Editing Bipedalism (section)

==Bipedal animals==
The great majority of living terrestrial vertebrates are quadrupeds, with bipedalism exhibited by only a handful of living groups. Humans, gibbons and large birds [[walking|walk]] by raising one foot at a time. On the other hand, most macropods, smaller birds, lemurs and bipedal rodents move by hopping on both legs simultaneously. [[Tree kangaroo]]s are able to walk or hop, most commonly alternating feet when moving arboreally and hopping on both feet simultaneously when on the ground.

===Extant reptiles===
Many species of [[lizards]] become bipedal during high-speed, sprint locomotion,<ref name=":0" /> including the world's fastest lizard, the spiny-tailed iguana (genus ''[[Ctenosaura]]'').

====Early reptiles and lizards====
The first known biped is the [[bolosaurid]] ''[[Eudibamus]]'' whose fossils date from 290 million years ago.<ref>{{Cite news |title=Upright lizard leaves dinosaur standing |date=2000-11-03 |work=cnn.com |access-date=2007-10-17 |url=http://archives.cnn.com/2000/NATURE/11/03/germany.dinosaur/index.html |archive-url=https://web.archive.org/web/20071031005956/http://archives.cnn.com/2000/NATURE/11/03/germany.dinosaur/index.html <!-- Bot retrieved archive --> |archive-date=2007-10-31}}</ref><ref>
{{Cite journal |author=Berman, David S. |title=Early Permian Bipedal Reptile |journal=[[Science (journal)|Science]] |year=2000 |volume=290 |issue=5493| pages=969–972 |doi=10.1126/science.290.5493.969 |pmid=11062126 |bibcode=2000Sci...290..969B |display-authors=etal }}</ref> Its long hind-legs, short forelegs, and distinctive joints all suggest bipedalism. The species became extinct in the [[Cisuralian|early Permian]].

===Archosaurs (includes crocodilians and dinosaurs)===

====Birds====
All [[birds]] are bipeds, as is the case for all [[theropod]] [[dinosaurs]]. However, [[hoatzin]] chicks have claws on their wings which they use for climbing.

====Other archosaurs====
Bipedalism evolved more than once in [[archosaurs]], the group that includes both dinosaurs and [[crocodilia]]ns.<ref>{{Cite journal |title=The evolution of locomotion in archosaurs |last=Hutchinson |first=J. R.| journal=Comptes Rendus Palevol |volume=5 |issue=3–4 |year=2006 |pages=519–530 |doi=10.1016/j.crpv.2005.09.002 |bibcode=2006CRPal...5..519H |url=http://doc.rero.ch/record/15518/files/PAL_E2922.pdf}}</ref> All dinosaurs are thought to be descended from a fully bipedal ancestor, perhaps similar to ''[[Eoraptor]]''.

Dinosaurs diverged from their [[archosaur]] ancestors approximately 230 million years ago during the Middle to Late [[Triassic]] period, roughly 20 million years after the [[Permian-Triassic extinction event]] wiped out an estimated 95 percent of all life on Earth.<ref>{{cite web |author=Penn State |title=Global Warming Led To Atmospheric Hydrogen Sulfide And Permian Extinction |website=ScienceDaily |date=1 March 2005 |url=https://www.sciencedaily.com/releases/2005/02/050223130549.htm |url-status=live |archive-url=https://web.archive.org/web/20110605025707/http://www.sciencedaily.com/releases/2005/02/050223130549.htm|archive-date=2011-06-05}}</ref><ref>{{cite web |title=The Day The Earth Nearly Died – programme summary |website=Science & Nature > TV & Radio Follow-up |publisher=BBC |url=http://www.bbc.co.uk/science/horizon/2002/dayearthdied.shtml |url-status=live |archive-url=https://web.archive.org/web/20120901070225/http://www.bbc.co.uk/science/horizon/2002/dayearthdied.shtml|archive-date=2012-09-01}}</ref> [[Radiometric dating]] of fossils from the early dinosaur [[genus]] ''[[Eoraptor]]'' establishes its presence in the fossil record at this time. Paleontologists suspect ''Eoraptor'' resembles the [[Common descent|common ancestor]] of all dinosaurs;<ref>Hayward, T. (1997). The First Dinosaurs. ''Dinosaur Cards''. Orbis Publishing Ltd. D36040612.</ref> if this is true, its traits suggest that the first dinosaurs were small, bipedal predators.<ref>{{Cite journal |last=Sereno |first=Paul C. |author2=Catherine A. Forster |author3=Raymond R. Rogers |author4=Alfredo M. Monetta |date=January 1993 |title=Primitive dinosaur skeleton from Argentina and the early evolution of Dinosauria |journal=Nature |volume=361 |issue=6407 |pages=64–66 |bibcode=1993Natur.361...64S |doi=10.1038/361064a0 |s2cid=4270484}}</ref> The discovery of primitive, dinosaur-like ornithodirans such as ''[[Marasuchus]]'' and ''[[Lagerpeton]]'' in [[Argentina|Argentinian]] [[Middle Triassic]] strata supports this view; analysis of recovered fossils suggests that these animals were indeed small, bipedal predators.

