Facultative bipedalism

Animal capable of walking or running on two legs in response to exceptional circumstances

A facultative biped is an animal that is capable of walking or running on two legs (bipedal), as a response to exceptional or discretionary (facultative) circumstances, while normally walking or running on four limbs or more. In contrast, obligate bipedalism is where walking or running on two legs is the primary method of locomotion, as occurs in birds and generally in humans. Facultative bipedalism has been observed in several families of lizards and multiple species of primates, including species of sifakas, capuchin monkeys, baboons, gibbons, gorillas, and chimpanzees.

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