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Re: Thought for Food (was CRETACEOUS VARANIDS)



At 08:53 PM 12/9/97 -0800, Toby White wrote:

>I expect that one of the reasons theropods are taken for strict 
>carnivores is that their teeth do not provide suitable grinding surfaces. 
> This is a little odd when you think about it.  A good scavenger, for 
>example, should have powerful jaws and a variety of teeth, including 
>grinding teeth, to make the most of the parts the primary predator left 
>behind.  Surely this niche must have been explored by some theropods, 
>and, if so, the transition to omnivore might not be too difficult.  

Actually, this would make more sense if all animals were concerned were
mammals.  However, typical occlusion (grinding surfaces) are very rare
outside of mammals among amniotes.  Herbivorous turtles and lizards crush
and slice and squish their food, but do not grind it: they are pretty sloppy
eaters.  Even among dinosaurs, big occlusal surfaces are an iguanodontoid
trait, although some other ornithischians (ceratopsians) had quite
sophisticated eating appartus (slicing batteries, in this case).  Other
ornithischians (pachycephalosaurs, thyreophorans, etc.) have pretty simple
teeth and jaws, as do basal sauropodomorphs.

Paul Barrett has been doing a lot of work on feeding adaptations in
dinosaurs, so (if he's online here) maybe he can post something about it.

Greg Paul was the first (to my knowledge) to postulate on omnivorous
ceratopsians, so maybe he can post something along those lines.

As for theropod scavanging adaptations: scavenging in general does not have
any special morphological correlates.  Once food is dead, eating it is
pretty much the same, whether you killed it or something else did.
(Different predatory behaviors, on the other hand, might require specific
adaptations, as would specific scavenging behaviors, such as bone-cracking).

Part of the reason theropods are generally interpreted as stict carnivores
(hypercarnivores, to use the mammal ecological term) is phylogenetic:
archosauriforms seem to be basally carnivorous, unless they develop specific
features otherwise.  (As has been discussed elsewhere, long-snouted
cone-toothed fish eaters and hatched-headed blade-toothed meat eaters are
common among archosauriforms, but only a handful show specific adapations
towards plant-eating).

Thomas R. Holtz, Jr.
Vertebrate Paleontologist     Webpage: http://www.geol.umd.edu
Dept. of Geology              Email:th81@umail.umd.edu
University of Maryland        Phone:301-405-4084
College Park, MD  20742       Fax:  301-314-9661