by Oracle » Tue Oct 13, 2009 10:34 am
Here's the summary on Ardi, from the utmost authority in Nature (which you might not be able to get without subscription) ...
Fossil rewrites early human evolution
Ethiopian find dates back 4.4 million years.
A 17-year investigation into a fossilized early
human skeleton from Ethiopia culminated last
week with 11 papers published in Science.
Detailed descriptions of the skeleton, of a
fairly complete 4.4-million-year-old female,
show that humans did not evolve from ancient
knuckle-walking chimpanzees, as has long
been believed. The new fossils of Ardipithecus
ramidus — known as ‘Ardi’ — offer the first
substantial view of the biology of a species
close to the time of the last common ancestor
shared by humans and apes. Like modern
humans, Ardi could walk upright (see depiction,
right) and didn’t use her arms for walking,
as chimps do. Still, she retains a primitive big
toe that could grasp a tree like an ape1.
Previously, the oldest near-complete skeleton
of an early human was the 3.2-millionyear-
old Australopithecus afarensis skeleton
known as Lucy, also from Ethiopia. Because
Lucy had many traits in common with modern
humans, she didn’t provide much of a picture of
the earlier lineage between apes and humans,
says Alan Walker, a biological anthropologist
at Pennsylvania State University in University
Park. The new A. ramidus “is so much more
important — and strange”, he says.
The earliest Ardipithecus, A. kadabba, lived
around 5.8 million years ago in Ethiopia2. The
other oldest known hominids are Orrorin tugenensis,
from about 6 million years ago in Kenya3,
and Sahelanthropus tchadensis, from at least
6 million years ago in Chad4 (see graphic).
In addition to describing the fossils, the
Science papers provide details about the geology
and palaeoenvironment of the discovery
site, in the Afar desert 230 kilometres
northeast of Addis Ababa. The research
team, known as the Middle Awash
Project, involves 70 investigators, 47 of
whom are authors on the papers.
In 1992, team member Gen Suwa
found the first specimen of A. ramidus
near the Ethiopian village of Aramis.
Within two years, enough fossils
had been found to produce the first
article that named and sketchily
described the animal, from a total
of 17 fossils5.
Some researchers have complained how
long it has taken to publish work about the
fossils. But Berhane Asfaw, a co-director
of the Middle Awash Project at the Rift
Valley Research Service in Addis Ababa, says:
“We weren’t interested in how many papers
we could publish. Our interest was in the full
chain of information; that produces the power
of the work.”
From more than 135,000 vertebrate bone or
tooth pieces, the team identified 110 as being
from A. ramidus, representing a minimum of
36 individuals. The fossils come from a sediment
layer sandwiched between two layers of
volcanic rock known as tuff — each dated to
4.4 million years ago, says a team led by Giday
WoldeGabriel, of Los Alamos National Laboratory
in New Mexico. Fossils in the sediments
include plants, pollen, invertebrates and birds,
which helped to pinpoint the woodland environment
where Ardi lived.
Years of field work uncovered Ardi’s
skull, teeth, arms, hands, pelvis, legs
and feet — all of which had to be
painstakingly prepared. Ardi’s skull
was recovered crushed in more than
60 pieces that were broken and scattered
about. The bone was poorly
fossilized — so soft that each piece
had to be moulded in a silicon rubber
cast then digitized by computed
tomography scans.
Ardi’s hands and wrists don’t
show several distinctive chimp
characteristics, such as some larger
bones and a tendon ‘shock absorber’
system to withstand bodyweight, says
team member Owen Lovejoy of Kent
State University in Ohio. The foot,
with its big toe sticking out sideways, would
have allowed Ardi to clamber in trees, walking
along branches on her palms. And her
teeth show no tusk-like upper canines, which
most apes have for weapons or display during
conflict. “This is a major feature showing that
Ardi is not in the lineage of modern chimps,”
Suwa says. ■
Rex Dalton
1. White, T. D. et al. Science 326, 75–86 (2009).
2. Haile-Selassie, Y. Nature 412, 178–181 (2001).
3. Senut, B. et al. C. R. Acad. Sci. Paris Ser. IIa 332, 137–144
(2001).
4. Brunet, M. et al. Nature 418, 145–151 (2002).
5. White, T. D., Suwa, G. & Asfaw, B. Nature 371, 306–312
(1994).
I thought Ardi would complicate the matter. The assertion from Insan's thread-post was that the earliest species of Homo was found at Georgia and Ardi is not Homo. I think when they first found the Georgia fossils they placed them in Homo erectus but since then, they've been assigned their own species because of the degree of differences. I just thought the pictogram of the skulls was simple and clear enough to show the older ancestral lines back to Africa, which Insan doubted.
