THE EPIC OF EVOLUTION 



509 



EVOLUTION OF THE CAMELS 



Plexstocew 



Recent 



Wiocene 



Miocene 



Ol\goccnc 



Sliull 



Feet 



Teeth 



Procomelus 



Pocbrotherium 



Eocerie 



PrOtylopuS 



two continents have been separated long enough, even if they were 

 ever in communication, to allow their characteristic faunas to evolve 

 independently. 



There is geological evidence of an ancient Pleistocene land-bridge 

 in the region of Bering Strait, between North America and Eurasia. 

 The presence of this former bridge explains why similar native ani- 

 mals, such as bears, sheep, antelopes, moose, bison, and caribou, 

 occur in these two great regions now separated from each other, and 

 are not represented on 

 other continents. 



One of the best exam- 

 ples of the connection 

 between evolutionary 

 processes and distribu- 

 tion, which has been un- 

 earthed quite completely 

 by paleontologists, is that 

 of the camel-like mam- 

 mals. The ancestral 

 home of these animals, 

 as shown by fossils, was 

 North America, where 

 they went through a long 

 preliminary evolution, 

 but where none of them 

 are present today. Pro- 

 tylopus was an Eocene 

 ''camel"; Poebrotherium 

 followed in Oligocene 

 times ; and Procamelus 

 in the Miocene period. 

 Later, in the Pliocene period some of these ancestral camels migrated 

 in two directions from their birth place. One stream went across 

 the Bering Sea bridge into Eurasia and evolved into Bactrian camels 

 with two humps and the Arabian dromedaries with a single hump. 

 The other stream migrated southward over the Isthmus of Panama 

 into South America, and became modified into the wild guanacos and 

 vicunas, from w^hich much later the domestic llamas and alpacas were 

 derived. Thus, the transformed descendants of these pecuhar an- 

 cient fossil forms of North America are found today occupying habi- 



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Meso/oic or Age of Reptiles 



Hypothetical fiKe-toed Ancestor 



American Miisevm of Natural History 



Evolution of the camel. 



