A skull from the earliest known member of the human family has been unearthed in a central African desert in what has been described as the most important anthropological discovery for 75 years.
Scientists believe that the skull, which is dated at between six million and seven million years old, could lead to a fundamental reappraisal of human origins and a radical rethink of the increasingly complex ancestry of man.
The fossilised skull is about three million years older than the next-oldest skull of a hominid and its discovery at a sandblown site in the middle of the Djurab desert of northern Chad has astonished scientists, who once thought that the earliest humans were confined to a region stretching from southern Africa to the Great Rift Valley more than 1,000 miles to the east.
The journal Nature, which publishes details of the find and the site today, says it is the most important research paper in this field since Nature published the landmark discovery of a three-million-year-old "ape man" in 1925.
Nicknamed Toumai, which means "hope of life" in the local Goran language of Chad, the skull has a human-like face with a braincase similar to a chimpanzee. The creature was probably a male no bigger than a small chimp, it lived mainly on a diet of fruit and may even have walked on two legs.
Toumai's age is the most significant factor. It falls in the middle of a five-million-year gap between the point some 10 million years ago when the human family diverged from chimps and the appearance of the many hominid fossils that are less than five million years old.
In addition to the nearly complete skull, the scientists, led by Michel Brunet of the University of Poitiers in France, have also found two lower jaw fragments and a selection of teeth from the same species, which they have formally called Sahelanthropus tchadensis.
"It's a lot of emotion; I have in my hand the beginning of the human lineage. I have been looking for this for so long. I knew I would one day find it," Professor Brunet said. "But there are lots of new questions. This is the oldest hominid. It's seven million years old, so the divergence between chimp and human must be even older than we thought before."
The hominid remains were found at a remote location that also includes more than 700 fossils of mammal species, including three-toed horses, hippos, giraffes and a large species of extinct boar. In addition, the scientists have found fossils of fish, crocodiles and other aquatic animals, which suggest that these early ape-like humans lived near a large lake surrounded by open grassland and mature forests.
Without finding other bones, they will be unable to discover whether Toumai lived in the trees or walked around on two legs. "We have [found] no legs, but this new guy with the position of where his spine enters his head doesn't prove that he is bipedal, but it shows he could be," Professor Brunet said.
Toumai's relatively small teeth, with the enamel of his canines worn away mainly at the tips, are typically human rather than ape-like and his flat face lacks the snout-like protuberance of chimpanzee skulls.
Ahounta Djimdoubmalbaye, a graduate student from the University of Ndjamena in Chad, found the skull in July 2001 but its importance was only fully realised after its date was confirmed by an analysis of other fossils found in the same sedimentary layers.
Henry Gee, the scientific editor at Nature responsible for anthropological research, said the skull's age, state of preservation and location hundreds of miles from the usual places in east Africa where early hominids had been found singled out the find as a landmark.
"Toumai is arguably the most important fossil discovery in living memory, rivalling the discovery of the first 'ape man', Australopithecus africanus, 77 years ago – the find which effectively founded the modern science of palaeoanthropology," Dr Gee said. "We've entered a brand new era where the Rift Valley is not the only place to look for human ancestors... These creatures are going to turn up all over the place."
Chris Stringer, head of human origins at the Natural History Museum in London, said Toumai man displayed a mix of primitive and more evolved characteristics that had never been seen before in the same individual.
"It has an ape-like brain size and skull shape, combined with a more human-like face and teeth. It also sported a remarkably large browridge, more like that of a younger human species," Professor Stringer said. "Its discovery shows how much evidence has been missing up to now.... It is too soon so say whether Sahelanthropus might lie directly on our evolutionary line."
* The best preserved skeleton of a dinosaur discovered in France has been uncovered south of Carcassonne. The nearly complete, fossilised skeleton of an ampelosaurus, 36ft long and 8ft high, was found by a student palaeontologist in an ancient river bed at Campagne-sur-ude last August.
Excavation of the site has exposed the dinosaur from its jaw-bone to its tail. The whole of the skeleton should be uncovered by the end of summer. The ampelosaurus was a herbivorous dinosaur that lived about 72 million years ago.
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