THE PLIOCENE PERIOD 841 



now living in the Canaries. In Europe generally there was still 

 much commingling of species now separated geographically. Some 

 of this later separation is in longitude, and does not carry climatic 

 suggestiveness. The evidence, on the whole, points to a general 

 movement in latitude, in anticipation of the present distribution 

 and adaptations of the plants. 



The land animals. The history of the mammals continued 

 to be the great center of interest. Three important features char- 

 acterized it: (1) A notable intermigration of the continental 

 faunas, including those of North and South America; (2) the 

 initiation of the present divergence between Old and New World 

 types; and (3) the culmination and perhaps initial decline of the 

 placentals, the human and domestic species aside. 



The intermigration of the early part of the period was a conse- 

 quence of the land connections, not yet worked out in detail, brought 

 about by deformative movements. The extent of the connection 

 of North America with Eurasia at the northwest and northeast 

 respectively is uncertain, but the evidence of good migratory routes 

 for the land mammals during a portion of the period may be accepted 

 as conclusive. There are also strong hints of the existence of a 

 connection which afforded passage for some species, but not for 

 others. The prohibition was perhaps the increasing cold in the 

 later stages of the period, leading up to the glacial period which 

 followed. The increasing cold, with its effect on intermigration, 

 was perhaps the chief factor in developing the difference between 

 the mammals of the Old World and the New. 



The connection between North and South America introduced 

 a biological movement of dramatic interest. There appears to 

 have been no effective isthmian thoroughfare for land animals be- 

 tween the earliest Eocene and the Pliocene, when a way was opened. 

 During the Eocene connection, a few North American mammals 

 seem to have sent representatives into South America, and these 

 had evolved on distinctive lines in the interval. A remarkable 

 group of sloths, armadillos, and ant-eaters had developed from an 

 edentate stem; strange hoofed animals of orders unknown else- 

 where (Typotheria, Toxodontia, Litopterna) had arisen from some 

 very primitive ungulate form; monkeys of the South American 



