Anthropology Arguments: Two New Papers Reach Opposing Conclusions on Early Human Ancestor Sahelanthropus tchanensis Locomotion

Hey All!

Thought I would force-feed the forum some interesting news in anthropology with regard to the hominin known as Sahelanthropus tchadensis!

This hominin has been thought to be the earliest in the human lineage succeeding the split from those of modern panins. It is most well known from a partial cranium found in 2002, that is notable for it’s small selection of decidedly derived features among what is otherwise very “chimp-like”.

S. tchadensis had reducing canines, a modest braincase for a Miocene hominin (350-380cc) and a foremen magnum whose position and angle was more derived than those seen in chimpanzees. A recently published femur find has been examined by two teams who have essentially reached opposite conclusions on it’s locomotion: the earlier team saying it was a certain biped, and the later team suggesting it was more likely a quadruped.

Team A: Guy et al. (September 2020)

“The original material was discovered at locality TM 266 (Toros-Menalla fossiliferous area), and consists in one left femur and two antimeric ulnae. These new findings confirm that hominins were already terrestrial biped relatively soon after the human-chimpanzee divergence but also suggest that careful climbing arboreal behaviors was still a significant part of their locomotor repertoire.”

Team B: Machiarelli et al (December 2020)


“The results of our preliminary functional analysis suggest the TM 266 femoral shaft belongs to an individual that was not habitually bipedal, something that should be taken into account when considering the relationships of S . tchadensis . The circumstances of its discovery should encourage researchers to check to see whether there is more postcranial evidence of S . tchadensis among the fossils recovered from Toros-Menalla.”

I personally think this is all very fascinating, and that both papers make excellent points. Only time will tell where S. tchadensis ends up!

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Interesting. It has to be said that the fact that scientists can’t agree on it’s mode of locomotion is itself a good argument for it being a transitional fossil.

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I had seen your post and then this popular level article came up in my feed. It’s odd that it leaves a very different impression (forcefully not a hominin) than the abstract of the actual research. But I can’t see the full paper unfortunately to see the discussion.

They also noted that the size of the teeth as argued by Brunet and his team was not sufficient evidence to claim the remains were hominin —they could have come from a small female ape. The researchers conclude that their evidence shows that Sahelanthropus tchadensis was not a hominin and was therefore not an early human ancestor.