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polyphyletic Alvarezsauria assemblage



Mickey, Jaime, and others,
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.
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.
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.
Gotta run,
More later,
Ken


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Mickey Mortimer wrote:
NO ONE has EVER placed Alvarezsaurus close to ANYTHING except for Patagonykus and mononykines. Bonaparte (1991) didn't, but other alvarezsaurids weren't recognized yet. He just put it in Alvarezsauria among theropods, not knowing what it was related to specifically. Why won't you believe the following list of characters connecting Alvarezsaurus to Patagonykus and Mononykinae?

- short and low cervical neural spines (Novas, 1996)
- rudimentary cervical epipophyses (Novas, 1997)
- procoelous sacral vertebrae (Novas, 1996)
- posterior sacral centra transversely compressed (Novas, 1996)
- procoelous caudal vertebrae (Chiappe et al., 1996)
- first caudal centrum keeled ventrally (Chiappe et al., 1998)
- elongate proximal chevrons (Novas, 1996)
- stout, robust manual ungual I, with quadrangular articular surface (Novas, 1996)
- m. cuppedicus fossa of ilium absent (Novas, 1996)
- supracetabular crest ends above acetabulum (Novas, 1996)
- brevis shelf caudolaterally oriented and medial flange ventrally curved (Novas, 1996)
- pubic peduncle anteroventrally projected (Novas, 1996)
- slender pubic peduncle (Novas, 1996)


Sure some have problems, but in general the list seems good to me.  As far
as I know, EVERYONE (and I mean everyone, Holtz, Norell, Sereno, Martin,
Chiappe, etc.) agrees the clade is monophyletic.



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