Hippopotamidea

Definition: The Family Hippopotamidea includes two species of hippos (the hippopotamus and the pigmy hippopotamus) both of which lead semi-aquatic lives. Hippos have webbed feet, short legs, a large head and wide-spreading jaws. Their body density is well-suited for living in water, enabling them to easily sink lightly to the bottom of a pond or stream and, when their lungs are filled with air, float just beneath the surface of the water. Whales and hippos are thought to be more-closely related than hippos and other even-toed hoofed mammals.