The earliest known human ancestor walked on two legs and climbed through trees about seven million years ago, scientists said Wednesday after examining three limb bones.
When the skull of Sahelanthropus tchadensis was discovered in Chad in 2001, it pushed back the age of humanity’s oldest known representative species by a million years.
The nearly complete skull, nicknamed “Toumai”, should indicate that the species walked on two legs based on the position of its spine and other factors.
However, the topic sparked heated debate among scientists, partly due to the scarcity and quality of available bones, with some even claiming that Toumai was not a human relative, just an ancient ape.
In a study published Wednesday in the Nature journal, a team of researchers analyzed in depth a femur and two forearm bones found in the same location as the Toumai skull.
“The skull tells us that Sahelanthropus is part of the human lineage,” said paleoanthropologist Franck Guy, one of the study’s authors.
The new research on the limb bones shows that walking on two legs was the “preferred mode of locomotion, depending on the situation,” he told a news conference.
But they also sometimes moved through the trees, he added.
– ‘No magical property’ –
The leg and arm bones were found along with thousands of other fossils in 2001, and researchers could not confirm they belonged to the same individual as the Toumai skull.
After years of testing and measuring the bones, they identified 23 features that were then compared to fossils of great apes and hominins — species more closely related to humans than chimpanzees.
They concluded that “these traits are much closer to what you would see in a hominin than in any other primate,” study lead author Guillaume Daver said at the press conference.
For example, the forearm bones showed no evidence that the Sahelanthropus supported itself on the backs of its hands like gorillas and chimpanzees do.
The Sahelanthropus lived in an area with a combination of forests, palm groves and tropical savannas, meaning being able to walk and climb through trees would have been beneficial.
There have been previous suggestions that it was the ability to walk on two legs that caused humans to evolve separately from chimpanzees that set us on the path to where we are today.
However, the researchers emphasized that what made Sahelanthropus human was its ability to adapt to its environment.
“Bipedalism (walking on two legs) is not a magical trait that strictly defines humanity,” paleontologist Jean-Renaud Boisserie said at the press conference.
“It is a quality that we find in all representatives of humanity at this time.”
– Our ‘bushy’ family tree –
Paleoanthropologist Antoine Balzeau of France’s National Museum of Natural History said the “extremely comprehensive” study gave “a more complete picture of Toumai, and therefore of the first humans.”
It also supported the theory that the human family tree is “bushy,” rather than the “plain picture of people following one another, with skills that improve over time,” said Balzeau, who wasn’t involved with the research , to AFP .
Daniel Lieberman, a professor of human evolutionary biology at Harvard University, said in a linked article in Nature that the study’s authors “squeezed out as much information as possible from the fossil record.”
But he added that the research will not provide a “complete solution” to the debate.
Milford Wolpoff, a paleoanthropologist at the US University of Michigan, questioned whether Toumai is a hominin, telling AFP that “extraordinary claims require extraordinary evidence.”
Wednesday’s study was carried out by researchers from the paleontological institute PALEVOPRIM, a collaboration between the French research center CNRS and the University of Poitiers, and scientists in Chad.
Guy said the team hopes to continue their research in Chad over the next year – “if safety permits”.
Chadian paleontologist Clarisse Nekoulnang said the team was “trying to find sites older than Toumai”.
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