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Last Updated: Wednesday, 31 August 2005, 22:41 GMT 23:41 UK
First chimpanzee fossils found
Chimp teeth, Nature
Different views of a single fossil chimp tooth from Kenya
The only chimpanzee fossils known to science have been unearthed in Kenya, the journal Nature reports.

The three 545,000-year-old chimp teeth were dug up in the country's Tugen Hills and probably belonged to the same individual, the US discoverers say.

Plenty of fossils belonging to early human ancestors, or hominids, have been found at dig sites all over the world.

But until now, scientists had not identified a single fossil belonging to humankind's closest living relative.

I actually suspect there may be [chimp fossils] lurking in museum collections
Sally McBrearty, University of Connecticut
The teeth were excavated from the Kapthurin Formation of the Tugen Hills late in 2004.

"Once you realise what they are, they're dead ringers," Professor Sally McBrearty, of the University of Connecticut, in Storrs, US, told the BBC News website.

"The thick bases of the incisors, in particular, are very characteristic of chimpanzees and also the fact that all of the teeth have thin enamel.

"The molars you might think: 'maybe this is human'; but the cusp pattern isn't really right."

The chimp probably died on the shore of a lake in a wet, wooded habitat.

The fossil remains of hippos, crocodiles, catfish and turtles have been found at the site. And about 1km away, human fossils probably belonging to Homo erectus have been uncovered.

Treasure trove

A fourth tooth has also been found, but this has not yet been published in a scientific journal.

Co-author Nina Jablonski, of the California Academy of Sciences, in San Francisco, estimates that the chimp was seven or eight years old when it died.

Common chimpanzees, Getty Images
The teeth share affinities with the common chimpanzee
The teeth seem to share more affinites with the common chimpanzee (Pan troglodytes) than they do with its "sister" species, the bonobo (Pan paniscus). But the authors say it could equally represent a member of an extinct chimp lineage.

"I think that now people are alerted that there are chimpanzees in the fossil record, they will start looking for them more seriously. I actually suspect there may be some lurking in museum collections," said Professor McBrearty.

"I don't think they were ever very numerous wherever they lived, and if they lived in western and central Africa like they do now, the conditions there are not very good for preservation."

This is because bones tend to rot away in wet habitats. East Africa's semi-arid Rift Valley, on the other hand, is a treasure trove for fossil hunters. Sediments empty into the valley burying animal and plant remains only for tectonic movement to expose the fossils thousands of years later.

Torn apart

East Africa is being torn apart at the rift, which is deepening and widening with time. Eventually, ocean waters will rush in to form a new gulf as Somalia breaks away from Africa.

Many researchers have suggested that humans and chimps have occupied quite separate ecological zones since they split away from a common ancestor between five and eight million years ago.

Modern chimp populations are found in tropical west and central Africa, whereas the Rift Valley is widely regarded as the "cradle of humanity" (though some speculate that hominids could have been more widely dispersed across Africa).

The new discovery demonstrates that half a million years ago, the Rift Valley contained habitats suitable for both early humans and chimps.

Professor McBrearty says that she will now return to the site to see whether there are any more remains to be excavated.

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