Beaver

Beaver, large rodent (family Castoridae), weighing up to 100 lb (45 kg) or over, of northern lands. Beavers have thick, furry waterproof coats, powerful, web-footed hindlegs, and small forelimbs with dexterous, sensitive paws. Although lissencephalic (smooth-brained), they are the most intelligent rodents, building dams and lodges (domes up to 23 ft/7 m in diameter, in which they live) from logs and mud. They use their powerful incisor teeth to fell trees and gnaw logs into shape. Their large, heavy tails are used on land for balance and in the water as rudders. Their respiratory system enables them to remain underwater for up to 15 minutes.