The beaver is the largest North American rodent. It spends a whole lot of its time acquiring and cutting wood. Some would say that it has been perfectly adapted to its function and aquatic environment. For one thing, its nose and ear valves shut as the animal submerges and nictitating membranes serve as goggles to protect the eyes from irritation.
Additionally, its lips are located behind its teeth so that it can carry branches around without drowning. With their strong jaws and teeth, beavers can chew through a six-inch tree in 15 minutes. A single beaver can chew down hundreds of trees each year.