A fresh storm has broken out over an ancient fossil presented by its defenders as a forebear of humanity and dismissed by its critics as the remains of a vulgar chimp.

Controversy has swirled around Toumai, the name given to the nearly-complete skull, ever since it was found in the Chadian desert in 2001.

Toumai's big defender is French palaeontologist Michel Brunet, a professor
at the prestigious College de France, who says Toumai walked the Earth shortly
after chimpanzees and hominids diverged from a common ancestral primate.

Brunet has been roundly attacked in other quarters. Critics are incensed that he has given a hominid honorific (Sahelanthropus tchadensis) to a creature whose cranium, in their view, was too squashed to be that of a pre-cursor of Homo sapiens.

They calculate that Toumai's height was no more than 120 centimetres (four
feet) -- or that of an adult chimpanzee.

Brunet appeared to have scored a knockout blow in February this year, when
radiological measurements estimated that the soil where Toumai was found was between 6.8 million and 7.2 million years old.

The study appeared in a top-line US journal, the Proceedings of the National Academy of Sciences.

But the man who discovered Toumai, Alain Beauvilain, of the University of Paris at Nanterre, has now publicly challenged this estimate.

Beauvilain declined to take part in the hominid-vs.-chimp debate, but said
he questioned the dating's methods and the way it had been presented to the
public.

"It's time to set the record straight," he told AFP.

In general, radiodating of the sediment in which a fossil is found is considered to be a good guide to when the creature died, its remains eventually becoming covered by soil or other debris.

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