Sticky or fluid? The great dinosaur pee debate offers experts no relief

To pee or not to pee, that is the question set to spark controversy at a forthcoming meeting of the world's leading dinosaur experts.

Research by Gale Bishop, director of the South Dakota school of mines and technology museum of geology, and Katherine McCarville, a PhD student, suggests that an unusual geological formation may constitute evidence that plant-eating sauropod dinosaurs peed liquid.

Most experts believe they produced a sticky substance as modern birds do. Some were annoyed that the BBC series Walking with Dinosaurs depicted extinct reptiles marking territory with fluid without evidence to support this.

Dr Bishop and Ms McCarville studied a depression - 3m by 1.5m - discovered among petrified trackways at Picketwire Canyonlands in southern Colorado, US.

The palaeontologists believe it was created when one of the many long-necked apatosaurs that left their prints in the muddy shore of a freshwater lake 150 million years ago relieved itself.

Ms McCarville said the depression seemed to be a back-filled fluid scour created by a release of liquid from several metres up. Experiments confirmed that such features could be made in this way.

"When we start looking for similar features at other trackways, we might see a lot of them," she said.

The research will be presented to the annual meeting of the society of vertebrate paleontology in Oklahoma in a fortnight's time.

Martin Lockley, curator of the Colorado University Denver fossil footprint collection, who has surveyed the Picketwire Canyonlands trackways, said the interpretation was possible though he had yet to assess the research. "My gut reaction is that there must be good sedimentological evidence to make such a case," he said.

David Norman, director of the Sedgwick Museum at Cambridge University, was sceptical, adding that the issue seemed rather trivial.