Bipedalism is the term which describes creatures who travel on two legs. When considering the criteria for this term, humans are probably the first examples which come to mind. There are, however, other creatures who qualify as bipeds. Although four legs is the norm within the animal kingdom, there are a few distinct members of the animal kingdom who get around on only two legs.
Although they possess four legs, kangaroos regularly stand and walk on only two. Their long tail is thick and powerful, and assists them with balance. There are times when these marsupials drop onto four legs when eating, but their standing and walking is done on their two hind legs.
Birds have two modes of transportation - flying and walking. When walking, they are among the creatures who walk on two feet. They also use their status as bipeds for landing and gaining proximity to food.
Dinosaurs are no longer among us, but the Tyrannosaurus Rex, the Deinonychus, and the Velociraptor were three carnivorous creatures who roamed the earth on their two hind legs. Ancient footprints further support the theory of bipedal dinosaurs. These prints suggest that bipedal dinosaurs walked in the same manner that birds do: by putting one foot in front of the other, with their toes turned slightly inward. Anthropologists believe that walking upright was a more efficient way for dinosaurs to get around.
Apes, monkeys, gibbons, baboons, chimpanzees, and gorillas are primates who have four appendages but who walk on just two. These animals are able to stand upright and not use their arms to support their body weight. Not all of their travel time is spent on two legs, but primates are able to walk upright for short periods.
Some lizards, believed to be descendants of the dinosaur, are able to assume bipedal postures when running. Dragon lizards, which are found in the Australian outback, for example, routinely walk around on all four of their legs, but when they burst into a high rate of speed while running, these reptiles rise up onto their hind legs, resembling miniature dinosaurs. Their forelimbs are lifted from the ground and their trunk becomes elevated. Only their two back limbs are used to power their movement. This sudden need for speed is associated with the need to escape predators and to obtain prey.