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Re: polyphyletic Alvarezsauria assemblage



Ken Kinman wrote-

>       I've been looking at the characters that supposedly unite
> Alvarezsauria, and all I can see is a bunch of homoplasic "noise".  The
> first two (small cervical epipophyses and neural spines) seem to be very
> subject to convergence and found in other groups.  Procoelous caudals and
> sacrals pop up here and there in all kinds of archosauromorphs (incl. the
> bird Patagopteryx), and they grade into slightly
procoelous-to-amphiplatyan
> forms in a variety of neotheropods.  I find nothing convincing in this
list
> of so-called synapomorphies.  The similarities appear to be pretty
> superficial and homoplasic.

Well, the neural spines are similar in Avimimus and probably some
oviraptorosaurs, but epipophyses that reduced are only known in
Elaphrosaurus, Avimimus and perhaps ornithomimids.  Strongly procoelous
caudals are only found in Patagopteryx among non-alvarezsaurid theropods.
Not really important what other taxa they are found in though, as long as
there is good evidence they evolved convergently.

>      My conclusion is that Alvarezsaurus is fairly closely related to
> segnosaurians, and it would not surprise me if they form a clade.  On the
> other hand, the differences between Alvarezsaurus and Mononykiformes are
> considerable, and I can certainly discuss those when I have more time.  I
> never did think they were related (as I have expressed on this list from
> time to time), and now I am even more convinced such an assemblage is
> polyphyletic.

Here's the big question- WHY?
What CHARACTERS (you know, those things we use to form hypotheses about
phylogenetic relationships) can you present that SUPPORT (that evidence
stuff that gives your view a chance to be taken seriously) your view?  What
characters do oviraptorosaurs, Patagonykus, mononykines and paravians share
that Alvarezsaurus lacks?  Indeed, Alvarezsaurus is actually more bird-like
in a couple characters- supracetabular crest very reduced; no fourth
trochantor.  No matter how potentially homoplasious you think the
alvarezsaurid synapomorphies are, they're better than your nonexistant ones.

>      Order Mononykiformes, is much closer to birds, as is Family
Avimimidae.
>   It would not even surprise me if mononykiforms and Avimimus form a
> holophyletic group.  They are certainly far more alike than either is to
> Alvarezsaurus.  It is really too bad Alvarezsauria is anchored on
> Mononychus, because I think we have another Ornithosuchia problem here.
> Alvarezsaurus may be several outgroups away from Alvarezsauria (if you do
> anchor it on Mononykus).  This is a mess.  Sorry, but EVERYONE doesn't not
> think this is a holophyletic group, and what surprises me is that it has
> gone almost unchallenged after so many different cladistic analyses.

While I like the idea of Avimimus being close to alvarezsaurids, I think
that if it is, it's still outside Alvarezsauridae.  It is never inside the
clade in my analyses, even when it is the alvarezsaurid sister group.
Besides the hyperarctometatarsalian metatarsus and strongly transversely
expanded postacetabular process, Alvarezsaurus is more similar to
mononykines than Avimimus is.  And perhaps I spoke to quickly, EVERYONE who
has used proper phylogenetic principles (and some who haven't- Sereno,
Martin, etc.) agrees mononykines are alvarezsaurids.  The sad thing is, you
could have actually argued your case well, by countering that the AMNH team
and Novas only included a few non-alvarezsaurid taxa in their 1996-1998
analyses (tyrannosaurids, ornithomimids, Archaeopteryx, dromaeosaurids,
ornithothoracines), so Alvarezsaurus couldn't help but be sister to
mononykines (sort of like how Ji et al. 1998 didn't give Caudipteryx a
chance to be an oviraptorosaur).  However, more recent analyses, like Norell
et al. 2001 and presumedly Holtz 2001 have properly tested the monophyly of
alvarezsaurids, as has mine.

Nick Longrich wrote-

> Protarchaeopteryx for example has distal carpals 1 and 2, unfused, capping
metacarpals 1 > and 2. The holotype of _Oviraptor philoceratops_ preserves a
full fusion of the carpals
> and metacarpals, forming a carpometacarpus, which has not been reported in
other
> oviraptorids.

Now that's interesting, because both my personal examination of
Protarchaeopteryx and Padian et al. (2001) indicate distal carpals 1 and 2
are fused.  Perhaps you have some insight that would clarify this
discrepancy?
As for Oviraptor, how can you be sure the proximal end of metacarpal II
isn't just expanded more than usual for oviraptorids?  Metacarpals I and III
aren't fused to metacarpal II, so you would expect to see some extension of
the semilunate past the medial edge of metacarpal II, for articulation with
metacarpal I.  But that doesn't occur.

Mickey Mortimer