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Volcanic
Blast Likely Killed and Preserved Juvenile Fossil Plesiosaur
Found in Antarctica
Skeleton to be
unveiled at U.S. museum Dec. 13
December 11, 2006
Temperatures in Antarctica
were much warmer 70 million years ago.
Credit:
Nicolle Rager, National Science Foundation
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Amid 70-mile-an-hour winds
and freezing Antarctic conditions, an American-Argentine research
team has recovered the well-preserved fossil skeleton of a
juvenile plesiosaur--a marine reptile that swam the waters of the
Southern Ocean roughly 70 million years ago.
The fossil remains represent
one of the most-complete plesiosaur skeletons ever found and is
thought to be the best-articulated fossil skeleton ever recovered
from Antarctica. The creature would have inhabited Antarctic
waters during a period when the Earth and oceans were far warmer
than they are today.
James E. Martin, curator of
vertebrate paleontology and coordinator of the paleontology
program at the South Dakota School of Mines and Technology's
Museum of Geology, announced today the plesiosaur bones will be
unveiled at the museum on Dec.13, 2006.
The long-necked, diamond-finned
plesiosaurs are probably most familiar as the legendary
inhabitants of Scotland's Loch Ness, although scientific evidence
indicates the marine carnivores have been extinct for millions of
years. But when the creatures were alive, their paddle-like fins
would have allowed them to "fly through the water" in a
motion very similar to modern-day penguins.
Martin, an expert on fossil
marine reptiles, co-led the 2005 expedition to Antarctica that
recovered the plesiosaur. Judd Case, of Eastern Washington
University, and Marcelo Reguero of the Museo de La Plata,
Argentina, were also co- leaders.
The National Science Foundation
(NSF) and the Instituto Antártico Argentino, directed by
Sergio Marenssi, funded the expedition. The Argentine Air Force
provided helicopter support.
NSF manages the U.S Antarctic
Program, which coordinates all U.S. research on the southernmost
continent. The White House has designated NSF as the lead federal
agency for the International Polar Year, a 2-year global research
campaign in the polar regions that begins in March 2007.
Preserved by a volcanic
blast?
A mother and juvenile
plesiosaur probably looked like this artist's
rendering.
Credit: Nicolle Rager, National
Science Foundation
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After it was prepared in
the United States, Martin said, the specimen was discovered tobe
the 5-foot-long (1.5 meters) skeleton of a long-necked
(elasmosaurid) plesiosaur. An adult specimen could reach over 32
feet (10 meters) in length. Most of the bones of the baby
plesiosaur had not developed distinct ends due to the youth of
the specimen, he said.
But the animal's stomach area
was spectacularly preserved. Stomach ribs (gastralia) span the
abdomen, and rather than being long, straight bones like those of
most plesiosaurs, these are forked, sometimes into three prongs.
Moreover, numerous small, rounded stomach stones (gastroliths)
are concentrated within the abdominal cavity, indicating stomach
stones were ingested even by juvenile plesiosaurs to help
maintain buoyancy or to aid digestion.
The skeleton is nearly
perfectly articulated as it would have been in life, but the
skull has eroded away from the body. Extreme weather at the
excavation site on Vega Island off the Antarctic Peninsula and
lack of field time prevented further exploration for the eroded
skull.
The researchers speculate
volcanism similar to the massive eruption of Mt. St. Helens in
Washington in 1980, may have caused the animal's death.
Excavation turned up volcanic ash beds layered within the shallow
marine sands at the site, and chunks of ash were found with plant
material inside. That suggests a major blow-down of trees as was
observed when Mt. St. Helens erupted. Either the blast or ash
dumped into the ocean, the scientists say, may have caused the
baby's demise. Moreover, silica released from the ash allowed
spectacular preservation of the skeleton.
High winds, freezing
water, hard work
A researcher carefully
excavates a fossilized juvenile plesiosaur on Vega Island,
Antarctica.
Credit: James E. Martin, South
Dakota School of Mines and Technology
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As with the find of a new
species of dinosaur Martin and Case made in Antarctica several
years ago, the weather and the harsh Antarctic climate made
collecting the plesiosaur specimen exceedingly difficult. Weeks
of winds exceeding 70 miles an hour hindered the excavation. At
the end of the work, icy temperatures turned water to slush
before plaster could be mixed to encase the fossil for
transportation. The ground was so frozen a digging tool snapped
in half during the excavation. Finally, a jackhammer had to be
carried up to the site in backpacks along with gasoline, plaster,
and water.
The resulting package of
plesiosaur remains encased in a protective plaster jacket was too
large to carry, so the Argentine air force brought helicopters to
the rescue. It took five men to lift the specimen into the
chopper, which delivered the cargo to the tent camp on the shores
of Herbert Sound. The specimen was later picked up by the
Laurence M. Gould,
an NSF-chartered research vessel.
At the Museum of Geology, the
reptile was prepared by Michelle Pinsdorf and replicated by
Shawna Johnson, both master's degree students of paleontology at
the South Dakota School of Mines.
A prehistoric nursery?
This animation shows how the
juvenile plesiosaur, discovered in Antarctica by an
American-Argentine research team, might have
appeared.
Credit: Trent Schindler, National
Science Foundation
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J. Foster Sawyer, of the
South Dakota Geological Survey and the School of Mines, found the
skeleton while working with Martin at an elevation of 650 feet
(200 meters) on Vega Island. Sawyer found vertebrae exposed by
wind from the ancient sandy seabed. The bones were embedded in
rocks and associated with marine shellfish that suggest the area
was a shallow-water marine environment roughly 70 million years
ago. Two other partial plesiosaurs were also collected, as well
as finds of very advanced shore birds.
Since 1998, expeditions by the
American-Argentine team to the area--in part to compare the
ancient climates of South Dakota and Antarctica--have secured
numerous isolated elements of juvenile plesiosaurs and mosasaurs,
a giant marine reptile that looked like an alligator with fins.
Martin and his colleagues believe the site may have been a
shallow-water area where marine reptiles had their young, and
where the young remained until they were of sufficient size and
ability to survive in open waters.
Whether plesiosaurs gave live
birth has not been proved, but numerous bones and partial
skeletons of larger plesiosaurs were found in the same area as
the young. Given the long history of plesiosaurs, evolution would
have had ample time for them to develop a form of live birth.
The juvenile plesiosaur appears
to be related to one discovered in New Zealand in 1874. That
plesiosaur was named Mauisaurus
and is characterized by a rounded
end of the major paddle bone. It was confined to the southern
oceans where it existed more than 5 million years.
Source
/ Credit: NSF
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