By Paul Rincon
BBC News Online science staff
Sauropods - the largest and heaviest dinosaurs that ever existed - floated in water, according to new claims.
Brachiosaurus may have spent some of their time in water
A Canadian palaeontologist has used computer simulations to investigate how the extinct animals would have fared when immersed in a lake or river.
He found the multi-tonne behemoths became buoyant, supporting the idea that unusual fossil trackways were made by sauropods floating in water.
Details of the research appear in the scientific journal Biology Letters.
Dr Donald Henderson of the University of Calgary in Canada has developed a computer simulation to investigate what would happen if a sauropod was submerged in water deep enough for it to either sink or float.
"We were originally using the computer model for crocodiles, to see what they do. I decided to put the sauropod in as a laugh and was surprised to see that it did float," said Dr Henderson.
Dr Henderson tested the simulation with four well-known sauropod dinosaurs: Apatosaurus, Brachiosaurus, Camarasaurus and Diplodocus. All four species achieved buoyancy in water.
"They all seem to have lived near water, but they would have been in trouble if that water had been too deep," he told BBC News Online.
If sauropods had floated clear of the river or lake bed, they would most likely have rolled on to their sides, said Henderson, although their necks would have saved them from totally capsizing.
When initial discoveries of sauropod fossils were made in the 1800s, most palaeontologists settled on a theory that the animals were aquatic because of their great size.
This theory took a blow in the late 1940s when a US researcher proposed that if a sauropod were submerged under several metres of water, the pressure would have collapsed its lungs and airways, killing it.
This view was dependent on sauropods having very dense bodies that would make them sink to the bottom. But sauropods were subsequently found to have hollow, or pneumatized, vertebrae which might have made them more buoyant in water.
"Whether they would be stable in water or tip over is a bit hypothetical," said Professor Martin Lockley, a geologist at the University of Colorado, Denver.
"It looks to me like sauropods liked dry land and didn't spend a lot of time in water. We do find their footprints along shorelines, so they must have gone there to drink and so on.
"But we also find them inland at fossil sites like the Morrison Formation, which millions of years ago would have been semi-arid and without much water," Professor Lockley told BBC News Online.
Palaeontologists have found numerous "manus-only" fossil trackways, which may have been made by sauropods propelling themselves along the bottom of a lake or river with their front feet only.
Dr Henderson said it was possible that Brachiosaurus could have used its long front legs to "punt" along the bottom of a lake or river.