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Re: Greg Paul is right (again); or "Archie's not a birdy"



 Given that Ornithurae rests on a highly autapomorphic stem clade
 (Hesperornithes),

This is one of about five phylogenetic definitions of Ornithurae.

 the plesiomorphic part of which remains entirely unknown,

We do have *Pasquiaornis* and *Enaliornis*, fragmentary though they are, and *Gansus* is somewhere close.

 and given the general lack of known basal diversity in
 Ornithuromorpha,

*Archaeorhynchus* and *Yanornis* are not exactly the same thing.

(That's assuming they actually belong to Ornithuromorpha, which depends on the positions of *Patagopteryx* and -- under one of the two definitions -- *Vorona*. But in any case, they belong to Euornithes.)

 In a similar vein, the supposed apomorphies of Pygostylia and
 Ornithothoraces (whose non-apomorphy-based definitions implicitly
 rest on the assumption that the supposed apomorphies *are*
 apomorphies)

No, that's not how it works. The PhyloCode, at least, is not concerned with such etymological implications.

 seem to be homoplasies at least for the largest part, or even - in
 case of the pygostyle - hint at nonmonophyly.

The birds with a pygostyle -- as opposed to, presumably, the oviraptorosaurs and segnosaurs that may have one -- clearly do form a clade, even though *Sapeornis* is outside Pygostylia.

 Neornithes is good as it is; contesting its validity is unlikely to
 gain acceptance among neontologists. Hence, if we'd need a
 phylogenetic definition of Aves RIGHT NOW, the only one that pertains
 to a clade that is proven beyond all reasonable doubt, and to a clade
 interesting enough to warrant such a familiar name, and that is not
 wrought with a whole damn lot of controversy, would be: "Anything
 closer to _Struthio camelus_ + _Vultur gryphus/Passer
 domesticus/Gallus gallus_ than to _Enantiornis leali_ + _Sapeornis
 chaoyangensis_ + _Confuciusornis sanctus_" or equivalent.

But this clade already has a name, Euornithes. Why give it a new one?

And why not include Enantiornithes in Aves? Remember that there are several pretty obvious ornithothoraceans of which it is not clear whether they are enanti- or euornitheans: *Eoalulavis*, *Eoenantiornis*, *Liaoningornis*, *Aberratiodontus*...

 That clade would include only stem branches for which *non*survival
 at the K-Pg event would be quite parsimonious due to their being
 restricted taxonomically and/or biogeographically (it was a mass
 extinction after all) but it would NOT contain any stem group that
 was so successful that there is a real need to explain why they (i.e.
 Enantiornithes) are *not* around anymore today. This makes it
 attractive from an evolutionary standpoint too.

Hence its name Euornithes, "true birds". :-)

 This solution might also be considered "not more bloody than
 necessary", because it takes a widely-known name and restricts its
 use to the one and only robust and major and significant clade within
 Avialae and including Neornithes according to present data, which is
 not very likely to be overturned by future data.

As now explained, I disagree.

 In a nutshell: 1. It is probably not a good idea to use Archie to
 define Aves

Agreed (unsurprisingly).

 2. It is probably a good idea to retain Avialae

Yes -- there are so many clades that should be named that retaining this name for something (actually, why not the apomorphy-based definition by Gauthier & de Queiroz 2001) can hardly do harm.

 3. It is probably a good idea to retain Neornithes

Yes.

 4. It is probably not a good idea to use Aves for an insufficiently
 robust "clade" or insufficiently large/significant clade

I agree partially, and disagree with your opinion on which clades are currently robust.

 (It would also stand an actual chance of settling the question "what
 is a bird?" in general knowledge, because it would at the present
 state of knowledge very nicely fit with "Paraves" and "Avialae" and
 "Neornithes" - we get "birdish dinosaurs" of which one part are
 "bird-winged dinosaurs" of which one part are "birds" of which the
 part that still exists today are "modern birds". As opposed to the
 present mess, you could teach this even to Junior High kids and they
 would understand it and learn nothing that is wrong now or likely to
 be wrong in the future.)

Agreed.