A duck-billed dinosaur from North America had a fleshy cock's comb that it probably used to communicate with others of its species, say researchers.
The comb, found in a rare mummified specimen of Edmontosaurus regalis, is reported today in Current Biology.
"The discovery of the comb was a total surprise because there is no indication from any other dinosaur that these animals had such a structure," says palaeontologist and lead author Dr Phil Bell of the University of New England.
At 10-12 metres long and weighing up to 4 tonnes, Edmontosaurus regalis was one of the most common dinosaurs to live 70 million years ago.
"It was a big gentle herbivore," says Bell. "It would have filled the same ecological role as a kangaroo would, or a deer."
He says the animal's skull is long and low like a horse's skull, and the front end of its jaws have no teeth and is broad like a duck bill.
Scientists have known about Edmontosaurus for a century, and there are numerous complete skeletons, some even with skin, but the latest discovery was never expected, says Bell.
He says co-author Frederico Fanti discovered the new specimen while the two of them were prospecting in a river in Northern Alberta.
Back in the lab, Bell started to chip away at the surrounding earth and that's when he struck gold.
"I'd uncovered the skin on parts of the neck and I could see where the head was going, so I put my chisel in the rock where there shouldn't have been skin, and low and behold, there was," he says.
"It was a mistake but a lucky blow, in the end."
Bell says the findings suggested a three-dimensional cranial crest, or comb, made of soft tissue.
"There was a fleshy substance and wrinkles on the preserved skin so we know it was supple. It was probably a fatty tissue underneath," he says.
Bell says some relatives of the dinosaur have been found to have a bony crest, which are extensions of the nasal passages and were used as resonators when the animals called out to each other.
He says the bony crests disappeared at the end of the Cretaceous when Edmontosaurus appeared.
Its fleshy crest was in the same place as the previous bony crests but had no connections to the nasal passage.
Bell says it's likely that Edmontosaurus, which travelled in herds for protection, used the crest to communicate.
"There's always some kind of hierarchy in a herd," he says. "We believe this crest was used to signal to mates or to confer its position within the herd hierarchy - 'he with the biggest crest wins' kind of thing."
Bell says this is supported by the fact that modern-day birds - from the rooster to the Andean condor - all have brightly coloured crests that are used to signal to each other.
It's all in the skin
While most scientists are interested in skeletons, Bell has devoted his career to looking at skin on dinosaurs.
"It's the skin and the flesh that really give you that true life picture," he says.
The preservation of soft tissues like this is made possible by a special "mummification" process that was common in the area he and colleagues were exploring, says Bell.
"Animals were dying but getting buried very rapidly, probably within a space of a couple of days after they died," he says.
And, says Bell, the sediment that "entombed" the dinosaurs was anaerobic and probably contained bacteria that precipitated out certain elements like manganese, iron and calcium from the water to help preserve the skin.
Bell says it is interesting the comb was found in a herbivore like Edmontosaurus which is not closely related to birds.
But, he says, there may well be combs on therapods that have yet to be discovered.
"This opens the possibility that we have all kinds of soft tissue structures that we've never seen," he says. "We're in for more surprises, I think."