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Wednesday, 10 July, 2002, 18:00 GMT 19:00 UK
Q&A: Chad fossil discovery
Q&A, BBC
A fossil skull unearthed in Chad has been described as one of the great paleoanthropological discoveries of the last 80 years. BBC News Online asks what is so special about the creature called Sahelanthropus tchadensis.

What exactly have the researchers found?

Michel Brunet and his colleagues have unearthed 6-7-million-year-old fossil fragments of a human-like creature - a so-called hominid - in Chad, Central Africa. The team found a near-complete cranium; there are jaw fragments and several teeth also. The scientists have nicknamed the skull Toumai, or "hope of life" in Africa's Goran language.

What is significant about this particular hominid?

It is very old for a start - far older than most of the hominid specimens so far discovered. But its features are the real surprise. These are a mixture of primitive and advanced features.

The braincase is ape-like, but the face is short and the teeth, especially the canines, are small, more like those of a human. In particular, Toumai has brow-ridges (bony structures on the skull above the eye sockets) of a kind not seen outside the Homo genus (which includes modern humans).

What are the implications for our understanding of human evolution?

If, as scientists believe, humans came out of a common ancestor with chimps (our closest living animal relatives) then the age of Toumai would suggest that creature existed further back in time than is currently thought.

Estimates of when this common ancestor might have existed have been based on DNA comparisons between humans and chimps, and put at between five and seven million years ago. Toumai could indicate that this "molecular clock" actually runs much slower than thought.

The modern features seen in Toumai could also indicate that he (the specimen is probably male) has a more direct line of ascent to modern humans than all of the various African "ape-men" from between five and two million years ago, discovered over the past 70 years or so.

The location of the discovery is significant as well. This is well over a thousand kilometres to the west of the East African hominid finds that have been the focus of early human investigation up until now.

Is there a "missing link" yet to be discovered linking us to a common ancestor with apes?

To some extent, what Toumai does is further complicate an already murky picture of human origins. Many of those scientists who have so far commented on the discovery say it supports a theory of hominid evolution that has many branches - and many dead ends.

We should not look at human emergence as a simple ladder with a missing link at the bottom, they argue. This extraordinary mosaic will only become clearer as more hominid creatures - and more ancestors of gorillas and chimps - are discovered, they believe.

What would this creature have looked like?

That is very difficult to say based on these small fragments. One of the central questions, however, centres on whether this creature could walk upright. "We have [found] no legs, but this new guy with the position of where his spine enters his head doesn't prove that he was bipedal, but it shows he could be," Michel Brunet said.

Can we say anything about how this creature might have lived?

Toumai was found with a wide range of other animal fossils - the excavation site has thrown up more than 700 specimens, including fish, crocodiles and rodents. Not only have these been used to date Toumai, they have also helped to open a window on the local environment 6-7 million years ago. They suggest Toumai lived in an area with a diverse range of habitats, which included lush forest and a lake.

See also:

10 Jul 02 | Science/Nature
10 Jul 02 | Science/Nature
10 Jul 02 | Science/Nature
21 Mar 01 | Science/Nature
07 Feb 01 | Science/Nature
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