North American Beaver
It serves as a rudder (its webbed hind feet give it propulsion).
It serves as a support when it is up on its hind legs, either while it is gnawing or while it moves material around with its front feet.
It serves as a warning in the case of danger. It dives while hitting the water very hard, thus alerting the predator and warning its family to seek shelter.
It is its energy reserve, as it accumulates fat.