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. Low-speed facultative bipedality is less common; the
gibbon, a
primate with an anatomy highly specialized for
arboreal locomotion, can walk bipedally in trees or on the ground with their arms raised for balance.