The "inflatable" dinosaurs of the Mesozoic
They were the biggest animals ever to walk the earth. And now the giant
sauropod dinosaurs - known as "long-necks" to millions of kids - have
another claim to fame. They were also the largest to ever float.
"The sauropod dinosaurs were the colossal corks of the Mesozoic,"
says Dr. Donald Henderson, a postdoctoral researcher in paleontology at the
University of Calgary, who presented his NSERC-funded discovery two weeks ago at
the annual meeting of the Society of Vertebrate Paleontology in St. Paul,
Minnesota.
While it's well known that many modern large animals, including Indian
elephants, can swim, sauropods have long been viewed as bulky leviathans in a
class of their own. These giants of the Jurassic and Cretaceous periods tipped
the scales at between 10 and 30 tonnes and were up to 30 metres long and 12
metres in height.
Scientists initially thought they were swampy waders, too huge to have
survived on land without crushing themselves. In the 1950s, however, changes in
scientific interpretation hauled them onto dry land. The thinking was that a
submerged sauropod would be covered with water to such a depth that the water
pressure wouldn't allow it to expand its lungs.
Recently the picture of sauropod life has changed yet again with evidence
that these heavyweights had bird-like lungs and air sacs. Modern birds have a
series of balloon-like air sacs in their bodies that reduce their weight and aid
respiration.
Research on sauropod vertebrae found the telltale marks of bird-like air
sacs. Scientists now think that sauropods were full of air - at least 15 percent
of their body volume was air sacs.
"Using 3-D computer modelling, I found that when you give sauropods
bird-like lung systems and air sacs they're actually really light. Their body
density is about 80 per cent that of water, so they float really high in the
water," says Dr. Henderson. He made the startling discovery using 3-D
mathematical and computer models of animal buoyancy that he developed and
applied to modern crocodiles and elephants as his first test subjects.
So, if these giant ancient reptiles floated, can we expect a new TV series
Swimming with Sauropods?
Not likely, says Dr. Henderson, who specializes in the study of how dinosaurs
moved. His computer models indicate that sauropods had a centre of balance above
their centre of buoyancy and so would have been very unstable once afloat.
"If they lost contact with the bottom they would tip sideways and be in
serious trouble," he says.
But while they probably didn't swim, the discovery of sauropods surprising
lighter-than-water nature might be the explanation to a long-standing dinosaur
trackway mystery. Some sauropod trackways found in the United States and Korea
have perplexed paleontologists in that they only contain the front footprints,
as if the animals were walking on their hands.
Dr. Henderson's computer simulations show that a sub-group of sauropods with
longer legs, including Brachiosaurus, floated with their bodies tilted forward.
Thus their front feet were deeper than their hind feet enabling them to
"punt" along the bottom with only their front feet.
Says Dr. Henderson: "I think it's completely possible that some
sauropods could have made front-leg only trackways in this way." - NSERC
More information:
Contact: Dr. Donald M. Henderson, dmhender@ucalgary.ca or 403-220-8436.
View computer simulations of floating animals on Dr. Henderson's Web site at www.ucalgary.ca/~dmhender/Animations/flotation.html
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