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Re: ORNITHISCHIANS :-)



George Olshevsky (dinogeorge@usc.edu) wrote:

<This is not a character I would use. The acetabulum is partly
closed in all stegosaurs by an acetabular pocket off the
pubis--an enlargement of the pubic peduncle--which is a good
stegosaur apomorphy (literally all known stegos have it). There
is nothing like this in any ornithopod, or in any other
ornithischians for that matter.>

  Nope; this makes it autosynapomorphic and useless for outgroup
comparisons. A nice Stegosauria autapomorphy, but that's it. It
should be noted that Minmi, on which I've spent some time, has a
postpubic process, and despite its skull, is a fairly primitive
animal. The pelvis looks like stegosaurs only horizontally
expanded, but not by much.

  Synapomorphies of Thyreophora include:
  1. teeth bear distinct cingulum.
  2. ascending process of jugal broader than craniocaudal
distance.
  3. Sagittal dermal armor with keels and ventral excavations.
  4. More than one row of evenly spaced, arrayed armor alligned
into columns and rows [reversed in stegosaurids].
  5. More than 1 supraorbital ossification, as broad as the
postorbital or wider.
  6. Dorsal cranial surface ornamented with channels, grooves,
or more elaborate systems.
  7. Sacral centra wider than high.
  8.  Trunk elongate, supposedly increasing gut size, advent of
strict herbivory.
  9. Sigmoid maxillary/dentary tooth rows.
  10. No obturator process.

  *Scutellosaurus* actually lacks the "typical" stegosaurian
pubis, even though it is elongated and level with the ischium at
the distal end, as is *Scelidosaurus.* The ilia of both lack the
lateral overhang of the ilia in ankylosaurs and stegosaurs, and
both *Scelidosaurus* and *Scutellosaurus* lack the pubic
acetabular "tab".

  Features that unite ankylosaurs and stegosaurs include the
parasagittal arrangement of armor, the excessive broadening of
the skull so that the intraorbital width at the supraorbitals is
the widest portion of the skull, the overhanging ilia, robust
ulnae with convex external margins and huge olecranal expanse,
mediolaterally expanded tibia so that width equals or so the
craniocaudal length of the proximal end, mediolaterally expanded
calcaneum (resulting in Sereno's use of the name Eurypoda for
this group), and the parascapular spines.

  Strictly speaking, this is a robustly and well supported
group. I am currently working on mucking around in Sereno's 1999
matrices by adding taxa and some of my own characters. I am
always testing for polyphyly, so will try to see if the _for_
characters are outweighed by the _against_ characters. Here are
10 characters that support Thyreophora, and some that support a
Eurypoda exclusive of *Scelidosaurus* and *Scutellosaurus*. I
would enjoy any help in trying to place any group elsewhere....

----

  Hmm, btw, does anyone familiar with PAUP* know the means of
setting "ord" AND "unord" characters in the same matrix? The
manual does not seem to have any help in this regard.

=====
Jaime A. Headden

  Aaaaaaaaaaaaaaaaaaaahhhhhhhhhhhhhhhhhhr-gen-ti-na
  Where the Wind Comes Sweeping Down the Pampas!!!!

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