RE: Gaia theropod follow-up: a "new" phylogeny

["Thomas R. Holtz, Jr." <tholtz@geol.umd.edu>]

> From: owner-dinosaur@usc.edu [mailto:owner-dinosaur@usc.edu]On Behalf Of
> Dinogeorge@aol.com
>
> Is it just me, or do other people find this endless hunt for ever more
> "characters" just plain CRAZY? The computer will, of course,
> grind out trees
> as long as you give it "characters" to chew on, but do you really
> BELIEVE in
> the resulting phylogenies, or are they just so much nonsense, to
> be discarded
> when the next batch of computer-generated trees, crunching even more
> "characters," emerges? If so, why not hold out until you've found ALL
> possible "characters," grind out the one big tree and be done
> with it?

I lead it to the reader to re-read the above paragraph, substituting the
equally valid words "observations" or "data" for "character", and see how
Dinogeorge's comments are somewhat less-than-useful.

> But
> then how would you CHECK this tree against reality? Are synapomorphy wars
> what the search for truth in paleontology is really like?

Cute phrase, "synapomorphy wars".  However, in truth there is are good
paleobiological reasons to look for more complete distributions of
characters and character complexes.  If we took, as you do (intentionally or
not) a typological approach, then we would *know* that the presence of three
fingers on the manus unites Carnosauria and Coelurosauria (or whatever names
you want to use for them).  Yet the presence of a four-metacarpaled (and
potentially four-fingered) manus in "_Szechuanosaurus" zigongnesis_" is
documented.

We could take the typological approach and say "aha, this specimen does not
fit the features required to be a carnosaur, so it has to be in some other
category".  Or we can take an evolutionary approach, sort out the
distribution to the best of our current ability, and see what results (in
this case, that tridactyly evolves independantly in derived carnosaurs and
in coelurosaurs).

If your goal is recovering the history of life, then I recommend using a
repeatable scientific methodology.  If your goal is nice, neat lists of
names, then typology is fine.

                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