304 THE AGE OF MAMMALS 



climax in the temporary unification into one grand zoo- 

 logical region of all the great continents, excepting Australia. This 

 somewhat extreme statement may be made for the sake of emphasis, but 

 it is well within the bounds of truth to say that never before or since in 

 geologic time has the mammalian life of the globe enjoyed such a wide- 

 spread and uniform distribution as during closing Miocene and Pliocene 

 times. 



VI. SIXTH FAUNAL PHASE. — PLIOCENE TO MIDDLE PLEISTO- 

 CENE MODERNIZATION. INTERCHANGE AND WIDE DISTRI- 

 BUTION OF CERTAIN MIGRATING MAMMALS IN AFRICA, 

 EURASIA, AND NORTH AMERICA. SECOND ENTRANCE INTO 

 NORTH AMERICA OF SOUTH AMERICAN MAMMALS. INVA- 

 SION OF SOUTH AMERICA BY MAMMALS OF NORTH AMERI- 

 CAN, ASIATIC, EUROPEAN, AND AFRICAN ORIGIN. CONTINUED 

 INDEPENDENT EVOLUTION OF NON-MIGRATING MAMMALS 

 IN THE NEW AND OLD WORLDS. GRADUAL ADVANCE!" OF 

 MORE TEMPERATE CLIMATIC CONDITIONS IN THE NORTH- 

 ERN HEMISPHERE AND INVASION OF NEW FOREST OR BROWS- 

 ING TYPES FROM THE NORTH. 



I. PLIOCENE LIFE OF EUROPE 



Modernization. — The final modernization of the mammalian life of 

 southern Europe may be said to have commenced at the beginning of the 

 Pliocene, to have continued in the gradual withdrawal of plateau and desert 

 types and in the appearance from the north of new browsing forest and 

 aquatic types, and to have been completed during the glacial stage of the 

 Pleistocene. Contemporaneously with these life changes, the physiography, 

 climate, and flora also gradually assumed their present or modern condi- 

 tion, but only after the great fluctuations of the Pleistocene, or Ice Age. 



While the mammals of the early Pliocene are little knoAvn, the very 

 opening of the epoch is defined by many disappearances caused both by 

 emigration and extinction, whereby Europe lost much of its prevailing south- 

 Asiatic and Ethiopian aspect. The chief animals which had left the 

 country are the giralTes, most of the Asiatic or African antelopes, the two- 

 horned African rhinoceroses, the aardvarks, and the anthropoid apes allied 

 to the gibbon and chimpanzee. There remained only two types of antelopes 

 allied to Oryx and to the gazelle, and the hipparions, which may have re- 

 sembled the zebras in external appearance. 



PalceogeograpMj. — The Pliocene epoch opened with a reversal of the 

 conditions of the Upper Miocene, namely, a contraction of the vast land 

 areas or grazing plateaux of southern Europe, which had been so favorable 



