Controversial 7-million-year-old skull may not be as human as we thought

The question of whether a 7-million-year-old primate, nicknamed ‘Toumai’, walked on two or four legs, has stripped drama among paleontologists – complete with a vanished fever.

Since the discovery of Sahelanthropus tchadensis First fossil back in 2001, it has often been cited as our earliest known hamnin ancestor. Initial analysis suggested that Sahelanthropus Constantly went upright and has a combination of ape-like and human-like features.

These conclusions, however, are based on a single skull.

The skull has anatomical features that potentially indicate the primate has a straight spine, and therefore spent some of its time walking only on two legs. The small teeth are also more human than a monkey. A later reconstruction supported the findings.

But other researchers have argued that this alone is not enough evidence to class Sahelanthropus As a hominin beeped – a primate directly ancestral to humans – rather than a related, but not directly ancestral hominid.

Around the same time and in the same place where the skull was found, at Toros-Menalla in Chad, a part of the left femur was also recovered. The femur disappeared after another researcher started to examine it in 2004, still supposedly by chance.

Aude Bergeret-Medina and her supervisor, paleoanthropologist Roberto Macchiarelli of the University of Poitiers in France, eventually continued their analysis based on measurements and photos. They have just published their findings, which cast doubt on Sahelanthropus s Place in our family tree.

“Based on our analyzes, the partial femur lacks any feature consistent with regular bats of terrestrial bipedal travel,” Macchiarelli and team wrote in their paper.

“So, if there are compelling say that S. tchadensis Is a stem hominin, then bipedalism can no longer be seen as a requirement for inclusion in the hominin dress. “

Another paper still awaiting peers review from one of the authors of the original Sahelanthropus Studies dispute this, claiming the femur has a solid peak ridge that supports an upright stance.

Meanwhile, another paleontologist, Martin Pickford of the French National Museum of Natural History, wonders if the femur even belongs to Toumai, or at least another Sahelanthropus.

Still, others agree with Macchiarelli’s assessment of the fiver.

“I saw the pictures 10 or 12 years ago, and it was clear to me that this is more like a chimp than any other hominin,” said Madelaine Böhme, a phallontologist at the University of Tubingen. None of the studies, said New Scientist.

Analysis of molecular differences in our DNA suggests that humans parted ways about chimpanzees and bonobos (our closest surviving relatives), about 6-8 million years ago. The only other fossil evidence of a possible hominin from that time is from Orrorin tugenensis.

Macchiarelli and team compared the femur to one of O. tugenensis And determined that there is at least the difference between species.

Fter also comparing them with Australopithecus, Gorillas, and modern humans, they believe that the differences suggest the mode of locomotion of the two oldest species is also different.

They suspect Sahelanthropus Could be an ancestor relative with no remaining living descendants – a first pedigree that is extinct.

They also showed that others had suggested that the small teeth found in the original study could only indicate the primate was female. But the team agrees that fusing questions nevertheless remain, particularly around the lines we use to define what exactly makes a person a primate, citing a 2017 paper in their conclusion:

“Exactly where in Africa, and under what circumstances, did the open-human demarcation begin, and when, how and why the open-human border was established independently, are important research challenges that remain unresolved.”

We need much more fossils before we know the answers.

The research was published in the Journal of Human Evolution.

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