CENOZOIC ERA: AGE OF MAMMALS 617 



The next in line (Procamelus) lived in the Miocene and shows a 

 further approach to the modern camel, having a longer neck than 

 the preceding and more camel-like contour. In this stage the bones 

 of the forearm were united before birth, and certain bones of the foot 

 (metapodials, or " cannon bones ") were united early in life. The 

 splints were entirely absent. The animal was intermediate in size 

 between the llama and camel. Some of the Pliocene and Pleistocene 

 camels attained a larger size than any existing species. Besides 

 these in the direct line of descent, a number of side branches arose 

 to take advantage of various conditions of climate and food. 



The camel is, in the even-toed line (artiodactyl), what the horse 

 is in the odd-toed line (perissidactyl), each family having apparently 

 progressed almost as far as possible in the perfection of its foot 

 structure. 



The camel family lived in the New World for perhaps 3,000,000 

 years and then completely disappeared from the North American 

 continent, where its evolution had taken place. The camels (llamas 

 and alpacas) of South America succeeded in living on in that 

 continent, to which their ancestors had migrated in the Pliocene or 

 Pleistocene. The entire family was confined to North America until 

 the Pliocene, when it invaded the Old World, and in the Pliocene or 

 Pleistocene it invaded South America. The dromedary and camel 

 still survive in Africa and Asia, and the llama and vicuna in South 

 America. Here again is a great family which, having developed 

 into almost its present form in North America, became extinct on 

 this continent, although still living on in others. The cause of the 

 extinction of this family is as difficult to find as that of the horse ; 

 for, as in the case of the horse, the conditions in portions of America 

 to-day (Arizona, New Mexico, and Mexico) have been shown by ex- 

 periment to be as favorable for camels as those in their African and 

 Asiatic homes, and they would doubtless be used in arid and semi- 

 arid regions of western North America if economic necessity de- 

 manded. Their extinction in North America may have been due 

 to the same cause, or causes, that produced the extinction of so many 

 species at the close of the Pliocene. 



REFERENCES FOR CAMELS 



Beddard, F. E., — Mammalia. 



International Encyclopedia, — Camel. 



Scott, W. B., — A History of Land Mammals in the Western Hemisphere* pp. 386-402. 



