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HISTORICAL GEOLOGY 



i) 



animals — an evolution especially fitting them for life on the plains 

 and deserts. The camel, as is well known, is admirably adapted 

 for arid conditions. Its two-toed foot encased in a single pad is 

 efficient in traveling over desert sand, its long, well-nigh structurally 

 perfect legs enabling it to move rapidly and with the minimum effort, 



and its capacity for carrying water, were 

 the results of a long evolution under such 

 conditions. 



Although not as well known as the 

 ancestry of the horse, the history of the 

 camel is fairly complete (Fig. 550) from 

 the Eocene to the present. Following a 

 very generalized ancestor (Trigonolestes) 

 of the earlier Eocene, which may equally 

 well be considered ancestral to other 

 families, there appeared in the later 

 Eocene a very generalized camel (Proty- 

 lopus), a little larger 

 than a jack rabbit, 

 which is possibly an- 

 cestral to the mod- 

 ern camels. The 

 points in which it 

 differs most notice- 

 ably from living 

 members of the 

 family are : (1) the 

 size; (2) the small, 

 simple teeth of the 

 normal number (44) ; 

 (3) the presence of two side toes on each foot in addition to the two 

 useful toes ; and (4) the separate bones of the forearm (radius and 

 ulna), which did not grow together until late in the life of the in- 

 dividual. 



The Oligocene camel (Poebrotherium) was of slender proportions, 

 somewhat resembling a llama, though with a shorter neck. In this 

 camel evolution had progressed in two principal particulars : the 

 side toes were absent and were represented by splints, and the 

 bones of the forearm were joined when the animal was still very 

 young. 



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Fig. 550. — Evolution of the camel's foot from the Eocene 

 to the present. (After Scott.) 



