Facultative biped

From Wikipedia, the free encyclopedia
Jump to: navigation, search

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]


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]


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]


  1. ^ 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. 
  2. ^ 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. 
  3. ^ 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. 
  4. ^ 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. 
  5. ^ 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. 
  6. ^ 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.