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The question of whether a 7-million-year-old primate nicknamed “Toumai” walked on two or four legs has sparked drama among paleontologists, complete with a missing femur.
From the discovery of Sahelanthropus tchadensis’s first fossil in 2001, it has often been cited as our first known hominin ancestor. Initial analysis suggested this Sahelanthropus he walked regularly upright and had a combination of ape and human characteristics.
These conclusions, however, were based on a single skull.
The skull has anatomical features that potentially indicate that this primate had an upright spine and therefore spent some of its time walking on two legs only. Its small teeth also look more human than ape. A subsequent reconstruction supported these results.
But other researchers have since argued that this alone isn’t enough evidence to classify Sahelanthropus as a bipedal hominid – a primate directly ancestral to humans – rather than a related but not directly ancestral hominid.
In the same period and in the same place where the skull was found, in Toros-Menalla in Chad, a partial left femur was also recovered. The femur disappeared after another researcher began examining it in 2004, having allegedly stumbled upon it by accident.
Aude Bergeret-Medina and her supervisor, paleoanthropologist Roberto Macchiarelli of the University of Poitiers in France, finally continued their analysis based on measurements and photos. They just published their findings, which they question Sahelanthropus place in our family tree.
“Based on our analyzes, the partial femur lacks any features consistent with regular Earth bipedal travel attacks,” Macchiarelli and the team write in their paper.
“So if there is compelling evidence that S. tchadensis is a hominin root, so bipedalism can no longer be seen as a requirement for inclusion in the minin clade. “
Another article still awaiting peer review by one of the authors of the original Sahelanthropus Studies contest this, arguing that the femur has a hard top ridge that supports an upright position.
Meanwhile, another paleontologist, Martin Pickford of the French National Museum of Natural History, wonders if the femur even belongs to Toumai, or at least to another. Sahelanthropus.
Still others agree with Macchiarelli’s assessment of the femur.
“I saw the photos 10 or 12 years ago, and it became clear to me that it is more like a chimpanzee than any other hominin,” said University of Tübingen paleontologist Madelaine Böhme, who was not involved in any. of studies New Scientist.
Analysis of the molecular differences in our DNA suggests that humans separated from chimpanzees and bonobos (our closest living relatives) about 6-8 million years ago. The only other fossil evidence of a possible hominid from that period comes from Orrorin tugenensis.
Macchiarelli and team compared the femur with one of O. tugenensis and determined that there is at least one species difference between them.
after also compare them with Australopithecus, gorillas and modern humans, believe that these differences suggest that the mode of locomotion of the two oldest species was also different.
They suspect Sahelanthropus it may be an ancestral relative with no living descendants left – a primate lineage that has become extinct.
They also point out that others have suggested that the small teeth found in the original study may simply indicate that the primate is female. But the team agrees that fascinating questions still remain, particularly around the lines we use to define what exactly makes a primate a human, citing a 2017 article in their conclusion:
“Exactly where in Africa and under what circumstances the human-ape demarcation began and when, how and why the human-ape boundary became irrevocably established, are important research challenges that are still unresolved.”
We will need many more fossils before we know the answers.
This research was published in Journal of Human Evolution.
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