One of the most complete hominin skeletons (humans and their fossil ancestors) ever found in the world, StW 573 — affectionately nicknamed Little Foot — began to be unearthed in 1994, when bones of a small foot (hence the nickname) were found in the caves of Sterkfontein, South Africa.
After being patiently separated from the hardened rock that surrounded it — a process completed only in 2018 — the skeleton, around 3.7 million years old, became a key piece in understanding how the ancestors of the genus Homo they moved, balanced and interacted with the environment.
Paradoxically, the exceptional preservation of Little Foot gave rise to one of the biggest controversies in modern paleontology. Paleoanthropologist Ron Clarke, responsible for its excavation and reconstruction, rejected the traditional classification, arguing that the fossil should not be assigned to the species Australopithecus africanus.
For Clarke, the Little Foot would represent a different species — the Australopithecus prometheus —, originally proposed in 1948 for fossils found further north in the country, in Makapansgat, but which was never fully accepted by the scientific community, which continued to treat the species as a synonym for A. africanus.
Now, a recently published study has tested the hypothesis that the fossil specimen StW 573 (Little Foot) can be taxonomically assigned to Australopithecus prometheus. The conclusion was clear: there is no sufficient morphological basis for this classification.
How does the investigation of Little Foot put A. prometheus in check?
In the new study, researchers compared the anatomy of the StW 573 specimen in detail (Little Foot) with fossils attributed to Australopithecus africanus and with the only copy associated with A. prometheus: a cranial fragment known as MLD 1.
To do this, the team used a high-resolution 3D scanner, creating accurate digital reconstructions of StW 573, MLD 1 and fossils of A. africanus. The analysis revealed at least five anatomical differences, involving the posterior part of the skull, the sagittal crest (bone elevation associated with the chewing muscles), the plane of the neck and the bone sutures.
In an interview with The Guardian, the study’s lead researcher, Jesse Martin, from La Trobe University, in Australia, explained that, “when differences are found at the base of the skull, they are more likely to indicate different species, because this region evolves slowly. All the differences we identified are there”, he stated.
The authors realized that MLD 1 is, reinforcing the thesis that A. prometheus It is not supported as an independent species, but as an alternative name for a species already recognized since 1924.
This means that when trying to properly fit Little Foot, researchers ended up exposing the fragility of the concept of A. prometheusby showing that the MLD 1 fossil does not present sufficient characteristics to support this species as distinct.
Could Little Foot be a new species in the human family tree?
Even though this was not its objective, the study ended up creating a scientific paradox. How to test the hypothesis that the fossil specimen StW 573 (Little Foot) should be taxonomically assigned to Australopithecus prometheusif this designation does not represent, in itself, an autonomous species, but just another name for A. africanus?
And, to further deepen the debate, the authors concluded that, in addition to not being classified as A. prometheusspecimen StW 573 also presents important anatomical differences in relation to other fossils attributed to A. africanus. This leads to the question: are we facing a new species?
This scientific “plot twist” could have an impact on paleontology that goes beyond a simple name dispute. It highlights and reinforces the importance of rigorous — and more modern — criteria in evolutionary taxonomy. Even older fossils can have a lot to reveal to us.
In the article itself, the authors suggest: “It is more appropriate that a new species be named by the research team that spent more than two decades excavating and analyzing the remarkable specimen of Little Foot. We hope they see our suggestion in this regard as well-intentioned advice,” they conclude.
