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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.[1] The switch to facultative bipedalism often occurs when an animal begins to run at high speeds,[2] notably in many lizards, such as the basilisk lizard, and in some cockroaches.[3] 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 its arms raised for balance.[4] Species[edit] Facultative bipedalism occurs in primates, cockroaches, desert rodents, and lizards; specific lizard families known as facultative bipeds are the Agamidae, Crotaphytidae, Iguanidae, and Phrynosomatidae.[2][3] Facultative bipedalism evolved in the common ancestor of most major dinosaur groups, and it arose independently within lizards and mammals.[1][2] Functions[edit] In lizards, facultative bipedalism occurs as a result of rapid acceleration caused by the location of the lizards’ hind legs which induces a friction from the ground to produce a reaction force on the rear legs, effectively creating a turning moment about the lizards center of mass and allowing it to lift off the ground over short distances as a mechanism to evade oncoming predators.[2] In primates, bipedal movements consist of an irregular, shuffling gait, accomplished by rotating the hip and making short steps, which are constrained by wide pelvis shapes and short hind limbs;[5] primates, such as gelada baboons, use bipedalism to free up their hands for feeding or fighting.[6]

v t e

Animal locomotion on land

Gait
Gait
class

Legged

Arboreal locomotion
Arboreal locomotion
(Brachiation) Hand-walking Jumping Knuckle-walking Running Walking

Legless

Concertina movement Undulatory locomotion Rectilinear locomotion Rolling Sidewinding Other modes

Anatomy

Comparative foot morphology Arthropod leg Digitigrade Plantigrade Unguligrade Uniped Biped (Facultative) Triped Quadruped

Specific

Canine gait Horse gait Human gait

Animal locomotion on the surface layer of water Fish locomotion Volant animals

References[edit]

^ a b Persons, W. Scott; Currie, Philip J. (2017-05-07). "The functional origin of dinosaur bipedalism: Cumulative evidence from bipedally inclined reptiles and disinclined mammals". Journal of Theoretical Biology. 420 (Supplement C): 1–7. doi:10.1016/j.jtbi.2017.02.032.  ^ a b c d Schuett, Gordon W.; Reiserer, Randall S.; Earley, Ryan L. (2009-07-01). "The evolution of bipedal postures in varanoid lizards". Biological Journal of the Linnean Society. 97 (3): 652–663. doi:10.1111/j.1095-8312.2009.01227.x. ISSN 0024-4066.  ^ a b Alexander, R. McN. (2004-05-01). "Bipedal animals, and their differences from humans". Journal of Anatomy. 204 (5): 321–330. doi:10.1111/j.0021-8782.2004.00289.x. ISSN 1469-7580.  ^ Preuschoft, Holger (2004-05-01). "Mechanisms for the acquisition of habitual bipedality: are there biomechanical reasons for the acquisition of upright bipedal posture?". Journal of Anatomy. 204 (5): 363–384. doi:10.1111/j.0021-8782.2004.00303.x. ISSN 1469-7580.  ^ O'Neill, Matthew C.; Lee, Leng-Feng; Demes, Brigitte; Thompson, Nathan E.; Larson, Susan G.; Stern, Jack T.; Umberger, Brian R. "Three-dimensional kinematics of the pelvis and hind limbs in chimpanzee ( Pan troglodytes ) and human bipedal walking". Journal of Human Evolution. 86: 32–42. doi:10.1016/j.jhevol.2015.05.012.  ^ Wrangham, R.W. "Bipedal locomotion as a feeding adaptation in gelada baboons, and its implications for hominid evolution". Journal of Human Evolution. 9 (4): 329–331. doi:10.1016/0047-2484(80)90059-7. 

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