430 THE AGE OF MAMMALS 



between the two continents was interrupted. It is natural to suppose that 

 the hon, hyaena, hippopotamus, now so characteristic of Africa, entered 

 Europe from this North African region, but it appears quite as probable 

 that these animals, all of which occur in the Upper Pliocene of Asia (p. 321), 

 are of Asiatic rather than of African origin. If we adopt this Asiatic theory, 

 we must suppose that during Pliocene times Africa and southern Asia had 

 a great mammalian fauna in common. 



The theory of the relative isolation of Africa from Europe in Quaternary 

 times originated with Pomel ^ as a result of his exhaustive review of the 

 entire fauna of North Africa. He concludes that since the resemblances 

 between the European and North African Quaternary faunas are rare and 

 often doubtful, the two continents were separated by the Mediterranean 

 Sea and Straits of Gibraltar then as now. 



Climate. — Wliile in Europe the alternating glacial and inter-glacial 

 epochs caused extensive migrations and changes of fauna, Africa was out 

 of the reach of these vicissitudes. It seems well established ^ that after 

 Upper Pliocene times Algeria enjoyed a sub-tropical climate, characterized 

 by abruptly alternating dry and rainy seasons. At the beginning of the 

 Quaternary Period ^ North Africa was probably characterized by excessive 

 rainfall which led to the formation of great alluvial or river and flood plain 

 depositions in the Barbary and Sahara regions. 



At this time the mammalian fauna of North Africa, with the exception 

 of some peculiarly Eurasiatic forms (such as the bear, deer, wild boar, and 

 wild sheep) and certain American types (such as the camels), was closely 

 similar to the grand plateau life of equatorial Africa at the present time, 

 including elephants, rhinoceroses, zebras, wild asses, giraffes, wild cattle, 

 buffalo, antelopes, gazelles, gnus, elands, hippopotami, wart hogs, lions, 

 and hyaenas. The presence of these animals is consistent with the climatic 

 theory of sub-tropical temperature and alternating dry and rainy seasons. 



Various indications point to increasingly long periods of drought and 

 progressive secular desiccation of this great region as the Pleistocene ad- 

 vanced, resulting in the partial extinction and partial migration of the great 

 equatorial life to central and southern Africa. The bear, as a characteristic 

 forest dweller, also became extinct, while the deer, wild sheep, wild boar, 

 and smaller mammals of European type survived to establish for this region 

 its present affinity with Europe. 



Sources of African life. — It is premature to attempt to establish the 

 sources of all the various members of this imposing assemblage of mammals ; 

 there remains always a great element of doubt which can be eliminated only 



1 Pomel, A., Les Elephants Quaternaires. Carte Geol. Algerie, Paleont. Monogr., Algiers- 

 1895. 



* Lamothe, Le Climat de I'Afrique du Nord pendant le Pliocene superieur et le Pleisto, 

 c^ne. C. R. Congr. Geol. Internal., Sess. X, Mexico, 1906, Vol. I, 1907, pp. 341-347. 



' Pomel, A., Les Elephants Quaternaires. Carle Geol. Algerie, Paleont. Monogr., Algiers, 

 1S95, p. 39. 



