The femur of our oldest ancestor confirms that it was bipedal

The femur of our oldest ancestor confirms that it was bipedal

Views of the femur and the two ulnae of Toumaï. / Franck Guy / CNRS

Science | Evolution

Toumaï lived 7 million years ago in what is now Chad, he walked on two legs on the ground and probably also in the trees

The femur of Toumaï, a hominid that lived in what is now Chad 7 million years ago, confirms that it was bipedal on the ground and probably also in the trees, a group of researchers led by Guillaume Daver maintains in the journal 'Nature' and Franck Guy, paleoanthropologists at the University of Poitiers. The first fossils of Toumaï, a name that in the Goran language means 'hope of life', were discovered in 2001 in Toros-Menalla and gave name to a new species of hominid, 'Sahelanthropus tchadensis'.

Those remains were a skull, two jaw fragments and three teeth. The brain capacity of the individual was around 350 cubic centimeters, close to that of the chimpanzee and very far from our species (1,400 cubic centimeters), and it had a chimpanzee's cranial vault and a hominid face. Despite not having any postcranial bone (of the trunk and extremities) at that time, the authors of the find already pointed out that Toumaï was very possibly bipedal: this was indicated by the orientation and anterior position of the occipital foramen, the hole for where the spinal column inserts

Daver, Guy and colleagues now present the analysis of a left femur and a pair of forearm bones (ulnae) from the same site and corresponding to the same species. According to them, the anatomy of the femur is indicative of Toumaï's bipedalism. In addition, they highlight that the features of the ulnae coincide with those characteristic of adaptation to climbing.

Functional patterns of the forearm bones suggest that Sahelanthropus was able to climb up and down trees, probably with some form of grasping and irregular limb movement. This evidence shows, according to the researchers, that the first hominids developed the ability to walk on two legs shortly after the divergence of our lineage and that of the chimpanzee, although our ancestors initially retained anatomical characteristics suitable for arboreal life.

Twenty years ago, Toumaï's discovery revolutionized paleoanthropology. He showed that hominids had arisen earlier than previously believed and that the first had lived in an African region far from where our lineage was thought to have appeared, East Africa.

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