[meteorite-list] More on big dead (but not so suddenly) animals

From: Darren Garrison <cynapse_at_meteoritecentral.com>
Date: Fri, 20 Nov 2009 00:57:07 -0500
Message-ID: <opbcg5ln6li95nm50pcr7brq9u105fb7lf_at_4ax.com>

http://www.csmonitor.com/2009/1120/p02s13-usgn.html

The mystery of the mastodons gets a few big clues
When and how mammoths and mastodons went extinct has long puzzled scientists.
But a new study suggests the animals vanished much earlier than previously
thought.
By Peter N. Spotts | Staff writer of The Christian Science Monitor

from the November 19, 2009 edition

Ever since Europeans first uncovered mastodon fossils along Big Bone Lick in
Kentucky in 1739, the demise of these huge animals and other lumbering
contemporaries at the end of the last ice age has been an enduring puzzle to
paleontologists.

Now, a team of researchers has evidence that woolly mammoths, huge ground
sloths, and other Pleistocene giants became extinct earlier than previously
thought.

The results appear to rule out at least one explanation scientists have offered
up to explain the creatures' demise: an asteroid strike. Other theories ? such
as climate change and human hunters ? remain possible, though the findings would
shift the timeline more than 1,000 years backward.

Moreover, the research intriguingly suggests that the decline led to significant
changes in the types and groupings of different plants within the animals'
range, as well as an increase in the number of wildfires. In other words, it
could have literally altered the landscape.

An 'elegant' study

The work, which was conducted at Appleman Lake in Indiana, is "elegant," says
Eric Scott, a paleontologist at the San Berbardino County Museum who focuses on
Pleistocene fossils, in an e-mail.

It neatly sidesteps a significant challenge paleontologists studying this issue
face: "There is lack of sufficient numbers of well-dated vertebrate fossils,
from multiple sites, from the time period in question," writes Dr. Scott.

Jaquelyn Gill, a graduate student on the research team at Appleman Lake,
overcame that hurdle in an ingenious way: She used a particular species of
fungus, Sporormiella, as a stand-in for the huge mammals. Sporormiella needs the
digestive tracts of plant-eating animals to complete its life cycle. Spores
found in fossilized dung have been associated with the huge animals, called
megafauna.

"The use of Sporormiella as a proxy for the megaherbivores is rather inspired,"
Scott adds.

Surprise results

The results were something of a surprise, says John Williams, a University of
Wisconsin paleoecologist and a member of the research team.

He and his colleagues had set out to study changes to plant communities during
one period of the Pleistocene. They sought to gauge the relative role climate
and the presence of huge mammals may have played in altering the mix of
vegetation. The group was looking for clues that might help scientists
anticipate potential ecological changes ahead as global warming progresses this
century.

"Everything is happening all at once" during the time period his research
targeted, he explains. "We see ice sheets retreating. We see carbon-dioxide
concentrations rising. We see a major turnover in plant communities. Humans are
arriving. And there's this set of large animals going extinct."

He and most of his colleagues suspected that climate change was the biggest
driver behind the changes in plant communities at the time of the
megaherbivores. But the results offer another possible interpretation: that it
was the decline of the big animals that had the greatest impact on plant
groupings.

The decline in megafauna clearly overlapped changes in plant groupings and
changes in the presence of significant charcoal deposits, the research team
found.

This suggests that forests might have spread as megafauna declined. Big animals,
especially mammoths and mastodons, would have munched on small trees and
saplings, limiting the expansion of woodlands. The spread of forests, then,
would have provided fuel for more wildfires.

"What was very striking to me was how closely associated these three major
things are," Dr. Williams says.

Revising the timeline

The timing seems to rule out three notions of what triggered the extinction of
megafauna:

? A major collision between Earth and an asteroid or comet about 12,900 years
ago

? The onset of a 1,300 year-long cold spell known as the Younger Dryas, which
kicked in roughly 12,800 years ago.

? A blitzkrieg-like onslaught of human hunters as early as 13,300 years ago.

Yet climate and human involvement can't be ruled out, Williams says. The decline
in megafauna does coincide with the onset of warming coming out of the last ice
age. And some evidence suggests that humans were present on the continent at
that time.

The team anticipates using its fungal-spore approach to expand its research
beyond Appleman Lake to see if a similar picture emerges at other places around
the country.
Received on Fri 20 Nov 2009 12:57:07 AM PST