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Re: Avian Ancestors, new book on theropods

Mike Keesey <keesey@gmail.com> wrote:

> Don't forget that it was also defined as apomorphy-based: "'Avialae'
> refers to the clade stemming from the first panavian with feathered
> wings homologous (synapomorphic) with those of Aves (Vultur gryphus
> Linnaeus 1758) and used for powered flight"  (Gauthier and de Queiroz
> 2001).

No, I didn't forget that particular definition... though I would
dearly like to.  ;-)

Gauthier and de Queiroz's apomorphy-based definition was
well-intentioned but ridiculously impractical.  What exactly is a
"feathered wing"?  Does the forelimb plumage of ornithomimids qualify
(Zelenitsky et al., 2012)?  These "feathers" were undoubtedly
homologous to those of extant birds... but their exact function is
unknown (and perhaps unknow-able).

> That definition makes the inclusion of Archaeopteryx rather ambiguous.

_Archaeopteryx_ would likely qualify as an avialan under the above
apomorphy-based definition - especially if one equates "wing" with an
aerodynamic function.  Its large asymmetrical remiges almost certainly
had an aerodynamic function (even if that function wasn't necessarily
powered flight).

> But the intent was to provide a name for a clade that everyone's
> interested in over a clade with stable composition.

Very true.  However, when the precise function(s) of
wings/pennibrachia in non-avian theropods is such a contentious issue
(and likely one that will never be ultimately resolved), then this
apomorphy-based definition just provides more heat than light, IMHO.