120 OBIGIN OF LIFE IN AMERICA 



by the formation of a series of lake, river and flood -plain 

 basins, filled with volcanic and erosion sediments. During 

 the first faunal phase of the Eocene Period a land connec- 

 tion with South America seems to be indicated by the occur- 

 rence of similar mammals in the upper Cretaceous or basal 

 Eocene of Patagonia. Additional evidence of South American 

 connection is afforded by the subsequent occurrence of animals 

 related to the Edentata-Dasypoda in the American middle 

 Eocene. A momentous change occurs, according to Professor 

 Osborn, during the second faunal phase of the Eocene. 

 Similar faunas appear almost simultaneously in south -western 

 North America and in western Europe. In Professor 

 Osborn's * judgment this remarkable circumstance is due to 

 the gradual southward extension of the fauna from a hypo- 

 thetical northerly American- Asiatic land mass. 



Not a single specimen of an Eocene mammal has been dis- 

 covered in northern Asia or the northern parts of North 

 America. Professor Osborn and many other authorities 

 assume the Eocene existence of a great American- Asiatic 

 land mass, because large tracts of land in the north certainly 

 are very ancient, and must have been raised above the sea in 

 Eocene times. That is about all the evidence we possess 

 for the belief that the great similarity of the western European 

 and western North American fauna during the Eocene Period 

 was due to some land connection via northern Asia and 

 northern North America. 



I should prefer to throw my hypothetical land bridge 

 straight across the Atlantic from western Europe 'to North 

 America. In another chapter I shall endeavour to show that 

 we possess important zoogeographical evidence for the belief 

 in such a transatlantic bridge in Eocene times. Professor 

 Schlosserf contends that geological researches are alone 

 capable of yielding information about former land connec- 

 tions. He does not believe that much weight can be attached 

 to ancient reconstructions of continents based on zoogeo- 

 graphical or distributional data. I hold, on the contrary, that 

 since certain old groups of animals, even genera and species, 



* Osborn, H. F., " Cenozoic Mammal Horizons," pp. 19 35. 



t Schlosser, M., "Uber Tullberg's System der Nagetiere," p. 748. 



