A skull unearthed in the deserts of Chad pushes back the date when the ancestral line of humans diverged from that of the great apes
Tim Radford, science editor
Thursday July 11, 2002, Guardian UK

A seven million-year-old fossilised skull found in the southern Sahara could upset the orthodox picture of human evolution.
It pushes incontrovertible evidence of hominids - the line of "apemen" that ended with just one species, Homo sapiens - back another million years. It is the oldest member of the human family so far discovered and it is 3m years older than any skull previously found. It also suggests that the story of human beginnings in Africa is much more complex than anyone had imagined.

"This will have the impact of a small nuclear bomb," said Daniel Lieberman, of Harvard University. "It fills a gap of five million years really, in terms of the skulls of fossil creatures related to us," said Chris Stringer, head of human origins at the Natural History Museum in London. "This is opening a new window."

Sahelanthropus tchadensis - nicknamed Toumaï by its French, US and Chadian discoverers and announced today in the magazine Nature - is so far no more than a cranium and lower jaw unearthed in the wind-scoured sandstone of northern Chad. From behind, Toumaï looks like a chimpanzee, and its brain capacity matches that of a chimp.

From the front, however, it has a huge brow ridge, linked with much later human ancestors. Its face and teeth, too, are more human than ape.

"Toumaï is arguably the most important fossil discovery in living memory, rivalling the discovery of the first apeman, Australopithecus africanus, 77 years ago," said Henry Gee, the palaeontology editor of Nature.

Much of the search for human ancestors has concentrated on fossil beds in East Africa or Ethiopia. Many discoveries have been based on tantalising fragments of jaw or limb and in one case even footprints. But the skull of Toumaï was found more than 1,500 miles to the west in the Toros-Menalla region of the Djurab desert. The discoverer, Michel Brunet of the University of Poitiers, began working in west Africa more than 20 years ago, and he now directs the Mission Paleoanthropologiqué Franco-Tchadienne which has been combing the Chad deserts for more than a decade.

"I have been looking for this for so long. I knew I would one day find it, so it is a large part of my life too," Prof Brunet said yesterday in N'Djamena, Chad. "I've been looking for 25 years. It's my story, so it's a human story and a story of humanity too. It's a wonderful discovery.

"But it's a discovery of my team and it's a discovery that is wonderful for the people of Chad."

Toumaï was probably male, probably the size of a modern chimpanzee, and lived 6-7m years ago in what at the time was a mixed habitat of forested lake, wooded savannah and desert. Minute examination of the wear and tear on its teeth could answer questions about what the creature ate, and how it lived.

"The new hominid displays a unique combination of primitive and derived characters suggesting a close relationship to the last common ancestor between humans and chimpanzees, suggesting him as a likely ancestor of all later hominids," Prof Brunet's team said. "These discoveries strongly shake our conceptions of the earliest steps of hominid history."

The researchers dated the find indirectly from the tell-tale assembly of other creatures known to have roamed Africa more than six million years ago. In the same rocks, they identified the fossilised bones of more than 42 species of fish, reptile and primitive mammal, including carnivores, elephants, three-toed horses, giraffes, antelopes, hippopotamuses, wild boar, rodents and monkeys.

They called their find Toumaï - it means "hope of life" - because it is the name given locally to babies born just before the dry season.

"We need bones from the rest of its skeleton. Did it walk upright? That is a key question we cannot answer yet," said Prof Stringer. "It is not known whether it was meat-eating. The assumption is that it was probably vegetarian. Most of the apes were at that time."

Nine million years ago, there were ancestral apes in Africa. About 4m years ago, an Australopithecine or "southern ape" left behind a skull as evidence of the arrival of a possible human ancestor. Until Toumaï, the fossil evidence from the five-million-year gap would have filled only a shoe box. The Toumaï find confirms that the ancestral line that led to modern humans diverged from the one that led to the great apes such as chimpanzees more than 7m years ago.

But the real message of Toumaï, researchers warn, is that there may have been many unknown actors in the drama of human evolution. Several extinct lineages have been identified, but there may be more. Nobody is sure which species had walk-on parts and which were leading players in the story of human ancestry. Quite how and where Toumaï fits into the narrative is not certain. The sheer age of the find tempts researchers to place Toumaï near the point at which humans and chimpanzees diverge.

"But we must be cautious in jumping to the conclusion that this is the ancestor we have all been looking for," said Prof Stringer. "It might be a cousin, it might be directly on our line, it might even be the common ancestor, the long-awaited missing link - though we shouldn't use that term - that links us to the chimpanzees via a common ancestry."

Early anthropologists saw human evolution as a ladder, with simple steps from ape ancestor to modern man. Now the picture is of a family tree with murky connections.

Among the enigmatic cousins:

Orrorin tugenensis

So-called millennium man, announced in 2000. A few bones and teeth indicate a walking, tree-climbing creature that lived almost 6m years ago in the Tugen hills of Kenya. Orrorin means "original man" in Tugen language - but is it linked to apes, or men?

Ardipithecus ramidus

Also around more than 5m years ago, according to teeth, jawbone, collarbone and a single toe bone, found in Ethiopia in 1994 and again in 2001. The toe bone indicates that it walked upright. Ardipithecus hung on. A descendant species survived there until 2.5m years ago.

Australopithecus africanus

A dramatic find by Raymond Dart in South Africa in 1925. It lived more than 3.3m years ago. The most famous skeleton is "Lucy", found in 1974 in Ethiopia. Researchers were playing the Beatles song Lucy in the Sky With Diamonds at the time. Researchers are still not sure where Lucy fits in to the story of human ancestry.

Homo erectus

Large brain, upright stance, used stone tools and survived from 2m to 400,000 years ago. Best known for "Turkana boy" - a near complete skeleton dating from Lake Turkana in east Africa 1.65m years ago. It was - until last week - believed to have been the first human to migrate from Africa. But fossils freshly found in Georgia suggest some other small-brained humans got away first.