120 
ORIGIN 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 
Schlosser f 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, II. F., “ Cenozoic Mammal Horizons,” pp. 19 — 35. 
| Schlosser, M., “ Ubcr Tullberg’s System tier Nagetiere,” p. 74S. 
