Re: Dinosaurs and birds

["T. Michael Keesey" <keesey@gmail.com>]

On 4/3/07, Tim Williams <twilliams_alpha@hotmail.com> wrote:
> Yes, most models that provide a hypothetical pathway for the evolution of
> avian flight use _Archaeopteryx_ as the prototype for how later birds came
> to fly.  There's no phylogenetic or ecomorphological evidence to overturn
> that assumption, AFAIK.

No reason to presuppose it, either, though, except that for a long
time it has been the best ancestor model in that neighborhood of the
phylogenetic tree. More things are coming to light nowadays--will
_Archaeopteryx_ hold on to its special status? (Its special
phylogenetic status, that is--it will always have special historical
status.)

> This leads me to ask, are there any arboreal, volant dinosauromorphs aside
> from birds?

I should also note that Olshevsky's usage of "volant", like his usage
of "bird" is more lax than the norm (at least, as far as I recall).
But, no, there isn't anything. His explanation of this was (again,
from memory) that these "early birds" were small and dwelled in
forests, so fossils would be expected to be pretty scarce. (An
argument that works a lot better for pterosauromorphs and
pan-chiropterans than for avialans, IMHO.)

>  Microraptorans, while not avians, are darn close to birds; they
> were probably arboreal, and maybe volant (biplane-style).  I'd be willing to
> bet that basal oviraptorosaurs were arboreal too.

Why, what arboreal adaptations do oviraptorosaurs have? (Or
microraptorians, for that matter?)

> But that's about it.  I
> have trouble believing that the first sauropods lived in trees, or even the
> first tyrannosaurs.  Then again, as Mike Taylor says, "I have a hard time
> believing" is not admissable evidence.  :-)

True, and I think his case would be more for the first sauropodomorphs
being arboreal, which is slightly easier to imagine (although still
not backed by any evidence). (Then again, I seem to recall him
doubting the monophyly of Sauropodomorpha, but I'll leave that alone
for now.)

> >(Then again, some don't even think _Archaeopteryx_ was volant.)
>
> Is the non-flying _Archaeopteryx_ idea still around?

Yes.
--
Mike Keesey