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RE: I'm back...



> From: owner-dinosaur@usc.edu [mailto:owner-dinosaur@usc.edu]On Behalf Of
> David Marjanovic
>
> > > - Is it possible that I have found, in the famous illustrations, a
> > > synapomorphy for Arctometatarsalia: a rugose crest in the
> midline on the
> > > nasals? Do troodontids have such a thing (ornithomimo- and
> tyrannosaurs
> > do, dromaeosaurs don't, neither do oviraptorosaurs primitively)?
> >
> > [...] Regarding troodontids, both Byronosaurus and
> > Saurornithoides mongoliensis appear to have smooth nasals.
> While that of
> > Saurornithoides junior looks textured in my bad photocopy, it's
> not rugose
> > in the way tyrannosaurids' are as far as I can tell.
>
> I see. So unless it comes out as an arctometatarsalian synapomorphy,
> reversed in troodontids, in a parsimony analysis, I apparently
> can't use it.

A) That assumes that troodontids are arctometatarsalians, a position no one
I know of currently holds.

B) What do you mean "apparently can't use it"?  Observations are
observations; we don't play the old game (which, sadly, was the operational
paradigm of too many traditional taxonomists, and not a few cladists) of
"counting the hits and ignoring the misses".  If you see a shared feature
with a non-global (for the level you are examining) distribution, it is fair
game as a potential synapomorphy, and should a priori be treated as such.

                Thomas R. Holtz, Jr.
                Vertebrate Paleontologist
Department of Geology           Director, Earth, Life & Time Program
University of Maryland          College Park Scholars
                College Park, MD  20742
http://www.geol.umd.edu/~tholtz/tholtz.htm
http://www.geol.umd.edu/~jmerck/eltsite
Phone:  301-405-4084    Email:  tholtz@geol.umd.edu
Fax (Geol):  301-314-9661       Fax (CPS-ELT): 301-405-0796