Sahelanthropus tchadensis

Sahelanthropus tchadensis is an early fossil hominid, approximately 7 million years old. The fossils found, a cranium, two pieces of jaw, and some teeth, make up a head that has a mixture of human and chimpanzee features. The braincase suggests a chimpanzee, but the teeth are closer to those of humans, and the face includes brow ridges, a human feature not found on any living great ape. The point at the back of the skull where the neck muscles attach (mastoid process) suggests that this species walked upright.

The discoverers claim that S. tchadensis is the oldest known human ancestor after the split of our line from that of chimpanzees. The bones were found in Chad, far from most previous hominid fossil finds, i.e. eastern and southern Africa. However, an australopithecine mandible was found in Chad by Sahelanthropus' discoverers in 1993.

The fossil skull, nicknamed "Toumaï" ("hope of life" in the local Goran language of Chad), may be a common ancestor of humans and chimpanzees, though unlikely to be the most recent common ancestor, as evidence from the molecular clocks suggest humans and chimps diverged 1-2 million years after S. tchadensis (5mya).

This find complicates the picture of the human family tree. In particular, if Toumaï is a direct human ancestor, his facial features bring the status of Australopithecus into doubt.

Another possibility is that Toumaï is related to humans and chimpanzees, but the ancestor of neither. Brigitte Senut, the discoverer of Orrorin claims that the features of S. tchadensis are consistent with a female proto-gorilla. Even if Senut's claims are true the find would still be significant; there have been no chimp/bonobo or gorilla ancestors to be found anywhere in Africa and light would be shed on their family trees.

See also

• Evolution of Homo sapiens

External link

• http://www.nature.com/nsu/020708/020708-12.html

• Fossil Hominids: Toumai