36 



THE AGE OF MAMMALS 



study. The fundamental suggestion of Sclater to divide the world into 

 eastern (Palseogaea) and western (Neogala) divisions proved, however, to be 

 entirely inconsistent with the facts of past and present distribution. Hux- 

 ley as early as 18G8 had proposed a northerly (Arctogica) and southerly 

 (Notogaea) division, and it became gradually apparent ' that the six great 

 regions should be grouped into larger northern and .southern Realms. 

 Sclater (1874), J. A. Allen (1878), W. T. Blanford (1890), and Alfred 

 Newton (1893), along various lines contributed to the conclusion that 

 there are three such great primary realms based on a north and south divi- 

 sion, namely: Arctogcea, Notogcea, and Neogeva. The regions as embraced 

 in these realms are clearly set forth in the accompanying table. 



Realms 

 Arctog^a 



Regions 



Holardic Region 

 Near otic Region 

 Paloearctic Region 



Ethiopian Region 

 Oriental Region 



Geographic Boundaries 



Europe, Asia, and North America. 



North America north of Mexico. 



Asia, north of the Himalayas, Europe, and 

 Africa north of the Desert of Sahara. 



Africa, south of the Sahara Desert. 



Asia south of the Himalayas, including Su- 

 matra, Java, Borneo, and the Philippines. 



II. NOTOG^A 



III. Neog.ea 



Australian Region Australia. 

 Neotropical Region South America. 



This division into grand zoogeographic Realms and Regions broadly, 

 or in a general way only, conforms to the facts of distribution of mammals 

 in past and present times, and these divisions correspond with the main 

 events during the Age of Mammals, but are not to be understood as being 

 separated either by sharp or continuous barriers. For example, while Neo- 

 gaea, embracing the single Neotropical Region of South America, was 

 during the greater part of the Age of Mammals separate from the other 

 Realms, it shows at the beginning unmistakable proof of connection both 

 with Notogsea (Australia) and with Arctogaea (the northern hemisphere), 

 and toward the close of this Age it shows the most positive evidence of 

 renewed union with Arctogaea through a commingling of the North and 

 South American faunas. 



Realms. — Thus it appears that while these grand Realms were the 

 main centers of the adaptive radiation of the orders of mammals, the orders 

 were not confined to these realms, but during periods of land connection 

 certain members strayed into adjacent realms; that each realm, there- 

 fore, contains a mingling of its original, or autochthonous types and its 



^ The history of opinion on this subject is fully set forth in Lydekker's invaluable work, 

 A Geographical History of Mammals, 1896, chap. i. Additional interesting details are found 

 in R. F. Scharff's History of the European Fauna (1899). 



