Ancient skull challenges human origins

Fossil said to be more than 6 million years old

Dated between 6 million and 7 million years old, an intact skull found in Africa is at least 3 million years older than the next-oldest hominid skulls.

(CNN) -- A team of researchers in central Africa say they've uncovered what appears to be the earliest evidence of the human family ever found -- a skull, jawbone and teeth between 6 million and 7 million years old.

Scientists say the discovery, unearthed in the Djurab desert of northern Chad, is of considerable importance.

"This is a very exciting find. It expands our knowledge of early evolution in a couple of different ways, both in time and in space," said Ian Tattersall, an anthropologist at The American Museum of Natural History. It is the first hominid fossil found in central Africa.

Chad authorities are nicknaming the specimen "Toumai," a name usually given to babies born before the dry season in the region. Toumai means "hope of life" in the Goran language.

The discoveries are detailed in this week's edition of Nature magazine.

The initial discovery -- of the cranium -- was made by Ahounta Djimdoumalbaye, an undergraduate student, on July 19, 2001.

The team working on the site included more than three dozen researchers -- geologists, sedimentologists and paleontologists from 10 countries. It was led by Michel Brunet of the University of Poitiers, France, who directs the Mission Paleoanthropologique Franco-Tchadienne.

"It's a lot of emotion to have in my hand the beginning of the human lineage," Brunet told Nature. "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."

Unlocking secrets

EXTRA INFORMATION View close-up images of the ancient skull  Interactive: Ages of the Earth  Discover how the roots of the human fossil tree have deepened with this discovery

Toumai could unlock secrets of a time period in evolution that is virtually a blank right now. Ten million years ago, apes were abundant on Earth.

But it's not until 5 million years ago that there's good evidence of hominids. Hominids are distinctly human-like creatures, different from apes or chimpanzees.

Scientists describe Toumai as having characteristics of both apes and humans. Detailed study of the fossil shows a braincase that is ape-like, while the face is short and the teeth look like those of a human.

Toumai is so unlike fossils that currently exist that it is being assigned a new genus and a new species, Sahelanthropus tchadensis.

The discovery raises several new questions, said Brunet, and indicates the divergence between chimps and humans must have occurred earlier than currently believed.

The skull of Toumai shows it was probably close to the size of a common chimpanzee. Because only a skull, jawbone and teeth have been found, it is still not clear how big Toumai might have been, or whether it traveled on two legs.

Presumed origins

Other scientists familiar with the find say there are new questions about the presumed origins of humans.

"It's likely that this is a human ancestor. If you ask whether it's absolutely certain that this is a human ancestor my answer would have to be no we are not [sure]," said Bernard Wood of George Washington University.

The area where Toumai lived is believed to have been quite diverse, with both aquatic and amphibious vertebrates and other species living in forests, wooded savannas and grasslands. Both lakes and deserts would have been found in the region 7 million years ago.

Some of the animals this hominid may have interacted with include elephants, three-toed horses, giraffes, antelopes, wild boars and hippopotamids. The lakes would have contained fish, crocodiles, snakes and turtles.

Much study has been carried out on the skull, jawbone and teeth of Toumai since it was found.

Researchers have compared it with great apes in studies at the Peabody Museum at Harvard University in Cambridge, Massachusetts, and CAT scans and 3-D reconstruction of this new species have been conducted in Switzerland.

Studies planned over the next six years are expected to add details to the fossil find, from its environment to its ecological habits.