Toumaï, a knuckle-walker?

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Marc R. Meyer et al, “Knuckle-walking in Sahelanthropus? Locomotor inferences from the ulnae of fossil hominins and other hominoids”, Journal of Human Evolution, vol. 179, 2023

The debate over whether Toumaï, whose scientific name is Sahelanthropus tchadensis, belongs to the Hominins is still raging, and a new article may well provide the final blow.

Sahelanthropus tchadensis was discovered in 2001 at Toros-Menalla in Chad. Dated at around 7 million years, it is one of the 3 candidates for the title of oldest representative of the human lineage. For some researchers, Toumaï is indeed a member of the Hominins, since he was bipedal. Its bipedalism is confirmed by the anterior position of the foramen magnum, similar to that found in our own species. For other researchers, Toumaï is not bipedal and therefore not a Hominin. One of the arguments put forward, for example, is the conformation of the femur, which resembles a chimpanzee femur more than aHomo sapiens femur.

However, an article published in the Journal of Human Evolution has reshuffled the deck, demonstrating that Toumaï was in fact a significant knuckle-walker. To achieve this, the study carried out combined analyses of the conformation of the diaphysis and the proximal complex of the ulna. The results show that the ulna of S. tchadensis displays typical knuckle-walking characteristics. The authors propose 2 hypotheses to justify such a result. The first is that S. tchadensis is a very ancient Hominin having “retained” knuckle-walking behavior. The second is that Toumaï is indeed not a Hominin, but practiced knuckle-walking like that found in chimpanzees. However, such results need to be confirmed.

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