Sahelanthropus and Orrorin – Human Evolution

 

Human EvolutionLast week, we talked about the Red Deer Cave people, a seemingly anachronistic species of archaic humans. If you missed it, check it out to discover more about their distinct development.

You are probably familiar with Lucy, the most famous specimen of Austrolopithecus afarensis. Her species is often referred to as the missing link between humans and chimpanzees. But she actually represents a point in our shared history where hominids broke away from the species that would become our modern-day chimpanzees and bonobos. But the two species we’re going to be talking about today are not so clearly understood at the present moment.

 

Sahelanthropus is probably the ancestor of Orrorin, though even that is a little hazy. They were probably both related to Austrolopithecus, and might not be related to modern humans. If this is the case, then they represent another branch in the tree with the path leading to us and the path leading to chimps. Only their path wasn’t successful.

Fossil of Possible Human Ancestor
Sahelanthropus

Part of the confusion is the lack of fossil remains. Only a skull comprised the fossil record for Sahelanthropus. The skull is markedly different from both Lucy’s and modern humans’. The face is flatter than we might have expected, and the canines are smaller. Further, the skull has been distorted by time and so we still don’t have an entirely clear picture of what their heads would have looked like. And the fact that there is only a skull, and no other bones have been found, leaves everyone in the dark as to whether they were bipedel, and if not, what their hip and vertebrae structure were like, or how tall or short they were.

Orrorin, a descendant of Sahelanthropus, has a slightly larger fossil record. They also had smaller teeth than Austrolopithecus. Their teeth were very similar to those that modern day chimpanzees have. Enough exists that you could conclude that they were bipedal. Their skull rotated on the vertebrae in the same was ours does and and the connection of the hip to the leg indicates walking on two legs, but other parts of their skeleton show that they were adapted for regularly and naturally climbing trees. Likewise, their thumb was structured in a way that would have been useful for toolmaking, but it could also have aided Orrorin in climbing. The fact that both species would have been living in a wooded environment rather than a savanna supports the tree-climbing side more strongly.

 

If future discoveries or research shows that Sahelanthropus and Orrorin are direct human ancestors, that breakthrough could mean that Austrolopithecus afarensis is not. It would shift a significant portion of what we currently understand as our evolutionary history.

Thank you for reading. If you have a question or request, please leave it in the comments down below. We publish a new blog every Tuesday and Friday so, until next time, goodbye!

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