What insight has Toumaï brought ?
samedi 2 août 2003
What insight has Toumaï brought ?
African palaeo-anthropologist Ahounta Djimdoumalbaye’s discovery of a
fascinating new fossil skull in the Central African nation of Chad rocks the very roots of the human family tree as we know it. The fossil skull is the oldest of any hominid or pre-human ancestor skull found to date, yet its features appear much more human than many other ancient contenders for the title of "grandfather of humanity" found elsewhere on the continent.
Then again, some scientists claim that Toumaï is not hominid at all - merely
a well-preserved female gorilla, in which case both his name and his
classification are wrong. The 7-million year old fossil skull from central
Africa is called Toumaï, which means "hope of life" in Chad’s Goran
language, because it’s a name often given to boys born near the end of the
dry season - the time when he was uncovered.
Like the Mrs Ples skull and the Little Foot skeleton found in South Africa, and the Lucy skeleton in East Africa, Toumaï is certainly a distant relative of all humankind. Mrs Ples is of Australopithecus africanus, discovered at
South Africa’s Sterkfontein caves in 1947 and she represents a species which roamed the southern tip of Africa between about 3 and 2 million years ago.
Little Foot, at 4.17 million years old, found at the same caves just a few
years ago, is the oldest complete australopithecus skeleton.
Oldest known relative
Toumaï is far older. In fact, he’s the oldest known relative of the human
tribe thus far discovered. He has a small brain (between 320 and 380 cc)
comparable to that of chimpanzees. No bones below the skull have been
discovered yet, so it is not conclusively known whether Toumaï walked on two feet (bipedal) or not. He shares characteristics with other hominids known to be bipedal. But other scientists discount this, saying the foramen magnum (the hole through which the spinal cord exits the skull) of Toumaï is
positioned towards the back of the skull as in apes, indicating that the
skull was held forward and not balanced on top of an erect body.
Toumaï’s teeth have at least as much in common with early apes as they do
with hominids, say the scientists who claim he should be placed with
chimpanzees rather than with early human ancestors. Features like Toumaï’s
large brow ridge are indeed seen in relatively recent human ancestors but
not in earlier known hominids - meaning the brow would have to have evolved one way, then back, then evolved again to get into the human family.
An extinct branch
"To be honest, I think it could be an ancestor of both chimps and humans
before the species split, and probably this is an extinct branch," says Dr
Milford Wolpoff, of the University of Michigan in the USA. He confirmed
Toumaï’s importance regardless : "it’s the only fossil ape we’ve got from
between 10m years ago and today."
Professor Michel Brunet, who led the Toumaï dig, pointed out that in 1925,
when Nature magazine stunned the world with its publication of Raymond
Dart’s account of his discovery of a 3.3 million year old hominid fossil in
South Africa, critics said that skull was also that of an ape.
Professor Chris Stringer, head of human origins at the Natural History
Museum in London, was more cautious, pointing to growing evidence that human evolution was "bushy" rather than linear.
"It is premature to push the claims too far for any existing fossils to
represent the earliest members of the human family in the present patchy
state of our knowledge," he said.
If he is a hominid, Toumaï’s discovery in 2001, and his display to the world
last year, seems to have pushed back the date when human ancestors separated from our common ape ancestors by about two million years - and his team of discoverers, from the university of N’djamena in Chad and the University of Poitiers in France, say they will be digging at even older levels later in the year. The hominid fossil displays a unique combination of characters that clearly shows that it is close in time to the common ancestor of chimpanzees and humans.
Location is important
His location is as important as his age. The geographic location of Toumaï,
an astonishing 2,500 kilometres west of the Rift Valley, along with its
great antiquity, suggest an early, diverse and widespread hominid
distribution throughout the deserts of the Sahel as well as in East Africa,
and a somewhat earlier chimpanzee-human divergence (at least 7 million years ago) than previously indicated by many molecular studies.
"This is extraordinary. Nobody expected this. It means there may be fossils
even further west. What about Nigeria and Ivory Coast ? Why not ?" says
University of the Witwatersrand Professor Ron Clarke at Sterkfontein caves
in South Africa.
The fossil hominid cranium was recovered by the Mission Paleoanthropologique Franco-Tchadienne from the Djurab desert in northern Chad, home to bandits, huge sandstorms and very little water. Seven million years ago the environment was considerably more comfortable. Two dozen fossilised animal remains found there include aquatic and amphibious vertebrates, and species inhabiting gallery forest, wooded savanna and grassland.
For thirty years, the man who led the Toumaï team, palaeo-anthropologist
Michel Brunet of Poitiers University in France, has worked in geological and
palaeontological field missions in Africa (Chad, Cameroon, Nigeria, Togo,
South Africa), the Middle East (Afghanistan, Iraq, Pakistan), Eurasia
(Spain, Romania, Kazakhstan) and the Far East (Vietnam).
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