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 Scientists who studied DNA preserved in Arctic permafrost
sediments and in the remains of such ancient animals have concluded
that these Ice Age beasts relied heavily on the protein-rich
wildflowers that once blanketed the region.
But dramatic Ice Age climate change caused a huge decline in these
plants, leaving the Arctic covered instead in grasses and shrubs
that lacked the same nutritional value and could not sustain the big
herbivorous mammals, the scientists reported in the journal Nature
on Wednesday.
The change in vegetation began roughly 25,000 years ago and ended
about 10,000 years ago — a time when many of the big animals slipped
into extinction, the researchers said.
Scientists for years have been trying to figure out what caused this
mass extinction, when two-thirds of all the large-bodied mammals in
the Northern Hemisphere died out.
"Now we have, from my perspective at least, a very credible
explanation," Eske Willerslev of the University of Copenhagen, an
expert in ancient DNA who led an international team of researchers,
said in a telephone interview.
The findings contradicted the notion that humans arriving in these
regions during the Ice Age caused the mass extinction by hunting the
big animals into oblivion — the so-called overkill or Blitzkrieg
hypothesis.
"We think that the major driver (of the mass extinction) is not the
humans," Willerslev said, although he did not rule out that human
hunters may have delivered the coup de grace to some species already
diminished by the dwindling food supplies.
The Arctic region once teemed with herds of big animals, in some
ways resembling an African savanna. Large plant eaters included
woolly mammoths, woolly rhinos, horses, bison, reindeer and camels,
with predators including hyenas, saber-toothed cats, lions and huge
short-faced bears.
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The scientists carried out a 50,000-year history of the vegetation
across the Arctic in Siberia and North America.
They obtained 242 permafrost sediment samples from various Arctic
sites and studied the feces and stomach contents from the mummified
remains of Ice Age animals recovered in places like Siberia. They
determined the age of the samples and analyzed the DNA.
While many scientists had thought the ecosystem had been grasslands
and the big animals were grass eaters, this study showed it instead
was dominated by a kind of plant known as forbs — essentially
wildflowers.
"The whole Arctic ecosystem looked extremely different from today.
You can imagine these enormous steppes with no trees, no shrubs, but
dominated by these small flowering plants," Willerslev said.
Christian Brochmann, a botanist at the Natural History Museum at the
University of Oslo, said the permafrost contained "a vast, frozen
DNA archive left as footprints from past ecosystems," that could be
deciphered by exploring animal and plant collections already stored
in museums.
(Reporting by Will Dunham, editing by G Crosse)
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