The largest group of two-legged animal are birds, but there are a number of bipedal mammals as well, including many primates, kangaroos, wallabies and kangaroo rats. Many dinosaurs were bipedal, and several lizards can become bipedal when sprinting, including the green basilisk lizard, which can actually sprint across water for short bursts, though their normal method of locomotion is quadrupedal.
While many animals can stand upright for short periods of time, the ability to walk upright is unusual, but there are many benefits to bipedal locomotion. Walking upright allows creatures to carry objects as they go, gives a greater visual range in tall grass and allows for wading while foraging for aquatic foods. Walking upright also exposes less body surface to the sun's damaging rays and expends less energy than quadrupedal locomotion. All apes have the capacity to walk upright, though many, such as chimpanzees and gorillas, are more typically knuckle-walkers. According to Earthmagazine.org, there is controversy among anthropologists about whether humans and apes developed from a common knuckle-walking ancestor or whether humans evolved from tree-dwelling primates. Bipedalism in birds is a trait inherited from their dinosaur ancestors, a group known as theropods. The ability of birds to walk on two legs, along with other adaptations, allowed for the development of wings and flight.