What To Do With Crests


Over the course of looking at the new specimen of Edmontosaurus (Bell et al., 2014) sporting an odd accretion, I had an epiphany: The “cock’s comb” was, in fact, merely a segment of the neck, falsely and purposely isolated by the vagaries of taphonomy. There used to be more of it. But it occurs to me that I was wrong, that there is, in fact, an eboshi-shaped soft-tissue crest, or a “cock’s comb.” (Also, the shape of many eboshi is exactly the shape of the bony crest in several oviraptorids, a useful comparison as they also adorn the head.)

Cock-a-doodle-CowQuite the priestly sort, this one, not the plebian I drew earlier. But as I looked at the analogues for these soft-tissue crest, I came across some interesting dinosaur-like animals. Pterosaurs, as it turns out, often sport these ridiculous head pieces. I’d drawn a few before, and some key features are noticeable:

Part of my These skulls have a big block of bone, but only at the front of the head. And long the top of the skull is a thin ridge, running down the length. Some other pterosaurs have one, too, but without the block of bone at the front, and examination under UV light reveals that there was a decent amount of soft-tissue forming a parabolic curve up to the back of the head in Pterodactylus and Germanodactylus (Bennett, 2002, 2012).

It's not the size that counts, but how your mate mutually selects to you how to use it.But by all accounts, these crests seem fairly thin. And I’m not sure why. Are they held up by nothing? Pterosaur wing membranes are stiffened by aktinofibers and by use of the wing finger as a bony strut. But in the tapejarids above, there’s no real clue what the internal structure is. A skin membrane? Keratin plates? Those can get pretty heavy, actually, and as such a softer, more pliable tissue might be more useful. But in Germanodactylus and Pterodactylus, only the bony basal core is present … and in these pterosaurs it is pretty short.

But if the bony core at the base of the crest is useful as a support device for a cock’s comb in pterosaurs — as it is clearly analogous to — what about other taxa? So I started digging.

Turns out there’s a few other taxa with relatively high bony crests on their heads, some thin and short, some broad, some very, very high. First, I looked back at hadrosaurs, and it turns out hadrosaurs have a thin bony crest that arches up a bit between the supratemporal fossae. That seems a slam dunk: hadrosaurs with more distinct inter fossorial ridges would sport larger cock’s combs! Then I looked around and realized I was excluded the “actual” crested hadrosaurs, the lambeosaurs. Turns out they sport the thin ridges, too. But not on the backs of their heads — instead, it’s between their noses, and extends all the way backwards. Like Pterodactylus and Germanodactylus, the thin ridge is formed almost entirely from the premaxilla! This seems too good to be true.

Maybe the ridge helps the hinks resonate ... or whatever.Maybe in Saurolophus here, the rhamphotheca of the snout extended along the whole face and formed a sort of facial plate, as in swamphens (Porphyrio spp.). Some hadrosaurs may have combined the two, a harder facial structure and a softer, floppier comb-like structure at the back. The head fin helps it swim better.The prehistoric world has definitely had some truly monstrous creatures on land and in the sky, but my next trip was into the waters. Dolichorhynchops is a member of the plesiosaurian subgroup of Polycotylidae, all of which sport these tall crests in between their supratemporal fossae. Certainly, these must have been aquatic ebosi-bearers? The relatively featureless faces of these plesiosaurs must have needed the added pizzazz of a crest, for they lack the tremendous neck of the elasmosaurs or the great gaping maws of the pliosaurs (the rhomaleosaurs, which also lacked these things, did not develop the head crest, a result that can only be supported by the presence of another, perhaps flashier ornament).

Back on land, I realized that there were some lizards with these crests, and they certainly attested to my hypothesis! Not only did chameleons develop these enormous ridges (especially the veiled chameleon, Chameleo calyptratus), but some other iguanians such as Basiliscus as well.

Skulls of various Corytophanidae, © Dr. Raul Diaz, used with permission.

Skulls of various Corytophanidae, © Dr. Raul Diaz, used with permission.

This seems to be true on the mammal size of tetrapods, as well, as many of them — from tiny Oligokyphus to dire wolves (not the George Martin kind) to gorillas! — have just enormous crests as to leave one assured there is something funky going on. I took a few liberties with the Gorilla, but think I pulled this off:

Do not tell me these horrible things are still around?!Ultimately, this makes me hopeful for reconstructing some of my more favorite animals, such as oviraptorosaurs. As it is, it seems the sky’s the limit. There’s little reason for me to restrict the crest to slight extensions of the borders of bone. Not only does the keratinous casque of cassowaries barely follow the shape of the underlying bone, narrow ridges support wonderfully enlarged crests in tetrapods! So I present as my coup de grâce, a new reconstruction of Anzu wyliei, the oviraptorosaur with the largest known crest.

No mere duck, this -- nor meer duck, really.Bell, P. R., Fanti, D., Currie, P. J. & Arbour, V. A. 2014. A mummified duck-billed dinosaur with a soft-tissue cock’s comb. Current Biology 42 (1): 70-76. (Published online 12 Dec, 2013) doi: /10.1016/j.cub.2013.11.008
Bennett, S. C. 2002. Soft tissue preservation of the cranial crest of the pterosaur Germanodactylus from Solnhofen. Journal of Vertebrate Paleontology 22 (1): 43-48. doi:10.1671/0272-4634(2006)26[872:JSOTPG]2.0.CO;2
Bennett, S. C. 2013. New information on body size and cranial display structures of Pterodactylus antiquus, with a revision of the genus. Paläontologische Zeitschrift 87 (2): 269-289. doi:10.1007/s12542-012-0159-8

 

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5 Responses to What To Do With Crests

  1. Miss Chili says:

    Your reconstruction of Anzu wyliei looks wonderful, though you nearly lost me at the drawing of a gorilla with a cassowary-like skull ridge! :-D I’d thought, ‘Oh, no, no April Fool’s jokes here, please!’ Whew!

  2. Don’t know if Aprils Fools or not, but pterosaurian soft tissue crests are usually considered to be made of keratin. In most of these species, the underlying bone crest is fibrous and/or “spongy”, implicating fast growth from there.

    • To be fair, all crests everywhere are “keratin,” as they arise from the skin which is, essentially, keratin. The structure of the epidermis or epidermally-related tissues develop upon it generally differ by the concentration, arrangement and orientation of keratin fibers and similar structures, such as Sharpey’s fibers.

      As for the surface of some pterosaur crests, we’ll get into that in a bit. Bennett (2012) considers the “fibrous” bone of many pterosaurs to probably be incomplete on their surface, so the structure is not actually bone surface. There’s more to say on this, but otherwise the bone structure isn’t described as “spongy” when it comes to crests, nor would it be. Even hornbill casques aren’t so much as “spongy” as being intensively reinforced internally with trabuculae of bone but with bone walls so thin or which don’t ossify, forming the “open sponge” look. Again, more on this later.

  3. Pingback: What To Do With Crests – Updated | The Bite Stuff

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