ornithomimes and herbivory

[Norbik Nudley <longrich@phoenix.Princeton.EDU>]

        Somebody was talking about ornithomimes as herbivores, and 
somebody asked me recently about Diatryma, and I've been wondering...
        Diatryma doesn't really look like a big herbivorous bird. The 
problem is that skull- it's enormous, especially compared to herbivores 
like moas, elephant birds and the other ratites- which, if I recall, 
mainly eat plants, though some will take animal matter as well.
   Herbivorous birds generally don't have big beaks probably because they 
mainly serve to take in food, rather than to process it. The gizzard does 
the processing. Diatryma's beak would probably not have served well in 
the same capacity as a cow's jaws or a duckbills dental batteries. Those 
are animals big on the other end, the processing end, although they also 
have well-developed cropping mechanisms, and this explains their large 
skulls- built to house and power big grinding structures.    
        In this respect, ornithomimes certainly look like ratites- 
relatively small heads. Am I right in saying that they have generally 
the smallest heads? That's the other part, carnivores generally tend to
have pretty large skulls- a pattern Diatryma would fit.  
        Sorry to get so technical here- all this hard data and quantified 
observation I'm presenting can get pretty heavy ;) . I'm just making some 
generalizations... does anybody out there have any real information on 
the subject? 
        On the other hand, ornithomimes have claws that might be 
suited for catching animals, and a large brain, something 
typical of carnivores (or omnivores?). 

        Nick Longrich, class of '98
        Ecology and Evolutionary Biology major (former would-be 
Humanities/English/Literature/Philosophy/..... etc. major). 
        Creator/Writer/Illustrator of the "Norbik Nudley" comic
(http://stardot.com/~longrich/index.html)- which has a couple dinosaur 
illustrations (Ceratosaurus, Carnotaurus, Styracosaurus) tossed in there 
somewhere.
        I enjoy bones, origami, modelling dinosaurs, cartooning, writing, 
biology and evolution in general.