Ruminations on sauropsid cheeks

I noticed some FB flareup over dinosaur cheeks and had written all this in the box Facebook page and then decided it would be ludicrous to post so I moved it here…Apparently, dinosaur cheeks have become all the rage again in the blogosphere. Having only seen one published paper on the topic ever (Fabian Knoll’s 2008 paper) I’m still perturbed there aren’t other papers. But this region is way cool, apparently there is a new paper coming out on the topic. Being well aware of Witmer’s early work with Mike Papp on the cheeks vs freaks, Tobin H’s work on osteological correlates of skin (jeez I hope someone is pestering Tobin with a hot poker about this instead of just taking heavily from his published papers) and Ashley M’s still-evolving work on foramina…it is not an easy topic. My research on jaw muscles bumped into the buccinator/cheek/rictus problem alot, so I’m aware of the available evidence. (By the way, my favorite branch of the trigeminal nerve is the n. anguli oris—what’s your favorite CN V branch? Hmmm?)

 I hate the term cheeks as it always suggests the mammalian variety with a buccinator muscle (for which there is ZERO evidence for in saurpsids [yes, dinosaurs are also sauropsids!]).  The German anatomists (Luther, Lakjer, et al.) used either Mundplatte, and then later, the rictal plate, or rictus to describe the corner of the mouth in sauropsids (see my 2007 J Morph paper if you want more lit cited). Its rich with nerve endings, vasculature, glands etc and is easily seen in the corner of that snapping turtles mouth (see link above), crocodilian mouths, most birds. The rictus tends to directly cover the corner of the mouth where the temporal and  pterygoideus muscles cross paths as they attach to the mandible near the coronoid process, usually just underneath or caudal to the orbit.  Mammals have a rictus too– its the really sensitive edge of the cheek that lacks muscles but is packed with sensory receptors–go ahead, pinch it. Some snakes developed venom glands within the rictus (McDowell SB. 1986. The architecture of the corner of the mouth of colubroid snakes. J Herpetol 20:353–407.).

Anyway. I don’t see what’s so contentious aside from having a cutesy Dinocheek media event. Well endowed Mundplattes are not uncommon among sauropsids as people keep pointing out.  Why does there have to be one Dinosaurian bauplan for “cheeks” (ugh). Clearly with all the evolution that has happened in these groups, needing more/less skin over the mouth must have been necessary for chewing vs gape?  Clearly having a freaking giant osteoderm there lends cred to ankylosaurs having cheeks. but IMO, I never thought the old addage (err hypothesis?) “food would fall out of their mouth otherwise” to ever be a good approach to support the presence of skin there otherwise.  But perhaps there is upcoming evidence via SVP abstract to support it (yay!).  I feel like this whole debate is driven by paleoart, and not some true scientific endeavor (no offense artists-I understand the pains you often take to get things accurate). I sent most of this same information to Tylor Keillor, like 5 years ago to help with his sculptures-so its way cool to see his work progress that way it has been (see Project Dryptosaurus).

To me, a true cheek is when the rictus becomes decoupled from the true corner of the mouth (back near the coronoid process) and extends rostrally beyond to serve some function with the oral cavity.  So the cheekiest archosaur? My vote is the flamingo. Flamingos stretch the corner of the mouth past the corner of the mouth, past the orbit, past the antorbital cavity! past the transition from bony mandible to beaky mandible (holy crap!). And there is fairly clear function for this given the flamingo’s derived lingual pumping/filtration method of feeding. Here is an unpublished picture from our 2006 Anat Rec Flamingo Head Vessel paper.  Now that’s a @#$@# dinosaur cheek!

Flamingo extended rictus err dinosaur cheek

About Casey

I am an Associate Professor of Anatomy at University of Missouri-Columbia. I teach Anatomy for the Medical School. I conduct research on the evolutionary morphology of vertebrates, particularly the structure, function, and evolution of the feeding apparatus. Much of this involves studying the biology of bone, cartilage and muscle. of dinosaurs and fossil crocs. I have a great job.
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5 Responses to Ruminations on sauropsid cheeks

  1. Pingback: Memo Koseman Chides Me With Turtles, and Other Musings | The Bite Stuff

  2. David Marjanović says:

    Condors are extremely well endowed that way.


    Mundplatten. Like oxen.

  3. Pingback: Earthling Bulletin #9 | Earthling Nature

  4. Pingback: Facial Expressions | The Bite Stuff

  5. I was curious while the jaw muscles can usually infer the placement of rictus, are there any other correlates that can determine if the edge of a tetrapod’s mouth is skin, as seen on modern archosaurs and mammals, or gingiva, as seen in lepidosaurs? I am curious of this as I want to figure out how to properly draw the mouths of Mesozoic dinosaurs and other long extinct tetrapod groups.

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