The bones had been waiting 3.67 million years. Then they waited another few decades more, inside a limestone cave in South Africa’s Cradle of Humankind, slowly giving up their secrets to excavators working with dental picks and brushes. By the time the skeleton known as Little Foot was fully extracted in 2016, it was already the most complete early hominin ever found. There was just one problem: its face was a ruin.
Geological pressure over millions of years had buckled and displaced the facial bones. The lower face shoved upward into the frontal and zygomatic bones; the frontal squama pushed downward; fragments split and warped. Physical reconstruction was out of the question. You can’t undo that kind of deformation with glue and patience.
So a team led by Amélie Beaudet, now at the Laboratoire de Paléontologie at the Université de Poitiers, took the skull to a particle accelerator. At the Diamond Light Source synchrotron in Oxfordshire, they scanned the 3.67-million-year-old cranium using high-resolution X-ray tomography, generating 9,138 image slices at a voxel resolution finer than a quarter of a millimetre. Back at Cambridge’s supercomputer facility, semi-automated segmentation software separated bone from matrix, isolated the displaced fragments, and gave the team five distinct puzzle pieces to work with digitally. Then came the painstaking process of fitting them back together on screen. The result, published this week in Comptes Rendus Palevol, is one of the most complete Australopithecus faces ever reconstructed.
What it revealed was not what anyone expected.
Little Foot comes from Sterkfontein, in South Africa. It belongs, according to its discoverer Ron Clarke, to a species called Australopithecus prometheus. On biogeographical grounds alone you’d predict its face would look broadly like other southern African australopiths. Instead, the geometric morphometric analysis found Little Foot’s facial architecture more closely resembling A.L. 444-2, an Australopithecus afarensis specimen from Hadar in Ethiopia, than Sts 5, a younger Australopithecus africanus from the same South African cave system. The eye sockets especially, tall and wide with an oval shape, look more Ethiopian than South African, sharing proportions with the Hadar specimen and, curiously, with extant orangutans.
“This pattern is unexpected, given the geographic origin of Little Foot and suggests a more dynamic evolutionary history than previously assumed,” says Beaudet.
What that might mean, exactly, is still being pieced together. One reading is that Little Foot represents a lineage more closely related to East African populations than to the southern African hominins that came later. Another possibility, harder to rule out given the scarcity of complete fossil faces from this period, is that the facial anatomy now associated with Sts 5 and southern Australopithecus represents a regional divergence, a derived condition that emerged after the ancestral lineage had already spread across a much wider African range. The older form, perhaps, persisted longer in the east.
“While we know that the hominin face evolved through time to become less projected and more gracile, we still ignore when such changes occur, and the nature of the evolutionary mechanisms involved,” says Beaudet. The orbital region is a particular focus. The size and shape of primate eye sockets encode information about visual capacity and ecological behaviour; they vary independently of other facial features in a way that makes them useful diagnostic markers. The finding that Little Foot’s orbits show similarities to East African australopiths, and that orbital geometry may have been under active selective pressure in Pliocene southern Africa, opens questions about what exactly these early hominins were doing with their eyes. What were they looking for? How was their world changing around them?
Evidence from elsewhere in the fossil record suggests the southern African Pliocene was not a stable landscape. Seasonal dietary stress, read from the chemistry of australopith teeth, points to periods of resource scarcity. An orbital morphology under selection could, in that context, reflect adaptations to spotting fallback foods or navigating fragmenting environments.
Dominic Stratford, who is director of research at Sterkfontein and a co-author on the paper, frames the broader implication: “Rather than viewing early hominin evolution as occurring in isolated regions, the study supports the idea of Africa as a connected evolutionary landscape, with populations adapting to ecological pressures while remaining linked through shared ancestry.”
The reconstruction itself remains preliminary. Plastic deformation in the braincase could not be fully corrected: the fragments were repositioned without adjusting for warping, meaning some anatomical decisions are approximations. Future work would ideally model the taphonomic forces that crushed the skull during fossilisation, then run simulations in reverse to straighten the bones digitally before reassembling them. “The face is only part of the story,” Beaudet notes. “Other parts of the skull, especially the braincase, remain distorted by plastic deformation and will require similar digital reconstruction to better understand brain size and organisation in this early hominin.”
For now, what the team has produced is good enough to place Little Foot in a broader comparative context for the first time, alongside gorillas, chimpanzees, orangutans, modern humans, and three other australopith specimens, and to ask, with at least some statistical rigour, where it sits among them. The answer turns out to be surprisingly far from home, geographically speaking. A face from Sterkfontein that looks, in its orbital geometry, like it belongs somewhere in the Ethiopian Rift. Whether that reflects migration, shared ancestry, or something more complicated is the question that now sits waiting, alongside all the others, in the caves northwest of Johannesburg.
https://doi.org/10.5852/cr-palevol2026v25a3
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