MATTHEW, CLIMATE AND EVOLUTION 243 



were in different parts of the northern world, as we have seen among tlie 

 Perissodactyl groups. 



The camels appear to have been of American origin. An ancestral 

 series is found in the Tertiary of the western United States, going as far 

 back as the Upper Eocene.^" In the Old World, they first appear in the 

 Pliocene; in South America, in the Pleistocene (Pampean) ; and the 



Fig. 22. — The disijersal center of the VaineUdw was in North America 



They reached the Old World in the Pliocene, South America in the Pleistocene. They 

 survive on the margins of their range but became extinct in North America early in the 

 Pleistocene. North American Pleistocene camels were more advanced than the living 

 types of the marginal areas. 



camels of the Pleistocene in North America were about as specialized on 

 the whole as the living llamas of South America or the camels of Africa 

 and Asia. In North America, the race is now extinct. The center of 

 dispersal would appear to have been in this continent, — how far to the 

 north we have no means of estimating; but the exceptional directness of 

 the phylogenetic series as represented by our western fossils indicates, in 

 my opinion, that these fossils lived in or close to the racial dispersal 

 center. 



" It forms a singularly direct and complete phylum, so supercharged with intermediate 

 and connecting forms that it is very difficult to classify and arrange the fossils into 

 species and genera, while every gradation of structural evolution is abundantly illus- 

 trated. 



