Editing Orrorin (section)

== Evolution of bipedalism ==
The fossils of ''Orrorin tugenensis'' share no derived features of hominoid great-ape relatives.<ref name="Pickford et al 2002">{{cite journal |last1=Pickford |first1=Martin |last2=Senut |first2=Brigitte |last3=Gommery |first3=Dominique |last4=Treil |first4=Jacques |title=Bipedalism in Orrorin tugenensis revealed by its femora |journal=Comptes Rendus Palevol |date=September 2002 |volume=1 |issue=4 |pages=191–203 |doi=10.1016/s1631-0683(02)00028-3 |bibcode=2002CRPal...1..191P }}</ref> In contrast, "''Orrorin'' shares several apomorphic features with modern humans, as well as some with australopithecines, including the presence of an ''obturator externus'' groove, elongated femoral neck, anteriorly twisted head (posterior twist in ''Australopithecus''), [[wiktionary:anteroposteriorly|anteroposteriorly]] compressed femoral neck, asymmetric distribution of cortex in the femoral neck, shallow superior notch, and a well developed gluteal tuberosity which coalesces vertically with the crest that descends the femoral shaft posteriorly."<ref name="Pickford et al 2002" /> It does, however, also share many of such properties with several Miocene ape species, even showing some transitional elements between basal apes like the [[Aegyptopithecus]] and Australopithecus.<ref name=ncomms3888/>

According to recent studies ''Orrorin tugenensis'' is a basal hominid that adapted an early form of bipedalism.<ref name=science.1154197>{{cite journal |last1=Richmond |first1=B. G. |last2=Jungers |first2=W. L. |title=Orrorin tugenensis Femoral Morphology and the Evolution of Hominin Bipedalism |journal=Science |date=21 March 2008 |volume=319 |issue=5870 |pages=1662–1665 |doi=10.1126/science.1154197 |pmid=18356526 |bibcode=2008Sci...319.1662R |s2cid=20971393 |url=http://doc.rero.ch/record/15736/files/PAL_E3008.pdf }}</ref> Based on the structure of its femoral head it still exhibited some arboreal properties, likely to forage and build shelters.<ref name=science.1154197/> The length of the femoral neck in ''Orrorin tugenensis'' fossils is elongated and is similar in shape and length to modern humans and ''Australopithicines''.<ref name="Pickford et al 2002" /> While it was originally claimed that its femoral head is larger in comparison to ''Australopithicines'' and is much closer in shape and relative size to ''Homo sapiens'',<ref name="Pickford et al 2002" /> this claim has been challenged by some researchers who have noted that the femoral heads of male australopithicines are more akin to those of ''Orrorin'', and by extension modern humans, than those of female australopithicines. Proponents of the notion that ''Orrorin'' is more closely related to humans than Lucy is have addressed this by asserting that the male australopithicine femurs in question in fact belong to a different species than Lucy.<ref name=Balter/> ''O. tugenensis'' appears to have developed bipedalism 6 million years ago.<ref name=science.1154197/>

''O. tugenensis'' shares an early hominin feature in which their iliac blade is flared to help counter the torque of their body weight; this shows that they adapted bipedalism around 6 MYA.<ref name=science.1154197/> These features are shared with many species of ''Australopithecus''.<ref name=science.1154197/> It has been suggested by Pickford that the many features ''Orrorin'' shares with modern humans show that it is more closely related to ''Homo'' ''sapiens'' than to ''Australopithecus''.<ref name="Pickford et al 2002" /> This would mean that Australopithecus would represent a side branch in the homin evolution that does not directly lead to ''Homo''.<ref name="Pickford et al 2002" /> However the femora morphology of ''O. tugenensis'' shares many similarities with ''Australopithicine'' femora morphology, which weakens this claim.<ref name=science.1154197/> Another study conducted by Almecija suggested that ''Orrorin'' is more closely related to early hominins than to ''Homo''.<ref name=ncomms3888>{{cite journal |last1=Almécija |first1=Sergio |last2=Tallman |first2=Melissa |last3=Alba |first3=David M. |last4=Pina |first4=Marta |last5=Moyà-Solà |first5=Salvador |last6=Jungers |first6=William L. |title=The femur of Orrorin tugenensis exhibits morphometric affinities with both Miocene apes and later hominins |journal=Nature Communications |date=3 December 2013 |volume=4 |issue=1 |page=2888 |doi=10.1038/ncomms3888 |pmid=24301078 |bibcode=2013NatCo...4.2888A |doi-access=free }}</ref> An analysis of the BAR 10020' 00 femur showed that ''Orrorin'' is an intermediate between ''Pan'' and ''Australopithecus afarensis''.<ref name=ncomms3888/> The current prevailing theory is that ''Orrorin tugenensis'' is a basal hominin and that bipedalism developed early in the hominin clade and successfully evolved down the human evolutionary tree.<ref name=science.1154197/> While the phylogeny of ''Orrorin'' is uncertain, the evidence of the evolution of bipedalism is an invaluable discovery from this early fossil hominin. A recent phylogenetic analysis also recovered ''Orrorin'' as a hominin.<ref>{{Cite journal |last1=Sevim-Erol |first1=Ayla |last2=Begun |first2=D. R. |last3=Sözer |first3=Ç Sönmez |last4=Mayda |first4=S. |last5=van den Hoek Ostende |first5=L. W. |last6=Martin |first6=R. M. G. |last7=Alçiçek |first7=M. Cihat |date=2023-08-23 |title=A new ape from Türkiye and the radiation of late Miocene hominines |journal=Communications Biology |language=en |volume=6 |issue=1 |page=842 |doi=10.1038/s42003-023-05210-5 |issn=2399-3642 |pmc=10447513 |pmid=37612372}}</ref>