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NSF PR 01-57 - July 11, 2001
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Earliest Human Ancestors Discovered in Ethiopia
Discovery of bones and teeth date fossils back more
than 5.2 million years
Anthropologists have discovered the remains of the
earliest known human ancestor in Ethiopia, dating
to between 5.2 and 5.8 million years ago and which
predate the previously oldest-known fossils by almost
a million years. The previous discovery of the 4.4-million-year-old
Ardipithecus ramidus was up to this point the
oldest known hominid, the primate zoological family
that includes all species on the human side of the
evolutionary split with chimpanzees.
The fossil finds, reported in the July 12 issue of
Nature, were made by National Science Foundation
(NSF)-funded scientists over a four-year period in
Ethiopia's Middle Awash study area, about 140 miles
northeast of the capital, Addis Ababa. To the team
of scientists, the discovery represents more evidence
to confirm Darwin's conclusion that the earliest humans,
or hominids, arose in Africa.
Yohannes Haile-Selaissie, a paleontologist at the University
of California at Berkeley, made the recent fossil
discoveries from these earliest creatures. Working
under lead researcher and Berkeley colleague Tim D.
White, Haile-Selaissie found a jawbone and teeth in
December, 1997. More fossils were found, the last
a tooth, uncovered in January, 2001.
The area where this hominid discovery took place has
been the focus of much recent attention. Eleven hominid
specimens have been recovered from five late Miocene
localities within the Middle Awash region.
"The new fossils come from the oldest of the patches
of exposed sediment at Saitune Dora, Alayla, Aas Koma
and Digiba Dora," White said. "These bones and teeth
were difficult to find on surfaces that are littered
with stones ranging from pebbles to boulders."
The study of the Middle Awash has been ongoing since
1981 under the joint direction of White and Desmond
Clark of UC-Berkeley, Giday WoldeGabriel of Los Alamos
National Laboratory and Ethiopian researchers Berhane
Asfaw and Yonas Beyene.
The researchers explain that about six million years
ago, the Middle Awash region was already a well-defined
rift valley characterized by intense earth movements,
with active volcanoes nearby. "It is hard to imagine
life would go on normally under such hostile environmental
conditions -- Ardipithecus and the other animals inhabiting
the area were real survivors," WoldeGabriel said.
White says that an accurate portrayal of these creatures
is not yet possible because an intact skull or limb
bones have not yet been found. Researchers estimate
the size of the skeletal bones and the lower jaw is
roughly the same size as a modern chimpanzee.
"This is an exciting development," says Mark Weiss,
program director of physical anthropology at NSF.
"Not only are we gaining insights into the anatomy
of what may be some of our earliest ancestors, but
we are seeing a better picture of the environment
in which they lived. I'm really looking forward to
further finds by White and his colleagues." White
has received close to $1.2 million in NSF funding
for his work since 1995.
The age of these newly found fossils was determined
by the Berkeley Geochronology Center by employing
an argon-argon laser heating method -- a process that
determines the time elapsed since volcanic ashes and
lavas were erupted by measuring the argon gas trapped
in the rock after it cools. "The argon dating results
were corroborated by geomagnetic polarity data, then
further confirmed by biochronological analysis of
the primitive fossil animals found with the human
ancestor remains," White explains.
"These fossils are strong evidence that that lines
leading to chimpanzees and humans had already split
well before five million years ago," Haile-Selaissie
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