Ceratopsian dinosaurs: cheeky or beaky?

Keep the (great!) ceratopsian articles coming - this is a very interesting series.

Oh, for a time machine. (And a big Jesus iron cage!)

Awesome..I have wondered about the material covered in the last three posts for quite some time. I often wonder about the relative intelligence of the larger ceratopsians. were they somewhere between alligators and ostriches?

Quite frankly it depends on whereas the earliest ornithician had cheeks or not. If it had, logic would say all of its descendents had. However, it could had very well have had a cheek-less muzzle, like iguanas and tortoises. And later the descendents branched into cheeked and non-cheeked species

Since we're on the topic of cheeks in dinosaurs, I was wondering about two aspects of sauropod reconstruction. It is clear that sauropods did not have teeth capable of chewing, yet I often see diplodocids, which have all of their teeth close to the front of the mouth, reconstructed so that a fair portion of the mouth is enclosed with a flap of skin resembling a cheek (e.g. Greg Paul's Apatosaurus reconstructions). Camarasaurs and brachiosaurs have much longer tooth rows, and as such I have not seen them reconstructed in this fashion. Is there any reason to believe that diplodocids would have had any sort of skin flap covering the side of their mouth? Secondly, I've seen several reconstructions recently of sauropods (notably Rapetosaurus by (I think) Luis Rey) with long, fleshy, tubular nostrils running from the top of the skull to near the tip of the snout; what evidence is there for this? Cheers.

Did the ornithischians chew? Is there a way to tell from looking at the teeth? If yes, then the food would have fallen out of their cheekless mouths.

(note the new site)

@Steve Poropat: I believe thats just a "reconstruction inaccuracy", which can also be seen on the reconstructions of tropical giant ground sloths (which likely weren't as hairy as that). Either that, or diplodocids chewed with their bare jaws, which is unlikely I think. I'm pretty sure browsing sauropods didn't needed cheeks however, since they would just grab their food like iguanas and tortoises, not chew it

Thanks, Darren. I've always thought Mr. Witmer was right on the money when it came to re-orienting dinosaur noses on the front of the snout but dead wrong in claiming there were no cheeks in some dinosaurs like hadrosaurs and ceratopsians (how would they keep the food in their mouths when they chewed, as some of them certainly did?) I'm glad your analysis backs this up, as do some others, like that of David Norman and Robert Bakker.

Ceratopsian heads are full of interesting areas to discuss!..
Horns, frills, beaks, cheeks, gums, tongues.. and, seen in cheekless wonders, those fleshy webs at the jaw-angle, located medial to the teeth (the extent of which webs are surely quite rigorously constrained by the line between known muscle attachments above and below the mouth-line)..

Fenestrae, horn-sheaths, epoccipitals and jugals, integumental embellishments.. so much detail to fill in.

I wonder any artist ever gets their reconstruction drawn! And no wonder there are so many variants.

Still, that Leptoceratops just looks wrong to me.

Cheeks are primitive traits, they correlate with lower jaw, thumb and interdigital webbing (before derived long limbs). I don't know if Ceratopsians specifically lost their webbing.

Humans retain (chubby) cheeks and interdigital webbing, the fat is derived, the cheeks and webbing are primitive and older than teeth, I'd guess.

Amazing how a thread on ornithischian cheeks has prompted comments on 'aquatic apes'... :[

a bit cheeky there Nick...

DDeden, what on the planet are you talking about? If I understand you correctly, and that's a big "if", you're making lots and lots of extraordinary claims without providing any evidence.

I always thought that cheekless ornithischians was Witmer taking the EPB too far. So what if it's a third level inference? The teeth show that iguanodontians at the very least chewed their food and it would have ended up on the outside of their mouths if they didn't have cheeks. Add to that, the cheek armor of some ankylosaurs, and phylogenetic bracketing then says that cheeks were present in all genasaurs.

Plus, that Leptoceratops image is super-creepy....

Speaking of cheeks and "skin flaps" on the sides of mouths, it is interesting to note that condors have these extension of skin "flaps" on their beaks. A nice picture of this can be found here, and remember that condors do not chew, nor do they use their beaks as heavily as some other predatory birds.

You would think that for some taxa, especially ankylosaurs, that any sort of tissue lateral to the dental arcade and the "buccal chamber" would be helpful since the space between dental rows is tiny and the teeth small and inefficient from processing plants on a massive scale without aid. The presence of osteoderms lateral to a buccal chamber supports cheeks ... in that taxon. This can be inferred to other taxa with similar anatomies, but that only goes as far as nodosaurs and ankylosaurs directly. It does not hold true for ornithopods or marginocephalians, and in some of these taxa, the dental arcade and oral vault are broad and the teeth specialized. In some derived ornithopods (hadrosauroids) the oral vault is narrow, the dental arcades specialized toward plant processing on a massive scale, and this is aided by the presence of a lateral tissue and a buccal chamber.

