70 THE AGE OF MAMMALS 



Hypothesis of Africa as an evolution center. — The opposing view of the 

 invasion of Europe from Africa was independently thought out and set forth 

 by three authors in 1899-1900, namely, by Tulll)erg in his monograph on the 

 rodents,' by Stehlin in his monograph on the teeth of the pig family," and by 

 Osborn.^ 



Tullberg, as directly opposed to Haacke, is a strong believer in a great 

 southerly center of distribution, and stands, like Riitimeyer, as an advocate 

 of the bipolar theory. Thus he remarks (pp. 490-491) : 



"In the Miocene the great African region sent its heterogeneous fauna into 

 Asia by way of Syria or Arabia. In this way Eurasia received together with typical 

 (southwest) African types, others of Asiatic origin that had become differentiated 

 from their ancestral forms, in the Madagascar-East-African region. Among the 

 latter may be counted the Cavicornia, which, though a product of Africa, were 

 most likely originally derived from northern Artiodactyla. The Simla?, Proboscidea, 

 and the rodent Hystricognathi are probably purely African types whose first ap- 

 pearance in Eurasia followed the Miocene migration." When the Placentalia first 

 appear they have already undergone a considerable differentiation, and since they 

 sprang neither from the Marsupialia nor from the Monotremata, we must assume 

 that they went through the early undiscovered stages of their evolution in some 

 great geographic region (other than Australia) ; this region is presumably the great 

 southerly continent embracing South America and Africa and reaching over to 

 India by way of Madagascar with a broad tongue of land (the Lemuria and Gond- 

 wana Land of other authors) . Three great mammalian groups had already evolved : 

 (1) the ancestors of the Lemuroidea and Anthropoidea; (2) the ancestors of the 

 Ungulata; (3) the ancestors of the Rodentia-Simplicidentata. These stocks segre- 

 gated off into two great divisions : one, East-Africa-Madagascar-Europe-Asia-North- 

 America, the other Southwest-Africa-South-America. In the beginning of the Age 

 of Mammals, Africa became separated from South America; in the Lower Oligo- 

 cene (p. 488) Madagascar separated both from Asia (India) and from Africa. At 

 the same time, however, the east African region joined with the southwest African 

 region and an interchange of mammals took place. 



Stehlin's views (p. 478) are still more closely parallel to those independ- 

 ently developed by Osborn, as the following citation from his monograph ^ 

 shows : 



"Africa's part in the evolution of the animal life of the globe (p. 478) has 

 generally been represented as very passive, but the mere fact that Africa was a 

 large continental landraass during the entire Tertiary makes this view seem unten- 

 able. Among the living mammals of Africa there are a number of types such as 

 the coney (Hyrax), the aardvark (Oryderopus), and the pangolin (Manis), which 

 differ so widely from any Tertiary Asiatic or European forms, that the conclusion 



1 Tullberg, T., tjber das System der Nagethiere, 1899, pp. 485-495. 



2 Stehlin, H. G., Uber die Geschichte des Suiden-Gebisses, 1899-1900, pp. 478-488. 



' Osborn, H. F., Faunal Relations of Europe and America during the Tertiary Period 

 and Theory of the Successive Invasions of an African Fauna into Europe, 1900, pp. 56-59. 



