Re: rampant speculation

["David Marjanovic" <david.marjanovic@gmx.at>]

> David Marjanovic wrote:
>
> >But it assumes that coelurosaurs evolved herbivory in a world full of
> >already herbivorous ornithopods which, at the beginning, must have been
> >better adapted to that. Such things don't happen (competitive exclusion).
>
> Ah, so incumbent taxa (e.g. ornithischians and sauropods, among dinosaurs)
> have a monopoly on herbivory,

when & where they are established,

> and their apparent success precludes any new
> adaptive radiations from "nudging" them out of their niches.

Yep.

> Unless, of
> course, the existing herbivores go extinct, then evolution goes back to
the
> drawing board.

Indeed.

> This "competitive exclusion" hypothesis is nothing more than that: a
> hypothesis.  It overlooks the possibility of either (a) new plants making
an
> appearance in an ecosystem;

True, I forgot that; but which plants could have been new in Cretaceous
Asia? Angiosperms come to mind, but judging from the rest of the world,
ornithischians and sauropods don't seem to have got problems by this. Though
that's not particularly testable AFAIK.

> and (b) novel herbivory strategies emerging
> among existing omnivorous or partially herbivorous lineages (many modern
> carnivores include plant matter in their diets).

These can't be perfect from the beginning, and it's very unlikely they're
even as good as those of the existing herbivores.

> Notwithstanding the "isotopic studies (mentioned onlist whenever)" which
you
> mention, the manus of ornithomimosaurs does not seem to be very useful for
> seizing or handling prey.

Well, ask a tyrannosaur or carnivorous bird about the importance of hands...

> Nicholls and Russell (1985) suggested that the
> ornithomimosaurian manus was best suited for "hooking and clamping" (such
as
> tree branches), and I don't know of any study that has directly refuted
this
> interpretation.

No problem for interpreting them as omnivorous, and the hands look suited to
precision grasping with the long, opposable thumb, don't they?

> >[...] if the famous Lufeng jaw is
> >really from a segnosaur, then they may have evolved directly after the
Tr-J
> >mass extinction in an empty world.
>
> Try telling that to a prosauropod.

The empty world? Sure -- _right after_ the mass extinction, in the first 5
million years or less. Testing the speculation that segnosaurs evolved then
asks a lot from the fossil record, if the jaw is from a segnosaur.