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Re: oviraptor diet



Nick Longrich wrote-

 That, and the differences in morphology of
 the oviraptorid jaws is pretty striking- Dinosaur Provincial Park
 > alone seems to have three distinct jaw designs, presumably they were
 > not all up to exactly the same thing.

Wha?  Three oviraptorosaurs in Alberta?  Chirostenotes pergracilis, C.
elegans and..... what?

Okay, check out Currie et al. in the first Sino-Canadian issue of CJES, regarding new caenagnathid material. Currie illustrates Caenagnathus collinsi, as well as cf. Caenagnathus sternbergi. Thing is, if you look at the sternbergi, Fig.4 doesn't match up with Fig. 5.; (4) TMP 92.36.390, has a very steeply rising anterior jaw margin (ice cream scoop), (5) TMP 90.56.6 has a much shallower one (shovel). There is a bit of cracking in (5) which could maybe account for the shallower profile, however I've seen the specimen and other unpublished caenagnathid stuff and I'm not convinced it does. Crushing might be there but it's pretty minimal in my opinion. So as far as I can tell, you have C. collinsi (which I haven't looked at), and then the ice cream scoop, and then the shovel morphology. I could be wrong, lord knows I've a track record of it, but this was my impression. I'm not saying these are separate species for sure, I don't think we have the fossils to be sure yet, but I think it's a real possibility. They could be subspecies I suppose, or sexual dimorphs even, or maybe the jaw was just highly variable.
The question is what these morphs could correspond to. For postcrania, two published caenagnathids exist from DPP- Chirostenotes pergracilis and elegans, a much smaller animal. Its possible that the elegans stuff is actually two animals I suppose, I haven't seen any indication of this but I haven't looked either and it could be pretty subtle.
Oh, yeah, and then "C. pergracilis" from the later Horseshoe Canyon formation has a different shaped ischium and is substantially larger than the specimen from DPP... so is that dimorphism, or variation, or is it a separate species from the DPP ones?


My suspicion is that we could be underestimating species diversity for two reasons.
(1) in Late Cretaceous North America, there is generally a very strong bias towards the preservation and/or discovery of large animals, such as duckbills, ceratopsians, and tyrannosaurids. Horner has like a zillion tyrannosaur skeletons but just a couple small theropods. It's the same at the Tyrrell- lots of tyrannosaurids, a couple ornithomimids, but not a single complete or mostly complete skeleton for any of the other small guys (caenagnathids, troodontids, dromaeosaurids, Ricardoestesia whatever it is). For that matter, there isn't much to be said for small ornithopods, either. Without comparative material, its difficult to establish patterns of variation.


(2) there are tons of species recognized for duckbills and ceratopsians. For one thing, they apparently don't spread over a wide area and don't last long. What I've been told is that it's nearly impossible to tell these guys apart from the postcrania but that the skull and in particular, cranial ornamentation is very distinctive. This would make sense if these are fast-evolving sexual features. Identifying species of these guys is easy, since they have these huge bony features which, among other things, probably say "hey, I'm an available member of your species". For the most part, small theropods lack this kind of stuff. Their interspecific variation could have been much more subtle- say, calls, plumage coloration, mating plumage, maybe a bit of size variation... I think anyone would agree that you'd have a lot easier time trying to identify species of african antelope than african cats from the skeleton. My suspicion is that small theropods were very diverse, just like the big duckbills and ceratopsians, and maybe moreso (species richness tends to increase at smaller sizes), but that we don't have the material to start to nail this down, and if we did, their skeletons wouldn't advertise it very well. I think where you are getting the numbers and quality you need (Mongolia), we are starting to see this kind of diversity, with lots of new species of dromaeosaurs, oviraptorids, troodontids, etc. coming out of Mongolia and doubtless many more to come.

Nick L.