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. 2020 Mar 16;10(1):4285.
doi: 10.1038/s41598-020-60837-2.

The atlas of StW 573 and the late emergence of human-like head mobility and brain metabolism

Amélie Beaudet  1   2 , Ronald J Clarke  3 , Jason L Heaton  3   4   5 , Travis R Pickering  3   4   6 , Kristian J Carlson  3   7 , Robin H Crompton  3   8 , Tea Jashashvili  3   9   10 , Laurent Bruxelles  11   12   13 , Kudakwashe Jakata  3 , Lunga Bam  14 , Luc Van Hoorebeke  15 , Kathleen Kuman  11 , Dominic Stratford  11
Affiliations

The atlas of StW 573 and the late emergence of human-like head mobility and brain metabolism

Amélie Beaudet et al. Sci Rep. .

Abstract

Functional morphology of the atlas reflects multiple aspects of an organism's biology. More specifically, its shape indicates patterns of head mobility, while the size of its vascular foramina reflects blood flow to the brain. Anatomy and function of the early hominin atlas, and thus, its evolutionary history, are poorly documented because of a paucity of fossilized material. Meticulous excavation, cleaning and high-resolution micro-CT scanning of the StW 573 ('Little Foot') skull has revealed the most complete early hominin atlas yet found, having been cemented by breccia in its displaced and flipped over position on the cranial base anterolateral to the foramen magnum. Description and landmark-free morphometric analyses of the StW 573 atlas, along with other less complete hominin atlases from Sterkfontein (StW 679) and Hadar (AL 333-83), confirm the presence of an arboreal component in the positional repertoire of Australopithecus. Finally, assessment of the cross-sectional areas of the transverse foramina of the atlas and the left carotid canal in StW 573 further suggests there may have been lower metabolic costs for cerebral tissues in this hominin than have been attributed to extant humans and may support the idea that blood perfusion of these tissues increased over the course of hominin evolution.

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Conflict of interest statement

The authors declare no competing interests.

Figures

Figure 1
Figure 1
The StW 573 atlas. (a) Photograph of the StW 573 atlas cemented by breccia to the cranial base anterior to the foramen magnum. (b) In silico digital reconstruction of the atlas of StW 573 based on microtomographic data.
Figure 2
Figure 2
Comparison of the StW 573 atlas with extant and fossil specimens. Virtual renderings of the StW 573 atlas compared to the Australopithecus specimens StW 679 and AL 333-83 and to extant Homo, Pan, Gorilla and Pongo. Atlases are shown from left to right in superior, inferior, posterior, anterior and lateral left views, respectively. Images not to scale.
Figure 3
Figure 3
Statistical analyses of the StW 573 atlas and comparative extant and fossil specimens. Principal component analyses and backtransform morphospace of the deformation-based shape comparisons of the complete and partial atlases of StW 573, StW 679 and AL 333-83 and of extant Homo, Pan, Gorilla and Pongo. (a) Analysis of the complete atlases. (b) Analysis of the partial atlases.
Figure 4
Figure 4
Surface-based comparison of the complete atlases of StW 573 and comparative extant specimens. Topographical distribution of the deformation-based shape comparisons of the complete atlases of StW 573 and of extant Homo, Pan, Gorilla and Pongo. Cumulative displacement variations from the taxon mean shapes to StW 573 are rendered by a pseudo-colour scale ranging from dark blue (lowest values) to red (highest values) visualised on the fossil individual surfaces. Vectors represent both the magnitude and orientation of the deformations needed to deform the taxon mean shapes to StW 573. Maximum value of the colour bar is considered to be the most appropriate compromise representation of both global and local deformations. Atlases are shown from top to bottom rows in superior, inferior, posterior and lateral right views, respectively.
Figure 5
Figure 5
Surface-based comparison of fossil and extant partial atlases. Topographical distribution of the deformation-based shape comparisons of the partial atlases of StW 573, StW 679 and AL 333-83 and of extant Homo, Pan, Gorilla and Pongo. Cumulative displacement variations from the taxon mean shapes to the fossil specimens are rendered by a pseudo-colour scale ranging from dark blue (lowest values) to red (highest values) visualised on the fossil individual surfaces. Vectors represent both the magnitude and orientation of the deformations needed to deform the taxon mean shapes to StW 573. The maximum value of the colour bar is considered to be the most appropriate compromise representation of both global and local deformations. Atlas specimens within each of the four columns are shown from top to bottom rows in superior (left) and inferior (right) views, respectively.
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