112 



THE AGE OF MAMMALS 



//. LOWER EOCENE, SECOND FA UNAL PHASE — FIRST MODERNI- 

 ZATION IN EUROPE AND AMERICA, OR INVASION OF ANCESTORS 

 OF MODERN MAMMALS WHICH MINGLE AND COMPETE WITH 

 ARCHAIC. CLOSE FAUNAE CONNECTION BETWEEN WESTERN 

 EUROPE AND WESTERN NORTH AMERICA. APPARENT BREAK 

 BETWEEN NORTH AND SOUTH AMERICA. INITIAL ELIMINATION 

 OF ARCHAIC IN COMPETITION WITH MODERN MAMMALS. 



European palaeontologist s have usually attril)uted the source of the 

 modern families of the Second Faunal Phase to North America; while 

 this theory is without evidence, it is certain that this fauna originated neither 

 in South America nor in Africa. There remain four possible centers of 



Flu. ol. - ( 'ur\-phoduiita, txpical, larjro niainiiials of the Lowit Eocciio. Tu the hit a 

 coryphodon bull with large tusks ; to the right a cow, with small tusks. After the original by 

 Charles R. Knight in the American Museum of Natural History. ' 



origin, namely: (1) the Great Plains and Atlantic Border region of North 

 America; (2) the more northerly American Mountain Region, that is, 

 British Columbia; (3) the northerly American-Asiatic land mass or northern 

 Holarctica; (4) the northerly Eurasiatic region or northern Palaearctica. 

 Each of these regions was sufficiently large and varied to give origin to a 

 diversified modern fauna, but in the writer's judgment the nearly simul- 

 taneous appearance in western Europe (latitude 50°), and in North America 

 (latitude 40°), favors the fourth hypothesis, namely, that these mammals 

 had been previously developing in the northerly portion of Holarctica, or 

 in the North-American-Asiatic land mass. There was certainly such a 



