Recently, yet another wonderfully preserved hadrosaur specimen has been uncovered in Alberta, Canada that preserved a lot of soft tissue around the neck and head. This hadrosaur was Edmontosaurus regalis, a close, earlier relative to Edmontosaurus annectens. Since it's original discovery, Edmontosaurus was considered sort of a typical, basic hadrosaur. It had the wide, flat bill but unlike some of its relatives, it sported no fancy crest on its head...except it actually did.
|Image from the new paper showing where the crest is on the specimen by the white arrows.|
You see, the crest of Edmontosaurus was kept a mystery for so long because it wasn't made of bone like the crests of so many of its relatives such as Parasaurolophus or Tsintaosaurus. The crest of Edmontosaurus regalis was made of just skin so it would have rotted away rather quickly before the fossilization process could have happened. Luckily this particular specimen retained it! It was probably full of blood vessels and would have been soft, maybe even floppy, in life. This sort of thing isn't unheard of in living relatives, either. Just look at birds like chickens and turkeys for instance. Some lizards, like Green Iguanas and certain agamids have soft crests as well.
|My quick sketch-and-paint of Edmontosaurus ragalis' new look.|
So why would a dinosaur evolve such a thing? Well, the easy answer could always be display. (When in doubt just say display.) It's why a lot of extant animals have them. It could be possible that only the males had them, or possibly had larger ones which would go along with what you would find in chickens and iguanas. A soft crest like that could also help regulate the animal's body temperature. Within the crest, blood would be closer to the outside air, and cool off more easily. Then this blood would be circulated back into the body, thus helping to cool the whole animal off. Chickens do this with their crests, called crowns, and many mammals also do this with their ears. This is why a lot of desert mammals have large ears.
|All of these animals use body parts made of soft tissue for either display and/or thermoregulation. It is possible Edmontosaurus evolved its soft crest for similar purposes.|
Although this is pretty exciting, this doesn't in any way make up for the fact that Tsintaosaurus lost its hilarious penis-shaped crest. Nice try, science, but I'm still mad at you!
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