From
http://www.toptechnews.com/ttn-scnc/story.xhtml?story_title=Toumai-Fossil-Said-To-Be-Human-Ancestor&story_id=32460&category=ttn-scnc
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New fossil finds and a computer skull reconstruction bolster the case
that an ancient creature that grabbed headlines in 2002 really is the
earliest known ancestor of modern humans, researchers say.
In that year, scientists announced finding jaw fragments, some isolated
teeth and a skull of a creature nicknamed "Toumai" in Chad.
At some 6 million to 7 million years old, the fossils came from around
the time of a major split in the evolutionary tree, with one branch
leading eventually to humans and the other branch leading to chimps.
The researchers argued that the creature, which they dubbed
Sahelanthropus tchadensis, belongs on the human branch and so is the
oldest known hominid. Some others disagreed.
In any case, the skull provided a puzzling combination of human and
chimp traits and raised what one expert called "a wheelbarrow full of
questions" about evolution at that time.
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Many scientists now think S. tchadensis was probably a hominid, and more
evidence appears in Thursday's issue of the journal Nature. It comes
from Michel Brunet of the University of Poitiers in France, who led the
team that made the original discovery, and colleagues.
Other experts said the new work strengthens the case for hominid status
but doesn't clinch it.
"This isn't a smoking gun," said David Begun of the University of Toronto.
A big question is whether S. tchadensis walked upright, because that's a
key characteristic of hominids. Brunet, in an e-mail, said given the
available evidence it would be a "great surprise" if it didn't walk
upright. But he agreed with other scientists that to be sure, scientists
would have to find and analyze skeletal bones that carry signatures of
upright walking, like a knee, hip or foot.
In Nature, Brunet and colleagues report discovering two new jaw
fragments and the crown of a tooth in the same geographical area as the
earlier findings. Analysis shows similarities to hominid fossils and
differences from ape traits, they said.
They also present a computerized reconstruction of the skull, because
the fossil had been distorted in the ground. The reconstruction confirms
that S. tchadensis shared several features with later hominids, the
researchers wrote. In addition, the position of the hole where the
spinal cord enters is like what's seen in humans but not apes, which
suggests upright walking, they wrote.
Rick Potts, director of the Human Origins Program at the Smithsonian
Institution's National Museum of Natural History, said the position of
that hole doesn't necessarily prove S. tchadensis walked upright. Still,
Potts said he thinks the creature was probably a hominid.
Begun agreed, and said the chances are "pretty good" the creature walked
upright, although "I'll be convinced when they find a knee joint."
Bernard Wood of George Washington University said he finds too little
evidence to declare S. tchadensis a hominid with certainty, although it
might well be true. If it isn't, the creature might have belonged to a
branch of the evolutionary tree that has no living representatives, he
said.
© 2005 Associated Press.
© 2005 Top Tech News.
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