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A new report challenges the theory that Sahelanthropus tchadensis, a hominid who lived more than 6 million years ago, was our first known human ancestor.
French paleontologists discovered a Sahelanthropus in Chad nearly two decades ago.
Dubbing it “Toumai”, they announced the creature as an early biped, with a skull indicating it had an erect spine.
But a new report suggests that Toumai is just an ancient primate, more closely related to a chimpanzee than to a human.
The researchers are basing their claim on the shape of the femur which they say belongs to Toumi.
They keep the femur, curved like a monkey, was intentionally left unexamined, because it would have discredited the theory that he walked on two feet.
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French paleontologist Michel Brunet discovered remains belonging to Sahelanthropus tchadensis in northern Chad in 2001. Brunet claims that the creature, nicknamed “Toumai”, walked on two legs more than 6 million years ago and is the oldest known ancestor of the humanity
French paleontologist Michel Brunet first discovered the remains of a Sahelanthropus in the Djurab desert of northern Chad in 2001.
Brunet, a researcher at the University of Poitiers in France, dubbed the specimen “Toumai” and, in a 2002 nature report, claimed it was bipedal.
His main evidence was that the base of his skull would be connected to an erect spine.
Using radiometric dating, his team determined that Toumai was between 6.8 and 7.2 million years old and lived at some point during the Miocene era.
Brunet argues that the base of Tumai’s skull shows that it would have rested on an upright spine. But doubts that Sahelanthropus was bipedal only grew with the release of a new report suggesting the creature’s femur shows it walked on all fours, like a monkey.
This makes Toumai more than double the oldest known ancestor of humanity, “Lucy”, discovered in Ethiopia in 1974 and dating back about 3.2 million years.
A left femur and two forearm bones were also discovered, but for some reason Brunet never published anything about them and few other researchers had access to the bones.
In 2004, Aude Bergeret-Medina, a researcher from Poitiers, identified an unlabeled bone as a femur – most likely, she theorized, from a primate.
Eventually she and her mentor, paleoanthropologist Roberto Macchiarelli, came to believe they had stumbled upon Toumai’s femur.
Aude Bergeret-Medina, a researcher from Poitiers, identified an unlabeled bone as Tumai’s femur. The femur is not straight but curved, which according to Bergeret-Medina is more typical of a monkey
But after Bergeret-Medina took measurements and photographs, the bone disappeared and neither scientist saw it again.
When Brunet’s team failed to publish anything about the femur, she and Macchiarelli used her notes and prepared their report.
They attempted to present their findings at a lecture given by the Anthropological Society of Paris, but were rejected.
Their hypothesis that Toumai was not standing was finally published in the December 2020 edition of the Journal of Human Evolution.
The photos of the femur were reviewed by Bergeret-Medina and his mentor, Roberto Macchiarelli. Macchiarelli claims that Brunet blocked access to the actual femur because it would discredit the theory that Toumai walked on two legs.
According to the report, the femur is not straight but curved, which is more typical of a monkey.
Others have doubted that Toumai is a human ancestor before.
Shortly after the publication of Brunet’s first findings, Milford Wolpoff, a professor of anthropology at the University of Michigan, questioned them.
“Toumai may be a common ancestor of apes and humans, but he is not on the line that leads directly to humans,” Wolpoff wrote in a letter to Nature. “We think Toumai is a monkey and we think it’s probably a female because of her canines.”
The teeth were small, he said, but they could still easily belong to a female gorilla or a chimpanzee.
Wolpoff also pointed to the scars on the skull left by the neck muscles, arguing that they suggest that Toumai walked on all fours with his head horizontal to the spine.
A representation of what Sahelanthropus tchadensis looked like when it was alive
Geographer Alain Beauvilain, who helped excavate Toumai, even raised questions about where and when the bones were found, suggesting they had been disturbed by locals in the past.
In September, paleontologist Franck Guy, a co-author of the original Sahelanthropus paper, published a separate study doubling down on the bipedal theory.
He argued that the femur has a hard ridge near the top, which would support an erect body.
But his report was posted on a prepress server, which means it hasn’t been peer reviewed yet.
Brunet still claims that his Sahelanthropus is a missing link in the family tree of humanity.
“Toumai’s skull is, in essence, a hominid skull,” he told the Chinese state news agency Xinhua in 2019. He has a “very small” canine, like a human. “Only the dog can prove it’s not a great ape.”
Macchiarelli claims that Brunet and his colleagues blocked access to the femur and made his presentation pale, because it would discredit their theory that Toumai walked on two feet.
But Brunet insists that “there are no disputes”.
“Nobody can say scientifically that that femur belongs to Toumai.”
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