From: "Jaime A. Headden" <qilongia@yahoo.com>
To: dinosaur@usc.edu
CC: kinman@hotmail.com
Subject: Broader than Dinosauria
Date: Fri, 7 Sep 2001 21:16:55 -0700 (PDT)
It is just not a matter of the monophyly of Dinosauria that must be
questioned here, and though
I know that Kinman has included them in Theropoda, the synapomorphies for
the more inclusive
groups to Dinosauria must also be considered. That is, what puts
*Marasuchus*, *Lagerpeton*,
*Pseudolagosuchus*, *Lagosuchus*, and *Lewisuchus* closer to dinosaurs than
to crocodiles. This
means the synapomorphies of Dinosauromorpha and Dinosauriformes must also
be considered along with
those of Dinosauria.
For one thing, a fully perforate acetabulum is present in all except
*Lagerpeton*, and
*Lewisuchus* et al. have the distinct deltopectoral crest, and all have a
tall ascending process
of the astagalus, though *Lagerpeton* [odd name, "crawling bunny" :) ] has
a distinct morphology
that is perhaps not analogous, though homologous, I would code it absent on
this mark. Other
features, including vomeral extension, are unknown. *Lewisuchus* lacks the
apparent postemporal
fenestra, and no dinosaur except for maybe the well-nested and therefore
irrelevant theropod
*Scipionyx* have a postfrontal bone [see DalSasso and Signore, 1996;
Mortimer, pers. comm., 2001,
though I doubt the identification.] All possess a distinct femoral head,
but this _is_ an
adaptation to the position of the femur in a subvertical posture, as is the
"twisted" humeral
shaft to aligning the distal condyles parallel to the humeral head for most
quadrupedal dinosaurs.
I would not use this as an synautapomorphy based on it's functional aspect,
but it _is_ still a
feature not prezent in the immediate outgroups to the included paradigm,
and thus such a feature
becomes a diagnostic synapomorphy. Note: just because a group may reverse a
character state or
present an apomorphy that does not preserve the "original" synapomorphy,
does not mean that the
feature is no longer diagnostic for a group. Thus, it is singularly notable
that there is in fact
not one apparent synapomorphy present in all Dinosauria exclusive of it's
outgroups, or of
Dinosauromorpha, or Dinosauriformes. In this, Tracy is right and
commendably so. It is not
relevant for the reasons given above, addressed both to Tracy and to Ken.
Thanks for the air time...
=====
Jaime A. Headden
Aaaaaaaaaaaaaaaaaaaahhhhhhhhhhhhhhhhhhr-gen-ti-na
Where the Wind Comes Sweeping Down the Pampas!!!!
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