258 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1952 



distribution of the woolly mammoth, outstandingly an inhabitant of 

 this zone. The various musk oxen generally preferred the open 

 tundra ; in contrast, the mastodon and moose inhabited the subarctic 

 forest. 



It is well known that many of the large mammals that inhabited 

 northern North America during Pleistocene ages were immigrants 

 from northern Asia via the Bering Strait bridge. The strait is both 

 narrow and shallow. It could have become land at one or more times 

 as a result of a moderate lowering of sea level, such as is known to have 

 occurred during each glacial age when water was abstracted from the 

 sea to build the great terrestrial glaciers. A slight warping of the 

 earth's crust in the Alaska-Siberia region could also have converted 

 this shallow strait into land. However the land bridge may have 

 been made, there is little doubt that it existed and that over it moved a 

 varied fauna into Arctic North America. The arctic region therefore 

 was the corridor through which Asiatic mammals entered the New 

 World. 



In contrast with mammals on the lands, the vertebrate life in North 

 American Arctic waters does not seem to have undergone conspicuous 

 changes, probably because temperatures were fairly low during the 

 interglacial as well as the glacial ages. The chief differences thus far 

 noted consist of slight changes in postglacial faunal assemblages. 

 These changes are attributable to increased salinity of the sea water, 

 as dilution with glacial meltwater diminished, and to decreased depth, 

 as continuing crustal uplift elevated the sea floors (Richards, 1937). 



Among the mammals that crossed from Asia into North America 

 via the Bering Strait bridge was man. He came in several, perhaps 

 many, groups, over a considerable period of time. Very likely he 

 followed some of the migrating game animals as a hunter. 



Just where, or through how long a time, the diffusion of people 

 from Asia into Arctic North America took place, is not known. It 

 has been established that man was well settled in southern North 

 America at the time when the Mankato expansion of the Laurentide 

 Ice Sheet reached its maximum, roughly 10,000 years age. But how 

 long he had been there is still a question. When that question is an- 

 swered, and when the climatic and ecological circumstances of the 

 whole immigration become known, the arctic region will undoubtedly 

 assume a new and important perspective in the history of man in 

 America. 



