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Re: dinosaur synapomorphies? (especially postfrontals)



Ken Kinman (kinman@hotmail.com) wrote:

<Well I think Jaime hit the nail right on the head.  The similarities between 
dinosaurs and basal
Crurotarsi need to be very carefully reexamined. This especially true in view 
of the collapse of
Ornithodira (sensu Sereno), which was purportedly sister group to Crurotarsi. 
In fact, I think 
Crurotarsi is even in more jeopardy than Dinosauria.>

  As Chris said, Dinosauria is not in jeopardy unless you can find an alternate 
placement that
corrupts the character assignments and polarities. Until a contravening 
hypothesis can be
formulated (you have only attempted to destabilize characters based on "weight" 
which is
subjective to the mind) Dinosauria is stable and valid. So goes Crurotarsi and 
Archosauria. Dave
Peters finds a destabilizing position for Ornithodira and places Pterosaurs 
with protorosaurs, and
this provides the alternate hypothesis condition. Plus his characters have 
great consistency,
whereas the majority of Ornithodiran features are plesiomorphic, as in the 
sigmoid neck (oddly,
basal pterosaurs lack a sigmoid neck whereas basal archosauriforms have a 
slight one (like
*Euparkeria*, archosaurs like *Postosuchus*), suggesting this is not an strict 
ornithodiran
feature), or convergent features like the mesotarsal ankle, approached in some 
prolacertiforms and
archosauromorphs, and best used as a Dinosauromorph feature, or qualities of 
the hips which are
inferred as bipedal adaptations, hence the appearance in Archosauromorpha 
throughout multiple
lineages that are not otherwise allied.

  Which is what I tried to suggest earlier and thus I do not understand why Ken 
is implying I was
saying Crurotarsi needs to be looked at... Basal dinosaurs and dinosauromorphs 
will have
similarities to basal crurotarsans/pseudosuchians based on phyletic distance 
(they are both stems
of the same ancestor, there will be plesiomorphies that unite them, and these 
are normally
synapomorphic of Archosauria.

<I'm beginning to think that any large clade based on morphology of ankles or 
toes is likely to be
stuck clear up to its sternum or clavicles in a morass of homoplasy. What Dave 
did to ornithodiran
synapomorphies is very likely to happen to Crurotarsi, and I'm obviously still 
having doubts about
Dinosauria as well.>

  May I ask why you doubt the monophyly of these features? I'd like to think 
you are versed in the
gross anatomy of fossils with which to test convergence or homplasy among 
bones, but cannot see
how you are versing weight of features when polarity is all you can test in 
these taxa.

  Until then,


=====
Jaime A. Headden

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

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