An animal with two feet is called a biped. The word comes from Latin, and the equivalent term for an animal with four feet is "quadruped."
While many animals can support themselves on their hind legs for short periods of time, bipedalism as a primary form of locomotion is rare in the animal kingdom. Humans, members of the kangaroo family, springhares, kangaroo rats and several kinds of apes all use bipedal locomotion. Fossil evidence shows that a large number of dinosaurs were bipeds. While all birds are technically bipeds, only flightless birds, such as ostriches and cassowaries, use walking or running as their primary form of locomotion.