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Re: Broader than Dinosauria




Jaime,
Thank you for this feedback. I agree that there is not a "single" apparent synapomorphy for dinosaurs (luckily mammalogists do have one for mammals).
However, I do believe that a combination of a few (maybe 3 or 4) of the most significant "synapomorphies" could be combined to make a good case for dinosaur holophyly. What I don't like is a long list which throws the more significant ones in among a bunch of questionable ones.
The long deltopectoral crest is one which I think is significant enough, that it could be combined with a couple of others to clearly differentiate dinosaurs from non-dinosaurs.
Perhaps the astragalar ascending process should be the next one I take a hard look at. But I rejected the "fully open acetabulum" from my list back in 2000 (and Tom Holtz agreed that it probably developed at least three times among dinosaurs), and to me it is still (dare I say it?) "weak", and it detracts from more "significant" characters. I would like to have a highly significant skull character as well, but "vomeral extension" sounds rather nebulous (although if it could be quantified, perhaps it could be shown to be significant).
---Cheers,
Ken
P.S. One correction. I did not include Lagerpetonidae, Lagosuchidae, or Plesion Pseudolagosuchus in the Theropoda, but rather as basal clades of Saurischiformes. I think it may be George who regards lagosuchids as early theropods (but I will need more convincing if I am to do this in my classification). I am open to the idea, but presently that's as far as it goes (and the same applies to the position of Pisanosauridae among ornithischians).
********************************************
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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