Prehistoric World

Experts are a step closer to answering whether an ancient skull from Africa belonged to a possible human ancestor or to a creature closer to apes.

Fresh fossil finds from Chad in central Africa, as well as a new analysis of the skull, seem to confirm "Toumaï" was closer to us. The Toumaï specimen was unearthed in Chad in 2002 to international acclaim. But rival researchers attacked claims by the discovery team that it was the oldest hominid, or human-like creature.

The near-complete skull, pieces of jawbone and several teeth unveiled in 2002 were found in the desert of northern Chad by a team led by Michel Brunet, at the University of Poitiers, France.

At six to seven million years old, Sahelanthropus tchadensis, (better known by its nickname Toumaï), dates to about the time where, according to genetic data, the ancestors of humans and the ancestors of chimpanzees went their separate evolutionary ways.

The find had a puzzling combination of modern and primitive features, with an ape-like brain size and skull shape, combined with a more human-like face and teeth. It also sported a remarkably large brow-ridge, more similar to that of hominids.

But at least one anthropologist argued that the fossil could belong to a female forerunner of the gorilla.

Now Brunet and colleagues report discovering two new jaw fragments and the crown of a tooth in the same geographical area as the earlier fossils. The authors say their analysis reveals key similarities to hominid fossils and differences from African apes that support the idea Toumaï was a hominid.

Virtual Reconstruction

In a separate paper, a team including Brunet and Christoph Zollikofer of the University of Zurich in Switzerland, presents a 3D computer reconstruction of the skull, which had been badly distorted in the ground.

The team has essentially "unmangled" the skull, and the reconstruction appears to confirm that tchadensis shared key features with later hominids.

In addition, the position of the foramen magnum - the hole where the spinal cord enters - is similar to that in humans but not apes. This suggests Toumaï was bipedal; the creature walked upright like modern humans.

"We performed a virtual reconstruction because the skull is heavily mineralised and distorted. It is impossible to do one by physical means," Professor Zollikofer said. "[The find] is absolutely unique for several reasons. First, because of its age. Then because of its geographical location. Third, because it is incredibly complete."

Not swayed

Martin Pickford, of the National Museum of Natural History in Paris, is one of those scientists unconvinced by arguments that Toumaï is a hominid.

"What we're saying is that it is an ape-like animal. It may well have given rise to bipedal hominids, but it's not yet a bipedal hominid," Dr Pickford said.

Professor Zollikofer commented: "I would say most of the disagreement over the fossil came from the fact that it is distorted, so it is quite difficult to recognise the diagnostic hominid features."

If Toumaï really does belong on the human branch of the evolutionary tree, its discovery calls into question certain assumptions about our prehistory. The fossils were found some 2,500km (1,500 miles) west of the African Great Rift Valley - traditionally seen as humankind's ancestral home due to the wealth of hominid fossils that have been discovered there.

The discovery of tchadensis implies early hominids ranged far wider from East Africa, and far earlier, than previously thought. It also suggests that hominids evolved quickly when they set off on their own evolutionary path.

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