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First, I have to apologize for the apparent gigantism of fonts in some recent
emails I sent. I don't know why AOL's mail software does it, and I'm getting
a little more than annoyed.
Last week, Jaime touched on the subject of competition between possibly
omnivorous ornithischians and possibly omnivorous theropods in the Late
Cretaceous. It should be noted however that many ornithischians, although
they might be omnivores were probably far from predators.
Basal ornithopods (Thescelosaurus, Hypsilophodon, Zephyrosaurus etc) and
basal ornithischians like Lesothosaurus and Agilisaurus have fairly small and
broad hands with hoof-like claws, and their premaxillary teeth are somewhat
blade-like but pretty small. These animals, although suited in some ways to
being omnivores were probably at most occasional carrion feeders, or hunters
of sedentary prey like mollusks.
Heterodontosaurids on the other hand have longer forelimbs, long fingers and
sharp claws, as well as gigantic premaxillary teeth. The hands of
pachycephalosaurs are at present unknown, but I would guess they too would
have long, sharp clawed fingers. Basal pachycephalosaurs (Goyocephale,
Homalocephale) and ceratopians (Psittacosaurus, Protoceratops, Chaoyangsaurus
) have substantial premaxillary teeth, like heterodontosaurids.
Marginocephalian stem ornithischians (this group does not have an official
name as of yet) seem to have been better suited to actually hunting some
small game, be it mammals, lizards, etc. Pachycephalosaurids may have gone
to a more solidly herbivorous diet as they seem to have shortened their
forelimbs quite a bit. Ceratopids may have hunted slow things like turtles
or mollusks and crushed them in their beaks.
These possible lifestyle differences should be taken into consideration when
discussing niche partitioning among ornithischians and theropods. This is a
subject I think we're just scratching the surface of, and as alarming as the
image of Triceratops munching a turtle may be, it's a subject I see a lot of
interesting findings coming out of.