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Re: Say this slowly: theropoda is paraphylitic, theropoda is paraphlyitic.....



Doc Tom Holtz wrote:

<<As for your idea that Theropoda is polyphyletic: it
is to laugh, not to put too fine a point on it. 
Polyphyly of Primates or of Cetacea seems more likely
than a polyphyletic Theropoda: the theropods were very
much variations on the same detailed anatomical
design.>>

<Let's see, I get told that the term  paraphyletic is
actually the term polyphyletic. right then you tell me
that it isn't. Hmmmmm......>

  I think there's a misunderstanding or some thing
that is inducing a state of facetiousness in some
members of the list on this topic.

  Polyphyletism is what Mr. Lurio agreed his theory
represented: a multiple series of evolutionary
sidelines being grouped into a whole, rather than
representing a monophyletic whole. Whereas
paraphyletism is two convergent lineages grouped into
a monophyletic whole.

  Saying *Marasuchus* is a herrerasaurid is a
refuteable paraphyletic hypothesis. Saying that
*Ornithosuchus*, *Poposaurus* (or the way cooler
*Vjushkovia*), and *Parasuchus* are crocodiles is a
refutable polyphyletic whole. There are convergences,
but multiple, repeatable tests have come to the same
conclusion: these are not groups that find a natural
clade. Anatomy precludes their being more closely
related than the serial whole. Thus, *Marasuchus* is
most likely not a herrerasaurid since, based on the
shared anatomy of *Caseosaurus*, *Herrerasaurus*,
*Staurikosaurus*, *Aliwalia*, etc., *Marasuchus* lacks
so many qualities to suggest it is more closely
related to these forms than is, say, *Eoraptor*; a
host of data suggest that the latter form is not a
herrerasaurid (See Sereno et al., 1993, on *Eoraptor*;
Novas and Sereno, 1993, and Novas, 1994, on
*Herrerasaurus*) Further, some analyses suggest that
both taxa may not be theropods, based on the
definition (which is essentially {birds >
sauropodomorphs}).

  It can be assumed under these analyses that the
basal radiation of dinosaurs was predatory and
cursorial (ie, bipedal). Working our way down the
stems, down to Ornithosuchia, it is clear that many of
these forms are bipedal, yet lack many other
dinosaurian innovations, which were elaborated on
earlier this and last month (check the archives); a
partial perforation of the acetabulum is a feature
that suggests that *Marasuchus*, *Psuedolagosuchus*,
*Eoraptor*, *Herrerasaurus*, sauropodomorphs,
ornithischians, and theropods form a natural group.
There are about 10 other features that have only been
reversed among dinosaurs (the perforate acetabulum is
lacking in most avians and in ankylosaurids) but these
forms have been demonstrated as being dinosaurian in
nature, based on _that_ definition. Diagnoses can
change, but for stability of a name, the definition
must be final (there are provisions, I'm sure, to
names that are invalid = "Caenagnathus", or nominally
problematic = *Titanosaurus*, etc.).

<this is getting old. When further reserch confirms my
beliefs, then we'll talk...>

  It would be unwise to dismiss the findings of
previous analyses. Test them objectively. Subject your
own doubts to your own hypothesis, test it rigorously.
In Doc Tom's defense, he has been saying this for
years on the list. Do not take a stance you cannot
back down out of, especially in a field as theoretical
as phylogentic taxonomy.

  I will say this, and this is something I had hoped
would be pointed out previously, but to no avail: is
it possible that the numerous convergences with which
you note may be related to the plesiomorphies
("primitive" features also present in outgroups)
inherent in many primitive dinosaurs, and thus would
lead one to suggest polyphyly? This is usually the
first test in a phylogeny.

  I personally hope to refute the idea that the
proximodorsal flange above the articular face in manal
claws is a synapomorphy of oviraptorosaurs, because it
is present in ornithomimids, troodontids,
therizinosauroids, and some other stranger forms, but
that is a story for another time.

  Be objective, Eric Lurio, because a position built
on a wall of sand is an indefensible position. You
need to solidy your hypothesis with tests, and if that
cannot be done, abandon it.

=====
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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