiun (Dinocerus) an elephantine size. The Tf:)X(:)DONTIA of the 

 South American tertiaries combined perissodactyle, rodent, hyracoid, and 

 proboscidian features, while the TILLODONTIA of the eocene recall both 

 carnivores and rodents. 



Order VI. 



The elephants and their allies 



Proboscidia. 

 with their hoofs and herbivorous 

 dentition, are closely related to the ungulates. The}' are charac- 

 terized by their thick skin (' pachyderm ')> the large, massive, 

 five-toed legs, and especially hy the nose drawn out into a 



