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RE: Aves and Mononykus

> From: owner-dinosaur@usc.edu [mailto:owner-dinosaur@usc.edu]On Behalf Of
> Ken Kinman
>      I think Aves should remain as it is.  The cladistic definition
> coincides with what most people (past and present) consider to be
> birds.  We
> have to get use to the fact that characters like feathers and
> four-chambered
> hearts do not set birds apart, just as hair doesn't set the
> mammals apart.

[I snipped the rest, but I agree with it all!!  Well said.]

>      I would like to move on to a discussion of whether Alvarezsaurians
> (incl. Mononykus) belongs in Aves (Chiappe's view) or not
> (Sereno's view).
> I am completely undecided, but I suspect Sereno is probably correct.

Indeed, here is an interesting problem.

First, a clarification (or rather, an update):
Chiappe's latest analyses also find Alvarezsauridae as the sister taxon to
Aves, not within Aves.  Although the analyses themselves are not yet
publised (they are in press), the results are found in the Chiappe et al.'s
paper on confuciusornithids (Bull. AMNH 242).

Independantly of Sereno, I also found a lot of the potential synapomorphies
between Alvarezsauridae and Ornithomimosauria.  In fact, you can look at the
Perez-Moreno et al. description of _Pelecanimimus_ and see these features
pop up in the matrix there.  In my own analyses alvarezsaurids still pop out
as birds, but Sereno has found additional potential features that I have not
yet included in the matrix: we'll see how those affect the topology.

When the Ostrom Symposium volume comes out (supposedly later this year), as
well as the Mesozoic Birds: Above the Heads of Dinosaurs volume (not sure on
the publication date of that one), there will be quite a bit of information
on this topic published.  This includes a possible position different from
either the Chiappe or the Sereno position.

I've said it before, I'll say it again: wherever they fit, alvarezsaurids
are highly derived.  (Gee, go out on a limb, Tom... :-).

                Thomas R. Holtz, Jr.
                Vertebrate Paleontologist
Department of Geology           Director, Earth, Life & Time Program
University of Maryland          College Park Scholars
                College Park, MD  20742
Phone:  301-405-4084    Email:  tholtz@geol.umd.edu
Fax (Geol):  301-314-9661       Fax (CPS-ELT): 301-314-7843>