Spiznet
Wed, Aug-02-06, 17:16
http://www.uwyo.edu/news/showrelease.asp?id=9461
Aug. 1, 2006 -- A 7 million-year-old primate cranium found in
central Chad does not represent the earliest human ancestor as
reported previously, according to University of Wyoming
Anthropology Professor James Ahern.
When it was discovered in 1999, scientists thought the ancient
Toumai Skull was the earliest recorded hominid -- a unique
human ancestor representing evidence of the human evolutionary
line. But due to missing key features that could link
previously unknown crania with the earliest hominids, Ahern
and his research team dispute the previous findings.
In a recent edition of the online journal PaleoAnthropology
(www.paleoanthro.org/journal/contents.htm), Ahern writes with
colleagues from the universities of Michigan and Wisconsin,
and from the Museum National d'Histoire Naturelle and the
College de France in Paris. They expose inconsistencies
between Toumai Skull's characteristics and those of
definitive hominids.
Foremost among the details that identify all hominids is
evidence of posture and locomotion. According to Ahern, none
of these details on the Toumai Skull provide any indication
of obligate bipedalism -- the anatomy of walking only upright
on two legs. Ordinarily, he says, obligate bipedalism is
reflected in certain features on the base of the cranium that
support the neck muscles and that show how the spine meets
the cranium. In this case, the team suggests the Toumai Skull
characterizes the anatomy of living apes that walk on all
four limbs.
"One of the biggest issues that we raise (in the paper) is
that based on the skull alone, it can never be certain whether
or not an ape walked on two legs," he says. "To tell for sure,
you really need legs, a pelvis or a spinal column."
Scientists have known for some time that the chimpanzee is the
species most closely related to humans, Ahern says. Toumai's
age, however, is much before the time geneticists agree the
two species began to diverge.
"Evidence suggests humans and chimps diverged as recently as
4.5 million years ago, so that would post-date this fossil,"
Ahern says.
The size and wear pattern of canine teeth also are important
in assessing whether early primates could be hominids.
"What probably spurred the founding scientists to conclude the
Toumai Skull was a hominid was the canine. The Chad fossil has
a relatively small canine compared to living apes and
gorillas, and, the wear on it also is unlike most male chimps
and gorillas," Ahern says. Generally, humans wear their
canines from the tip while nonhuman primates wear from the
back, keeping the tooth constantly pointed.
"In the Chad fossil, the canines are worn from the front and
the back. If we just had apes and humans to look at we'd say
it's probably a species in between," he says. "However, we can
demonstrate similar canine wear when we compare (the skull) to
several genuine apes that we know not to be hominids."
While the Toumai Skull could be a common ancestor to both
human and chimpanzee lines, so little is known of primate
fossils during the time between six and 12 million years ago,
that Ahern and his team say "the critter" could just as easily
be something else.
Even if Toumai doesn't represent human ancestry, Ahern insists
the skull is still a significant discovery and jokes that his
team is not suggesting that someone "throw the fossil away."
"Most Miocene apes that we know of are 10 million years old or
older, so instead of being the earliest hominid, the Toumai
Skull becomes an example of the latest Miocene apes," he says.
"The fossil is still informative about hominid origins and can
help us see what some of the potential ancestors for hominids
look like."
Posted on Tuesday, August 01, 2006
Aug. 1, 2006 -- A 7 million-year-old primate cranium found in
central Chad does not represent the earliest human ancestor as
reported previously, according to University of Wyoming
Anthropology Professor James Ahern.
When it was discovered in 1999, scientists thought the ancient
Toumai Skull was the earliest recorded hominid -- a unique
human ancestor representing evidence of the human evolutionary
line. But due to missing key features that could link
previously unknown crania with the earliest hominids, Ahern
and his research team dispute the previous findings.
In a recent edition of the online journal PaleoAnthropology
(www.paleoanthro.org/journal/contents.htm), Ahern writes with
colleagues from the universities of Michigan and Wisconsin,
and from the Museum National d'Histoire Naturelle and the
College de France in Paris. They expose inconsistencies
between Toumai Skull's characteristics and those of
definitive hominids.
Foremost among the details that identify all hominids is
evidence of posture and locomotion. According to Ahern, none
of these details on the Toumai Skull provide any indication
of obligate bipedalism -- the anatomy of walking only upright
on two legs. Ordinarily, he says, obligate bipedalism is
reflected in certain features on the base of the cranium that
support the neck muscles and that show how the spine meets
the cranium. In this case, the team suggests the Toumai Skull
characterizes the anatomy of living apes that walk on all
four limbs.
"One of the biggest issues that we raise (in the paper) is
that based on the skull alone, it can never be certain whether
or not an ape walked on two legs," he says. "To tell for sure,
you really need legs, a pelvis or a spinal column."
Scientists have known for some time that the chimpanzee is the
species most closely related to humans, Ahern says. Toumai's
age, however, is much before the time geneticists agree the
two species began to diverge.
"Evidence suggests humans and chimps diverged as recently as
4.5 million years ago, so that would post-date this fossil,"
Ahern says.
The size and wear pattern of canine teeth also are important
in assessing whether early primates could be hominids.
"What probably spurred the founding scientists to conclude the
Toumai Skull was a hominid was the canine. The Chad fossil has
a relatively small canine compared to living apes and
gorillas, and, the wear on it also is unlike most male chimps
and gorillas," Ahern says. Generally, humans wear their
canines from the tip while nonhuman primates wear from the
back, keeping the tooth constantly pointed.
"In the Chad fossil, the canines are worn from the front and
the back. If we just had apes and humans to look at we'd say
it's probably a species in between," he says. "However, we can
demonstrate similar canine wear when we compare (the skull) to
several genuine apes that we know not to be hominids."
While the Toumai Skull could be a common ancestor to both
human and chimpanzee lines, so little is known of primate
fossils during the time between six and 12 million years ago,
that Ahern and his team say "the critter" could just as easily
be something else.
Even if Toumai doesn't represent human ancestry, Ahern insists
the skull is still a significant discovery and jokes that his
team is not suggesting that someone "throw the fossil away."
"Most Miocene apes that we know of are 10 million years old or
older, so instead of being the earliest hominid, the Toumai
Skull becomes an example of the latest Miocene apes," he says.
"The fossil is still informative about hominid origins and can
help us see what some of the potential ancestors for hominids
look like."
Posted on Tuesday, August 01, 2006