LOS ANGELES — Searching across the Tibetan plateau,
paleontologists have discovered a species of woolly rhinoceros that may
be an ancestor of the great Ice Age beasts that roamed the icy plains of
North America, Europe and Asia.
The Coelodonta
thibetana fossil dates to about 3.7 million years ago, about a million
years before other known woolly rhinos. The findings, published in
Friday’s edition of the journal Science, lead researchers to believe
that before the Ice Age began, the chilly Tibetan highlands may have
served as an evolutionary cradle for cold-hardy mammals whose
descendants thrived in the glacial times that followed.
Paleontologists
have yet to fully trace the origins of many of the giant, hairy beasts
that lived during the most recent Ice Age, which lasted from about 2.6
million to 10,000 years ago. Many of these animals, whose massive bodies
conserved heat effectively, were thought to have evolved in Eurasia
from animals that managed to survive and adapt to an increasingly cold
environment.
The new fossil from the Zanda Basin
in Tibet may provide an alternative evolutionary explanation for some of
those animals, said study co-author Xiaoming Wang, a vertebrate
paleontologist with the Natural History Museum of Los Angeles County.
Wang’s
international team did not go to the Tibetan highlands expecting to bag
such a find. Tibet’s elevated plains are relatively untouched
paleontologically, and the scientists were simply looking to learn about
the history of the area’s animal life from whatever fossil evidence
they could dig up. Team members would often walk five to 10 miles in a
day, scanning the earth for signs of fossil fragments.
It
was Wang who discovered a neck-bone fragment poking out of the ground
one August afternoon in 2007. He had barely begun digging when his
hammer hit the skull. He brushed away dirt, baring giant teeth.
Short
on supplies and with just a few days left on this expedition, Wang and
colleagues were faced with a dilemma. They could wait for their next
trip to take the fossil home — but leaving it partially exposed would
make it vulnerable to the elements.
Instead, the
team decided to dig out the fossil as fast as they could. The scientists
sped to the nearest hospital, about 60 miles away, and begged a doctor
for plaster they could use to protect the fragile specimen. Without the
plaster to encase the bones, Wang said, the fossil “would have fallen
apart into a thousand pieces before we got back into Beijing.”
“The
doctor was really gracious,” Wang added. “We managed to convince him
that this is a special case, that he will be able to make a big
contribution to science.”
Several months after a
harrowingly bumpy ride back to Lhasa and then Beijing, the researchers
realized the significance of their discovery: a new species of
rhinoceros that had developed cold-hardy attributes at least a million
years before the Ice Age got under way. The rhino, about 10 percent
lighter than its Ice-Age descendant, had a hairy body and a flattened
horn useful for sweeping away snow to get at the vegetation underneath.
The
team also found other creatures — blue sheep, snow leopards and Tibetan
antelope — that had acquired similarly snow-ready qualities. Perhaps
this part of Tibet had been a specialized breeding ground for
cold-tolerant animals that were able to thrive and spread once the big
freeze hit. It will take more digging to find out.
“This
is just the first shot across the bow in terms of possible evidence of
pre-adaptations to cold climates,” said Donald Prothero, a mammalian
paleontologist at Occidental College. “It’s possible that quite a few
more of these major Ice Age groups will turn out to be from Tibet. We’ll
see when they get more specimens.”
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