FOSSIL VERTEBRATES— MAMMALIA 1 83 



the London Clay seems to indicate the presence of a related 

 form in Europe. 



Tillotherium from the Bridger of the United States is the 

 largest form known; the skull measured about a foot in length. 

 The developed incisor teeth are of large size, and the second 

 pairs of incisors and the canines are even smaller than in the 

 preceding genus. 



Duplicidentata. — This group contains the hares and rabbits. 

 They seem to have been developed about the Middle Miocene, 

 Paleolagns, White River. During the Pliocene they spread over 

 all of Europe and North and South America. 



Simplicidcntata. — This group is far larger than the preceding ; 

 it contains the rats, mice, squirrels, and all the remaining forms 

 of the rodents. None of the forms appear before the Miocene, 

 and during that time and the Pliocene differentiated and spread 

 all over the world. 



Primates. — The order is divided into two suborders, the 

 Lemuroidea, containing the lemurs, and the Anthropoidea, contain- 

 ing the apes and man. 



Among the primitive lemurs are many forms which are so 

 clearly intermediate between the two suborders that they must be 

 regarded as the direct ancestors of the Anthropoidea. The living 

 lemurs are confined to the island of Madagascar and to parts of 

 Africa and southern Asia. In the Miocene and Eocene times 

 they seem to have spread over the greater part of Europe and 

 North America ; they became extinct in the latter countries 

 about the end of the Miocene time. Among the most important 

 forms of the lemurs are Anaptomorphus, Adapts and Megaladapis. 



Anaptomorphus is from the Wasatch Eocene of Wyoming; 

 related forms are known from the lower Eocene of France and 

 England. The animal exhibits the very large cerebral hemi- 

 spheres that are characteristic of all the Primates and thus indi- 

 cates the starting point of the specialization in the nervous 

 system that has culminated in man. 



Adapts is from the Lower Eocene of Europe ; a closely 

 related form is Tomitherium from the Eocene of New Mexico. 



