Fossil finds give
new details on
ancient relative
Species proposed to have
given rise to first humans
By Bruce Bower
Newly described fossils provide the closest look yet at an anatomically quirky,
2-million-year-old member of the
human evolutionary family. Discoverers of the ancient bones suspect they
come from a species that served as an
evolutionary bridge from relatively
apelike ancestors to the Homo genus,
which includes modern people.
Four papers published in the Sept. 9
Science describe a mosaic of humanlike
and apelike skeletal traits on
Australopithecus sediba, a species found at South
Africa’s Malapa cave site. Dates for newly
exposed cave sediments, presented in a
fifth paper in the same issue of Science,
indicate that A. sediba lived there 1.977
million years ago, give or take several
thousand years.
An international team led by
anthropologist Lee Berger of the
Bumps and furrows in a nearly 2-million-
year-old A. sediba skull show similarities
with modern humans, researchers say.
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University of the Witwatersrand in
Johannesburg views the new
findings as consistent with
its previous suggestion that
A. sediba fossils at Malapa
represent late-surviving
members of a hominid line
that gave rise to Homo.
That proposal is controversial.
Some researchers doubt that
A. sediba set the stage for the Homo
genus. Others regard the Malapa fossils either as an early Homo species or
as late-surviving members of
Australopithecus africanus, a dead-end hominid
species that lived from about 3 million
to 2. 4 million years ago in South Africa.
“There’s still not enough evidence to
place A. sediba squarely at the root of the
Homo genus,” remarks anthropologist
Brian Richmond of George Washington
University in Washington, D.C. Several
Homo fossils date to more than 2 million years ago, suggesting that A. sediba
evolved too late to serve as a transition,
Richmond says.
A. sediba — represented in the new
studies by fossils from a young male and
an adult female — possessed traits typical of both Australopithecus and Homo
species, Berger’s team contends.
A virtual, 3-D reconstruction of bumps
and furrows on the A. sediba male’s brain
surface allowed Witwatersrand anthropologist Kristian Carlson and his colleagues to peer through rock and into
the male’s skull to measure impressions
made by his brain on surrounding bone.
Surface landmarks of A. sediba’s brain
look humanlike, though the ancient hominid’s brain is small even by A. africanus
standards, Carlson says. Markers of
frontal-brain expansion in A. sediba align
it closely with modern humans.
Reorganization of the frontal brain, not
a larger overall brain as is often argued,
characterized the transition from
Australopithecus to Homo, Carlson theorizes.
It’s not clear that A. sediba’s frontal
brain was more humanlike than that of
A. africanus, says anthropologist Dean
r
l
The fossil right hand of an adult A. sediba female may
hint at tree climbing as well
as a precision grip.
Falk of Florida State University in Tallahassee, who was
not involved in the research.
A. sediba’s reconstructed
brain surface includes a
frontal landmark found in apes
but not people, Falk says.
Both A. sediba individuals, and especially the female, possessed bowl-shaped,
humanlike hip bones, an unexpected trait
for hominids with such small brains, says
Wit watersrand anthropologist Job Kibii.
This anatomical combination challenges
the long-standing idea that wide pelvic
openings in the Homo genus evolved
in response to brain expansion, allowing females to give birth to babies with
relatively big heads, Kibii contends.
o o
Pelvic widening in A. sediba may have
evolved in response to an increasing
emphasis on walking, he suggests.
Foot, ankle and lower-leg bones from
both Malapa individuals underscore that
A. sediba walked upright, although more
stiffly than modern humans and without
abandoning tree climbing, says Witwatersrand anthropologist Bernhard Zipfel.
A nearly complete right hand from
the female A. sediba skeleton shows
key humanlike features, says anthropologist Tracy Kivell of the Max Planck
Institute for Evolutionary Anthropology
in Leipzig, Germany. Shortened fingers
and a long thumb, as well as evidence of
powerful grasping muscles, indicate that
A. sediba was capable of making and
using stone tools, Kivell says.
In Kivell’s opinion, A. sediba’s hand
and wrist were more humanlike than
those of the 1.75 million-year-old Homo
habilis, which means “handy man.” Stone
tools found in 1960 among some handy
man remains in East Africa — including
parts of a left hand — cemented his reputation as a toolmaker. Researchers have
unearthed no stone tools at Malapa.
FROM TOP: BRETT ELOFF, COURTESY L. BERGER/U. OF WITWATERSRAND; PETER SCHMID, COURTESY L. BERGER/U. OF WITWATERSRAND
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