PALEONTOLOGY 



329 



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to the camels was Protylopus of late Eocene time. From it appear to 

 have sprung three lines of descent, two of which became extinct. The 

 third led to the camels of today. Members of this third evolutionary 

 series lived in North America until Pliocene or Pleistocene time, when 

 they migrated to South America, Asia and Africa, and none have been re- 

 covered from later deposits in North America. In South America their 

 descendants became the guanaco and the vicuna (both belonging to the 

 genus Auchenia) from which the domestic llama 

 and alpaca have been derived. In Asia and 

 Africa the migrants gave rise to two species of 

 camels, the one-humped Arabian camel, or 

 dromedary, and the two-humped camel of 

 central Asia. Both of these species are domes- 

 ticated; indeed, it is doubtful whether there have 

 been any truly wild camels in the Old World for 

 thousands of years, since the undomesticated 

 camels of Turkestan are probably feral, that is, 

 they have escaped from domestication. 



The evolutionary changes undergone by the 

 camels resemble to some extent those of the 

 horse, and are described here in less detail. 

 Protylopus, the "original" camel, was of about 

 the size of a large rabbit. It had 44 teeth in a 

 continuous row, of which the molars were low- 

 crowned. The orbit of the eye was open at its 

 posterior margin, the fore feet possessed four 

 separate and functional toes, and the hind feet 

 two functional and two reduced toes (Fig. 226). 

 From such an animal have come, by changes 

 which were not evenly distributed over the inter- 

 vening ages, the guanaco, the vicuna and the 

 huge camels of Asia and Africa. The teeth of 

 these recent animals are but 34 in number, and 

 are separated into several groups by wide tooth- 

 less spaces. The molars have relatively long 

 crowns. The orbit of the eye is completely 

 closed posteriorly. The two lateral toes have 

 been completely lost, so that no vestige of them 

 remains, and of the two toes that do remain the 

 metacarpals in front and the metatarsals behind 

 have fused into a single bone in each foot, divided at the distal end to 

 bear two distinct series of phalanges. The structure of the toes is such 

 as to allow them to spread, and a pad has been developed beneath them. 

 Nothing is known of the evolution of the hump, since this elevation is 



f \ 



Fig. 226. — Diagram rep- 

 resenting the evolution of 

 the fore feet in tlie camel 

 family. The carpal bones 

 are not separately distin- 

 guished. The Roman nu- 

 merals indicate the numbers 

 of the digits, the inner digit 

 being designated I. .4, Pro- 

 tylopus, from the late 

 Eocene; B, Poebrotherium, 

 from the early Oligocene; C, 

 the guanaco, a living species. 



