segunda-feira, 22 de março de 2010

Laetoli Footprints Preserve Earliest Direct Evidence of Human-Like Bipedal Biomechanics

Laetoli Footprints Preserve Earliest Direct Evidence of Human-Like Bipedal Biomechanics

David A. Raichlen1*, Adam D. Gordon2, William E. H. Harcourt-Smith3,4, Adam D. Foster1, Wm. Randall Haas, Jr1

1 School of Anthropology, University of Arizona, Tucson, Arizona, United States of America, 23 Department of Anthropology, Lehman College, Bronx, New York, United States of America, 4 Division of Vertebrate Paleontology, American Museum of Natural History, New York, New York, United States of America Department of Anthropology, University at Albany–SUNY, Albany, New York, United States of America,

Abstract

Background

Debates over the evolution of hominin bipedalism, a defining human characteristic, revolve around whether early bipeds walked more like humans, with energetically efficient extended hind limbs, or more like apes with flexed hind limbs. The 3.6 million year old hominin footprints at Laetoli, Tanzania represent the earliest direct evidence of hominin bipedalism. Determining the kinematics of Laetoli hominins will allow us to understand whether selection acted to decrease energy costs of bipedalism by 3.6 Ma.

Methodology/Principal Findings

Using an experimental design, we show that the Laetoli hominins walked with weight transfer most similar to the economical extended limb bipedalism of humans. Humans walked through a sand trackway using both extended limb bipedalism, and more flexed limb bipedalism. Footprint morphology from extended limb trials matches weight distribution patterns found in the Laetoli footprints.

Conclusions

These results provide us with the earliest direct evidence of kinematically human-like bipedalism currently known, and show that extended limb bipedalism evolved long before the appearance of the genus Homo. Since extended-limb bipedalism is more energetically economical than ape-like bipedalism, energy expenditure was likely an important selection pressure on hominin bipeds by 3.6 Ma.

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