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Edmontosaurus annectens and the Crest That Wasn't
By Qilong   |   Watch
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Published: December 26, 2013
I don't think the data confirms a medial "cocks'-comb was present in Edmontosaurus regalis, and parsimony suggests that the restored version I show may be just as likely, given its consistency with the data. The structure is associated with the side of the skull, and we should always be very careful about assuming that a preserved structure is intact when the specimen is mangled or otherwise not available in all dimensions. My alternate take, here of Edmontosaurus annectens, suggests the "crest" was just the front end above the head of a large mass of tissue that lay around and above the neck.
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anonymous's avatar
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Nazrindi's avatar
NazrindiHobbyist General Artist
I agree, just because it appears as though Edmontosaurus had a "comb" from the fossil doesn't mean it necessarily did, since the integument could have easily drifted after decay and/or fossilization. I don't see many depictions of hadrosaurs without cheeks, what's the reasoning behind it? It certainly looks interesting though.
Qilong's avatar
qilong.wordpress.com/2012/09/1… and qilong.wordpress.com/2012/10/1…

There's very little evidence for cheeks. Lips are the default state among sauropsids, so without further evidence to the contrary we should opt for this when testing alternate perspectives. Unfortunately, the main reason people cite for cheeks is "inset jaw margins," which in hadrosaurs at least isn't really the case, and doesn't hold true for most mammals, who have them.
DovahsaurPaleoKnight's avatar
What about the fact that it had to chew food?
Qilong's avatar
In mammals, the muscles on the sides of the mouth and around the mouth opening in some, but not all of them, form muscle leverage that takes the place of the protractor adductor (jaw closer and muscles that help pull the jaw forward) functions of palatal muscles, and share adduction (closing) loading for the temporal muscles, due to the rear of the mandible having been "lost" (it's shrunk and becomes part of the ear bones). Reptiles for the most part never lost this equipment, and even stem mammals like Dimetrodon have functionally "reptilian" jaw muscles and bone arrangements. The palatal muscles are large, not vestigial or associated with a small mobile structure near the ear designed to stabilize the jaw.

In mammals, a special set of muscles developed in some groups to take up the loss of those muscles that helped the jaws close, and these muscles are associated with the lateral temporal muscles adjusted to inserting onto the dentary bones -- because there are no other bones of the lower jaw anymore. No other animal has such a muscle arrangement: it's simply not necessary, and if it were plausible to assume they existed, there would have to be extraordinary evidence for their existence. To date, no such evidence has been proven to connect the muscular "cheek" to an animal and the bones that underlie it.

Thus, the muscles form a necessary function of helping close the jaw; there is no peculiarity to which their function is necessary for a style of eating. They are present in meat eaters, plant eaters, bug eaters, whales, etc. The masseter types of muscles are merely useful for closing the jaw in a efficient manner, and so they remain selected for. "Chewing" is a dietary function principally of the teeth, and in those dinosaurs for which "chewing" has been inferred, the process is often different from typical vertical mashing or side-to-side stroke-based oral processing, as seen in elephants, for example. Moreover, the muscle components in reptile jaws from which "masseter" like muscles might arise has no necessity for being anywhere near the dentary, as there is plenty of space, and no positive inference to suggest otherwise, for the muscles at the back of the jaws. Indeed, almost all muscle reconstructions for framing the jaws only these back-of-the-head temporal/palatal muscle sets are needed to explain most, if not all, of the muscle efficiency needed to explain tooth wear in hadrosaurs, ceratopsians, ankylosaurs, etc.

As for food processing, no one has ever argued a model by which food would fall out and the animal starve should it not possess some skin-based or muscular structure on the sides of its jaws anterior to the muscles. The fact that food regularly falls out of the mouths of animals with such structures, it seems hard to really make such an argument, but of course, it would have to counter how mere lips could not achieve that effect, given that lip-like oral tissues are the null condition for reptiles and mammals alike.
DovahsaurPaleoKnight's avatar
Thanks for the info (very interesting), but I should have made myself clearer. I said that it needed to chew food thanks to it's teeth, not thanks to the shape of it's jaw. Well, take a look at this: www.acupunctureproducts.com/co… you can see that masseter muscle of a cow is far from covering all the teeth that are needed to chew it's food and it happens with mny other mammals, even meat eaters (the cheeks of a lion cover their "molars", even tough their masseter muscles do not).

I meant that it should have had skinny muscles in order to chew food. Well, if food may fall from the mouths of aninals with cheeks an animal without them would have even more problems in chewing.
Qilong's avatar
Nothing about the teeth refutes what I said. The shapes of the teeth are important, but what matters is the way that the teeth and the jaws work together to process food. Even the cow you suggest maintains a masseter complex that helps maximize force along the molars, especially near the front of them, and this is important in making the process of orthal crushing and translation slicing work. Even in carnivorans, where the masseter is principally located around the carnassials, this is true, because that's where the force they provide is most useful.

