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.<ref name="constraints">Tracy J. Thomson (2019) Three‐Legged Locomotion and the Constraints on Limb Number: Why Tripeds Don’t Have a Leg to Stand On, ''BioEssays'' 41 (10): 1900061 https://doi.org/10.1002/bies.201900061</ref>

==In nature== [[File:ClimbingCockatiel.jpg|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.<ref name="forbidden phenotype"></ref> They generate propulsive and tangential forces equal to or greater than those of forelimbs in non-human primates when climbing vertical surfaces.<ref name="forbidden phenotype">Melody W. Young, Edwin Dickinson, Nicholas D. Flaim and Michael C. Granatosky (2022). Overcoming a ‘forbidden phenotype’: the parrot’s head supports, propels and powers tripedal locomotion, ''Proceedings of the Royal Society B: Biological Sciences'', 20220245, https://doi.org/10.1098/rspb.2022.0245</ref>

Non-standard tripedal gaits are also observed in primates when they use one limb to grasp an object.<ref>{{cite journal |doi=10.1007/BF02381373 |title=Standardized descriptions of primate locomotor and postural modes |journal=Primates |volume=37 |issue=4 |pages=363–387 |year=1996 |last1=Hunt |first1=Kevin D. |last2=Cant |first2=John G. H. |last3=Gebo |first3=Daniel L. |last4=Rose |first4=Michael D. |last5=Walker |first5=Suzanne E. |last6=Youlatos |first6=Dionisios |s2cid=37235291 }}</ref>

==Quadrupedal amputees and mutations== [[File:Three-legged-dog sheila 32nd day past amputation.jpg|thumb|Health consequences vary depending on which limb was lost, with hind legs being less consequential of a loss than front legs in quadrupeds like dogs]] There are some three-legged creatures in the world today, namely four-legged animals (such as pet dogs and cats) which have had one limb amputated. Animals made into tripeds through amputation may suffer from long term health consequences; these issues include osteoarthritis and spinal deformity and are largely a result of disruption to natural locomotion cycles and symmetry.<ref>{{Cite web |last=jerry |date=2020-03-25 |title=Osteoarthritis Problems in Three Legged Dogs |url=https://tripawds.com/2020/03/25/osteoarthritis-problems-in-three-legged-dogs/ |access-date=2025-05-22 |website=Tripawds |language=en-US}}</ref>

There are also cases of mutations or birth abnormalities in animals (including humans) which have resulted in three legs. With humans, a third limb may arise from the surgical bisection of conjoined or parasitic twins. Such conditions will often result in a limb with reduced or limited mobility. In rarer cases such as with Frank Lentini, a third limb may be usable in activities requiring moderate motor function, such as kicking a football, but will still lack the fine motor skills of the natural limbs.<ref>{{Cite web |title=Frank Lentini {{!}} English version |url=http://www.franklentini.it/english-version.html |access-date=2025-05-22 |website=www.franklentini.it}}</ref>

==See also== * Bipedalism * Quadrupedalism * Terrestrial locomotion * Tetrapod * {{annotated link|Three-legged crow}} * Uniped

==References== {{Reflist}}

Category:Ethology Category:Terrestrial locomotion Category:Animal anatomy Pedalism