CHAPTER II 
ANCESTRY; THE GIANT BEAVER; RACES OF THE BEAVER; 
DISTRIBUTION; BEAVER PLAcE NAMES; HISTORICAL 
ANCESTRY 
It is rather difficult to write anything definite concerning 
the ancestry of the beaver, or the genus Castor, of which 
several fossil species have been described in Europe and 
America. Steneofiber, a genus which made its appearance 
shortly before the middle of the Tertiary Period, in the 
Middle Oligocene Epoch of Europe, has been said to be the 
first known ancestor of the beaver. It was about the size 
of a marmot. 
Certain mammals whose remains are found in North 
America in somewhat later formations were at one time 
placed in the genus Séeneofiber, but are now referred to 
other genera, and are, moreover, placed in different families 
from Castor. Steneofiber is therefore not known from 
North America, and if Castor is descended from it, then this 
latter genus is not really a native of this continent, but an 
immigrant from Eurasia via the land bridge across Bering 
Strait. 
Castor first appeared in the Pliocene of Europe. I do not 
know what the forms intermediate between it and Steneo- 
fiber are, but Castor has persisted as a genus to the present 
day. 
An allied genus, Trogontherium of Europe, first appeared 
in the Upper Pliocene, and 7. cuvieri of the Pleistocene was 
about one-fifth larger than the modern beaver. It is 
placed in the family Castoride with the beaver. In the 
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