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Re: Phytodinosauria status



Mickey Mortimer (mickey_mortimer11@email.msn.com) wrote:

<<Also, I see no reason ornithischians would have to evolve 
dinosaurian characters independently of saurichians, as the
near-universal consensus is that Dinosauria is monophyletic and
the two are sister groups.>>

  Not to trounce on Mickey, but to argue that Dinosauria is
monophyletic is irrelevant to the comment. George assumes it to
be so, so we're working on where the major splits are. However,
this is a functional consideration.

 George Olshevsky (Dinogeorge@aol.com) wrote:

<For one thing, ornithischians have to lose the fifth toe
independently of the saurischians, since sauropods still have
it. Not impossible, of course, but it makes you wonder.>

  But, it has happened. Evolutionarily, that which is not used,
is lost.

<How odd to group obligatory quadrupedal dinosaurs with
obligatory bipedal dinosaurs, and leave facultatively bipedal
dinosaurs outside these groups instead of between them, where
you might readily expect them to go.>

  All basal dinosaurs, whether ornithischian, sauropodomorphan,
or theropodan, are basally obligate bipeds; faculative
bipedality in basal thyreophores, marginocephalians, and
iguanodontians is not considered implausible based on the weight
of evidence that they split off separate and all evolved
obligate quadrupeds. Only iguanodontians retain a number of
faculative quadrupeds. Sauropodomorphans are obligate quadrupeds
rather early on, and even plateosaurs (independantly) appear to
have obligate quadrupeds (melanorosaurs, blikanasaurs?). This is
size related, and trends toward immense size without
quadrupedality is almost unheard of.

=====
Jaime A. Headden

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

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