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Beavers are the largest rodent in North America (Internet3, 2003). They are directly descended from the prehistoric Castoridae, which also included other related rodents that are now extinct. The prehistoric beaver that roamed the earth during the Pleistocene epoch a million years ago was originally gigantic, weighing between 700 and 800 pounds. There are as many as 25 subspecies of the genus Castor, differing in color, size, and range. But today, crossbreeding has made it difficult to differentiate between each species (Rue, 1986). They are primarily nocturnal and are only occasionally seen during the day (Internet2, 2003). To escape a potential predator, a beaver can remain underwater for 15 to 20 minutes (Internet3, 2003). Their tails are one of the defining characteristics of beavers. They are broad and flat with large, blackish scales (Internet2, 2003). They are aquatic animals that have waterproof, rich, glossy, lustrous brown fur, and large, black, webbed feet. They have powerful hind legs used to increase their swimming ability. Beavers have the ability to close their noses and ears while they are swimming underwater. They have a clear eyelid to protect their eyes from the water and debris. Like all rodents, beavers have large central incisors, which are their front teeth, that are always rowing. They must keep them trimmed which is why they gnaw bark (Internet2, 2003). Fur on the upper parts of the body is a rich reddish brown in the winder and darker in the summer. The belly is a pale buff gray. They are stocky in body shape with short legs and have a very wide tail (Internet3, 2003). Sexes are colored a like, and adults may weigh over 40 pounds (Internet1, 2003). The average total length of the beaver is 1,160 millimeters. The tail is usually 400 millimeters, their hind feet are 178 millimeters each, and their weight averages from 18 kilograms to 27 kilograms (Internet4, 2003). Beavers breed only once a year.
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