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Unfossilized Bone "Record" Compared With Fossil Record
Interesting re hazards of what can be deduced from the fossil record.
Several meters away, through the wavering heat of a desert afternoon, a
paleontologist spies what looks like a thumb-size chip of bone. As he
approaches the relic, he wonders what it will be: A piece of leg bone? A
fragment of skull? A chunk of a vertebra? What sort of creature does this
remnant represent? The paleontologist reaches the find, kneels, and whips
out a whisk broom. Delicately, he brushes away loose grains of sand to
reveal the fragile skull of a nine-banded armadillo. "Jackpot!" the
scientist thinks. From the bits of flesh still on a few bones, he knows
that this animal roamed the Earth, oh, maybe a couple of months ago.
A jackpot indeed. Increasingly, paleontologists are concerned not only
with creatures that lived, died, and fossilized millions of years ago.
Bone hounds today are broadening their investigations to include modern
times. They scout remote, undisturbed areas to survey and identify
unfossilized bones lying about on the ground and then compare the
resulting list of species with the known inhabitants of that ecosystem.
These analyses of the earliest steps in the fossilization process are
providing scientists with insights into how completeor, in some cases, how
incompleteEarth's fossil record may be.
Scientists have begun to study the fossilization process to understand how
likely various species were to be preserved. That information could revise
some estimates of the relative abundance and dominance of various animal
species in the fossil record.
In one long-term investigation, researchers have been studying the bones
littering the landscape in Kenya's Amboseli National Park, a
392-square-kilometer reserve just northwest of Mount Kilimanjaro. During
the dry season, wildlife flocks to the park's spring-fed marshes. Amboseli
also contains woodlands, grasslands, and a low area that becomes a lake
during rainy spells, says Anna K. Behrensmeyer of the Smithsonian
Institution in Washington, D.C. She and her colleagues have systematically
scoured certain paths across the plain and through the woodlands of the
park since the 1970s, recording the bones they find. Most they leave in
place and revisit during later surveys, but some they take back to the lab
for identification and analysis.
In the past few decades, the park has experienced an ecological shift that
has influenced the quantity of bones there. The park in the 1970s and
1980s hosted a diverse set of predatorsincluding lions, hyenas, cheetahs,
and jackals. The bones of their prey, large and small, were abundant.
However, climate change and other factors transformed a large part of
Amboseli's woodlands to open grasslands by the 1990s. As a result,
populations of hyenas skyrocketed.
Unlike most of the predators in the park, scavenging hyenas use their
massive jaws to crush all but the largest bones of big carcasses.
Therefore, Behrensmeyer and her colleagues now find few bones from prey
weighing less than around 400 kilograms, the size of a Cape buffalo. That
change has consequences for the future fossil record.
Scientists could use detailed analyses of the remains in the park to infer
predator-to-scavenger ratios in ancient ecosystems, Behrensmeyer says. She
described the team's findings last fall in Norman, Okla., at the annual
meeting of the Society of Vertebrate Paleontology.