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Re: Waiting for a giant bird and dino physiology revisted



HP John Bois wrote:

> On Sat, 12 May 2001, David Marjanovic wrote:
>
> > This should still be enough for *T. rex* sizes. _All_ theropods, not
just
> > birds, have bent knees and are bipedal. Of course, there was no
selective
> > pressure for any neornithine to get that big.
>
> Maybe a better way to say this is that were _stronger_ selection pressures
> keeping birds small.  For example, in the absence of predation in New
> Zealand, selection pressures were plenty strong enough--what selection
> pressures for large size could there be on NZ that were absent everywhere
> else (most places, anyway).  None, I think!

Not total absence of predation. There was, after all, the poo'akai, an eagle
with 3 m wingspan and terrible foot claws. Moa pelves pierced by such claws
and rock paintings showing such scenes are known.
        Of course, the size of flying predators is limited (though we still
don't know where the limit is... *Argentavis*...), so the selection pressure
for larger size in herbivores so that they are safe from predation stops
somewhere, I'd say.