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World�s oldest human-linked skeleton found [In Ethiopia]
�Ardi� predates Lucy by a million years, changes scientific view
of origins
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Science / AAAS / Discovery Channel
A digital rendition shows the partial skeleton of Ardipithecus
ramidus arranged in a walking posture.
View
related photos
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INTERACTIVE
Seven
signs of evolution in action
Indications
that species evolve through process of natural selection.
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By Randolph E. Schmid
October 1, 2009
WASHINGTON - The story of humankind is reaching back another million
years with the discovery of �Ardi,� a hominid who lived 4.4 million
years ago in what is now Ethiopia.
The 110-pound, 4-foot female roamed forests a million years before the
famous Lucy, long studied as the earliest skeleton of a human ancestor.
This older skeleton reverses the common wisdom of human evolution, said
anthropologist C. Owen Lovejoy of Kent State University.
Rather than humans evolving from an ancient chimplike creature, the new
find provides evidence that chimps and humans evolved from some long-ago
common ancestor � but each evolved and changed separately along the way.
�This is not that common ancestor, but it�s the closest we have
ever been able to come,� said Tim White, director of the Human Evolution
Research Center at the University of California, Berkeley.
The lines that evolved into modern humans and living apes probably
shared an ancestor 6 million to 7 million years ago, White said in a telephone
interview.
But Ardi has many traits that do not appear in modern-day African apes,
leading to the conclusion that the apes evolved extensively since we
shared that last common ancestor.
A study of Ardi, under way since the first bones were discovered in
1994, indicates the species lived in the woodlands and could climb on all
fours along tree branches, but the development of their arms and legs
indicates they didn�t spend much time in the trees. And they could walk
upright, on two legs, when on the ground.
Formally dubbed Ardipithecus ramidus � which means root of the ground
ape � the find is detailed in 11 research papers published Thursday by
the journal Science.
�This is one of the most important discoveries for the study of human
evolution,� said David Pilbeam, curator of paleoanthropology at Harvard�s
Peabody Museum of Archaeology and Ethnology.
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Science / AAAS
The area where "Ardi" was found is rich in sites where
the fossils of human ancestors have been found.
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�It is relatively complete in that it preserves head, hands, feet and
some critical parts in between. It represents a genus plausibly ancestral
to Australopithecus � itself ancestral to our genus Homo,� said
Pilbeam, who was not part of the research teams.
Scientists assembled the skeleton from 125 pieces.
Lucy, also found in Africa, thrived a million years after Ardi and was
of the more humanlike genus Australopithecus.
�In Ardipithecus we have an unspecialized form that hasn�t evolved
very far in the direction of Australopithecus. So when you go from head to
toe, you�re seeing a mosaic creature that is neither chimpanzee, nor is
it human. It is Ardipithecus,� said White.
White noted that Charles
Darwin,
whose research in the 19th century paved the way for the science of
evolution, was cautious about the last common ancestor between humans and
apes.
�Darwin said we have to be really careful. The only way we�re
really going to know what this last common ancestor looked like is to go
and find it. Well, at 4.4 million years ago we found something pretty
close to it,� White said. �And, just like Darwin appreciated,
evolution of the ape lineages and the human lineage has been going on
independently since the time those lines split, since that last common
ancestor we shared.�
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J.H. Matternes
An artist's rendering shows Ardipithecus ramidus as it might have
looked in life.
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Some details about Ardi in the collection of papers:
� Ardi was found in Ethiopia�s
Afar Rift, where many fossils of ancient plants and animals have been
discovered. Findings near the skeleton indicate that at the time it was
a wooded environment.
Fossils of 29 species of birds and 20 species of small mammals were
found at the site.
� Geologist Giday WoldeGabriel
of Los Alamos National Laboratory was able to use volcanic layers above
and below the fossil to date it to 4.4 million years ago.
� Ardi�s upper canine teeth
are more like the stubby ones of modern humans than the long, sharp,
pointed ones of male chimpanzees and most other primates. An analysis of
the tooth enamel suggests a diverse diet, including fruit and other
woodland-based foods such as nuts and leaves.
� Paleoanthropologist Gen Suwa
of the University of Tokyo reported that Ardi�s face had a projecting
muzzle, giving her an ape-like appearance. But it didn�t thrust
forward quite as much as the lower faces of modern African apes do. Some
features of her skull, such as the ridge above the eye socket, are quite
different from those of chimpanzees. The details of the bottom of the
skull, where nerves and blood vessels enter the brain, indicate that
Ardi�s brain was positioned in a way similar to modern humans,
possibly suggesting that the hominid brain may have been already poised
to expand areas involving aspects of visual and spatial perception.
� Ardi�s hand and wrist were
a mix of primitive traits and a few new ones, but they don�t include
the hallmark traits of the modern tree-hanging, knuckle-walking chimps
and gorillas. She had relatively short palms and fingers which were
flexible, allowing her to support her body weight on her palms while
moving along tree branches, but she had to be a careful climber because
she lacked the anatomical features that allow modern-day African apes to
swing, hang and easily move through the trees.
� The pelvis and hip show the
gluteal muscles were positioned so she could walk upright.
� Her feet were rigid enough
for walking but still had a grasping big toe for use in climbing.
The research was funded by the National
Science Foundation,
the Institute of Geophysics and Planetary Physics of the University of
California, Los Alamos National Laboratory, the Japan Society for the
Promotion of Science and others.
� 2009 The Associated Press. All rights reserved. This material may
not be published, broadcast, rewritten or redistributed.
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