Bipedal movement also re-evolved in a number of other [[dinosaur]] lineages such as the [[Iguanodontia|iguanodonts]]. Some extinct members of [[Pseudosuchia]], a sister group to the avemetatarsalians (the group including dinosaurs and relatives), also evolved bipedal forms – a poposauroid from the [[Triassic]], ''[[Effigia okeeffeae]]'', is thought to have been bipedal.<ref>{{Cite magazine |last=Handwerk| first=Brian |title=Dino-Era Fossil Reveals Two-Footed Croc Relative |magazine=[[National Geographic Magazine|National Geographic]] |url=http://news.nationalgeographic.com/news/2006/01/0125_060125_crocodile.html |date=2006-01-26 |access-date=2007-10-29 |url-status=dead |archive-date=2007-10-31 |archive-url=https://web.archive.org/web/20071031013504/http://news.nationalgeographic.com/news/2006/01/0125_060125_crocodile.html}}</ref> [[Pterosaur]]s were previously thought to have been bipedal, but recent trackways have all shown quadrupedal locomotion.

===Mammals===
A number of groups of extant mammals have independently evolved bipedalism as their main form of locomotion{{snd}} for example, humans, [[ground pangolin]]s, the extinct [[Megatheriidae|giant ground sloths]], numerous species of jumping [[rodent]]s and [[Macropodidae|macropod]]s. Humans, as their bipedalism has been extensively studied, are documented in the next section. Macropods are believed to have evolved bipedal hopping only once in their evolution, at some time no later than 45 million years ago.<ref name="Burk 1998">{{Cite journal |last=Burk |first=Angela |author2=Michael Westerman|author3=Mark Springer |date=September 1988 |title=The Phylogenetic Position of the Musky Rat-Kangaroo and the Evolution of Bipedal Hopping in Kangaroos (Macropodidae: Diprotodontia) |journal=Systematic Biology |volume=47 |issue=3 |pages=457–474 |pmid=12066687 |doi=10.1080/106351598260824 |doi-access=free}}</ref>

Bipedal movement is less common among [[mammal]]s, most of which are [[quadruped]]al. All primates possess some bipedal ability, though most species primarily use quadrupedal locomotion on land. Primates aside, the [[Macropodidae|macropod]]s (kangaroos, wallabies and their relatives), [[Dipodomyinae|kangaroo rats and mice]], [[Hopping mouse|hopping mice]] and [[springhare]] move bipedally by hopping. Very few non-primate mammals commonly move bipedally with an alternating leg gait. Exceptions are the [[ground pangolin]] and in some circumstances the [[tree kangaroo]].<ref>{{Cite journal |url=http://blogs.scientificamerican.com/tetrapod-zoology/2011/10/17/tree-kangaroos-come-first/ |title=A new Pleistocene tree-kangaroo (Diprotodontia: Macropodidae) from the Nullarbor Plain of south-central Australia |journal=Journal of Vertebrate Paleontology |volume=28 |issue=2 |pages=463–478 |access-date=2011-10-18 |url-status=live |archive-url=https://web.archive.org/web/20111019101553/http://blogs.scientificamerican.com/tetrapod-zoology/2011/10/17/tree-kangaroos-come-first/ |archive-date=2011-10-19 |doi=10.1671/0272-4634(2008)28[463:ANPTDM]2.0.CO;2 |year=2008 |last1=Prideaux |first1=Gavin J. |last2=Warburton |first2=Natalie M.|s2cid=84129882 }}</ref> One black bear, [[Pedals (bear)|Pedals]], became famous locally and on the internet for having a frequent bipedal gait, although this is attributed to injuries on the bear's front paws. A two-legged fox was filmed in a [[Derbyshire]] garden in 2023, most likely having been born that way.<ref>{{Cite news |date=2023-01-05 |title=Two-legged fox is nature conquering all, says wildlife expert |language=en-GB |work=BBC News |url=https://www.bbc.com/news/uk-england-derbyshire-64172621 |access-date=2023-01-06}}</ref>

