Was Australopithecus ancestral to humans? Were they merely cousins in the evolutionary chain? Or simply a stage between apes and humans? Among various debates about these early hominids is the argument whether or not they could stand and walk upright like people do.

William Sanders, a paleontologist at the University of Michigan, has found that Australopithecus shared many, but not all, of the anatomical features that enable humans to walk upright. He will present his findings April 3 at the Geological Society of America's North-Central Section and Southeastern Section Joint Meeting in Lexington, Kentucky.

"It turns out that in mammals, there is a strong correlation between structural differences in the lower back, and particular types of locomotion and posture," Sanders said. "Humans display a large number of lower back specializations that allow us to stand upright habitually, and to walk effectively and efficiently on two legs. These differ from the anatomical complexes seen in the backs of apes and monkeys."

Sanders examined the association between soft and bony tissue in the lower back and function of this region for posture and movement in a number of animals related to australopithecines, including baboons, gibbons, chimpanzees, and modern humans. He compared these observations with his examination of australopithecine specimens, including the partial skeleton of a 2.8 million year-old large male Australopithecus africanus (Stw-431). This individual was found in South Africa and had never been analyzed before.

"Like humans, Australopithecus had an S-shaped spine to hold an upright trunk on a tilted pelvis, and vertebral facets that are immense and become wider as you progress downward through the column—lending stability to an upright column. They also had powerful ilio-lumbar and lumbo-sacral ligaments to stabilize the sacrum and lower back on a tilted pelvis," Sanders said. "The pelvis is tilted in humans to give leverage to leg muscles that extend the legs backward during bipedal striding and running. However, unlike modern humans, Australopithecines have relatively small vertebral bodies and exhibit much pathology in these vertebral bodies. This suggests that while the back part of their vertebrae (the neural arch) was well designed for bipedal behaviors, the front part of their vertebrae had not yet evolved into an efficient weight-bearing pillar."

He concludes that the differences in spinal anatomy between humans and Australopithecines are not just due to gross size differences but are more likely to be biomechanical differences.

"Australopithecines were likely habitual bipeds, but differed in overall spinal mechanics and efficiency," he said. "They are also important because they show that all anatomical regions should be considered together in behavioral reconstructions of fossil animals."

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By Kara LeBeau, GSA Staff Writer

Contact information:
William J. Sanders
Museum of Paleontology
University of Michigan
1109 Geddes Avenue
Ann Arbor, MI 48109
E-mail: wsanders@umich.edu
Phone: 734-647-2098

Abstract available at:
http://gsa.confex.com/gsa/2002NC/finalprogram/abstract_32071.htm

Geological Society of America
Southeastern Section and North-Central Section Joint Meeting
April 3-5, 2002
Hyatt Regency Hotel and Lexington Civic Center
Lexington, KY

For information and assistance during the meeting, please see the media assistant at the GSA registration table or call 859-253-1234.

Contact: Ann Cairns, acairns@geosociety.org, 303-357-1056, Geological Society of America

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