TY - JOUR
T1 - First steps of bipedality in hominids
T2 - Evidence from the atelid and proconsulid pelvis
AU - Machnicki, Allison L.
AU - Spurlock, Linda B.
AU - Strier, Karen B.
AU - Reno, Philip L.
AU - Lovejoy, C. Owen
N1 - Funding Information:
This material is based upon work supported by the National Science Foundation under Grant No. DGE1255832. Any opinions, findings, and conclusions or recommendations expressed in this material are those of the author(s) and do not necessarily reflect the views of the National Science Foundation. The field study has been supported by a variety of sources to KBS including NSF BCS-0921013, the Vilas Research Professors Fund of the University of Wisconsin-Madison, and CAPES/BRASIL Special Visiting Researcher Program-PVE. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.
Publisher Copyright:
© 2016 Machnicki et al.
PY - 2016
Y1 - 2016
N2 - 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 support from other anatomical systems preserved in Ardipithecus ramidus.
AB - 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 support from other anatomical systems preserved in Ardipithecus ramidus.
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U2 - 10.7717/peerj.1521
DO - 10.7717/peerj.1521
M3 - Article
C2 - 26793418
AN - SCOPUS:84955573610
VL - 2016
JO - PeerJ
JF - PeerJ
SN - 2167-8359
IS - 1
M1 - e1521
ER -