Surprise! Well-Studied Dinosaur Actually Had a Cock’s Comb

Here’s the skeletons of two elephants, facing to the right. If you saw their skulls, and had never seen a picture of an elephant before, you’d probably never deduce that their faces carried long, muscular trunks.

Here’s the skull of a chicken. If the animal was still alive, you’d easily be able to tell if it was a rooster or a hen. The former would have wattles and a cock’s comb, all bright red. But the bones alone preserve no traces of these soft tissues.

See the pattern here? Soft tissues like combs, wattles and trunks don’t usually survive the process of decay, much less fossilisation. Bones and skeletons rarely hint at their presence.

But there are exceptions.

Here’s a fossil of an Edmontosaurus regalis—a 12-metre-long duck-billed dinosaur that lived in North America around 73 million years ago. You’re looking at the top half of its shoulders, head and neck. Its head is bent over its back in the classic “death pose”, and its snout would have extended up into the white space at the top of the image.

Many of the duck-billed dinosaurs, or hadrosaurs, were famed for their elaborate bony crests. Corythosaurus had a helmet, Tsintaosaurus had a shoehorn, and Parasaurolophus looked like an HR Giger design. But Edmonotosaurus supposedly lacked such flamboyant headgear. At of the time of writing, Wikipedia calls it “crestless”. It was a vanilla hadrosaur.

But Phil Bell and Federico Fanti has just given the species a makeover by unearthing the specimen in the image above. On the top of its skull, preserved in rock and marked by the white arrow, are the fossilised traces of a crest. It wasn’t a hard, bony structure like those of other hadrosaurs. It was soft. This was a dinosaur with a cock’s comb.

“It opens up a whole new realm of possibility for soft tissue structures,” says Bell. “Trunks on sauropods, wattles on tyrannosaurs… the possibilities are as endless as there species.”

“It is an incredible specimen,” says David Evans from the University of Toronto. “With its extensive fossil record, Edmontosaurus is generally thought to be one of the very best known dinosaurs, but it will never be that plain, unornamented duck-billed dinosaur ever again.”

Bell and Fanti discovered the specimen in western Alberta, while scanning the rocks along the Red Willow River. “It didn’t look like much when he spotted it – just a string of vertebrae—but we decided it should be collected anyway,” says Bell. “It was a herculean task since they lay in a coffin-sized boulder that was difficult to get to.” As the duo were sawing through the boulder to break it into more manageable chunks, they realised that there were marks near neck and back that looks like traces of skin.

Some of these impressions formed a tall crest on the top of the animal’s skull, 33 centimetres long and 20 centimetres tall. That was strange enough. But when Bell and Fanti examined the specimen in a medical scanner, they couldn’t see any signs of bones or other internal structures inside the crest. This wasn’t a standard hadrosaur crest. The skin was wrinkled in places, implying that it was soft and supple. And it was clearly connected to the skull rather than being a loose piece of torn skin.

Unlike many other hadrosaur crests, Edmontosaurus’s comb was too soft to play any role in making sounds. It wasn’t tough enough to be used for combat or defence. It was too small to be a fat store, like a camel’s hump. Most likely, it was used for social reasons—perhaps as a badge of species identity, a sign of age, or a way of displaying to the opposite sex.

“We’ve known for decades that dinosaurs were likely very visual animals, given the presence of bony crests, frills, and horns in many groups,” says Evans. “Given the diversity of these hard-tissue display structures, it makes sense that dinosaurs would have also employed soft-tissue signals as well.”

Dinosaur skin sometimes fossilises, and hadrosaur skin more than most. Maybe their skins were especially tough. Maybe they were prone to instantaneous burial, in sediments with the right qualities to halt the process of decay. Whatever the case, fossil-hunters have often uncovered their mummified remains, complete with skin impressions. But until now, none of the other Edmonotosaurus mummies had traces of the soft crest. Why?

The boring explanation is that every other Edmontosaurus mummy belongs to the species E.annectens, which (unlike E.regalis) didn’t have a crest.

The more interesting possibility is that other specimens did have crests, but scientists just glossed over them. Worse still, maybe they destroyed the skin impressions in an effort to get to the skull. Bell suspects this happened to one of the most famous Edmontosaurus specimens—the “Trachodon mummy” in New York’s American Museum of Natural History.

“When Henry Osborn wrote about that specimen in 1912, he commented that they didn’t notice skin on other parts of the body until after the skull was exposed,” says Bell. “Even now you can see patches of skin at the back of the jaw and within the nostril, indicating that skin was probably preserved over a far greater area of the skull. We will never know whether a crest was preserved on the AMNH mummy, but my suspicion is that it probably was.”

Larry Witmer from Ohio University wants to see evidence of fleshy crests in other Edmonotosaurus specimens but he’s grateful that we now know what to look for. “That’s the typical course of science: a serendipitous discovery by insightful scientists provides the search image leading to broader investigations,” he says. “A key task now will be to scrutinize skulls for the tell-tale signatures of the fleshy crest so that we can perhaps infer it in the absence of remarkable and rare preservation.”

For example, Parasaurolophus had small divots at both ends of its trumpet-headed crest, and some scientists have suggested that these mark the ends of soft structures, like glands or an inflatable sac. But Bell and Fanti’s Edmontosaurus doesn’t have any similar skull features that would mark the presence of a crest. Without the skin impressions, you’d have no way of telling that the feature was there.

And that’s almost more exciting!

Just think about your favourite dinosaurs and imagine a whole range of sacs, wattles, trunks or combs on them.

“There is a long and sad history of neglect in the study of dinosaur skin,” says Bell. “The scaly skin of dinosaurs has been known for well over a century but we’re only now starting to get an understanding of its importance.”

Reference: Bell, Fanti, Currie & Arbour. 2013. A Mummified Duck-Billed Dinosaur with a Soft-Tissue Cock’s Comb. Current Biology http://dx.doi.org/10.1016/j.cub.2013.11.008