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Lucy's Baby, a Stunning New Human Fossil
Originally posted on sciy.org by Ron Anastasia on Thu 21 Sep 2006 01:41 PM PDT
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SCIENCE NEWS
September 20, 2006
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Special Report: Lucy's Baby, a Stunning New Human Fossil
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An extraordinary new human fossil comes to light
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The arid badlands of Ethiopia's Afar region have long
been a favorite hunting ground for paleoanthropologists. The area is
perhaps best known for having yielded "Lucy," the 3.2 million-year-old
skeleton of a human ancestor known as Australopithecus afarensis.
Now researchers have unveiled another incredible find, from a site
called Dikika, just four kilometers from where Lucy turned up. It is
the skeleton of an A. afarensis child who lived 3.3 million
years ago. No other hominin of such antiquity--including Lucy--is as
complete as this one. Moreover, as the earliest juvenile hominin ever
found, the Dikika fossil provides a rare opportunity to study growth
processes in our long ago relatives.
Fossil hunters led by paleoanthropologist Zeresenay Alemseged,
now at the Max-Planck-Institute for Evolutionary Anthropology in
Leipzig, Germany, discovered the remains--believed to be those of a
three-year-old girl--in 1999. Most of the upper part of the skeleton
was entombed in sandstone when it was found. It has taken Alemseged
five years to remove enough of the cementlike matrix to expose the key
elements, and many more bones remain obscured by the sediment. Still,
the specimen has already yielded precious insights into a species that
most researchers agree gave rise to our own genus, Homo.
Alemseged and his colleagues describe the fossil and its geological and
paleontological context in two papers that will be published tomorrow
in Nature.
The skeleton consists of a virtually complete skull, the entire
torso and parts of the arms and legs. Many of the bones were still in
articulation. The exceptional preservation of the baby, as well as
other animals found at the site, indicates to team geologist Jonathan
G. Wynn of the University of South Florida that her body was buried
shortly after death by a flood event. Whether she perished in the flood
or before the flood is unknown. Although she was only three when she died, the Dikika youngster
already possessed the distinctive characteristics of her species. Some
of the most intriguing ones pertain to locomotion. |
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Scholars agree that A. afarensis
was a creature that got around capably on two legs. But starting in the
1980s, a debate over whether the species was also adapted for life in
the trees emerged. The argument centered on the observation that
whereas A. afarensis has clear adaptations to bipedal walking
in its lower body, its upper body exhibits a number of primitive traits
better suited to an arboreal existence, such as long, curved fingers
for grasping tree branches. One camp held that A. afarensis had
transitioned fully to terrestrial life, and that the tree-friendly
features of the upper body were just evolutionary baggage handed down
from an arboreal ancestor. The other side contended that if A. afarensis
had retained those traits for hundreds of thousands of years, then
tree-climbing must have still formed an important part of its locomotor
repertoire. |
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Image: Zeresenay Alemseged and Copyright Authority for Research and Conservation of Cultural Heritages (ARCCH)
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IT'S A GIRL:
The Dikika skeleton is believed to be that of a three-year-old girl, based on certain characteristics of the teeth.
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Like adult A. afarensis, the Dikika baby had
long, curved fingers. But the fossil also brings new data to the debate
in the form of two shoulder blades, or scapulae--bones previously
unknown for this species. According to Alemseged, the shoulder blades
of the child look most like those of a gorilla. The upward facing
shoulder socket is particularly apelike, contrasting sharply with the
laterally facing socket modern humans have. This, Alemseged says, may
indicate that the individual was raising its hands above its
head--something primates do when they climb. Further hints of arboreal tendencies reside in the baby's inner
ear. Using computed tomographic imaging, the team was able to glimpse
her semicircular canal system, which is important for maintaining
balance. The researchers determined that the infant's semicircular
canals resemble those of African apes and another australopithecine, A. africanus. This, they suggest, could indicate that A. afarensis was not as fast and agile on two legs as we modern humans are. It could also mean that A. afarensis
was limited in its ability to decouple its head and torso, a feat that
is said to play a key role in endurance running in our own species. | |
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