User:Lilly861/Orrorin

The fossils of Orrorin tugenensis shares no derived features of homin great-ape relatives. "In contrast,Orrorin shares several apomorphic features  with  humans  and  some  with  australopithecines,including the presence of an obturator externus groove,elongated  femoral  neck,  anteriorly  twisted  head  (posterior twist in Australopithecus), antero-posteriorly compressed femoral neck, asymmetric distribution of cortexin the femoral neck, shallow superior notch, and a well developed gluteal tuberosity which coalesces vertically with  the  crest  that  descends  the  femoral  shaft  poste-riorly." According to recent studies Orrorin tugenensis is a basal hominid that adapted an early form of bipedalism. Based on the structure of it's femoral head it still exhibited some arboreal properties, likely to forage and build shelters. The length of the femoral neck in Orrorin tugenensis fossils is elongated and is similar in shape and length to Australopithicines and modern humans. Additionally, it's femoral head is larger in comparison to Australopithicines and is much closer in shape and relative size to Homo sapiens. This archaic morphology suggests that O. tugenensis developed bipedalism 6 million years ago.

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. These features are shared with many species of Australopithecus. 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. This would mean that Australopithecus would represent a side branch in the homin evolution that does not directly lead to Homo. However the femora morphology of O. tugenensis shares many similarities with Australopithicine femora morphology \, which wekens this claim. Another study conducted by Almecija suggested that Orrorin is more closely related to early hominins than to Homo. An analysis of the BAR 10020' 00 femur showed that Orrorin is an intermediate between Pan and Australopithecus afarensis. 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. It is clear that the phylogeny of Orrorin is uncertain, however the evidence of the evolution of bipedalism is an invaluable discovery from this early fossil hominin.