Reacción a "New evidence confirms that the oldest known hominid walked on two legs 7 million years ago"

The study is based on solid data and methods and is included in various previous works that defend or criticise the presence of bipedalism in Sahelanthropus. The main new findings are the description of an anteversion of the femoral diaphysis, which may be related to the presence of a bicondylar angle in this bone, and the description of a well-developed femoral tubercle. Both anatomical features are related to bipedal locomotion. The main limitation is that the anteversion and femoral tubercle have been described in an incomplete femur.

In practice, the relevance of this article is that the demonstration of bipedalism in Sahelanthropus would be the oldest known, placing it very close to the evolutionary split in the two lines that gave rise to chimpanzees and humans.

Sahelanthropus tchadensis is one of the fossil primates potentially located in the evolutionary line of the oldest known humans. Its fossil remains have been dated to about 7 million years ago, but its bipedal locomotion, a determining factor in placing a fossil primate within the evolutionary line of Homo sapiens, has not been clearly demonstrated. Some authors defend the bipedal locomotion of this primate based on the anatomy of the femur (Daver et al., Nature 2022), while others find no relationship between the bone morphology of the postcranial skeleton of Sahelanthropus tchadensis and bipedal locomotion (Cazenave et al., Journal of Human Evolution 2025).

This article by Williams et al. in Science Advances (2025) presents new evidence pointing to possible bipedal locomotion in Sahelanthropus tchadensis, based mainly on femoral anatomy. The presence of an anteversion in the femoral diaphysis, which can be related to the presence of a bicondylar angle in this bone, an anatomical feature typical of bipedal primates such as Homo sapiens, as well as the presence of a well-developed femoral tubercle, are novel evidence that would support the presence of bipedal terrestrial locomotion in this fossil primate.

The development of bipedalism in Sahelanthropus tchadensis, shared with other types of common arboreal locomotion, would support the position of this fossil primate in the evolutionary line of humans, placing it very close to the common ancestor from which the two evolutionary lines that gave rise to chimpanzees and modern humans originated some 7 million years ago.