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September 10, 2012
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Some people here are aware of my blog, some are not. I spend most of my time posting crap there, and shunting some of the illustrations I prepare here and there.

The Bite Stuff: qilong.wordpress.com/

If you care to follow, you will know that I've also been spending some time trying to answer the question about whether dinosaurs had "lips" or "cheeks," a common feature of illustrators and reconstructors for paleontology. Lately, scientifically informed illustrators like Crash McCreedy and Tyler Keillor have been rendering their dinosaurs without "cheeks" and without "lips" in the mammal sense, but rather with "lips" in the lizard and snake sense, structures that have no muscles in them, and were thus immobile.

I've gone into quite a lot of detail about this on my blog, beginning with

"Making Lip of It" qilong.wordpress.com/2011/09/1… , then

"Support for a Lipless, Cheekless Dinosaur World" qilong.wordpress.com/2012/09/0… , then most recently

"Cheeky Commentary on Ornithischians" qilong.wordpress.com/2012/09/1… ,

where I specifically talk about taking the cheeks off ornithischian dinosaurs, which makes them look a little funny. I am not the first person, nor the only one doing this generally, but I'm making a public stink about it because there is real important need in getting our artists informed about the biology. You're all smart enough to do it! Anatomy is an important first step to dealing with dinosaur art, because it is the only way you will know to tell you that that dino "looks real." You need to know WHY. Part of that is knowing also that we don't have all the answers now, but there are several philosophical techniques that help us approach the data, and scientific methods in discriminating "true" from "false" with that information.
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:iconzimices:
Zimices Featured By Owner May 24, 2014  Hobbyist
After have reading your post, I want to ask you: what do you think about the lips in sebecosuchians?
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:iconqilong:
Qilong Featured By Owner May 24, 2014
That's a bit tricky, because in some the teeth pass beyond the jaw margin in a manner consistent with modern crocs. Sebecosuchians are also secondarily terrestrial, so I'd imagine they'd have fleshy tissues, but they'd not form full lips. It's hard to really imagine their morphology without a look towards direct analogues for the soft tissues and examining them in particular.
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:iconzimices:
Zimices Featured By Owner May 25, 2014  Hobbyist
It's interesting, considering that are not true crocodylians, but more primitive, but effectively a lot of species have "fangs" that surpassed the jaws... On another hand, then the first crocodylomorphs could have a form of lips?
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:iconqilong:
Qilong Featured By Owner May 26, 2014
The very earliest ones? Most likely, in my opinion.
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:iconthepuertoricandragon:
That just makes me curious. What ARE the names of those flesh things that are at the vertices of the jaws of a dinosaur?
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:iconqilong:
Qilong Featured By Owner Sep 26, 2013
It's called a rictus. More here: hollidaylab.wordpress.com/2012….
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:iconqilong:
Qilong Featured By Owner Sep 10, 2012
Incidentally, please, ask many questions. Engage me, call me on my shit, if you see it. I want to see if I missed something, and especially if I forgot a nuance that I need to use to evaluate my conclusions or data. It is important! It is Science!
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:iconkazuma27:
Kazuma27 Featured By Owner Sep 10, 2012  Hobbyist General Artist
Your last posts about dinosaur mouths are very interesting, something that definitely should be talked about instead of those endless, quite boring discussions about systematics that experts and non-experts seem to love these days (nothing wrong with classification and such, but man... There are many more topics about dinosaurs people can talk about).

Not completely convinced about "cheekless" ornithischians, though... Not saying you or Witmer are wrong, but i wouldn't rule out the possibility some of those guys evolved a mouth configuration vaguely reminiscent of mammalian cheeks... I mean, if i look at an hadrosaur skull (just an example) and see the way the bones around the teeth are arranged, well, it immediately reminds me of the skull of many, many, many modern herbivorous mammals and BAM, i envision cheeks for this beaked guy.
Plus the lacertian example for ornithischians looks flawed IMHO... Correct me if i'm wrong but no lizard ever evolved an array of teeth similar to those of hadrosaurs, ceratopsians and such; or maybe we're both wrong and ornithischians had some crazy stuff sealin' their smiles (i actually found intriguing your example of a non-muscular cheek; looks like a good compromise between your position and mine) ;)
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:iconqilong:
Qilong Featured By Owner Sep 10, 2012
I make some effort to show that the degree of "inset" of the jaws is produced by something of an illusion, where the inset is about natural jawbone curvature, as well as inner rotation of the mandible; this latter bit also helps exaggerate the profile of the "lateral ridge".

And it is actually true that no lizard has evolved teeth exactly like those of hadrosaurs or ceratopsians. That isn't really the point. As I responded to a comment on my blog: [link]

"It would be keen of me to describe at this point the morphology of the tooth rows in hadrosaurs, ceratopsians, or ankylosaurs, but references I’ve linked to (including some with pdfs) actually do this for most of these taxa. I will abstract that by saying that these taxa have lower teeth that are generally lingual to the upper, and occlude inside the upper; moreover, all groups are capable and in some cases specialized for unilateral precise occlusion, rather than bilaterally. This tells me that they will favor jaw mechanics that control the bolus’ position in the jaw better than those whose function is to re-render continuously a small portion of the food in the oral cavity. Thus, there is less need to retain the bolus in the mouth. It is about rendering food as quickly as possible. This may also be why the oral cavity in hadrosaurs and ceratopsians tend to be so narrow at the front, or completely: food is not meant to be retained. These animals should thus not require substantive time spent “keeping food in”: if it can be chopped small enough (and chop indeed is the operative mechanic) then swallowing is the next course.

As for Uromastyx lizards, this appears to be the same as with most agamids: acquire, chop up, and swallow … let the gut do the processing. I will have to check my references, but my understanding is that Uromastyx have a substantially larger body relative to head size than most agamids, relating to the massive gut due to its extremely herbivorous diet."

Here's a proposition I offer you, and it helps when it comes to comparing lizards to dinosaurs: If we think of the teeth of hadrosaurs as a continue blade edge, even if it has a second edge on it (as it does) which occludes the upper and lower teeth, then the morphology suggests the lateral teeth function as a form of shears. Shears that, were they concealed by cheeks, would be rendered having to process material entering the mouth from a smaller, front opening. In lizards like iguanas and uromastyx mastigures, the lateral margins of the jaws are used to also acquire, and chop, food into the mouth, which is then swallowed. There is a sense that only the rostrum of hadrosaurs is engaged in food acquisition; it is, after all, often quite ridiculously wide, sometimes three times wider than the tooth battery at the sections I illustrate them at. However, this does not say that they should not have been somewhat exposed. Note that my model still permits a "pseudocheek" in the presence of large lizard lips, just like the lizards I compared them to.

If intraoral processing is limited, and the teeth function best when they can engage food from the sides, but that the "lips" can work to retain food inside the jaws effectively, then I see no problem in hadrosaur jaw function working as a lizard's does.
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:iconkazuma27:
Kazuma27 Featured By Owner Sep 10, 2012  Hobbyist General Artist
Yeah, i see your point and you could be kinda right... Actually i like the idea of "pseudocheeks" as you call it, more than the totally cheekless scenario... Another problem, i guess, when it comes to restoring ornithischians, is that it seems they are quite under-researched, at least in regards of saurischians (theropods, especially), so many aspects of their morphology that, with a lil' more study, could be better understood, well, remain obscure or poorly understood.
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