Toumaï, the oldest known representative of humanity, walked well on two legs seven million years ago. But he could still climb trees, according to a study in Nature, resting on three bones belonging to a representative of his species.
The story begins in Toros-Ménalla, in northern Chad, when in 2001 a team from the Franco-Chadian paleoanthropological mission unearthed a skull. Sahelanthropus tchadensis, Toumaï for those close to him, then ousts Orrorin tugenensis, six million years old and discovered in Kenya, as the oldest known representative of humanity.
The position of the foramen magnum in the skull of Toumaï, with a vertebral column located under the skull and not behind as in a quadruped, places it as a bipedal primate. A few specialists have disputed this conclusion, arguing that the fossil is incomplete.
Bipedalism, preferred means of transport
The study by researchers from PALEVOPRIM, the evolution laboratory of the University of Poitiers, the CNRS and Chadian academics makes a decisive contribution to this discovery.
“The skull tells us that Sahelanthropus is part of the human lineage,” explained Franck Guy, paleoanthropologist and one of the authors of the study, on Tuesday. The latter demonstrates that “bipedalism was his preferred mode of locomotion, depending on the situation,” he added during a press conference.
“A little bit of arborealism”
This bipedalism was “usual but not only, with also a little bit of arborealism”, in other words the ability to move in trees. A legacy of the hypothetical common ancestor of the human line and that of chimpanzees.
The team demonstrates this with the detailed study of a femur and two bones of the forearm, the ulna. Bones which we will never know if they were those corresponding to the individual Toumaï, but found on the same site and belonging like him to those of a hominin, the human line.
Battery of tests
The scientists of the Franco-Chadian mission studied them, over several years, with an exhaustive battery of tests and measurements. They identified 23 morphological and functional traits, before comparing them with those of other living and fossil hominins and great apes.
Their conclusion is that “the set of these character traits is much closer to what one would see in a hominin than in any other primate”, said Guillaume Daver, paleoanthropologist of the PALEVOPRIM team and first author. of the study, during the press conference.
For example, whereas in quadruped mode a gorilla or a chimpanzee, the closest cousin of the current human being, advances by leaning on the back of the phalanges of its hand, this is not observed with Sahelanthropus.
Forests and wet savannah
The individual whose bones were thus studied weighed between 43 and 50 kilos. The bare desert landscape that today hosts his remains mixed forests with palm groves and humid savannah in his time. A framework favoring both walking and a “cautious” quadruped in the foliage.
The study thus provides “a more complete image of Toumaï and finally of the first humans”, remarked to AFP the paleoanthropologist Antoine Balzeau, of the National Museum of Natural History, welcoming an “extremely substantial” work.
“Bushy” evolution
It brings additional arguments to the proponents of a “bushy” evolution of the human line, with multiple branches, going against a “simplistic image of humans who follow one another, with capacities which improve over time. over time”, remarks Mr. Balzeau.
What made Sahelanthropus human was its ability to adapt to a given environment, according to the PALEVOPRIM researchers, who stressed the importance of not seeing bipedalism as a “magical trait” defining the humanity of strict manner.
In an article accompanying the study, Daniel Lieberman, professor of evolutionary biology at Harvard, believes that the study does not yet offer a “definitive solution” to the question of the nature of Toumaï.
The PALEVOPRIM team intends to resume its research in Chad next spring, “security permitting”, said Mr. Guy. Because as indicated by the Chadian paleontologist Clarisse Nekoulnang, of the National Center for Research and Development, the teams on site “try to find sites older than that of Toumaï”.
This article has been published automatically. Sources: ats / afp