Meticulous excavation, cleaning and high-resolution micro-CT scanning of the skull of the ~3.67 million-year-old fossil specimen known as “Little Foot” has revealed the most complete Australopithecus first cervical vertebra yet found. A description of the vertebra by Wits researchers Dr Amélie Beaudet and the Sterkfontein team was published today in the Scientific Reports.

Pictures of the “Little Foot” skull. The inferior view (left) shows the original position of the first cervical vertebra still embedded in the matrix.

© Beaudet et al.

The morphology of the first cervical vertebra, or atlas, reflects multiple aspects of an organism’s life. In particular, the nearly complete atlas of ‘Little Foot’ has the potential to provide novel insights into the evolution of head mobility and the arterial supply to the brain in the human lineage. Indeed, the shape of the atlas determines the range of head motions while the size of the arteries passing through the vertebrae to the skull is useful for estimating blood flow supplying the brain.

The atlas of “Little Foot” was compared to two other Australopithecus specimens from Ethiopia and South Africa, as well as to living human and nonhuman primates. The overall dimensions and shape of the atlas of “Little Foot” are similar to living chimpanzees. More specifically, the ligament insertions (that could be inferred from the presence and configuration of bony tubercles) and the morphology of the facet joints linking the head and the neck all suggest that “Little Foot” was moving regularly in trees. While “Little Foot” is similar to the Australopithecus specimen from Ethiopia, the additional specimen from South Africa, which comes from the geologically younger deposits of Sterkfontein, is more human-like. These observations could indicate that at least some earlier species of Australopithecus may have spent much more time in trees than the later representatives of the genus.

Comparison of the nearly intact first cervical vertebra of “Little Foot” and two other Australopithecus from Sterkfontein in South Africa (StW 679) and from Hadar in Ethiopia (AL 333-83)

© Beaudet et al.

Because of the exceptional preservation of “Little Foot”, for the first time blood flow supplying the brain could be reconstructed by using the bony canals of the arteries in the skull and vertebra of the same fossil individual. The estimation of the size of the arteries in “Little Foot” falls within the variation observed in living chimpanzees but it differs from the human condition. Moreover, blood flow estimation could be used to compute brain glucose utilization of the fossil specimen that turned out to be significantly less than in humans. The low energetic investment in the brain of Australopithecus could be tentatively explained by a relatively small brain of the specimen (i.e., 408 cubic centimetres), a low quality diet (e.g., low proportion of animal products) or high costs of other aspects of the biology of Australopithecus (e.g., upright walking). In any case, this might suggest that the human brain’s vascular system emerged much later in our history

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About the author

Amélie Beaudet is a paleoanthropologist at the University of the Witwatersrand. Her research focus on human origins and how human ancestors evolved in Africa a couple of million years ago. As a member of the Sterkfontein team, she works on the in silico analysis of “Little Foot” that contributes to our understanding of the human evolutionary story.

Reference

Beaudet A., Clarke R.J., Heaton J.L., Pickering T.R., Carlson K.J., Crompton R., Jashashvili T., Bruxelles L., Jakata K., Bam L., Van Hoorebeke L., Kuman K. & Stratford D. - The atlas of StW 573 and the late emergence of human-like head mobility and brain metabolism. Scientific Reports.