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Re: Removing segnosaurs from Theropoda



In a message dated 95-08-29 18:56:51 EDT, head@lust.isem.smu.edu (Jason Head)
writes:

>
>        You cannot determine whether or not a character state is convergant
>between two taxa until after your analysis has been performed.  To state
>that a character is homoplasious before hand is an a priori hypothesis,
>which is the staple of religion, NOT science.  It is the analysis that
>determines the status of a character.

Right. I've already done my own analysis, based on characters other than the
interdental plates, and found that segnosaurs fall somewhere in between
prosauropods and ornithischians within the monophyletic clade
Phytodinosauria. The fact that interdental plates occur in prosauropods (let
alone proterosuchians) demolishes the use of interdental plates, as such, as
a synapomorphy uniting segnosaurs with theropods, and the fact that the
interdental plates of segnosaurs quite strongly resemble those of
prosauropods and do not resemble those of most theropods supports (weakly or
strongly) my contention that prosauropods and segnosaurs share a close common
ancestry. This is all pretty elementary stuff, I think.

I have yet to find a character or suite of characters whose distribution
within Dinosauria would render Phytodinosauria paraphyletic or polyphyletic.
I have yet to find a character or suite of characters whose distribution
within Dinosauria would render Saurischia monophyletic. I'm still looking,
and if I do find such a character or suite of characters, I will certainly
change my opinion about dinosaur phylogeny; but as time goes on, it is
becoming less and less likely.

G.O.