Biomechanical Inferences about the Origins of Bipedal Locomotion from Ancient African Femora
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Volume 135, Issue 5
Abstract
Reported here are the diaphyseal cross-sectional geometrical properties of two fossilized femora from Kenya dated at (million years ago), designated as the taxon Orrorin tugenensis. These femora are sampled at a temporal level near the divergence of ape and human lineages. The geometric properties of the bones are compared with previous findings from SK 82 and SK 97, hominid fossils from 2 million years later, and a sample of extant humans from Pecos Pueblo, N. M. The Orrorin femoral specimens BAR 1002’00 and BAR 1003’00 are notably robust, exhibiting cross-sectional areas with relatively high percentages of cortical bone in comparison to a contemporary sample. Total cross-sectional area is markedly smaller for BAR 1002’00 and BAR 1003’00 than for either of the Swartkrans early hominid proximal femora or the Pecos Pueblo sample, but %CA of the two Kenyan fossil femurs are comparable to those from Swartkrans and one third higher than the modern sample. Despite their relatively thicker cortical areas BAR 1002’00 and BAR 1003’00 do not exhibit higher bending resistance ( and ) or torsional rigidity in compared to a modern human sample. These findings extend our knowledge of internal femoral structure related to the origins of human locomotion.
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Acknowledgments
The writers thank Dr. Brigitte Senut of the Département Histoire de la Terre, Muséum National d’Histoire Naturelle, Paris, and Dr. Martin PickfordChaire de Paléoanthropologie et de Préhistoire, Collège de France, Paris for making the casts and CT scans of BAR 1002’00 and BAR 1003’00 available to them us. Appreciation is due also to Dr. Jacques Treil, Service du Radiologie, Clinique Pasteur, Toulouse, France for making the scans. Mr. Eustace Gitonga, Director of the Community Museums of Kenya, has the writers gratitude for making further casts available and for continuing valuable assistance throughout their several years of work on the Kenyan fossil material. Dr. Janet Monge, Department of Anthropology, University of Pennsylvania, Philadelphia provided human and chimpanzee femora as well as measuring instruments, plus valuable advice on their use. Dr. Christopher Ruff at the Center for Functional Anatomy and Evolution, Johns Hopkins University, Baltimore, supplied unpublished data on the angle of femoral torsion in hominoid primates. Dr. Ann Stirland, Independent Consulting Archaeologist, Northants, United Kingdom, furnished particularly valuable perspective on difficulties in measuring the angle of femoral torsion. Dr. David A. Eckhardt at the Department of Computer Science, Carnegie Mellon University, Pittsburgh, was a source of much valuable technical assistance and thoughtful discussion throughout the project.
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Published In
Journal of Engineering Mechanics
Volume 135 • Issue 5 • May 2009
Pages: 479 - 484
Copyright
© 2009 ASCE.
History
Received: Aug 20, 2007
Accepted: Oct 15, 2008
Published online: May 1, 2009
Published in print: May 2009
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