He was already walking on two legs, while maintaining the ability to climb and move on all fours in trees, the ancient hominid Sahelanthropus tchadensis lived 7 million years ago in the’Central Africa. This is demonstrated by the analysis dthe three bones of the upper and lower limbs found in 2001 in Chad, in the Toros-Menalla site located in the Djurab desert. I study, published in the journal Nature by a team led by the French National Scientific Research Center (CNRS), suggests therefore that the bipedalism – crucial to human evolution – would have been acquired immediately after the separation between the ancestor of the current anthropomorphic apes and the ancestor of modern humans.
The hypothesis had already been advanced in the past, in light of the morphology of the skull of Sahelanthropus tchadensis, found almost complete and nicknamed Toumai (‘life expectancy’ in the local language). The orientation and anterior position of the foramen occipital (the opening that connects the base of the skull with the vertebral canal) indicated a bipedal mode of locomotion. A study published in 2020 in the Journal of Human Evolution, with the participation of the anthropologist Damiano Marchi of the University of Pisa, had instead contested this possibility on the basis of an analysis of the functional morphology of a partial fossil femur, also found in Toros- Menalla.
The same finding is now at the center of the new French study, along with two ulnae of S. tchadensis. The finds were examined for their morphology and internal structure according to about twenty different parameters. The data thus obtained were then compared with those relating to the bones of fossil and existing monkeys (such as chimpanzees, gorillas, orangutans, Miocene monkeys and even Homo sapiens).
According to the researchers, the structure of the femur would indicate that Sahelanthropus used to be move on two legs on the ground and probably also on trees. The characteristics of the forearmshowever, they suggest that the hominid was capable of to climb on trees and move on all fours thanks to a strong grip, very different from that of gorillas and chimpanzees who instead rest on the backs of the phalanges.
According to paleoanthropologist Daniel E. Lieberman of Harvard University, Sahelanthropus’s femur may not be considered the smoking gun of bipedalism, but it still looks more like the femur of a bipedal human ancestor than that of a quadrupedal ape. “When considered together with the orientation of the foramen magnum, which is compatible only with bipedalism, it seems reasonable to deduce that Sahelanthropus was in a sense bipedal and that it was also well adapted to climbing trees”, writes the expert in an article by comment in Nature.
“A few million years later, Australopithecus also evolved to be an efficient walker while maintaining various adaptations needed to climb trees. It is only in mankind, Homo, that the necessary adaptations to move among the trees have been lost as they become skilled runners. Having said that – adds the expert – we know little else about Sahelanthropus’ gait. A mix of walking and climbing makes sense, considering that Sahelanthropus lived near a lake with an adjacent forest. “