Researchers say two skeletons found in a cave in South Africa may
belong to a species that was the direct ancestor of Homo erectus, and
hence modern humans
Ian Sample, science correspondent
Friday September 9 2011
The Guardian
http://www.guardian.co.uk/science/2011/sep/08/australopithecus-sediba-ancestor-modern-humans
It was a traumatic and lingering death. The adult female and young
male probably fell through a fissure in a cave roof and remained alive
for days or weeks with little or no food before finally meeting their
end. The pair ? possibly a mother and her son ? were then washed by a
rainstorm into an underground pool where they gradually solidified
into rock.
Their unusual demise nearly 2m years ago, and the preservation of most
of their fossilised skeletons, has given scientists a unique glimpse
of what kind of creature they were. The researchers who have studied
them in detail believe they may be direct ancestors of modern humans.
The ancient bones were recovered from sediments in a subterranean cave
at Malapa [http://en.wikipedia.org/wiki/
Malapa_Fossil_Site,_Cradle_of_Humankind" title="Malapa Fossil Site,
Cradle of Humankind], South Africa, 25 miles (40km) from Johannesburg.
The discovery of the partial skeletons was made public last year
[http://www.guardian.co.uk/science/2010/apr/08/fossil-skeletons-
unknown-human-ancestor" title="Guardian: Fossil skeletons may belong
to an unknown human ancestor], but in a series of papers published in
the US journal Science [http://www.sciencemag.org/" title="Science:
Australopithecus sediba papers] on Thursday, researchers report the
first comprehensive analysis of the individuals' anatomy.
Through a combination of high resolution scans and precision
measurements of the skull, pelvis, hand and foot, the authors argue
that [http://www.nhm.ac.uk/about-us/news/2010/april/new-human-like-
species-unveiled64876.html" title="NHM: Australopithecus
sediba]Australopithecus sediba, or the "southern ape", was an
immediate ancestor of Homo erectus, the ancient form from which modern
humans arose.
Lee Burger, a palaeoanthropologist at the University of Witwatersrand
in Johannesburg [http://www.wits.ac.za/academic/research/ihe/staff/
7120/leeberger.html" title="Wits: Lee Burger]who led the team, said
the skeletons possessed an extraordinary mix of primitive, ape-like
features alongside traits that define modern humans today.
"What is remarkable about Australopithecus sediba is that, as a field,
it is a discovery we never thought would be made: a bona fide
transitional species," Burger told the Guardian.
"It is a humbling experience. These are skeletons that you realise are
going to be studied by humans for as long as humans study themselves.
And that gives you some pause," he added.
At least 25 other animals died alongside them, including sabre-toothed
cats, hyenas, woodland antelope and at least one primitive form of
zebra. Around the cave was a sub-tropical alpine forest, with mixed
woodlands and forests, Burger said.
A. sediba walked upright and stood around 1.3m tall. It had a chimp-
sized body, long arms similar to those of orang-utans, and was adept
at climbing.
But other features appear distinctly human, Burger said. "The pelvis
is shaped like a human pelvis, but longer, almost like a
Neanderthal's. The hand is incredibly human-like, with short fingers
and a long thumb. And then there is the brain," he added.
Researchers used a powerful x-ray scanner at the European Synchrotron
Facility in Grenoble [http://www.esrf.eu/" title="ESRF], France, to
create exquisitely detailed maps of the interior of the skull of one
of the individuals. The bumps and other contours revealed the imprint
of a small brain, only 420 cubic centimetres in volume, but one that
was apparently reorganising from a primitive structure into a more
modern form.
Kristian Carlson [http://www.wits.ac.za/academic/research/ihe/staff/
7117/kristiancarlson.html" title="Wits: Kris Carlson], a colleague of
Burger's who worked on the brain scans, said some areas of the organ
appeared more developed than expected.
"There are areas above and behind the eyes that are expanded and they
are responsible for multitasking, reasoning and long-term planning.
These are changes that mirror the differences that humans exhibit from
chimpanzees," Carlson said. The discovery challenges the previously
held theory that our ancient ancestors grew large brains before they
reorganised to resemble the modern human brain.
Further measurements of the brain, skull and hand suggest that the
creature may have been intelligent enough to wield tools and even
communicate non-verbally, Burger said. "They could probably smile, and
that is something unique to humans that chimps cannot do, they
grimace. Australopithecus sediba has the beginning of our face," he
said.
Other palaeontologists have yet to be convinced that the creature was
an immediate ancestor of H. erectus - and hence our own species H.
sapiens. But if Burger is correct, the fossils fill a gap between
Lucy, the 3.2m-year-old hominin unearthed in Ethiopia [http://
en.wikipedia.org/wiki/Lucy_%28Australopithecus%29" title="Lucy:
Australopithecus afarensis.], and H. erectus, which lived from 1.8m to
1.3m years ago and likely gave rise to modern humans in Africa.
"No matter where this species is eventually put in the family tree,
whether you agree with our idea that it's the best candidate ancestor
of Homo erectus, or whether it is a species that mimicked the
developmental processes that led to our genus, or whether it turned
out to be an evolutionary dead end, these are some of the finest
transitional fossils that have ever been discovered for any mammal
species, and I don't say that lightly," Burger told the Guardian.
Chris Stringer, head of human origins at the Natural History Museum in
London, [http://www.nhm.ac.uk/research-curation/staff-directory/
palaeontology/c-stringer/index.html" title="NHM: Chris Stringer] said:
"For the last 30 years, attention has focused on East Africa as the
place where the first humans evolved, with a possible transition from
Australopithecus to [http://www.nhm.ac.uk/visit-us/galleries/green-
zone/our-place-in-evolution/index.html" title="NHM: Homo erectus]Homo
erectus, via the intermediate species Homo habilis occurring there
about 2 million years ago.
"In that view, the South African australopithecines were side-branches
in human evolution, leading only to extinction. These new and detailed
descriptions of the skeletons of two individuals from the Malapa site
return the spotlight to South Africa as the possible location for the
postulated transition from Australopithecus to Homo.
"Australopithecus sediba resembles its presumed local ancestor,
Australopithecus africanus, in its ape-sized brain, ape-like body
shape, and the form of the shoulders and arms. Yet despite the fact
that the hands had a powerful grip, they show more human proportions,
suggesting greater dexterity. And the shape of the front of the brain
cavity, the face, teeth, pelvis and legs also show more human
characteristics, confirming that sediba is the most human-like
australopithecine yet discovered, providing valuable clues to the
evolutionary changes that led to the genus Homo.
"However, it is possible that australopithecines in different parts of
Africa were taking up tool-making, meat-eating and travelling longer
distances overground, which could have driven the parallel evolution
of human-like features," he said.
"Whatever you call these things, there seem to be a number of
different species running around at the same time ? a number of
experiments in being hominin," Carol Ward, a palaeoanthroplogist at
the University of Missouri, Columbia [http://web.missouri.edu/~wardcv/
Carol_Wards_site/Lab_Home.html" title="U. Missouri: Carol Ward], told
the journal Science.
guardian.co.uk Copyright (c) Guardian News and Media Limited. 2011
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