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

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

I'll try and double up on this reply:
>
> With respect to Theropoda, cladistic analysis hasn't turned up anything
> strikingly new and basically confirms Barsbold's 1983 phylogeny,
> which was
> done without cladistics, the "old fashioned way."

In point of fact, and with due respect to Barsbold, this is crap.
Barsbold's study was useful for setting up a situation where you could list
names, and it was good in showing that there was more diversity in
anatomical form than a two-fold Big Guy-Small Guy set up: however, it said
practically nothing about the recovery of the history of the theropods or
the transitions of anatomical forms and functions through time.  A bunch of
bubbles popping out of the same base was not helpful in this sense.

> We need
> to find some
> good specimens of key transitional early theropods in order to
> resolve their
> phylogeny through the noise of convergence and homoplasy.

I agree with this to a certain degree: recovery of early members of the
major lineages will go GREATLY to resolving current contraversies!!


Tracy writes:
>Crazy, that's to kind a word. I've just seen an article redescribing a
>Jurassic lizard with 100 or so characters The Character matrix is nearly as
>long as the article. It's getting way out of hand.

You know something: it's a sad day when people who purport to be interested
in science are afraid of "too much information."

To put this another way, my Gaia matrix is 41x386.  That is less than 10
characters per operational taxonomic units.

>Tom says his article in
>Gaia is going to torn apart at the SVP. Give me a break!!!

Okay, I was being OVERLY harsh to my own work.

In support of theropod systematics, it is *VASTLY* more stable than (say)
eutherian systematics.  Even if coelophysoids and neoceratosaurs don't form
a clade, they are still found in all analyses in the same general sector of
the tree: no one finds (for example) coelophysoids closer to birds than to
dromaeosaurs, for instance.  Furthermore, although unresolved, the basal
tetanurines seem to fall outside _Allosaurus_+birds, with one or two
potential exceptions.  All three models of the position of tyrannosaurids
(just outside Maniraptoriformes, as primitive arctomets, as primitive
maniraptorans) are just a node or two away from each other.  Almost all
studies have found the structure Ornithomimidae + (Oviraptorosauria +
(Dromaeosauridae + Avialae)); my 1994 study didn't, but correction and
addition of various observations brought my results in line with most
everyone elses.

Where conflict does exist, it gives us specific research topics to
investigate: alvarezsaurids and troodontids and therizinosauroids come to
mind.

Contrast the above to the situation in Eutheria or in Neognathae, and you'll
see that we general theropod systematicists are in agreement over the basic
structure; it is the nitty gritty details that have to be sorted out, and
this means looking at the fine-level structure of anatomy and phylogeny.

>It's constantly
>changing. Now instead of naming a node, cladis just say unnamed node. They
>don't have to worry about Order, Family, etc. so they just place new nodes
>were ever they want. Its frustrating, especially for me because I'm trying
>to put together a complete taxa list for all the named Paleozoic and
>Mesozoic tetrapods (I believe I've done it, using both Cladist and Linnean
>systems).

If we were following George's suggestion, you would wait until all possible
Paleozoic and Mesozoic tetrapods were discovered, and only then make your
list.  After all, the rate at which new pre-Cenozoic taxa are found is at
least as fast (if not faster) then the rate of publication of new
characters!!

                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


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