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, N., “Synopsis of Muskrats.” 
f Brown, Barnum, “ Conard Fissure,” p. 197. 
