tripedalism

Tripedalism (from the Latin tri = three + ped = foot) is locomotion by the use of three limbs. Real-world tripedalism is rare, in contrast to the common bipedalism of two-legged animals and quadrupedalism of four-legged animals. Bilateral symmetry seems to have become entrenched very early in evolution, appearing even before appendages like legs, fins or flippers had evolved.

==In nature== thumb|Male cockatiel climbing from a log to a ladder using his beak Parrots (birds of the order Psittaciformes) are the only creatures to naturally use tripedal forms of locomotion, as they use their heads as a third limb when climbing. They generate propulsive and tangential forces equal to or greater than those of forelimbs in non-human primates when climbing vertical surfaces.