Bipedalism refers to locomoting (e.g., walking, jogging, running, etc.) on 2 legs. It is not uncommon to see animals standing or walking on 2 legs, but only a few animals practice bipedalism as their usual means of locomotion. Animals, including chimpanzees and gorillas, that assume bipedalism on a temporary basis in order to perform a particular function practice a form of locomotion called facultative bipedalism. For example, octopodes sometime walk bipedally in order to camouflage themselves from predators1. The octopus piles 6 of its 8 limbs on top of its head, assuming the shape of a drifting plant, and then uses the 2 remaining limbs to quite literally walk away. As for quadrupeds (animals that
move on four limbs), it is not uncommon to see antelope standing on their 2 hind limbs while supporting themselves on their forelimbs when reaching for food in high branches. Chimpanzees have been documented walking on 2 legs in order to carry things with their hands.
Habitual bipedalism, or obligate bipedalism, is rare. This is the form of bipedalism that is assumed as a regular (i.e., habitual) means of locomotion. Today, very few mammals (e.g., humans and kangaroos) demonstrate habitual bipedalism. However, many early hominins (i.e., a classification term that includes modern humans and all their bipedal fossil relatives) show a combination of primitive and novel adaptations that suggest these species utilized bipedalism but still engaged in arboreal behaviors.
