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Re: Details on SVP 2002 Part 1

George Olshevsky (Dinogeorge@aol.com) wrote:
<This is not such an odd result; it occurs when you simply remove
Ornithischia from below "Saurischia" up to sisterhood with some clade
within Sauropoda. It still seems pretty clear to me that ornithischians
are derived prosauropods of some basal level of organization (just because
segnosaurs no longer fill the gap doesn't make the gap go away). And then
all those "saurischian synapomorphies" simply become dinosaurian
synapomorphies, some lost (e.g., skeletal pneumaticity) in

  Not to sound dogmatic (because I looked into it, being a doubting thomas
myself) but there has been a strong support for the monophyly of
Saurischia for about 20 years now, going back to Bakker and Galton since
Romer tried to work on the group. Nothing seems most imminently unstable
than placing ornithischians as basal sauropodomorphans or as
"prosauropods." Trancing mutiple lines of evidence (femoral, pelvic,
manus, pes, skull, shoulder, axis) one can see the ultimate dichotomy is
between an ornithischian/saurischian animal; later, a split occurs in the
gracilization of the skeleton into a cursorial one, with prosauropods and
theropods. The root of this tree is *Eoraptor*. Specific specializations
appear to show that changes in the teeth and skull occur along these paths
that do not cross until well into the stems of each lineage. Basal
ornithischians all possess features not seen in any saurischian, and in
fact, not where any saurischian shares a character (except, again, with
very derived taxa). The robusticity of the shared characters, not just the
pelvis, but primarily in the skull and hip/leg (including femur and
tibia), appears to preclude any ornithischian from being a saurischian or
arising from within a traditional saurischian assembly or from any
"saurischian" taxon. If you have special data to support the claim, you
should present it now, or indicate in which available publication this
will be provided. Perhaps you should do a presentation as the St. Louis


Jaime A. Headden

  Little steps are often the hardest to take.  We are too used to making leaps 
in the face of adversity, that a simple skip is so hard to do.  We should all 
learn to walk soft, walk small, see the world around us rather than zoom by it.

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