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Re: Removing segnosaurs from Theropoda



>From: head@lust.isem.smu.edu (Jason Head)
 > >  In addition,
 > >how does one use the indentary plates of "thecodontia" to resolve
 > >dinosaurian systematics, when the plates appear and disappear throughout
 > >the various lineages so paraphyletically defined?  Which member of the
 > >thecodonts will you use for your outgroup(s): aetosaurs? riojasuchids?
 > >Rutiodon? 

In constructung a cladogram I do not use paraphyletic groups.
In fact I prefer not to use groups at all - just individual species.

 > > Using paraphyletic groups in fine for paleontology in
 > >situations where you want to discuss a lineage of critters, w/ out
 > >involving their DIRECT descendants.  That was the crux of my posting a few
 > >weeks back. 

They are also useful for defining cohesive, maximally similar groups
among living forms.

 > >  What, besides Triassic extinctions, can be discussed about
 > >thecodonts, that doesn't also imply dinos', pterosaurs, and crocs'?  If
 > >you want to snip birds off of the dino' tree to talk about the big, dead
 > >fellas, fine- but to snip dinos' pteros' AND crocs' off of archosauria (ne
 > >"thecodontia")?  What information will that give you?

Potentially lot.  Try reading chapters 9 & 10 of Mayr and Ashlock, 1991
(I think that's the year) - _Principles of Systematic Zoology, 2nd Ed._.

Or even better, read Kent Carpenter, 1993 in Syst. Biol. 42(2),
pp 142-154

The only point I will admit here is that I have not yet performed an
actual informaion content analysis of the division I proposed.  It
is possible that when this becomes possible, I will revise my
classification.

In general, however, the thecodontians are a collection of quadrupedal,
semi-erect archosaurians with no special locomotory adaptations.
[Hmm, on this basis, Olshevsky's inclusion of the crocodylians there
may be appropriate].

swf@elsegundoca.attgis.com              sarima@netcom.com

The peace of God be with you.