Research Reveals How Australopithecus sediba Walked, Chewed, Moved

New research appearing in six papers in the journal Science describes how the hominid Australopithecus sediba walked, chewed, and moved around 2 million years ago. The research offers a comprehensive depiction of some of the most complete early human ancestral remains ever discovered.

This image shows Australopithecus sediba, center, compared to the skeleton of a modern human, left, and a chimpanzee, right (Lee Berger / University of the Witwatersrand)

This image shows Australopithecus sediba, center, compared to the skeleton of a modern human, left, and a chimpanzee, right (Lee Berger / University of the Witwatersrand)

The site of Malapa, located about 30 miles northwest of Johannesburg, South Africa, has yielded more than 220 bones of early hominins representing more than five individuals, including the remains of babies, juveniles, and adults. The new research is based on fossils of two individuals dating to 1.977 to 1.98 million years ago.

“The abundance and remarkable preservation of fossils from Malapa provide unique insights into the way this fascinating extinct species interacted with and moved around in its environment,” said Dr Scott Williams of New York University, lead author of one of the six Science papers.

Dr Williams’ team authored a paper describing Australopithecus sediba’s vertebral column. The paper is the first to analyze elements of the cervical, thoracic, lumbar, and sacral regions of the vertebral column in Australopithecus sediba.

Their study reveals that Australopithecus sediba had a human-like curvature of the lower back, but it was functionally longer and more flexible than that of modern humans.

“They probably walked in a way that we might find strange – a ‘compromise’ form of bipedalism indicative of a hominin that still partially relied on climbing trees,” Dr Williams explained.

“The adult female is the first early hominin skeleton that preserves an intact terminal thoracic region and this provides critical information on the transition in inter-vertebral joints, and, by inference, mobility of the lower back.”

“The bony spine of Australopithecus sediba likely had the same number of vertebrae as that of modern humans. However, it differed in one primary aspect of its configuration – the transition in inter-vertebral articular facets occurred at a higher level of the spine that than normally occurs in modern humans. In combination with other features, a functionally longer lower back would have allowed for a more flexible spine in Australopithecus sediba relative to that of modern humans.”

Reconstructed skull and mandible of Australopithecus sediba (Peter Schmid)

Reconstructed skull and mandible of Australopithecus sediba (Peter Schmid)

In addition, morphological indicators of strong lumbar curvature suggest that Australopithecus sediba evolved in this regard relative to Australopithecus africanus, which lived between 3.03 and 2.04 million years ago, and closer to the more recent Nariokotome Homo erectus skeleton – to date, the most complete early human skeleton discovered.

“Overall, the fossils provide an unprecedented insight into the anatomy and phylogenetic position of an early human ancestor,” said Prof Lee Berger, the project leader from the Wits Evolutionary Studies Institute.

“This examination of a large number of associated, often complete and undistorted elements, gives us a glimpse of a hominin species that appears to be mosaic in its anatomy and that presents a suite of functional complexes that are both different from that predicted for other australopiths, as well as that for early Homo.

“Such clear insight into the anatomy of an early hominin species will clearly have implications for interpreting the evolutionary processes that affected the mode and tempo of hominin evolution and the interpretation of the anatomy of less well preserved species.”

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Bibliographic information: Joel D. Irish et al. 2013. Dental Morphology and the Phylogenetic “Place” of Australopithecus sediba. Science, vol. 340, no. 6129; doi: 10.1126/science.1233062

Darryl J. de Ruiter. 2013. Mandibular Remains Support Taxonomic Validity of Australopithecus sediba. Science, vol. 340, no. 6129; doi: 10.1126/science.1232997

Steven E. Churchill et al. 2013. The Upper Limb of Australopithecus sediba. Science, vol. 340, no. 6129; doi: 10.1126/science.1233477

Peter Schmid et al. 2013. Mosaic Morphology in the Thorax of Australopithecus sediba. Science, vol. 340, no. 6129; doi: 10.1126/science.1234598

Scott A. Williams et al. 2013. The Vertebral Column of Australopithecus sediba. Science, vol. 340, no. 6129; doi: 10.1126/science.1232996

Jeremy M. DeSilva et al. 2013. The Lower Limb and Mechanics of Walking in Australopithecus sediba. Science, vol. 340, no. 6129; doi: 10.1126/science.1232999