I 



III.] RELATIONS OF THE FAUNA. 119 



the middle portion of the Tertiary epoch 1 . When the connection 

 between North and South America was completed is not precisely 

 fixed by geological evidence ; but the occurrence of a glyptodont 

 in the Nebraska stage of the Loup-Fork group, shows that it must 

 have been by the end of the Miocene 2 . The question of a con- 

 nection between the two continents by way of the West Indies 

 is discussed later in this chapter, where it is concluded that if 

 such a connection existed at all, it must have been of a transient 

 nature. 



Having thus shown, both from palaeontological and geological 

 evidence, that the early mammalian fauna of 



Incursion of 



Neogaea appears to have been totally isolated from Northern 

 that of North America up to about the end of the 

 Miocene, the question of the origin of that fauna may be deferred, 

 and the irruption of northern types after the connection between 

 North and South America had been established taken into con- 

 sideration. It may be mentioned, however, that it was not till 

 after this irruption of the northern forms that the essentially 

 Neogaeic fauna attained its maximum development in respect to 

 the bodily size of its constituents ; since a gradual increase in this 

 respect maybe traced from the small glyptodonts and sloths of the 

 Santa Cruz epoch, through the larger ones of the Monte Hermoso 

 horizon, to the gigantic forms characteristic of the Pampean and 

 the cavern deposits of Brazil. 



The presence of a glyptodont in the Nebraska stage of the 

 Loup-Fork group in North America, and of northern forms in the 

 Monte Hermoso horizon of South America, marks, then, the first 

 commingling of the original faunas of the two halves of the New 

 World. For the first time in the history of the southern continent 

 this connection allowed of the immigration from the north of the 

 true Carnivora, such as the existing cats (Felts) the extinct sabre- 

 toothed tigers (Macharodus), dogs and foxes (Canida), bears 

 (Ursus and Arctotherium\ raccoons (Procyonidtz), skunks and 

 their allies (Mustetida), together with various ungulates belonging 

 to sub-orders previously unknown in the realm. These latter 

 include the guanaco and vicuna (Lama] of which ancestral forms 



1 See J. W. Gregory, Quart. Joum. GeoL Soc. Vol. LI. pp. 299, 300 (1895). 



2 As stated above, many refer the whole Loup-Fork group to the Miocene. 



