New Fossils Add Link to the Chain of the Evolution of Humans

http://www.nytimes.com/2006/04/13/science/13fossil.html

NY Times, April 13, 2006
New Fossils Add Link to the Chain of the Evolution of Humans

By JOHN NOBLE WILFORD

In 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 =97
resembling apes in stature and brain size but unlike the great apes in
that it walked on two legs =97 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.

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.