228 ORIGIN OF LIFE IN AMERICA 



North America remains as before. The new feature is the 

 sudden appearance of true carnivores, ungulates, primates 

 and rodents. I have already referred to Eohippus 

 (p. 147) as an early representative of the hoirke family. 

 Another modem family which traces its origin back to 

 these remote times is that of the tapirs, for the Eocene 

 Systemodon has all the characters peculiar to the recent 

 Tapiridae. Whether the early primates were lemurs or true 

 monkeys is as yet undecided. The rodents all belong to the 

 extinct Ischyromyidae, which Dr. Matthew * believes to 

 have been arboreal creatures, somewhat resembling squirrels 

 in shape, although more nearly related to the peculiar and 

 typically west American sewellel (Aplodontia). 



This sudden and simultaneous appearance of modern 

 families of mammals, along with several extinct ones, in 

 western Europe and south-western North America is very 

 striking, and has to be accounted for. To begin with, we 

 have to determine the origin, or original centre of dispersal 

 of this fauna. Professor Osborn feels certain that this fauna 

 originated neither in Africa nor in South America. There 

 remain, he thinks, four possible sources. They may have 

 come from the Great Plains Region of North America, from 

 the more northerly American Mountain Region, from the 

 northerly Eurasiatic Region, or from the American-Asiatic 

 land -mass. He is in favour of the last theory, namely, that 

 of the intermediate or North American -Asiatic source of 

 this fauna. Still he believes that the actual origin of this 

 modernised fauna will not be determined until Eocene fossil 

 mammal beds in the northern portions of America and Asia 

 shall have been discovered. Such beds have not yet been met 

 with, nor is there any reason to suppose that they will be. 

 Have we any geological evidence for the supposition that 

 there actually existed any such large and intimately connected 

 northern land-mass at this stage of the geological history of 

 the earth as Professor Osborn f implies ? No doubt it is 

 generally assumed that Alaska and north-eastern Asia were 

 joined by land in Eocene times, and Professor Schuchert,J 



* Matthew, W. D., " Osteology of Paramys," pp. 6469. 

 t Osborn, H. F., " Cenozoic Mammal Horizons," pp. 35 36. 

 J Schuchert, C., " Paleogeography of North America," Plan 96. 



