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Article Date: 25 Sep 2006 - 9:00am (PDT)
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Discovery of a nearly intact 3.3 million year-old
juvenile skeleton is filling an important gap in
understanding the evolution of a species thought to
be among the earliest direct ancestors to humans,
says William Kimbel, a paleoanthropologist with
ASU's Institute of Human Origins. Kimbel is part of
the team that studied the skeleton of an
approximately three-year-old female Australopithecus
afarensis, the same species as the well known Lucy,
from Dikika, Ethiopia.
"It's extraordinarily rare to have such a complete
skeleton," said Kimbel, science director at the
Institute of Human Origins. "It's unprecedented to
have such a complete skeleton of a young child."
The researchers describe their discovery and initial
analysis of it in "A juvenile early hominin skeleton
from Dikika, Ethiopia," in the current issue of
Nature (Sept. 21, 2006). The skeleton was discovered
by lead author Zeresenay Alemseged, director of the
Dikika Research Project and a former postdoctoral
researcher at ASU's Institute of Human Origins.
Alemseged is now at the Max Planck Institute for
Evolutionary Anthropology, Leipzig, Germany.
Other authors of the paper are Fred Spoor,
University College London; Rene Bobe, State
University of New York at Buffalo; Denis Geraads,
National Center for Scientific Research, Paris;
Denne Reed, University of Texas at Austin; and
Jonathan G. Wynn, University of South Florida.
Alemseged has been carefully preparing the skeleton
for the last five years by chipping away sandstone
from the fragile bone fragments. He still has
several years more work to complete it. The skeletal
remains include the skull and jaws with teeth, and
parts of the shoulders, spinal column, ribs, right
arm, fingers, legs and left foot.
Analysis of the skeleton by Alemseged and his team
has shown that its lower body is adapted for bipedal
locomotion, like that of adult Australopithecus,
while the upper body, especially the scapula, or
shoulder blade, exhibits some gorilla-like features,
Kimbel said. However, there continues to be debate
about the interpretation of these features and what
was the preferred mode of locomotion for this
species.
Some researchers have argued that the ape-like
features of the upper limb are just retained from a
common ancestor, but are not functional, while
others argue the features are functional and
indicate that the species spent some time climbing
trees.
"I don't think a 3-year-old adapted to bipedality is
going to spend much time climbing in trees, but the
mix of features in this skeleton is going to stir up
the debate about locomotion in early
Australopithecus," Kimbel said.
Alemseged uncovered a hyoid bone in the skeletal
remains, which is the first time that bone has been
discovered in the early part of the hominin fossil
record. The hyoid bone is located in the larynx, or
voice-box, and supports muscles of the throat and
tongue involved in speech. The one discovered in the
infant appeared to be primitive and more similar to
hyoids found in apes than humans, according to
Spoor, who has studied the evolution of this region
in humans and other primates.
The findings are expected to provide insights into
the growth and development cycle of Australopithecus
afarensis since the infant remains will be compared
to Lucy, a remarkably complete adult female skeleton
which was among the first Australopithecus afarensis
to be discovered. Lucy dates back 3.18 million
years, and was discovered in 1974 in the Hadar
region of Ethiopia by Donald Johanson, who directs
ASU's Institute of Human Origins.
Understanding growth and development and how it has
changed in human ancestry is central to the study of
human evolution, Kimbel explained. He said that
information about growth and development can help
answer questions about the mechanisms that drove
changes in body form that we see in the fossil
record.
"Most differences between humans and their ancestors
can be associated with developmental changes,"
Kimbel said. The genetic makeup of humans is so
similar to that of our close relatives like the
chimpanzee that most anatomical differences are
explained by changes in the pattern of growth from
infant to adult.
The infant Dikika skeleton is expected to provide an
important reference point that will help researchers
explain how changes in growth and development
contributed to the evolution of humans.
Alemseged will announced the publication of the
research on the Dikika skeleton at a press
conference in Addis Ababa, Ethiopia September 20,
2006.
###
Source: William Kimbel
Contact: Skip Derra
Arizona State University
