64 ORIGIN OF LIFE IN AMERICA 



case, the presence of flying squirrels in America seems to be 

 due to a migration from Asia, and that this took place at a 

 time when a land bridge existed between the two continents 

 is evident. 



The musk rat (Fiber zibethicus) * derives its popular fame 

 chiefly from the fact that thousands of its skins are annually, 

 exported from North America by the fur traders. Having 

 adopted the more attractive name of "musquash" for these 

 skins, the dealers have no difficulty in disposing of them. Like 

 beavers, these creatures inhabit subterranean burrows on the 

 banks of lakes and streams, and are expert swimmers, yet they 

 are really more allied to the voles. Varieties of the common 

 musk rat are met with from the Mackenzie River to Labrador 

 and southward as far as New Mexico. In the Yukon district 

 and westward Fiber spathulatus replaces the common musk 

 rat; and far to the east in Newfoundland the district dusky 

 musk rat (Fiber obscurus) occurs. Only two other living 

 kinds of musk rat are known to science. One of them 

 inhabits the State of Oregon, the other the dismal swamp 

 in Virginia. This genus, therefore, is one of the most 

 typically North American we have noticed so far, and no 

 doubt it has originated in North America. This view is 

 entirely confirmed by fossil evidence, for no musk rat 

 remains are known outside North America. The common 

 musk rat has been observed in the Pleistocene deposits 

 of South Carolina, New Jersey, and Pennsylvania, while 

 the jaw of an extinct species (Fiber annectens) has been 

 found by Mr. Barnum Brown f in the Conard fissure of 

 Arkansas. The remarkable circumstance about this jaw is 

 that the teeth it contains strongly resemble those of Neofiber, 

 a sub-genus of Microtus. Hence this cave species forms a 

 connecting link between the genera Fiber and Microtus, and 

 this fact supports the opinion I ventured to put forward 

 (p. 29) as to the American origin of the latter. 



Before describing some of the other small beasts, I must 

 refer now to an animal which is not only the largest living 

 terrestrial American mammal, but likewise one that we, from 



* Hollister, T$., " Synopsis of Muskrats." 



f Brown, Barnum, "Conard Fissure," p. 197. 



