Overview:

Sahelanthropus tchadensis is one of the oldest known species in the human family tree. This species lived sometime between 7 and 6 million years ago in West-Central Africa (Chad). Walking upright may have helped this species survive in diverse habitats, including forests and grasslands. Although we have only cranial material from Sahelanthropus, studies so far show this species had a combination of ape-like and human-like features. Ape-like features included a small brain (even slightly smaller than a chimpanzee’s), sloping face, very prominent browridges, and elongated skull. Human-like features included small canine teeth, a short middle part of the face, and a spinal cord opening underneath the skull instead of towards the back as seen in non-bipedal apes.

 How do we know Sahelanthropus walked upright?

Some of the oldest evidence of a humanlike species moving about in an upright position comes from Sahelanthropus. The foramen magnum (the large opening where the spinal cord exits out of the cranium from the brain) is located further forward (on the underside of the cranium) than in apes or any other primate except humans. This feature indicates that the head of Sahelanthropus was held on an upright body, probably associated with walking on two legs.

History of Discovery:

The first (and, so far, only) fossils of Sahelanthropus are nine cranial specimens from northern Chad. A research team of scientists led by French paleontologist Michael Brunet uncovered the fossils in 2001, including the type specimen TM 266-01-0606-1. Before 2001, early humans in Africa had only been found in the Great Rift Valley in East Africa and sites in South Africa, so the discovery of Sahelanthropus fossils in West-Central Africa shows that the earliest humans were more widely distributed than previously thought.

How They Survived:

Unfortunately, most of Sahelanthropus’ teeth are heavily worn, and there have not yet been studies of its tooth wear or tooth isotopes to indicate diet. However, we can infer based on its environment and other early human species that it ate a mainly plant-based diet. This probably included leaves, fruit, seeds, roots, nuts, and insects.

Evolutionary Tree Information:

The first early humans, or hominins, diverged from apes sometime between 6 and 7 million years ago in Africa. Sahelanthropus tchadensis has two defining human anatomical traits: 1) small canine teeth, and 2) walking upright on two legs instead of on four legs.

Questions:

We don’t know everything about our early ancestors—but we keep learning more! Paleoanthropologists are constantly in the field, excavating new areas with groundbreaking technology, and continually filling in some of the gaps about our understanding of human evolution.

Below are some of the still unanswered questions about Sahelanthropus tchadensis that may be answered with future discoveries:

1. What did the body of Sahelanthropus tchadensis look like? So far paleoanthropologists have only uncovered cranial fossils of this species.
2. What was their primary form of locomotion?
3. What did they eat?
4. Why did Sahelanthropus tchadensis males have smaller canines? This is unlike male chimpanzees and most other primates who use their long canine teeth to threaten others, especially when competing for mates.
5. Were there size differences between Sahelanthropus tchadensis males and females?
6. Was Sahelanthropus tchadensis a common ancestor of humans and chimpanzees?

References:

First Paper:

Brunet ,M., Guy, F., Pilbeam,. D., Mackaye, H.T., Likius, A., Ahounta, D., Beauvilain, A., Blondel, C., Bocherens, H., Boisserie, J.R., De Bonis, L., Coppens, Y., Dejax, J., Denys, C., Duringer, P., Eisenmann, V.R., Fanone, G., Fronty, P., Geraads, D., Lehmann, T., Lihoreau, F., Louchart, A., Mahamat, A., Merceron, G., Mouchelin, G., Otero, O., Campomanes, P.P., De Leon, M.P., Rage, J.C., Sapanet, M., Schuster, M., Sudre, J., Tassy, P., Valentin, X., Vignaud, P., Viriot, L., Zazzo, A., Zollikofer, C., 2002. A new hominid from the Upper Miocene of Chad, central Africa. Nature 418(6894), 145-151

Other recommended reading:

Brunet, M., Guy, F., Pilbeam, D., Lieberman, D.E., Likius, A., Mackaye, H.T., de Leon, M.S.P., Zollikofer, C.P.E., Vignaud, P., 2005. New material of the earliest hominid from the Upper Miocene of Chad. Nature 434(7034), 752-755.