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Lip service; Ornithischians


While researching Stegosaurus for the reconstruction test above, some kind soul (Nick Gardner?) from the DML referred me to this insightful article on Stegosaur lips by Stephan A.Czerkas. To Nick or whoever it was who gave me this tip, please allow me to properly give credit! I did this a while back – feels like ages – and drag it out now in response to Jaime’s theropod lips post.

The paper deals with a number of observations and comparative analysis – the deep-set teeth, the ambiguity of an upper beak, feeding necessities, cladistic inference and the similarity in bone surface to turtle jaws. Overall very convincing, particularly when formulated as a sculpture by the masterful hand of the author himself:


Most convincing of all is the general flimsiness of cheeked alternatives. The more realistic they are, the less seem plausible. There seems to be a cheek-meme in which they look like a sock-like, rubbery jaw-sleeve. I even see it in digital TV versions and the JP Triceratops is at least related. Where does this come from?


I tried to reproduce it here, with closed and open incarnations. Not convinced? Me neither. Czerkas extends likely liplessness to all advanced ornithischians, and except for mention of the many beaked theropods, leaves saurischians open to interpretation.

There are 3 Comments to this article

Jaime Headden says:

It should be noted that the skull Czerkas uses for his model is a specific Stegosaurus stenops skull in which one side has been skewed around its long axis relative to the other, twisting the jaw weirdly. The other side, miraculously enough, is in fine condition and matches other skulls (and other stegosaur skulls) but the chosen illustrated side is not, which results in the mandible facing dorsomedially, the tooth row is hidden laterally by the lamina extending anteriorly from the coronoid process, and Czerkas thinking that this is continuous with the predentary rhamphotheca.

I will attempt to discuss the “coronoid lamina,” that thin lateral ridge that extends along the mandibular tooth row and is one of the primary reasons there’s been an inferred cheek in ornithischians, segnosaurs, etc., at some point. It’s worth noting, at least, that some dinosaurs with inset tooth rows lack this ridge, but its generally always present.

Traumador the Tyrannosaur says:

Lips vs. Cheeks is an interesting topic (there was a very public battle between two ART Evolved members on deviantart a few months ago over it).

I wouldn’t blame this “meme” on artists this time. In talking with all my Hadrosaur expert friends (all my palaeo PHD friends seem to have dabbled in duckbills) they’re of the opinion Hadros had some sort of cheek LIKE structure. What it looked like or how it functioned is up for debate…

The point is artists working with such an opinioned scientist would have put a cheek into their reconstruction, and it would have taken off from there…

drip | david’s really interesting pages… says:

[...] I’ve been optimizing my massive 3D scene, so today’s rant is likely going to be short on time. That’s okay, because there’s not a lot to say about sock mouths. You know what I’m talking about… that beak tip emerging from a fleshy sleeve that stretches when the beastie opens its mouth and hopefully stretches back when it closes it, lest it be bitten off. I drew a quick version way back when. [...]

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