'Ardi:' 4.4 Million-Year-Old Fossil is Oldest Human Ancestor

Oct. 1, 2009 — -- Scientists today told the world what they know about Ardipithecus ramidus -- "Ardi" for short -- the oldest pre-human species yet found. Ardi lived 4.4 million years ago in what is now Ethiopia.

"This may be the most important specimen in the history of evolutionary biology," said C. Owen Lovejoy, an anthropologist at Kent State University in Ohio, in an interview with ABCNews.com.

Lovejoy was one of more than 40 researchers from around the world who analyzed the Ardi fossils.

Ardipithecus is not the long-sought "missing link" -- the ancestor that scientists say humans and apes have in common -- but comes close. And it helps show that both human beings and apes have evolved from something, about six million years ago, that did not look much like either.

"Six months ago, we would have said our common ancestor looked something like a chimp," said Tim White of the University of California at Berkeley, a senior researcher on the project. "Now all that has changed.

"What we found in Ethiopia at 4.4 million years ago is the closest we've ever come to that ancestor along our own line," White said.

The most complete skeleton, out of more than 30 found, was female, about four feet tall. They discerned the sex from the shape of the pelvis, which was wide enough for her to have borne a baby in her womb.

There are older specimens from other locations, but they are not complete enough for the analysis that has now been applied to Ardipithecus.

The scientists said the fossils show that Ardipithecus walked upright, and that her teeth resemble modern human teeth more closely than they do those of a chimpanzee.

Curiously, though, her feet were capable of grasping, something chimps need in order to climb in trees. She would have been able to climb trees, but she probably did not swing from branches the way modern chimps do.

The back of her skull is small, indicating she had a small brain.

The Ardipithecus bone fragments came from a layer of rock beneath the Afar region of Ethiopia. Afar is now desert, but the scientists said it was woodland 4 million years ago. They found fossilized wood and seeds around the Afar bones.

The fossil hunters, from Ethiopia and the United States, sent the bone fragments they found to a team in Japan. There, 3-D computer models were made of each piece, and the pieces were digitally reassembled, a bit like a jigsaw puzzle.