Some dinosaurs had cheeks, but maybe not in the way you'd think

[Halichoeres]

I'm not especially knowledgeable about the osteological indicators of soft tissue attachments, so I'll be interested in reactions from people who are, but this is an interesting paper describing what they call a 'buccal' structure, which to me usually means pertaining to cheeks. But this is more of a jaw stabilizer during chewing and biting, rather than something to move a wad of chewed matter around in the mouth (like the mammalian buccinator muscle).

Here's a diagram of the new structure, the 'exoparia,' in various dinosaur taxa:


Open access in Journal of Anatomy: https://onlinelibrary.wiley.com/doi/full/10.1111/joa.14242

[dinofelid]

I see they call it a "strong connective tissue structure" and say it's unclear if it's ligament or muscle, but lean towards latter:

A ligamentous or muscular identity for the exoparia cannot be determined with the available data, but the size and shape of the zygomatic entheses in many dinosaurs are more consistent with a muscular attachment.

This may add to the picture of dinosaur cheeks given in the papers by Ali Nabavizadeh here and here which argued that dinosaurs didn't have mammal-like cheek muscles that actively pushed the food around during chewing, although Nabavizadeh was proposing that a different jaw muscle called the mAMES was attached in such a way that in some species it could have blocked off the teeth and helped prevent food from falling out the sides of the mouth. But in his reconstruction, other ornithischian species that chewed their food wouldn't have had the teeth wholly blocked by this muscle (see fig. 8 in the first paper or figures 9 - 11 in the second one). He also noted in the section of the first paper titled "Other buccal soft tissues" that in addition to muscle these dinosaurs may also have had non-muscular cheeks of skin blocking off the teeth, and that there's at least some fossil evidence for this.

[Concavenator]

Interesting how Eofauna predicted this structure with their Tyrannosaurus figure, as far as I can tell.