The Miocene primate was therefore a tree climber. But whether he walked upright on the ground or moved in four-legged motion is unclear. Probably also because the only leg bone that has been found so far is heavily fragmented. Only the shaft of the femur survives; the joint head to the hip is broken off, the articular process to the knee is also missing.
After detailed analysis, Daver and his team want to recognize similarities with the bones of early pre-humans as well as with the possible hominins Orrorin tugenensiswho probably trudged along upright from time to time six million years ago.
But whether the leg bone of Sahelanthropus to be interpreted in this way seems to be a matter of opinion. Scott A. Williams of New York University, who studies the evolution of upright walking, disagrees. “In my opinion, the femur differs significantly from the femurs of other hominins – and modern humans,” Williams told “Spektrum.de”. And are there any similarities between the older Sahelanthropus and the younger Orrorin tugenensis? The paleoanthropologist also disagrees. “I don’t see a great resemblance there.”
The paleontologist Madelaine Böhme from the University of Tübingen takes the same view. She is not very convinced of Davers and Guy’s results: “The femur is extremely fragmentary and in my opinion the conclusions are not very certain.” In 2019, Böhme and her team had the fossils of Danuvius guggenmosi presented, a previously unknown, twelve-million-year-old primate whose bones came from a clay pit in the Eastern Allgäu. Danuvius was possibly also walking on two legs – but that too is controversial.
© MPFT / Palevoprim / CNRS – Université de Poitiers (detail)
Location Djurab Desert | Late Miocene fossil remains have been found at several sites in the desert of Chad. Bones also came from some sites Sahelanthropus to the light.
A bone thickening, two different theses
Daver and Guy point to the calcar femoris as the most powerful argument for their thesis. This bony thickening is located in the neck area of the femur. The seven-million-year-old femur from Chad also has one. What does the calcar femoris do? The thickening is said to help support body weight when walking on two legs.
However, it is not as certain as Davers and Guy’s explanations would suggest that only upright walkers are blessed with it. In any case, a study in the “Journal of Human Evolution” from 2022 came to the opposite conclusion. Marine Cazenave from the American Museum of Natural History in New York and a working group studied the bone structure of surviving and extinct hominids, i.e. great apes, homo sapiens and its predecessors examined. In each of the groups, they found examples with and without bone thickening. “The femoral calcar [femoris] cannot be considered a ‘magical trait’ or diagnostic of bipeds,” concludes Cazenave.