Oldest 'Human' Skeleton Found -- Disproves 'Missing Link'
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OLDEST "HUMAN" SKELETON FOUND--DISPROVES "MISSING LINK"
By Jamie Shreeve
National Geographic Magazine
October 1, 2009
[Visit the link above for additional links, articles, and illustrations
related to this important story. --DS]
Move over, Lucy. And kiss the missing link goodbye.
Scientists today announced the discovery of the oldest fossil skeleton of a
human ancestor. The find reveals that our forebears underwent a previously
unknown stage of evolution more than a million years before Lucy, the iconic
early human ancestor specimen that walked the Earth 3.2 million years ago.
The centerpiece of a treasure trove of new fossils, the skeleton -- assigned
to a species called Ardipithecus ramidus -- belonged to a small-brained,
110-pound (50-kilogram) female nicknamed "Ardi."
The fossil puts to rest the notion, popular since Darwin's time, that a
chimpanzee-like missing link -- resembling something between humans and
today's apes -- would eventually be found at the root of the human family
tree. Indeed, the new evidence suggests that the study of chimpanzee anatomy
and behavior -- long used to infer the nature of the earliest human
ancestors -- is largely irrelevant to understanding our beginnings.
Ardi instead shows an unexpected mix of advanced characteristics and of
primitive traits seen in much older apes that were unlike chimps or gorillas
(interactive: Ardi's key features). As such, the skeleton offers a window on
what the last common ancestor of humans and living apes might have been
Announced at joint press conferences in Washington, D.C., and Addis Ababa,
Ethiopia, the analysis of the Ardipithecus ramidus bones will be published
in a collection of papers tomorrow in a special edition of the journal
Science, along with an avalanche of supporting materials published online.
"This find is far more important than Lucy," said Alan Walker, a
paleontologist from Pennsylvania State University who was not part of the
research. "It shows that the last common ancestor with chimps didn't look
like a chimp, or a human, or some funny thing in between."
Ardi Surrounded by Family
The Ardipithecus ramidus fossils were discovered in Ethiopia's harsh Afar
desert at a site called Aramis in the Middle Awash region, just 46 miles (74
kilometers) from where Lucy's species, Australopithecus afarensis, was found
in 1974. Radiometric dating of two layers of volcanic ash that tightly
sandwiched the fossil deposits revealed that Ardi lived 4.4 million years
Older hominid fossils have been uncovered, including a skull from Chad at
least six million years old and some more fragmentary, slightly younger
remains from Kenya and nearby in the Middle Awash.
While important, however, none of those earlier fossils are nearly as
revealing as the newly announced remains, which in addition to Ardi's
partial skeleton include bones representing at least 36 other individuals.
"All of a sudden you've got fingers and toes and arms and legs and heads and
teeth," said Tim White of the University of California, Berkeley, who
co-directed the work with Berhane Asfaw, a paleoanthropologist and former
director of the National Museum of Ethiopia, and Giday WoldeGabriel, a
geologist at Los Alamos National Laboratory in New Mexico.
"That allows you to do something you can't do with isolated specimens,"
White said. "It allows you to do biology."
Ardi's Weird Way of Moving
The biggest surprise about Ardipithecus's biology is its bizarre means of
All previously known hominids -- members of our ancestral lineage -- walked
upright on two legs, like us. But Ardi's feet, pelvis, legs, and hands
suggest she was a biped on the ground but a quadruped when moving about in
Her big toe, for instance, splays out from her foot like an ape's, the
better to grasp tree limbs. Unlike a chimpanzee foot, however,
Ardipithecus's contains a special small bone inside a tendon, passed down
from more primitive ancestors, that keeps the divergent toe more rigid.
Combined with modifications to the other toes, the bone would have helped
Ardi walk bipedally on the ground, though less efficiently than later
hominids like Lucy. The bone was lost in the lineages of chimps and
According to the researchers, the pelvis shows a similar mosaic of traits.
The large flaring bones of the upper pelvis were positioned so that Ardi
could walk on two legs without lurching from side to side like a chimp. But
the lower pelvis was built like an ape's, to accommodate huge hind limb
muscles used in climbing.
Even in the trees, Ardi was nothing like a modern ape, the researchers say.
Modern chimps and gorillas have evolved limb anatomy specialized to climbing
vertically up tree trunks, hanging and swinging from branches, and
knuckle-walking on the ground.
While these behaviors require very rigid wrist bones, for instance, the
wrists and finger joints of Ardipithecus were highly flexible. As a result
Ardi would have walked on her palms as she moved about in the trees -- more
like some primitive fossil apes than like chimps and gorillas.
