A cranium (a skull without the mandible) of the Sahelanthropus tchadensis species was found in Toros-Menalla, Chad. It was deformed but the discoverers proposed that it belonged to a hominin. In 2001, they found at the same place a part of a very damaged femur, eaten by carnivores. After studies in 2004, the femur seemed to belong to a primate and so it was concluded parsimoniously that it probably belonged to the same species. In this article, this femur is studied to determine if it, and thus the cranium, come from a hominid (that is, if it belonged to a lineage before the shared ancestor with chimpanzees/bonobos) or a hominin (the “human family” after the common ancestor with chimpanzees/bonobos). Morphological and biomechanical features associated with bipedalism were studied to determine if the femur belonged to a habitual biped, and so to a hominin.
This study compared the femur of S. tchadensis to another primitive potential hominin from Kenya (Orrorin tugenensis) and concluded that they had different locomotion modes and didn’t belong to the same species. This study also concluded that S. tchadensis was probably not a habitual biped and so was likely to be a hominid rather than a hominin. Nevertheless, more material from this species (more numerous and better-preserved fossils from other body parts) is needed to do more comprehensive studies to have a more confidence in the results of this study and its hypotheses on this issue.
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