TY - JOUR
T1 - Limb Bone Structural Proportions and Locomotor Behavior in A.L. 288-1 ("Lucy")
AU - Ruff, Christopher B.
AU - Burgess, M. Loring
AU - Ketcham, Richard A.
AU - Kappelman, John
N1 - Funding Information:
We thank the Authority for Research and Conservation of Cultural Heritage and the National Museum of Ethiopia of the Ministry of Tourism and Culture for permission to scan, study, and photograph Lucy; A. Admassu, K. Ayele, J. A. Bartsch, Y. Beyene, Y. Desta, R. Diehl, R. Flores, R. Harvey, G. Kebede, R. Lariviere, J. H. Mariam, S. M. Miller, L. Rebori, B. Roberts, J. Ten Barge, J. M. Sanchez, D. Slesnick, D. Van Tuerenhout, S. Wilson, M. Woldehan, and M. Yilma for facilitating and assisting with the scanning; T. Getachew and M. Endalamaw for assisting with the photography, and S. Mattox for the photograph in Extended Data ; A. Witzel for assistance with 3D printing; and Paleoanthropology Lab Fund, College of Liberal Arts UT Austin, and Houston Museum of Natural Science for financial and logistical support, and Owen-Coates Fund of the Geology Foundation of UT Austin for publication costs. The University of Texas High-Resolution X-ray CT Facility was supported by U.S. National Science Foundation grants EAR-0646848, EAR-0948842, and EAR-1258878 ( www.nsf.gov ). We would also like to thank L. Rodriguez and J. M. Carretero for making available unpublished data on several Atapuerca specimens and Gombore MK3; B. Holt, M. Niskanen, V. Sládek, and M. Berner for collaboration in obtaining the modern European comparative data set, which was supported by NSF ( www.nsf.gov ) grant BCS-0642297; J-A. Junno for collaboration on obtaining the chimpanzee comparative data set, which was supported by NSF grant ( www.nsf.gov ) BCS-1316104, with institutional support from the University of Oulu; and J-J. Hublin and C. Boesch for access to chimpanzee specimens in their care. The paper benefited from the comments of three anonymous reviewers.
Publisher Copyright:
© 2016 Ruff et al. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
PY - 2016/11
Y1 - 2016/11
N2 - While there is broad agreement that early hominins practiced some form of terrestrial bipedality, there is also evidence that arboreal behavior remained a part of the locomotor repertoire in some taxa, and that bipedal locomotion may not have been identical to that of modern humans. It has been difficult to evaluate such evidence, however, because of the possibility that early hominins retained primitive traits (such as relatively long upper limbs) of little contemporaneous adaptive significance. Here we examine bone structural properties of the femur and humerus in the Australopithecus afarensis A.L. 288-1 ("Lucy", 3.2 Myr) that are known to be developmentally plastic, and compare them with other early hominins, modern humans, and modern chimpanzees. Cross-sectional images were obtained from micro-CT scans of the original specimens and used to derive section properties of the diaphyses, as well as superior and inferior cortical thicknesses of the femoral neck. A.L. 288-1 shows femoral/humeral diaphyseal strength proportions that are intermediate between those of modern humans and chimpanzees, indicating more mechanical loading of the forelimb than in modern humans, and by implication, a significant arboreal locomotor component. Several features of the proximal femur in A.L. 288-1 and other australopiths, including relative femoral head size, distribution of cortical bone in the femoral neck, and cross-sectional shape of the proximal shaft, support the inference of a bipedal gait pattern that differed slightly from that of modern humans, involving more lateral deviation of the body center of mass over the support limb, which would have entailed increased cost of terrestrial locomotion. There is also evidence consistent with increased muscular strength among australopiths in both the forelimb and hind limb, possibly reflecting metabolic trade-offs between muscle and brain development during hominin evolution. Together these findings imply significant differences in both locomotor behavior and ecology between australopiths and later Homo.
AB - While there is broad agreement that early hominins practiced some form of terrestrial bipedality, there is also evidence that arboreal behavior remained a part of the locomotor repertoire in some taxa, and that bipedal locomotion may not have been identical to that of modern humans. It has been difficult to evaluate such evidence, however, because of the possibility that early hominins retained primitive traits (such as relatively long upper limbs) of little contemporaneous adaptive significance. Here we examine bone structural properties of the femur and humerus in the Australopithecus afarensis A.L. 288-1 ("Lucy", 3.2 Myr) that are known to be developmentally plastic, and compare them with other early hominins, modern humans, and modern chimpanzees. Cross-sectional images were obtained from micro-CT scans of the original specimens and used to derive section properties of the diaphyses, as well as superior and inferior cortical thicknesses of the femoral neck. A.L. 288-1 shows femoral/humeral diaphyseal strength proportions that are intermediate between those of modern humans and chimpanzees, indicating more mechanical loading of the forelimb than in modern humans, and by implication, a significant arboreal locomotor component. Several features of the proximal femur in A.L. 288-1 and other australopiths, including relative femoral head size, distribution of cortical bone in the femoral neck, and cross-sectional shape of the proximal shaft, support the inference of a bipedal gait pattern that differed slightly from that of modern humans, involving more lateral deviation of the body center of mass over the support limb, which would have entailed increased cost of terrestrial locomotion. There is also evidence consistent with increased muscular strength among australopiths in both the forelimb and hind limb, possibly reflecting metabolic trade-offs between muscle and brain development during hominin evolution. Together these findings imply significant differences in both locomotor behavior and ecology between australopiths and later Homo.
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U2 - 10.1371/journal.pone.0166095
DO - 10.1371/journal.pone.0166095
M3 - Article
C2 - 27902687
AN - SCOPUS:85001070769
SN - 1932-6203
VL - 11
JO - PloS one
JF - PloS one
IS - 11
M1 - e0166095
ER -