A unique fossil of the duck-billed dinosaur Edmontosaurus regalis shows for the first time that those dinosaurs’ heads were adorned with a fleshy comb, similar to that of a rooster.

The duck-billed dinosaurs, or the hadrosaurs, lived in what is now North America between 75 and 65 million years ago.

They were giant plant-eaters – about 12 m long – and filled a similar ecological role to deer, sheep, horses, cows or kangaroos today.

“No one ever suspected dinosaurs may have combs like roosters, because the evidence of soft tissue usually decays before fossilization,” said Dr Phil Bell from the University of New England in Australia, who is the first author of the study published in the journal Current Biology.

“An elephant’s trunk or a rooster’s comb might never fossilize because there is no bone in them. This discovery is equivalent to learning for the first time that elephants had trunks. We have lots of skulls of Edmontosaurus, but until now there have been no clues to suggest they might have had a big fleshy crest.”

The fossil in question was found in deposits west of the city of Grande Prairie in west-central Alberta, Canada.

“While we had found skin impressions on parts of the fossil’s body, we had no clues that a fleshy structure might have adorned the skull. When I put a chisel into the top of the skull and found the crest I realized that, based on what we thought we knew, it wasn’t meant to be there.”

Dr Bell noted the significance of this discovery may not be limited to this one species of dinosaur.

“We have lots of skulls of Edmontosaurus but nothing to suggest this find so 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.”

“It is hard to say exactly what evolutionary purpose the combs served, but similar appendages on roosters and other male birds are used to get the girls.”

“We could imagine a pair of Edmontosaurus sizing each other up, bellowing, and showing off their head gear to see who would come out as the dominant male and who would take charge of the herd.”

“We may never know exactly, but it is a reminder of how much is still out there for us to learn about these fabulously bizarre creatures,” Dr Bell said.

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Phil R. Bell et al. A Mummified Duck-Billed Dinosaur with a Soft-Tissue Cock’s Comb. Current Biology, published online December 12, 2013; doi: 10.1016/j.cub.2013.11.008