I.

Introduction

Beaver, semi-aquatic mammal noted for the building of dams. One species of beaver occurs in Eurasia, the other in North America. The two species differ chiefly in the shape of the nasal bones and are so much alike that some authorities consider them to be varieties of the same species. They are large rodents; an average adult beaver weighs about 16 kg (35 lb), but specimens as heavy as 40 kg (90 lb) have been found, and some extinct beavers were almost as large as bears.