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Beaver, semiaquatic mammal noted for the building of dams. One species of beaver occurs in North America, the other in Eurasia. 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 ....

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.... the muscles that work the jaws. The two front teeth on either jaw are like those of other rodents, wearing away more rapidly behind so as to leave a sharp, enameled chisel edge. With these can cut down large trees. It usually selects trees 5 to 20 cm (2 to 8 in) in diameter, but it can fell trees with diameters as large as 76 cm (30 in). Beavers have a pair of anal scent glands, called castors, that secrete a musklike substance called castoreum, probably for marking territories. The animals tend to be monogamous and may live 20 years or more. The female has one litter a year, usually of two to four young. Beavers are social animals. In areas wher ....