====Primates====
[[File:Muybridge runner.jpg|thumb|upright=1.15|A Man Running; by [[Eadweard Muybridge]]]]
Most bipedal animals move with their backs close to horizontal, using a long tail to balance the weight of their bodies. The primate version of bipedalism is unusual because the back is close to upright (completely upright in humans), and the tail may be absent entirely. Many primates can stand upright on their hind legs without any support. 
[[Chimpanzee]]s, [[bonobo]]s, [[gorilla]]s, gibbons<ref>{{Cite journal |last1=Aerts |first1=Peter |author2=Evie E. Vereeckea |author3=Kristiaan D'Aoûta |year=2006 |title=Locomotor versatility in the white-handed gibbon (Hylobates lar): A spatiotemporal analysis of the bipedal, tripedal, and quadrupedal gaits |journal=Journal of Human Evolution |volume=50 |issue=5 |pages=552–567 |doi=10.1016/j.jhevol.2005.12.011 |pmid=16516949|bibcode=2006JHumE..50..552V |url=https://lirias.kuleuven.be/handle/123456789/281630 }}</ref> and [[baboon]]s<ref>{{Cite journal |last=Rose |first=M.D. |title=Bipedal behavior of olive baboons (Papio anubis) and its relevance to an understanding of the evolution of human bipedalism |year=1976 |journal=American Journal of Physical Anthropology |volume=44 |issue=2 |pages=247–261 |url=http://www3.interscience.wiley.com/journal/110488308/abstract |archive-url=https://archive.today/20130105142336/http://www3.interscience.wiley.com/journal/110488308/abstract |url-status=dead |archive-date=2013-01-05 |doi=10.1002/ajpa.1330440207 |pmid=816205}}</ref> exhibit forms of bipedalism. On the ground [[sifaka]]s move like all [[Indriidae|indrids]] with bipedal sideways hopping movements of the hind legs, holding their forelimbs up for balance.<ref name="DULC_coquerel">{{Cite web |url=http://lemur.duke.edu/category/diurnal-lemurs/coquerels-sifaka/ |title=Coquerel's Sifaka |publisher=Duke University Lemur Center |access-date=2009-06-15 |url-status=dead |archive-url=https://web.archive.org/web/20130923184429/http://lemur.duke.edu/category/diurnal-lemurs/coquerels-sifaka/|archive-date=2013-09-23}}</ref> [[Gelada]]s, although usually quadrupedal, will sometimes move between adjacent feeding patches with a squatting, shuffling bipedal form of locomotion.<ref>{{Cite web |url=http://pin.primate.wisc.edu/factsheets/entry/gelada_baboon/ |title=Primate Factsheets: Gelada baboon (Theropithecus gelada) Taxonomy, Morphology, & Ecology |access-date=2012-07-23 |url-status=live |archive-url=https://web.archive.org/web/20120509081838/http://pin.primate.wisc.edu/factsheets/entry/gelada_baboon |archive-date=2012-05-09}}</ref> However, they can only do so for brief amounts, as their bodies are not adapted for constant bipedal locomotion.

