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

["Jaime A. Headden" <qilongia@yahoo.com>]

Tracy Ford wrote:

<When you have a system that will tell you one group of animals, when
just the skull is used, is more closely related to the parareptilia,
and then when another author uses the skeleton, the animals come out
closer to lepidosauria. There is (AFIK) now consensus of characters
used. I would like there to be one.>

  What concensus? The various interpretations are fed from different
portions of the skeleton. One cannot say that the skull would possess
all the viable phylogenetic information of a taxon. If one feeds a
skull table into a matrix, and out pops this series of trees, then
takes _just_ the skeleton, and out pops another set of trees, or when
one combines them, and theres this third set, and they all differ, one
has just shown tha different portions of an animal contain information
subjective to one another. The skeleton may be more plesiomorphic than
the skull, for instance, which is the case in ceratopsids -- there are
virtually no centrosaurines distinguished from one another based on
postcrania. Temporal and stratigraphic knowledge become the basis for
evaluating the form. Same for non-maniraptoriform coelurosaurs, which
have so many similar conditions of the postcrania (without good skull
info in most recognized forms) that it is no wonder Mickey Mortimer
finds polytomies in this section of theropod phylogeny. Different
pulses of evolution and pressures of use are probably the reason why
Upchurch (1998) and Wilson and Sereno (1998) don't agree. If one were
to assume that certain features in forms would not be present, then
trees are biased not becuase of "tweaking" but because of initial data
input. Now correct me if I'm wrong, anyone, but the purpose of fixing
certain branches and tweaking certain characters in a matrix is to test
the subjectivity of characters and taxa? Isn't that what Holtz' (1999)
poster in Denver said ... in one way or another? This allows the
observer to understand the importance of character, whether its
subjectivity is due to coding, weight, etc..

<Then I would in brace it more. But there are hundreds of trees,
depending on which characters you use, which out groups you use, which
similar animals you use. Mononykus, what is it either a bird (one
author uses the PAUP) or a dinosaur (another author uses the PAUP, with
the same animal). How can this be correct?>

  Sereno (1999) did not use the same characters that Norell et al.
(1996) or Novas (1996) did. Not all of them, anyway. That was probably
a test to see the strength of *Mononykus,* rather than anything else.
That he named a taxon after it ... that's questionable, as is the
segregation of his analysis and then conjoining, there is an assumption
of descent in certain groups. *Guaibasaurus*, *Teyuwasu*, the use of
some of the higher content OTU's as separate OTU's may clarify basal
saurischians. I hope so. I think *Guaibasaurus* is too theropodan to be
a basal form, based on its shear similarity with herrerasaurs and
coelophysoids. Even coelophysoids are subjectively splittable, as are
the "euhelopodid," "brachiosaurid," and basal titanosaur sauropods,
into an extensive series. And I wouldn't be naming taxa after each
split, you could bet on that.

  Also note that previous statements about new studies refining older
ones. Your [Tracy] own study on dermal armor in ankylosaurs has never
been subjectively tested until now. I _really_ want to see that paper
because I think it is probably a very important study that can be added
to all the braincase and limb diagnoses of ankylosaurs in the past
(Coombs, Maryanska, both, Tatarinov, etc.). I'd also like to sink
*Shanxia* and *Nodocephalosaurus* becuase the paucity of their
diagnoses (two autapomorphies based on cranial armor each) are so
subjective and I would make a horn a diagnostic tool. As in my "Lumping
Taxa" introduction, I have every intention of stating this in more
detail as a perspective bit on my part. For fun. :)

  Problem is, using one single part of the anatomy to define loads of
taxa (skulls, armor, limbs, etc.) is probably quite subjective to
similar taxa of eggs, ichnites, pollen, etc., which are morphotaxa, and
based on trends in similar evolution, not always reflecting the maker's
osseous phylogeny (whatever truth it might have).

<Cladistics is a tool, that's all. How to use the tool can't even be
agreed upon. Some use morphology, others phylogeny.>

  My personal schtick is to use it for analyzing trends in morphology
with selective regions (similar to Gatesy and Middleton's work on limb
sectors in birds), by which multistates would be king -- this would
allow series and groups to be assembled without inferring that a tall
triangular ascending process in a troodontid and a ornithomimosaur are
convergent, whether their phylogeny is or not. Phylogeny would be
subjective to that, and I'd probably leave that to the
phylogeneticists. My outlook is more functional morphology anyway, and
reflects in some of my studies (jaw mechanism in oviraptorosaurs,
etc.).

-------

  My bit, anyway.

=====
Jaime "James" A. Headden

  Dinosaurs are horrible, terrible creatures! Even the
  fluffy ones, the snuggle-up-at-night-with ones. You think
  they're fun and sweet, but watch out for that stray tail
  spike! Down, gaston, down, boy! No, not on top of Momma!

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