When scientists discovered that some dinosaurs had feathers, it completely changed our perception of what the ancient animals looked like — and pissed a lot of people off. Now, in another twist, researchers have found that the duck-billed dinosaur Edmontosaurus regalis had a fleshy crest similar to a rooster's comb.
The Duck-Billed Dinosaurs
The hadrosaurs were herbivorous, "duck-billed" dinosaurs common in the Upper Cretaceous of Europe, Asia and North America. They came in various sizes and fell under one of two subfamilies: Lambeosaurinae, which had a large, hollow cranial crest made of bone; and Saurolophinae, which were mostly crestless (though some species had small solid crests). In recent years, scientists have modeled the hollow crests of the lambeosaurines to figure out what they were used for.
"People have been able to reconstruct the airflow through the nasal cavities and crests, and found that it's quite likely they were associated with sound-making," said Phil Bell, a paleontologist at the University of New England in Australia. Hadrosaurs were social animals that lived in herds of dozens of individuals, so the crests were mainly used for communication. "The crest sounds probably kept the herd tighter and were used for sexual displays."
In the past, some researchers suspected that the crestless hadrosaurs may have had crests after all, but the structures were made out of soft tissues, which don't preserve well. After an animal dies, skin and muscle are the first things to go because of decomposition and scavenging — if the body isn't buried very quickly, those features will not be preserved. And though the scientists noted that fleshy crests were pure speculation, there was always a possibility that such features existed.
"Take a look at the animal world today, at structures like the elephants' trunk, which might never fossilize," Bell told io9. "There would be no evidence from the actual skull or bones that such a structure would ever exist."
Complicating matters further is the fact that paleontologists in the past placed little weight on fossilized skin impressions, Bell said. They thought that skin was something extraneous compared with the importance of the bone, so skin impressions were often removed from dinosaur finds and tossed aside. Luckily, scientists' appreciation for those structures has flipped completely. And now, Bell and his colleagues have reaped the benefits of that significant change in thought.
Revealing the "Cock's Comb"
The researchers found their striking dinosaur specimen preserved in a sandstone boulder, in a deposit-rich area west of the city of Grande Prairie in west-central Alberta, Canada. The Saurolophinae dinosaur, Edmontosaurus regalis, was naturally "mummified" in the sands of a river, though the scientists don't know how it died or what exact biological or chemical features of the sands preserved the animal. Argon-argon dating of altered volcanic ash near the skeleton suggests the dinosaur died about 73 million years ago.
When Bell and his colleague Federico Fanti came across the specimen, they didn't immediately realize what they had found. They saw that scaly skin impressions had been preserved on parts of the body, including the neck, which was bent towards its back in the characteristic "death pose." But oddly, there were also skin impressions between the animal's skull and back — an area where there shouldn't have been anything.
Bell put his chisel to the odd feature and it went right through the impression, suggesting that there was no solid structure there. "As I exposed it more, I realized there that it was a bit of mound of flesh on the top of the head," Bell said. "It took a while to dawn on me that it was actually attached to the skull." Further investigation showed that the 20-centimeter high, 33-centimeter long crest spanned the width of the skull, and CT scans showed definitely that there were no bones in it. It was a comb made of soft-tissue.
So what would the crest have looked like in life? For one, it was dome-shaped and covered in scales. But the skin was also probably soft and supple, based on the wrinkles in the skin impressions, Bell said, adding that it was probably most like a rooster's comb. Based on comparisons with the avian combs of today, the dinosaur's "cock's comb" was probably brightly colored and was used to attract females or assert dominance over other males.
Importantly, hadrosaurs are not closely related to the birds of today, so roosters don't owe their famous combs to E. regalis.
"But the fact that we have hadrosaurs with combs — a bird-like characteristic — certainly means that combs could have been widespread throughout the dinosaur kingdom," Bell said. That is, other hadrosaurs species, as well as other types of dinosaurs, could also have had ornamental soft-tissue combs. "Even the bony crests of some of the animals may have been enhanced by fleshy components."
Bell said that the discovery is really just the "tip of the iceberg," and suggests there may be a lot more about dinosaur appearances that we don't know. "The discovery of feathered dinosaurs was a huge leap forward in our understanding of how dinosaurs looked," he said. "This discovery suggests that we're definitely in for more surprises about their appearances."
Check out the study over in the journal Current Biology.
Top image via Julius Csostonyi. Inset image via Federico Fanti.