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Re: Evidence For a Feathered Velociraptor...



On 9/24/07, Tim Williams <twilliams_alpha@hotmail.com> wrote:
>
> I'm not at all keen on Gauthier and de Queiroz (2001)'s proposed 
> apomorphy-based definition of Avialae: the presence of "feathered wings... 
> used for powered flight."

Like it or not, and whatever it includes, it's a useful taxon to have
a moniker for. (And the name does mean "bird wings"....)

> [Personally, I much prefer Senter's (2007) definition of Avialae, which is 
> "all taxa more closely related to birds than to Deinonychosauria"

That definition is much older than Senter (2007).

> Having said that, I agree that powered flight seems pretty secure for 
> Ornithurae.  I also agree that the usual interpretation that taxa like 
> _Archaeopteryx_ and _Rahonavis_ could fly, but microraptorines couldn't,

Microraptorians (and here I thought you were following Senter's nomenclature).

> does seem a little arbitrary.  It's really difficult to compile a list of 
> exclusively 'flight-related' characters, given that many flight-related 
> characters (a) precede the origin of flight (i.e., were exapted toward 
> powered flight); (b) are retained in secondarily flightless taxa; or (c) 
> evolved independently of Aves.

Or, better, of _Avialae_. (See, it is useful....)

> Characters such as the presence of quill knobs, or asymmetrical remiges and 
> rectrices, appear no longer to be exclusively 'flight-related'.

Agreed.

> It is really difficult to point to a character in _Archaeopteryx_ and call it 
> 100% flight-related.  You could find the same character in a microraptorine, 
> or even a velociraptorine.  I suspect it's the overall 'gestalt' of 
> _Archaeopteryx_'s morphology (both integument and skeleton) rather than 
> individual features that pushes it over the line.

I suspect it's its history as "the first bird".

> As Mike said, the size of the critter helps, given that _Archaeopteryx_ is 
> below the cut-off for a flying animal (although I don't know quantitatively 
> what the cut-off actually is), whereas velociraptorines and basal 
> oviraptorosaurs (_Protarchaeopteryx_, _Caudipteryx_ are clearly too 'big', or 
> have arms that are too short.

But not microraptorians....

> Also, _Archaeopteryx_ has only two wings associated with the limbs, as in 
> modern birds (not four as in microraptorines) which makes comparison with 
> modern avian flight easier.

It does have pretty long leg feathers (although not as long as in
_Microraptor_, true).

-- 
Mike Keesey