http://www.nytimes.com/2006/04/13/science/13fossil.htmlIn following the fossil tracks of human evolution, scientists have for years searched for links between Australopithecus, the kin of the famous "Lucy" skeleton, and even earlier possible ancestors. Now, they think they have found some connections in Ethiopia.
An international team of paleontologists is reporting the discovery of transitional species superimposed in sediments in the neighborhood of a single site. The findings appear today in the journal Nature.
Tim D. White, a paleontologist at the University of California, Berkeley, who was a team leader, and his colleagues said the 4.1-million-year-old fossils were anatomically intermediate between the earlier species Ardipithecus ramidus and the later species Australopithecus afarensis, the Lucy family. The newfound bones and teeth are the earliest remains of the most primitive Australopithecus, known as anamensis.
"This new discovery closes the gap between the fully blown australopithecines and earlier forms we call Ardipithecus," Dr. White said in a statement. "We now know where Australopithecus came from before four million years ago."
The scientists said the fossils supported the hypothesis that Australopithecus anamensis was a direct ancestor of afarensis, which lived 3 million to 3.6 million years ago. The Australopithecus genus — resembling apes in stature and brain size but unlike the great apes in that it walked on two legs — is thought to have given rise to our own genus, Homo.
Some later australopithecines survived until about 1.2 million years ago, existing in Africa as contemporaries with Homo erectus, a predecessor of modern humans.
The genus Ardipithecus, discovered by Dr. White in 1992, appears to have lived 4.4 million to 5.7 million years ago. It was even more apelike, but also walked on two legs.
The relationship between Ardipithecus and Australopithecus, scientists said, remains unclear because of the wide gap in their chronology. Still, they suggested that one probably led to the other.
Dr. White said a key to interpreting the new anamensis was where it was discovered, in the Middle Awash valley of the Afar region of Ethiopia. The area, about 140 miles northeast of Addis Ababa, Ethiopia's capital, has also yielded critical evidence of afarensis and the ramidus species of Ardipithecus.
"Finding these three things in time sequence in a single place, that's never happened before," he said.
In their journal article, the scientists said the evidence suggested "a relatively rapid shift from Ardipithecus to Australopithecus in this region of Africa."
The new anamensis fossils were uncovered first at Aramis and then at a place called Asa Issie. The teeth and jawbones of eight individuals were found at Asa Issie, the most recent of the discoveries last December. The fieldwork and analysis were conducted by scientists from Ethiopia, Japan, France and the United States, with support from the National Science Foundation.
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