First steps of bipedality in hominids: evidence from the atelid and proconsulid pelvis

PeerJ
Allison L MachnickiC Owen Lovejoy

Abstract

Upright walking absent a bent-hip-bent-knee gait requires lumbar lordosis, a ubiquitous feature in all hominids for which it can be observed. Its first appearance is therefore a central problem in human evolution. Atelids, which use the tail during suspension, exhibit demonstrable lordosis and can achieve full extension of their hind limbs during terrestrial upright stance. Although obviously homoplastic with hominids, the pelvic mechanisms facilitating lordosis appear largely similar in both taxa with respect to abbreviation of upper iliac height coupled with broad sacral alae. Both provide spatial separation of the most caudal lumbar(s) from the iliac blades. A broad sacrum is therefore a likely facet of earliest hominid bipedality. All tailed monkeys have broad alae. By contrast all extant apes have very narrow sacra, which promote "trapping" of their most caudal lumbars to achieve lower trunk rigidity during suspension. The alae in the tailless proconsul Ekembo nyanzae appear to have been quite broad, a character state that may have been primitive in Miocene hominoids not yet adapted to suspension and, by extension, exaptive for earliest bipedality in the hominid/panid last common ancestor. This hypothesis receives strong s...Continue Reading

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Citations

Apr 14, 2017·The Anatomical Record : Advances in Integrative Anatomy and Evolutionary Biology·Emily R MiddletonCarol V Ward
Apr 14, 2017·The Anatomical Record : Advances in Integrative Anatomy and Evolutionary Biology·Ashley S Hammond, Sergio Almécija
Apr 14, 2017·The Anatomical Record : Advances in Integrative Anatomy and Evolutionary Biology·Kristi L Lewton, Jeremiah E Scott
Feb 9, 2018·American Journal of Physical Anthropology·Carol V WardEmily R Middleton
Apr 22, 2016·American Journal of Physical Anthropology·Allison L MachnickiPhilip L Reno
Oct 14, 2018·The Anatomical Record : Advances in Integrative Anatomy and Evolutionary Biology·Gabrielle A Russo
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Dec 26, 2018·American Journal of Physical Anthropology·Travis Rayne PickeringDominic Stratford
May 16, 2019·Nature Ecology & Evolution·Scott A WilliamsMilena R Shattuck
Aug 10, 2018·Journal of the Royal Society, Interface·Matthew C O'NeillBrian R Umberger
May 11, 2020·Journal of Human Evolution·Allison L Machnicki, Philip L Reno
Sep 21, 2019·Journal of Human Evolution·Carol V WardDavid R Begun

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