"What Ardi tells us is there was this vast intermediate stage in our
evolution that nobody knew about," said Owen Lovejoy, an anatomist at Kent
State University in Ohio, who analyzed Ardi's bones below the neck. "It
Against All Odds, Ardi Emerges
The first, fragmentary specimens of Ardipithecus were found at Aramis in
1992 and published in 1994. The skeleton announced today was discovered that
same year and excavated with the bones of the other individuals over the
next three field seasons. But it took 15 years before the research team
could fully analyze and publish the skeleton, because the fossils were in
such bad shape.
After Ardi died, her remains apparently were trampled down into mud by
hippos and other passing herbivores. Millions of years later, erosion
brought the badly crushed and distorted bones back to the surface.
They were so fragile they would turn to dust at a touch. To save the
precious fragments, White and colleagues removed the fossils along with
their surrounding rock. Then, in a lab in Addis, the researchers carefully
tweaked out the bones from the rocky matrix using a needle under a
microscope, proceeding "millimeter by submillimeter," as the team puts it in
Science. This process alone took several years.
Pieces of the crushed skull were then CT-scanned and digitally fit back
together by Gen Suwa, a paleoanthropologist at the University of Tokyo.
In the end, the research team recovered more than 125 pieces of the
skeleton, including much of the feet and virtually all of the hands -- an
extreme rarity among hominid fossils of any age, let alone one so very
"Finding this skeleton was more than luck," said White. "It was against all
The team also found some 6,000 animal fossils and other specimens that offer
a picture of the world Ardi inhabited: a moist woodland very different from
the region's current, parched landscape. In addition to antelope and monkey
species associated with forests, the deposits contained forest-dwelling
birds and seeds from fig and palm trees.
Wear patterns and isotopes in the hominid teeth suggest a diet that included
fruits, nuts, and other forest foods.
If White and his team are right that Ardi walked upright as well as climbed
trees, the environmental evidence would seem to strike the death knell for
the "savanna hypothesis" -- a long-standing notion that our ancestors first
stood up in response to their move onto an open grassland environment.
Sex for Food
Some researchers, however, are unconvinced that Ardipithecus was quite so
"This is a fascinating skeleton, but based on what they present, the
evidence for bipedality is limited at best," said William Jungers, an
anatomist at Stony Brook University in New York State.
"Divergent big toes are associated with grasping, and this has one of the
most divergent big toes you can imagine," Jungers said. "Why would an animal
fully adapted to support its weight on its forelimbs in the trees elect to
walk bipedally on the ground?"
One provocative answer to that question -- originally proposed by Lovejoy in
the early 1980s and refined now in light of the Ardipithecus discoveries --
attributes the origin of bipedality to another trademark of humankind:
Virtually all apes and monkeys, especially males, have long upper canine
teeth -- formidable weapons in fights for mating opportunities.
But Ardipithecus appears to have already embarked on a uniquely human
evolutionary path, with canines reduced in size and dramatically "feminized"
to a stubby, diamond shape, according to the researchers. Males and female
specimens are also close to each other in body size.
Lovejoy sees these changes as part of an epochal shift in social behavior:
Instead of fighting for access to females, a male Ardipithecus would supply
a "targeted female" and her offspring with gathered foods and gain her
sexual loyalty in return.
To keep up his end of the deal, a male needed to have his hands free to
carry home the food. Bipedalism may have been a poor way for Ardipithecus to
get around, but through its contribution to the "sex for food" contract, it
would have been an excellent way to bear more offspring. And in evolution,
of course, more offspring is the name of the game.
Two hundred thousand years after Ardipithecus, another species called
Australopithecus anamensis appeared in the region. By most accounts, that
species soon evolved into Australopithecus afarensis, with a slightly larger
brain and a full commitment to a bipedal way of life. Then came early Homo,
with its even bigger brain and budding tool use.
Did primitive Ardipithecus undergo some accelerated change in the 200,000
years between it and Australopithecus -- and emerge as the ancestor of all
later hominids? Or was Ardipithecus a relict species, carrying its quaint
mosaic of primitive and advanced traits with it into extinction?
Study co-leader White sees nothing about the skeleton "that would exclude it
from ancestral status." But he said more fossils would be needed to fully
resolve the issue.
Stony Brook's Jungers added, "These finds are incredibly important, and
given the state of preservation of the bones, what they did was nothing
short of heroic.
But this is just the beginning of the story."
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