The structure above the fossil's head was so unexpected that Phil Bell put his chisel straight through the middle of it. "I was just expecting there to be rock, and all of a sudden there was skin underneath, and I thought to myself, 'Whoops,'" he said. What Bell had found was the first dinosaur fossil with a fleshy crest atop its head.
"We know that lots of dinosaurs had different kinds of head ornaments, but these are all made of bones," said Bell, a paleontologist at the University of New England, Australia. "There's never been any indication that any dinosaurs had something like this, so this was totally out of left field," he said.
Bell was studying a mummified specimen of Edmontosaurus regalis that had been found preserved in a single sandstone boulder in the Wapiti Formation in Alberta, Canada. E. regalis is a member of the hadrosaurids, or duck-billed dinosaurs, that were common around 75 to 65 million years ago. Researchers had previously described bony crests in many hadrosaurids.
But CT scans revealed that the new fossil's crest was made entirely out of soft tissue, similar to a rooster's comb. "This was a real surprise," Bell said. "Not only did we have skin associated with the head, but also this completely bizarre structure." The results were published in the December 12 issue of Current Biology.
David Evans, vertebrate paleontology curator at the Royal Ontario Museum in Toronto, who was not involved with the study, said he agreed with Bell's interpretation of the new fossil. "We have a better idea of what skin looked like on Edmontosaurus than probably any other dinosaur, but we rarely had a look at skin on the head until now, and that's what makes this discovery so exciting," he said. "I don't think we would have expected Edmontosaurus, which is a relatively plain, unornamented dinosaur, to have such a flashy soft-tissue crest, so that came as a bit of a surprise," Evans said.
Best Crest Gets the Girl
"I think it reminds us that even in dinosaurs that we think we know well, new discoveries can really change what we think about how these animals looked and behaved," Evans said. The new specimen was particularly exciting because it gave researchers a glimpse into the social lives of dinosaurs, he said.
The presence of bony crests, frills, and horns in many dinosaur groups has long indicated that dinosaurs were very likely visual animals, Evans said. "This is a rare glimpse of a soft-tissue display structure, and it gets us thinking that maybe soft-tissue structures were potentially just as important as hard-tissue ones in terms of socio-sexual displays," he said.
According to both Bell and Evans, the fleshy comb's prominent position on the head is similar to that found today in birds such as roosters, grouse, and condors, and it's possible it could have served a similar function. "They use these to get the girls, basically—to indicate how fertile and how strong the male is," Bell said. Edmontosaurus was a herding animal, so the fleshy structure could also have been used to indicate the top male within the herd, he said. "Perhaps the male with the biggest and brightest crest was the leader of the pack, so to speak," Bell said.
Opening the Door to More Soft-Tissue Finds
Unlike bones, soft tissue and skin are rarely preserved in fossils. "For the skin to preserve, these animals had to be buried very rapidly, probably within a day or two after they died, and the chemical environment in the sediment was just right," Bell said.
There have been a number of other similarly "mummified" dinosaurs, including of Edmontosaurus, but none of them have had similar soft tissues around the skull. The new fossil's fleshy crest could indicate that such soft-tissue structures may have been more prevalent than previously believed.
"The actual bones of Edmontosaurus have absolutely no indication that there's a crest of any sort in this animal, so similar crests or other fleshy structures could have been really widespread among dinosaurs," Bell said. "The fact that we have no evidence on the bones apparently means nothing about the external appearance of these animals," he said.
The discovery could make paleontologists look more carefully for such fleshy structures among fossils, Bell said. "Paleontologists are always in a rush to expose the bone, because that's seen as the most exciting thing," he said. "Fossilized skin is far more delicate than the bones. To actually leave the skin intact requires a lot of patience and a lot of very detailed work when you're preparing the specimen," Bell said.
"Now that we're seeing that dinosaurs could do anything in terms of the way they looked, perhaps people will be more open-minded when they're actually excavating, because that's the moment of discovery," Bell said. "Feathered dinosaurs from China are a prime example. Before, those kinds of structures were overlooked, but once people recognized what they were actually looking at, that these were feathers, they started appearing all over the world," he said.
(Related: "Pictures: Dinosaur's Flashy Feathers Revealed.")
The Royal Ontario Museum's Evans said the new Edmontosaurus specimen emphasizes how important the soft-tissue anatomy can be for understanding the biology of extinct animals, as well as how they looked when they were alive. "A discovery like this makes you think about what else we're not seeing in the fossil record. It kind of opens the door for even more bizarre dinosaur anatomies than we typically think of," he said.