At some point, the term "cheek" has become synonymous with and only used FOR mammalian buccinalis and extraoral musculature, in which case the term "cheek" a misnomer for nonmammals, and this seems to be what Witmer has started from (as the only animals with "cheeks" appear to be mammals), which is fine from an EPB standpoint, but hard to back up when there are analogues without strict homologues. In Witmer's defense, his argument is essentially that ornithischians lack mammal-style cheeks, which is certainly true, but he's extrapolated this to mean that any cheek-like structure must therefore have the same analogues to mammalian tissues, which resulted in one of the restorations (Parson's, Leptoceratops) above. This has said little about whether these taxa, for reasons of their oral anatomy, would have or have not had a tissue that acted, analogously, to a cheek in mammals in some functions.

Finally, it only takes a fairly complex but simple theoretical model to describe potential "cheek" gain in nonmammal vertebrates with oral processing requirements in their diet, especially ornithischians in which this tissue has been inferred. This model can be as simple as extrapolating jaw movements on a 3D digital object, and provide a "material" to be processed by orthal and complex jaw movements, constrained to possible jaw movements, and with and without a lateral tissue to determine whether the absence of such a tissue is likely (if an animal loses 40-60% of its mouthful volume in food in the smallest mean to oral processing, it's going to have a hard time without being really patient and having an overabundance of food available to it).

@ ZA: awesome.
@ DM: Basically 'Cheeky AND Beaky' is IMO most parsimonious, but unconfirmed.

Basically 'Cheeky AND Beaky' is IMO most parsimonious

I still don't understand.

Nobody disputes the beak at the tips of the jaws (brown in the Leptoceratops picture). The question is whether the rest of the jaws were lined with beak stuff or similar matter (yellow in that picture) or cheeks; both at the same time in the same place is not possible.

If memory serves, there is a brief discussion of this issue in Larry Witmer's 1995 paper on the EPB in 'Functional Morphology in Vertebrate Paleontology'. You're right to note that a full length discussion hasn't appeared. Czerkas also came up with a similar idea for rhampthotheca-lined jaws in a brief paper on stegosaurs (but I can't remember the reference offhand). I discussed both in my paper on thyreophoran feeding (Barrett 2001 - in 'The Armored Dinosaurs volume). In this same paper I also mentioned the fact that the osteoderms present in the buccal emargination of Panoplosaurus proved that at least one ornithischian had dermal tissue - a cheek - in this region.

Thanks Paul. To those interested...

Barrett, P. M. 2001. Tooth wear and possible jaw action of Scelidosaurus harrisonii Owen and a review of feeding mechanisms in other thyreophoran dinosaurs. In Carpenter, K. (ed) The Armored Dinosaurs. Indiana University Press (Bloomington and Indianapolis), pp. 25-52.

Czerkas, S. A. 1999. The beaked jaws of stegosaurs and their implications for other ornithischians. In Gillette, D. D. (ed) Vertebrate Paleontology in Utah. Miscellaneous Publications, Utah Geological Survey (Salt Lake City), pp. 143-150.

Witmer, L. M. 1995. The extant phylogenetic bracket and the importance of reconstructing soft tissues in fossils. In Thomason, J. (ed) Functional Morphology in Vertebrate Paleontology. Cambridge University Press, pp. 19-33.

I was told that human babies had fatty cheeks so that their oral cavities would not collapse inward when they suckled and make it more difficult to get milk. That seems logical and extends to Mammalia. So there's a distinction between skin at the sides of the mouth opening and thick cheeks.

I'm more interested in, "how much muscle did Ceratopsians have for chomping with those impressive beaks?" They are big enough for impressive bacterium-assisted digestion of woody, or at least very fibrous, plants. The gaunt, beaky reconstructions that I usually see would scarcely dent a nice cycad trunk.

Also, is it possible that the crest itself anchored some muscle?

Monado, the lower margins of the parietal fenestrae probably anchored the jaw muscles, but I doubt the entire fenestrae did--too vulnerable to injury, intraspecific and otherwise. And ceratopsians had very strong jaws. Once they got the food between their choppy teeth, there was no escape.

But here's a question for you (and anyone else): with its solid frill, where did Triceratops connects its jaw muscles?

So, beaky and cheeky, obviously.

@ Monado: fat cheeks are irrelevant to suckling, see newborn chimps, orangs, preemies without fat. Mouth (cheek), neck and pentadactyle digit webbing are all primitive, not talking of fat or muscle, just skin webbing. Maybe turtles and iguanas lost the cheeks due to fast biting underwater without suction, others with suction retain cheeks or balleen or so.

@DM: Cheeks.

... "But here's a question for you (and anyone else): with its solid frill, where did Triceratops connects its jaw muscles?"

the same place that other sauropsid taxa that don't have dorsal temporal fenestra do... on the ventral surface of the parietal...

Whoa...de ja vu big time right now. I feel like I've had this conversation before.