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Computerized Buoyancy Tests Suggest Sauropods Floated, Could Tip Over



has a cute little animated graphic

http://dsc.discovery.com/news/briefs/20031208/dinofloat.html#

Dec. 10, 2003  Sauropod dinosaurs, the largest terrestrial animals ever to
have lived on our planet, could float like corks in water, according to
computerized buoyancy tests on recreations of sauropods that lived during
the Mesozoic Era, which lasted from 248 to 65 million years ago.

This ability links the huge dinosaurs with birds, scientist say. Both
float in water despite often surprisingly large body sizes. The finding
also negates an earlier theory that sauropods escaped predators by hiding
themselves underwater. 

The computerized models were created by Donald Henderson, a paleontologist
in the Vertebrate Morphology and Palaeontology Research Group in the
Department of Biological Sciences at the University of Calgary. A paper on
his research is published in the current Royal Society Biology Letters.
Henderson digitized restorations of the animals into a 3-D format. The
computerized models show the shape and volume of the dinosaur, which
Henderson could then dunk in virtual water.

He explained to Discovery News that sauropods floated because air sacs
within their bodies gave them a surprising lightness for a reptile that
could grow as long as 130 feet and weigh as much as 85 tons, or ten times
the size of today's elephants. Sauropods also had lightweight bones.

"The bones of the spine are mostly a form of 'bony foam,'" said Henderson.
"There is also good evidence visible in their bones that these animals had
a system of air sacs just like birds. The air sac systems of birds fill up
a large volume of their bodies, and make them very light, (such as) how a
large swan can float on the water."

Sauropods were not very good swimmers, however. The shape of their bodies,
including their thick, long necks, would have made them tipsy and unstable
in water, according to Henderson. Only one species, Brachiosaurus, likely
moved with relative ease in water, punting along the bottom mud of lakes.

"If Brachio were in water up to about the base of its neck, the back legs
would lift off, but the hands would remain in contact with the lake or
river bed," said Henderson. "By slowly moving its arms in a walking
fashion, I could see it slowly moving forward, and even turning with a
wide arc."

Henderson's visualization matches evidence from mysterious sauropod tracks
that show mostly forefoot impressions. While these tracks are now dry,
during the Mesozoic the tracks might have been made on a lake bottom used
as a prehistoric highway by brachiosaurs. 
...