Re: oviraptor diet

[Nick Longrich <longrich@alumni.princeton.edu>]

> 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specimen and other unpublished caenagnathid stuff and I'm not 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.