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Toumai skull: is it man's earliest ancestor?

08 April 2005

New fossil finds and analysis of the ‘Toumai’ skull, discovered in Chad in 2002, strongly suggest it was closer to humans than to apes.

At six to seven million years old, Sahelanthropus tchadensis (nicknamed ‘Toumai’), would be man's earliest known ancestor - this being the period when scientists think the ancestors of humans split from the ancestors of chimpanzees.

The skull and other remains were excavated in 2002 by a team led by Michel Brunet of the University of Poitiers. Some anthropologists disagreed with the claim that it was the oldest known hominid and said that the fossil more closely resembled a gorilla.

New specimens and CT scan

Brunet and colleagues now report that new teeth and jaw specimens, have been found. The specimens and a CT (computed tomography) scan of Toumai's head, build on their original 2002 findings, that the Toumai skull is an ancestor of man. Brunet says ‘now it's completely confirmed that Toumai is not a chimp, or a gorilla, but a true hominid’ (reported on the Nature website).

The new teeth samples show Toumai had small canines, large molars and premolars that had thick enamel - a pattern similar to later members of the human family.

Also the positioning of the foramen magnum - the opening at the base of the skull where the spinal cord enters - is similar to humans but differs from apes. This suggests Toumai walked upright.

Comparing modern humans, chimps and gorillas

Professor Chris Stringer, Head of Human Origins at the Natural History Museum, said ‘these new analyses certainly go a long way to establishing that the Chad skull is an early member of the human family.’

‘However, it should be borne in mind that comparisons with modern humans, chimps and gorillas are not very appropriate, since all have evolved away from ancestral conditions over the last few million years and so would not be expected to resemble the Chad fossil closely.’

Prof Stringer added ‘while we have early fossil members of the human lineage for comparison with Toumai, we have little that seems to relate to the African apes.’

‘However, there are fossil apes older than Toumai, ones that probably pre-date the evolutionary divergence of the African ape and human lines, and these should be part of any comparisons to establish what the Chad find really represents.’

The findings are published in Nature (06/04/05).

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