Biped
a descriptive term, sometimes applied to man, but more frequently to birds. It may be used in two ways- (a) in reference to habit only (physiological), when animals use only their two hind limbs for moving along the ground-e. g., man, kangaroo, bird; (b) in reference to anatomy (morphology), when the typical number of four limbs is reduced to two. Thus among mammals the order of whales (cetacea) is marked by the absence of hind limbs; among birds the fore limbs are considerably reduced in the running birds of the ostrich sub-class, and especially in the New Zealand kiwi (apteryx); among reptiles, some serpents (e. g., pythons), retain traces of hind legs, while all the others have lost both pairs, and a few lizards have either only hind feet (pseudopus, ophiodes), or only fore feet (chirotes); among amphibians, a few (e. g., siren) have only fore feet; and the same is true of numerous fishes (e. g., among siluridæ), and especially of those which live to a large extent in mud.