858 ORIGIN OF LIFE IN AMERICA 



received its quota of European emigrants, they found suitable 

 accommodation on the newly-formed land of north-western 

 South America. The mid- At] an tic land bridge now ceased 

 to exist, and far-reaching geographical changes super- 

 vejied almost everywhere. Owing possibly to the extensive 

 subsidences in the Pacific Ocean, the land that I assume to 

 have occupied part of the eastern Pacific, was gradually re- 

 duced in size. But, being no longer tenanted by the more 

 vigorous and more advanced European types, South American 

 forms now commenced to occupy this land, thus first reaching 

 the Antilles and then North America as it again became fully 

 connected with the western land. Central America in its pre- 

 sent shape had not yet come into existence. Not long ago it 

 was thought that the Central American isthmus must have 

 been first utilised as a highway at the beginning of the Plio- 

 cene Period, and that then the great edentates began to pour 

 into North America. Now the surprising evidence has come 

 to hand that true edentates of the Megalonyx type occur in the 

 Middle Miocene Mascall beds of Oregon. Dr. Matthew writes 

 to inform me that the Megalonyx remains only doubtfully 

 belong to this horizon. Professor Osborn,* on the other hand, 

 believes in the discovery, and expresses the opinion that it 

 tells in favour of my theory of the former existence of a 

 western land connecting North and South America inde- 

 pendently of Central America. Still, he points out that it is 

 inconsistent with the fact that other animals did not pass 

 south or north. 



Let us examine some of the other new arrivals in North 

 America in Miocene times, and endeavour to trace their geo- 

 logical history. One of the most noteworthy of these is the 

 first appearance in North America of elephants (Mastodon). 

 Since Dr. Andrews' f surprising discoveries in northern 

 Africa were published, Africa is generally looked upon as the 

 original home of elephants, the earliest form being Moeri- 

 therium, from which later on Palaeomastodon and its more 

 modern relations arose. The first of the latter was the Mas- 



* Osborn, H. P., "Age of Mammals," pp. 289292. 

 t Andrews, C. W., "Tertiary Vertebrates of the Fayum," pp. xvi 

 xviii. 