But I also said that the muscles that attach to the dentary aren't homologous in mammals to the muscles of the mandible in any other group, especially stem-mammals and sauropsidans ("reptiles" et al.). This is rather peculiar, because it means you can't just swap the same muscle complex onto dinosaurs without supportive evidence. Muscles on the maxilla in mammals arise from a particular set of muscles associated with the palate and intraorbital sets, and on the dentary from similar. There is simply little way to get a "masseter" on a dinosaur other than from the temporal and palatal muscles (as in parrots, for instance), in which case the muscle is limited by its jugal/post-dentary relationships.

To look for a reasonable analogue, we can actually look at parrots, because their pseudomasseter and ethmomandibularis muscles function in much the same way as mammalian masseter complexes do. But the constraints they arise under follow the trends I outlined before: they are more or less restricted to the post-dentary bones, and they aren't attached to the maxilla.

I should repeat myself, then:

There's no reason we possess yet that suggests there is a muscle that passes from the maxilla to the dentary directly in any animal, and little reason to expect it should exist in dinosaurs. It just isn't required.
ScottHartman's avatar
ScottHartmanProfessional Digital Artist
I love the placement of the nostrils and the depth of the beak. 
GilbertHamilton's avatar
Agreed... someone has obviously been studying their mummies. Morris's Edmontosaurus maybe?
Qilong's avatar
Thanks! I do try to put the data to practice.
Dino-Mario's avatar
Dino-MarioHobbyist General Artist
That is a pretty good scaly skin.I also love your cheekless ornithischians.They look more badass.
Qilong's avatar
Well, the cheeks thing MIGHT be false. It's something that has to be investigated in more depth. But I thank you for the kind words! I personally think we should look into more diverse options for integument on a variety of animals; restoring animals based on some basic tenets of integumental reconstruction often suggests we know less (but sometimes more) than we think.
Pr0teusUnbound's avatar
Pr0teusUnboundHobbyist General Artist
do you use living animals as a reference?
Qilong's avatar
As the only reference! Some fossil animals are incomparable to living creatures in qualities of their skin, textures, proportions, etc., which makes it hard to just plop a dino into the flesh and make it "look real." But sometimes, you get great preservation that shows the original texture, weight, and even volume of an animal, so that you don't make too many guesses.
A2812's avatar
Nice :-)
Regards Jacek
DeinonychusEmpire's avatar
DeinonychusEmpireHobbyist General Artist
Props for keeping an open mind about this whole ordeal.
Qilong's avatar
Thank you. I always try.
Kazuma27's avatar
Kazuma27Hobbyist General Artist
Happy Holidays, ye mighty Qilong, and glad to see your interpretation of Ed and his integument... Not sure if i agree with the "cheekless look", other than that i guess the supposed head crest could have been a, ehr, genuine crest indeed or, as you suggest, just a lump of skin from the neck :)
Qilong's avatar
"Not sure if i agree with the "cheekless look" "

Not that many people do!
Kazuma27's avatar
Kazuma27Hobbyist General Artist
Yeah, guess i'm quite open minded when it comes to restore these guys, but ornithischians without cheeks, well, it somewhat irks me and it doesn't look very functional... Then again Nature doesn't give a damn about what us puny humans think of a certain animal, so i wouldn't be really surprised if it turned out that flatbeaks & co. had long smiles afterall ;)
Qilong's avatar
Well, there are ways to test the effectiveness of ornithischians without cheeks, and how cheeks aren't necessary for ornithischian oral processing -- never have been, lips can perform the same retentive aspect, and even cheeked animals spill food out of their mouths.
Krookodile0553's avatar
I for one agree with you, from the restorations I've seen of the Edmontosaur Waddle, it was very small and conservative. If you were say 100 yards away you couldn't even tell it was present
Qilong's avatar
Reasonably, this is true for a lot of display features, such as patches of colors on birds. That said, if it were colored it would likely be even more visible, so a combination of these factors influences the usability of an isolated cock's comb.
DinoBirdMan's avatar
DinoBirdManStudent Artist

Crestless/Cock-combless Edmontosaurus annectens are seem false if the other mummified fossil couldn't find a right fossil with a comb a right fossil with comb as Edmontosaurus regalis has.

 

(But I'm just too careless to typed a wrong word on DA.^^;)

Qilong's avatar
It's possible different hadrosaurs had different soft-tissue structures on the head. Turkey's are closely related to jungle fowl (which includes chickens) and lack the upright comb, instead displaying expanded facial skin and wattles. Cassowaries have wattles, but their closest relatives are emus, which do not. We can expect as much, if not more, soft-tissue variation as cranial crest variation in lambeosaurs, if soft-tissue is a marker of visual diversity as it might be in living animals.
anonymous's avatar
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