- They lumbered cautiously on land. But when the biggest
dinosaurs in history hit the water, they floated like giant inflatable
pool toys, new Canadian research has found.
-
- "They were like colossal corks," says Donald
Henderson, a University of Calgary researcher who says he may have solved
a long-standing mystery about the long-necked dinosaurs that were the biggest
creatures to ever walk the Earth.
-
- Fossil hunters have found that sauropods had spinal air
sacs, balloon-like air bags very similar to those birds use to breathe.
Dr. Henderson used three-dimensional computer modeling to show that these
air-filled sacs acted like built-in life jackets, and would have allowed
the sauropods to float easily in the water.
-
- Not that they would have been all that happy, particularly
if their feet couldn't touch the bottom. Sauropods may have been buoyant,
but they were not built for swimming. If they lost contact with land, they
would have been in danger of tipping over and might not have been able
to right themselves.
-
- But at least one sauropod species, the brachiosaurus,
probably tilted forward in the water so that his front legs touched the
bottom and were able to help propel him forwards.
-
- This is where the dinosaur mystery comes in. In many
places in the world, including Texas and Korea, researchers have found
preserved sauropod footprints ó but only from the front feet. It
was as if the animals were walking on their front legs.
-
- Dr. Henderson, whose work combines paleontology with
biomechanics, says his findings offer a good explanation for the mystery.
The dinosaurs were floating, and were able to punt along the bottom with
their front feet.
-
- Philip Currie, head of dinosaur research at the Royal
Tyrrell Museum in Drumheller, Alta., agrees. He says Dr. Henderson has
not only found a credible solution for the handprint puzzle, but that his
novel modeling approach may answer other difficult questions about how
such big animals got around.
-
- Sauropods were giants in a leviathan age, weighing as
much as 30 tonnes, five times as much as an African elephant. They appeared
about 210 million years ago, and disappeared with the rest of the dinosaurs
about 65 million years ago. There may have been as many as 70 sauropod
species.
-
- Theories about how such giant creatures moved have changed
dramatically over the years.
-
- Initially, researchers believed they wandered in swampy
waters, too big to survive on land without buckling under their own weight.
-
- By the 1970s, a careful examination of their bones revealed
that they could support their own weight and were land dwellers, says Jeff
Wilson, a paleontologist at the University of Michigan and an expert on
sauropods.
-
- The theory was that by the time they sank deep enough
to cover their massive bodies in water, the pressure of that water would
have made it too difficult for their lungs to expand.
-
- Now Dr. Henderson has found they were able to float.
-
- "It is interesting. It is something that wasn't
looked at before," said Dr. Wilson, who was at the conference in Minnesota
several weeks ago at which Dr. Henderson presented his findings.
-
- That ability to float was probably due to the sauropod's
unique respiratory system, says Dr. Henderson, who is doing post-doctoral
work financed by the Natural Sciences and Engineering Research Council.
The series of air sacs along the spine and inside their vertebrae allowed
the body to absorb oxygen more efficiently as it travelled down their long
necks to their lungs. The air sacs may also have allowed the sauropods
to get rid of excess body heat.
-
- Sauropods probably travelled in herds, and were wandering
vegetarians. Being able to float might have helped to find food, or to
survive the occasional flooding caused by monsoon rains, says Dr. Henderson.
-
- Like most paleontologists, Dr. Henderson believes not
only that birds descended from a group of two-legged dinosaurs, but that
birds are actually modern dinosaurs. That's why he investigated their system
of air sacs, and applied what he found to the sauropods.
-
- Dr. Currie says it is possible that other dinosaurs also
floated. Duck-billed dinosaurs left some mysterious footprints in B.C.,
he says. The foot prints show a nice long stride that gradually shortens.
Suddenly, however, they shift a metre-and-a-half to the side. It is hard
to imagine a four tonne creature suddenly jumping that far, says Dr. Currie.
It is easier to imagine one hitting the water and floating to the left,
he says, and Dr. Henderson's work gives that credence.
-
- © 2003 Bell Globemedia Publishing Inc. All Rights
Reserved.
-
- http://www.globeandmail.com/servlet/story/RTGAM.20031028.wdino1028/BNStory/National/
-
- http://www.ucalgary.ca/~dmhender/Animations/brachi_flyde.gif
|
