BANGE OF^ FOSSIL ELEPHANTS 409 



fied, from all available data, that North and South America 

 became joined at the commencement of the Pliocene Period. 

 It was supposed that the advance of northern types, such as 

 the mastodon and hosts of others, towards the southern con- 

 tinent must have coincided with the opening up of the new 

 land of Central America. The occurrence of edentate remains 

 in North American Miocene deposits upsets this theory, 

 because, if mammals were able to reach North America from 

 the south during the Miocene Period, northern species must 

 have had equal facilities for invading South America at this 

 time. If there is geological evidence that Central America was 

 not available as a safe land bridge between North and South 

 America in Miocene times, some other land connection 

 must have united the two continents. When I advanced the 

 theory of the former existence of a Pacific land bridge between 

 North and South America, westward of Central America,* I 

 was unaware of Professor Sinclair's interesting discovery 

 among the Mascall beds of Oregon. My theory was largely 

 founded on zoogeographical data on curious instances of 

 discontinuous distribution of ancient groups in North and 

 South America. Professor Osborn f regards my theory as 

 inconsistent with the fact that the Pacific land bridge should 

 only have been used by these gravigrade sloths. If such a 

 land connection really existed why was it not more exten- 

 sively used ? I think it was used by other animals, such as the 

 mastodons and the ancestors of the llamas to pass southward, 

 and by the ancestors of the North American tree porcupines 

 in entering North America. 



Since I wrote my essay on the problem of a former land 

 connection, other than the Central American one, between 

 North and South America, I have had opportunities of study- 

 ing the subject more at my leisure. I find that the affinity 

 existing between south-western North America and the 

 extreme south of South America among some of the more 

 ancient groups of animals is greater than I thought. Let 

 us examine this curious relationship between the two 

 widely separated faunas a little more closely. I explained 



* Scharff, R. F., " Early Tertiary Land-connection." 

 t Osborn, H. F., "Age of Mammals," p. 292. 



