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.

Non-standard tripedal gaits are also observed in primates when they use one limb to grasp an object.

Quadrupedal amputees and mutations

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