A new report challenges the theory that Sahelanthropus tchadensis, a hominid that lived more than 6 million years ago, is our earliest known human ancestor.
French paleontologists discovered Sahelantrop in Chad almost two decades ago.
Calling it “Tumai”, they announce the creature as an early biped – with a skull that indicates that it has a straight spine.
But a new report suggests that Tumai is just an ancient primate, more closely related to chimpanzees than humans.
The researchers base their claims on the shape of the femur, which they believe belongs to Tumi.
They keep a femur curved like a monkey, deliberately left unstudied, because that would discredit the theory that he walked on two legs.
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French paleontologist Michel Brunet discovered the remains of Sahelanthropus tchadensis in northern Chad in 2001. Brunet maintains a creature called Toumai, which walked on two legs more than 6 million years ago and is the oldest known ancestor of mankind.
French paleontologist Michel Brunet first discovered the remains of the Sahelantrop in the Jurab Desert in northern Chad in 2001.
Brunet, a researcher at the University of Poitiers in France, was nicknamed the “Toumai” and claimed in a 2002 Nature report that he was bipedal.
His main evidence was that the base of his skull would be connected to an upright spine.
Using radiometric dates, his team found that Tumai was between 6.8 and 7.2 million years old and had lived at some point during the Miocene era.
Brunet supports the base of Tumai’s skull, indicating that he would be relaxed on a straight spine. But doubts about whether Sahelantropus was a biped have only grown with the publication of a new report that suggests the creature’s femur shows it walked on all fours like a monkey.
This makes Tumay more than twice as old as humanity’s oldest known ancestor, Lucy, discovered in Ethiopia in 1974 and dating to about 3.2 million years ago.
The left femur and two forearms were also found, but for some reason Brunet never published anything on them, and few other researchers had access to the bones.
In 2004, Aude Bergeret-Medina, a researcher at Poitiers, identified unmarked bone as a femur – most likely, she theorized, from a primate.
Eventually, she and her mentor, paleoanthropologist Roberto Machiarelli, began to believe they had fallen on Tumai’s femur.
Aude Bergeret-Medina, a researcher at Poitiers, identified an unmarked bone as Tumai’s femur. The femur is not straight, but curved, which according to Bergeret-Medina is more characteristic of the monkey
But after Bergret-Medina took measurements and photographs, the bone disappeared and no scientist saw it again.
When Brunet’s team failed to publish anything about the femur, she and Machiarelli used her notes and made their own report.
They tried to present their findings at a conference held by the Paris Anthropological Society, but were rejected.
Their hypothesis that Tumay was not standing was finally published in the December 2020 issue of the Journal of Human Evolution.
Photographs of the femur were reviewed by Bergret-Medina and her mentor Roberto Machiarelli. Machiarelli claims that Brunet blocked access to the actual femur because it would discredit the theory that Tumai walked on two legs
According to the report, the femur is not straight, but curved, which is more typical of a monkey.
Others have suspected that Tumai was a human ancestor before.
Shortly after the publication of Brunet’s initial findings, Milford Wolpoff, a professor of anthropology at the University of Michigan, questioned them.
“Tumay may be the common ancestor of monkeys and humans, but he is not on the line leading directly to humans,” Walpoff wrote in a letter to Nature. “We think Toumai is a monkey and we think she’s probably female because of her canine teeth.”
The teeth were small, he said, but they could easily have belonged to a female gorilla or chimpanzee.
Walpoff also pointed to scars on the skull left by the muscles in his neck, claiming that they suggested that Tumai was walking on all fours with his head horizontal to his spine.
Transmission of what Sahelanthropus tchadensis might have looked like when he was alive
Geographer Alain Bovelen, who helped excavate Tumay, even raised questions about where and when the bones were found – suggesting that they were disturbed by locals at some point in the past.
In September, paleontologist Frank Guy, co-author of the original paper on Sahelanthropus, published a separate study doubling the theory of bipeds.
He claims that the femur has a hard spine at the top that would keep the body upright.
But his report has been published on a prepress server, which means it has not yet been reviewed.
Brunet still believes that his Sahelanthropus is the missing link in the family tree of mankind.
“Tumai’s skull is essentially a hominid skull,” he told China’s state-run Xinhua news agency in 2019. He has a “very small” dog tooth similar to a human. “It’s just that a dog can prove he’s not a big monkey.”
Machiarelli claims that Brunet and his colleagues blocked access to the femur and exposed his presentation, as this would discredit their theory that Tumai walked on two legs.
But Brunett insists there are “no contradictions.”
“No one can say scientifically that this femur belongs to Tumai.”