Humans are the only primates who are normally biped, due to an extra curve in the spine which stabilizes the upright position, as well as shorter arms relative to the legs than is the case for the nonhuman [[great ape]]s. The evolution of [[human clade|human]] [[Human skeletal changes due to bipedalism|bipedalism]] began in primates about four million years ago,<ref name=Shiro>{{Cite book |author=Kondō, Shirō |title=Primate morphophysiology, locomotor analyses, and human bipedalism |location=Tokyo |publisher=University of Tokyo Press |year=1985 |isbn=978-4-13-066093-8}}{{page needed|date=April 2014}}</ref> or as early as seven million years ago with ''[[Sahelanthropus#Fossils|Sahelanthropus]]''<ref name="Daver Guy Mackaye Likius 2022">{{cite journal |vauthors=Daver G, Guy F, Mackaye HT, Likius A, Boisserie J, Moussa A, Pallas L, Vignaud P, Clarisse ND |title=Postcranial evidence of late Miocene hominin bipedalism in Chad |journal=Nature |date=2022-08-24 |volume=609 |issue=7925 |pages=94–100 |issn=0028-0836 |doi=10.1038/s41586-022-04901-z |pmid=36002567 |bibcode=2022Natur.609...94D |s2cid=234630242 |url=https://hal.archives-ouvertes.fr/hal-03037386/file/383956_0_merged_1598881798.pdf |archive-url=https://web.archive.org/web/20220825162110/https://hal.archives-ouvertes.fr/hal-03037386/file/383956_0_merged_1598881798.pdf |archive-date=2022-08-25 |url-status=live}}</ref><ref name="SI-2016biped">{{Cite web |title=What Does It Mean To Be Human? – Walking Upright |url=http://humanorigins.si.edu/human-characteristics/walking-upright |date=August 14, 2016 |work=[[Smithsonian Institution]] |access-date=August 14, 2016 |url-status=live |archive-url=https://web.archive.org/web/20160818172223/http://humanorigins.si.edu/human-characteristics/walking-upright |archive-date=August 18, 2016}}</ref> or about 12 million years ago with ''[[Danuvius guggenmosi]]''. One hypothesis for human bipedalism is that it evolved as a result of differentially successful survival from carrying food to share with group members,<ref>{{Cite journal |url=http://www3.interscience.wiley.com/journal/93519752/abstract?CRETRY=1&SRETRY=0 |archive-url=https://archive.today/20130105072904/http://www3.interscience.wiley.com/journal/93519752/abstract?CRETRY=1&SRETRY=0 |url-status=dead |archive-date=2013-01-05 |title=Bipedality in chimpanzee (Pan troglodytes) and bonobo (Pan paniscus): Testing hypotheses on the evolution of bipedalism |date=2002-05-09 |access-date=2013-04-30|doi=10.1002/ajpa.10058 |pmid=12012370 |volume=118 |issue=2 |journal=American Journal of Physical Anthropology |pages=184–190 |last1=Videan |first1=Elaine N. |last2=McGrew |first2=W.C.}}</ref> although there are alternative hypotheses.

; Injured individuals
Injured chimpanzees and bonobos have been capable of sustained bipedalism.<ref>{{Cite journal |title=Chimpanzee bipedal locomotion in the Gombe National Park, East Africa |doi=10.1007/BF02382940 |last=Bauer |first=Harold |year=1976 |journal=Primates |volume=18 |pages=913–921 |issue=4 |s2cid=41892278}}</ref>

Three captive primates, one macaque [[Natasha (monkey)|Natasha]]<ref>{{Cite news| title=Monkey apes humans by walking on two legs| work=[[NBC News]]| url=https://www.nbcnews.com/id/wbna5479501| last=Waldman| first=Dan| date=2004-07-21| access-date=2007-10-29}}</ref> and two chimps, [[Oliver (chimpanzee)|Oliver]] and Poko<ref name="Crompton Thorpe 2007 pp. 1066–1066">{{cite journal |last1=Crompton |first1=R. H. |last2=Thorpe |first2=S. K. S. |date=2007-11-16 |title=Response to Comment on "Origin of Human Bipedalism As an Adaptation for Locomotion on Flexible Branches" |journal=Science |volume=318 |issue=5853 |pages=1066 |doi=10.1126/science.1146580 |bibcode=2007Sci...318.1066C |issn=0036-8075}}</ref> (chimpanzee), were found to move bipedally. Natasha switched to exclusive bipedalism after an illness, while Poko was discovered in captivity in a tall, narrow cage.<ref>{{Cite web |publisher=University of Liverpool |website=Research Intelligence |title=Walking tall after all |url=http://www.liv.ac.uk/researchintelligence/issue22/walkingtall.html |archive-url=https://web.archive.org/web/20121215050945/http://www.liv.ac.uk/researchintelligence/issue22/walkingtall.html |archive-date=2012-12-15 |url-status=dead |access-date=2013-04-30}}</ref><ref>{{cite web |last=Naish |first=Darren |date=April 28, 2008 |url=http://scienceblogs.com/tetrapodzoology/2008/04/functional_anatomy_part_i.php#more |website=Tetrapod Zoology |title=Bipedal orangs, gait of a dinosaur, and new-look Ichthyostega: exciting times in functional anatomy part I |url-status=dead |archive-url=https://web.archive.org/web/20120508143340/http://scienceblogs.com/tetrapodzoology/2008/04/functional_anatomy_part_i.php#more |archive-date=May 8, 2012}}</ref> Oliver reverted to [[knuckle-walking]] after developing arthritis. Non-human primates often use bipedal locomotion when carrying food, or while moving through shallow water.