[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index][Subject Index][Author Index]

Re: polyphyletic Alvarezsauria assemblage



Ken Kinman wrote-


>       The hindlimbs are quite different in Alvarezsaurus and mononykiforms
> (particularly the latter being hyperarctomet, as in Avimimus).
> Mononykiforms and Avimimus also share a fused carpometacarpus.
>       The absence of the m. cupped. fossa on Mickey's list also occurs in
> oviraptorosaurs and segnosaurians (the latter which I believe are probable
> Alvarezsaurus relatives).
>       And I believe Jaime mentioned that Alvarezsaurus had a wide
> supracetabular crest (which was interpreted as a reversal of sorts).
> Perhaps it is just primitive.
>       Alvarezsaurus lacks any large hypapophyses on the anterior dorsals.
> And it lacks carotid processes in intermediate cervicals.  Present in
> mononykiforms.
>       The caudals also seem to differ, other than the fact that that they
> share the procoelous caudals (and sacrals).  I should also mention that
> Gargantuavis had procoelous sacrals.
>      The anterior trochantor splits from the greater trochanter closer to
> femoral head in mononykiforms (as in other Class Aves sensu lato).

The hyperarctometatarsus had to have evolved from a non-arctometatarsalian
form at some point, so that doesn't matter.  The carpus of Alvarezsaurus is
unknown, so it doesn't matter if Mononykus and Avimimus have carpometacarpi.
The basal oviraptorosaur Microvenator has an m. cuppedicus fossa at least,
though I'll need to search the literature to see if others do.
Alvarezsaurus actually has a reduced supracetabular crest, unlike the more
primitive condition in mononykines and Patagonykus.  It is true that
Alvarezsaurus lacks enlarged cervicodorsal hypapophyses, but this one
character isn't enough to override the Alvarezsauridae synapomorphies (and
was included in my old analysis, which found Alvarezssauridae to be
monophyletic).  I'm not sure what clades the carotid processes may diagnose,
they're present in such varied forms as Eustreptospondylus, ornithomimids,
Mononykus, Avimimus, troodontids and ornithothoracines.  Even derived forms
like segnosaurs, oviraptorosaurs and Deinonychus lack them though, along
with Alvarezsaurus.  I don't know about Gargantuavis having procoelous
sacrals, The cranial articular surface is certainly concave, but what about
the caudal articular surface?  In any case, this taxon is deeply nested in
the Pygostylia, probably in the Ornithurae.  And finally, you're right about
the anterior trochantor separating from the greater trochantor more distally
in Alvarezsaurus, but this character also didn't make Alvarezsauridae
polyphyletic in my analysis.  And just for the sake of providing exceptions
to your postulated characters, Archaeopteryx and Microvenator also lack
large hypapophyses, and Chirostenotes and Avimimus both have distally
originating anterior trochantors.  Not that it makes your evidence any
worse, though by your reasoning it might.

> P.S.  By the way, now I understand why George and Tracy don't want to
> release their ideas about thyreophorans until they get a relatively
> air-tight case.  If you release your ideas piecemeal, it certainly leaves
> you wide open for having them picked apart and having the peanut gallery
> showering all manner of criticisms on you every step of the way.

George presented a few characters to support thyreophoran paraphyly, which
are greatly overwhelmed by the thyreophoran synapomorphies currently
recognized.  So of course it's going to get rejected.  We test these
hypotheses by seeing which alternative is most parsimonious, so unless you
can at least get close to being equally parsimonious to the alternative, you
don't stand much of a chance.  Tracy advocated a similar topology, but cites
unpublished data, so we can't consider the option seriously yet, with the
current evidence going against it.  Once that evidence is published, it will
be considered relative to the current evidence.  And remember, criticism is
good.

Mickey Mortimer