Facultative Biped

A facultative biped is an animal that is capable of walking or running on two legs, often for only a limited period, in spite of normally walking or running on four limbs or more. Well-known examples include many lizards such as the Basilisk lizard, and even some cockroaches when running at top speed. In order to be considered a true facultative biped, an animal must be capable of sustained movement over many strides while bipedal – simply adopting a static bipedal posture while resting or looking around is not sufficient.