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| Peter Ungar holds the skull of Australopithicus africanus,
the first hominin found in Africa |
New findings suggest that the ancient human "cousin" known
as the "Nutcracker Man" wasn't regularly eating anything
like nuts after all.
A University of Arkansas professor and his colleagues used a combination
of microscopy and fractal analysis to examine marks on the teeth
of members of an ancient human ancestor species and found that
what it actually ate does not correspond with the size and shape
of its teeth. This finding suggests that structure alone is not
enough to predict dietary preferences and that evolutionary adaptation
for eating may have been based on scarcity rather than on an animal's
regular diet.
"These findings totally run counter to what people have been
saying for the last half a century," said Peter Ungar, professor
of anthropology in the J. William Fulbright College of Arts and
Sciences. "We have to sit back and re-evaluate what we once
thought."
Ungar and his colleagues Frederick E. Grine of Cambridge University
and Stony Brook University and Mark F. Teaford of Johns Hopkins
University School of Medicine reported their findings in the PLoS
ONE, the online, open-access journal from the Public Library of
Science.
Ungar applies dental-impression material to the jaw of Australopithicus
afarensis, also known as Lucy.
The researchers examined the teeth of Paranthropus boisei, an ancient
hominin that lived between 2.3 million and 1.2 million years ago
and is known popularly as the "Nutcracker Man" because
it has the biggest, flattest cheek teeth and the thickest enamel
of any known hominin. Since the first specimen was reported by
Mary and Louis Leakey in 1959, scientists have believed that P.
boisei fed on nuts and seeds or roots and tubers found on the savannas
throughout eastern Africa because the teeth, cranium and mandible
appear to be built for chewing and crunching hard objects.
"The morphology suggests what P. boisei could eat, but not
necessarily what it did eat," Ungar said.
Anthropologists have traditionally inferred the diet of this and
other ancient human ancestors by looking at the size and shape
of the teeth and jaws. However, by looking at the patterns of microscopic
wear on a tooth, scientists can get direct evidence for what these
species actually ate.
Ungar and his colleagues used a combination of a scanning confocal
microscope, engineering software and scale-sensitive fractal analysis
to create a microwear texture analysis of the molars of seven specimens
of P. boisei. The specimens spanned a time frame of almost a million
years and were found in Kenya, Tanzania and Ethiopia. Using these
techniques, they were able to create three-dimensional "point
clouds" that showed the pits and scratches on the teeth.
The researchers looked at complexity and directionality of wear
textures in the teeth they examined. Since food interacts with
teeth, it leaves behind telltale signs that can be measured. Hard,
brittle foods like nuts and seeds tend to lead to more complex
tooth profiles, while tough foods like leaves lead to more parallel
scratches, which corresponds with directionality.
They compared the dental microwear profiles of P. boisei to the
microwear profiles of modern-day primates that eat different types
of diets - grey-cheeked mangabeys and brown capuchins, which eat
mostly soft items but fall back on hard nuts or palm fronds, and
the mantled howling monkey and silvered leaf monkey, which eat
mostly leaves and other tough foods. They also compared the microwear
analysis to analyses of teeth from some of the fossil's more contemporary
counterparts -- Australopithecus africanus, which lived between
3.3 million and 2.3 million years ago, and Paranthropus robustus,
which lived between 2 million and 1.5 million years ago.
The P. boisei teeth had light wear, suggesting that none of the
individuals ate extremely hard or tough foods in the days leading
up to death. It's a pattern more consistent with modern-day fruit-eating
animals than with most modern-day primates.
"It looks more like they were eating Jell-o," Ungar
said.
This finding, while contradictory to previous speculation on the
diet of P. boisei, is in line with a paradox that has been documented
in fish. Liem's Paradox states that animals may actively avoid
eating the very foods they have developed adaptations for when
they can find other food sources.
It appears that this paradox may hold true for P. boisei and for
some modern-day primates as well.
"If you give a gorilla a choice of eating a sugary fruit
or a leaf, it will take the fruit every time," Ungar said. "But
if you look at a gorilla's skull, its sharp teeth are adapted to
consuming tough leaves. They don't eat the leaves unless they have
to."
This finding represents a fundamental shift in the way researchers
look at the diets of these hominins.
"This challenges the fundamental assumptions of why such
specializations occur in nature," Ungar said. "It shows
that animals can develop an extreme degree of specialization without
the specialized object becoming a preferred resource."
This project was funded in part by grants from the National Science
Foundation. The researchers' study is available at http://www.plosone.org/doi/pone.0002044
Contact:
Peter Ungar, professor of anthropology
J. William Fulbright College of Arts and Sciences
(479) 575-6361, pungar@uark.edu
Matt McGowan, science and research communications officer
University Relations
(479) 575-4246, dmcgowa@uark.edu
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