Dino buoys glided gracefully

They may have shaken the dinosaur world with every footfall, but research suggests that sauropods could have glided like punts across shallow water.

Plant eaters such as Brachiosaurus, Diplodocus and Apatosaurus were thought to have walked on the bottom of lakes and rivers, while in recent years it was suggested they simply avoided water. But computer modelling, revealed at the Society of Vertebrate Paleontology annual meeting two weeks ago, suggests something rather different.

The sauropods were far too buoyant to have been able to submerge their bodies in the water, according to Donald Henderson, a postdoctoral fellow at the University of Calgary in Canada.

His calculations show that the air sacs found throughout the dinosaurs' bodies - a crucial part of their respiratory system - would have made them about 80 per cent as dense as water.

As a result, the animals would have bobbed on the surface, albeit in a rather unstable fashion.

"It would have been physically impossible for the buoyant sauropods to have walked on lake bottoms," Dr Henderson said.

Fossilised trackways that show only the prints of forefeet appear to support his theory. One from Texas shows just a single hindfoot print just as the sauropod changes direction, as if it were pushing itself off to continue punting through the water.

David Norman, director of the Sedgwick Museum at Cambridge University, said: "Sauropods could have swum like elephants because of their innate buoyancy, perhaps punt-poling themselves along in relatively shallow water."