An unusually well-preserved fossil of a duck-billed dinosaur has revealed a body part never seen before on any dinosaur.

The Edmontosaurus regalis specimen found west of Grand Prairie , Alta., last year had a soft, fleshy comb on its head, similar to those found on roosters.

"It's a structure that was completely unexpected," said Victoria Arbour, a University of Alberta paleontologist who co-authored the scientific paper published Thursday in the journal Current Biology, describing the new fossil.

"It kind of makes us wonder what other dinosaurs might have had."

Edmontosaurus had a duck-like bill, and was a plant-eating dinosaur that grew to be 12 metres long — about the length of a bus. It was thought to have roamed North America in herds during the late Cretaceous, about 75 and 65 million years ago, and belonged to a group of dinosaurs known as hadrosaurs, which were the most common dinosaurs on the continent at the time.

Edmontosaurus regalis

The Edmontosaurus regalis fossil in which the comb was found was so well preserved that paleontologists referred to it as "mummified." (Federico Fanti)

Fossils typically only preserve the bones of an animal, not fleshy structures such as a rooster's comb or an elephant's trunk.

Phil Bell, lead author of the paper, said the new findings are "equivalent to discovering for the first time that elephants had trunks."

Bell, a paleontologist at the University of New England in Armidale, Australia, added in a statement, "These findings dramatically alter our perception of the appearance and behaviour of this well-known dinosaur."

In particular, the existence of the comb adds to evidence that Edmontosaurus was a social animal, as ornaments like combs and crests are typically used for communication among animals such as roosters, especially in relation to competition for females.

"We might imagine a pair of  male Edmontosaurus sizing each other up, bellowing, and showing off their head gear to see who was the dominant male and who is in charge of the herd," Bell said.

Bell was a paleontologist with the Philip J. Currie Dinosaur Museum currently under construction in Grand Prairie, Alta., when he uncovered the fossil last summer with geologist Federico Fanti of the University of Bologna. The museum is named after a renowned University of Alberta dinosaur expert who also co-authored the new paper.

Not a true mummy

It was a rare fossil type of fossil that paleontologists describe as "mummified." Arbour said such fossils aren't true mummies, in which flesh is preserved under very dry conditions.

Rather, they are simply well-preserved fossils in which the bones are in the same positions relative to each other that they would have been in life, with impressions of the skin preserved on top.

At the time Edmontosaurus roamed Alberta, its habitat was actually a subtropical, swampy coastal area, Arbour said.

It's not clear what conditions lead the preservation of skin impressions, she added, but it likely involves the animals dying in a flood and being quickly buried by sand or mud.

She added that even when skin impressions are preserved, they are often only visible in certain lighting or when the rock breaks a certain way, which may be why combs hadn't been noticed on earlier "mummified" Edmontosaurus fossils.

"It's something that's kind of easy to miss."

Such impressions would have been lost from the fossils when paleontologists later cleaned the rock away from the bone.

While earlier hadrosaurs, had bony crests, researchers thought the crest had been completely lost in Edmontosaurus. The new discovery suggests that, in fact, the dinosaurs' crests had changed, but remained an important feature.

Bell said it also suggests that similar structures may have been missed in other dinosaurs.

"There's no reason that other strange fleshy structures couldn't have been present on a whole range of other dinosaurs, including T. rex or Triceratops."