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 hbrfee family. 
Another modern 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. 64—69. 
f Osborn, H. F., “ Cenozoic Mammal Horizons,” pp. 35—36. 
J Schuchert, C., “ Paleogeography of North America,” Plan 96. 
