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Re: Pygostyle

Why do you say unequiviocally that only advanced birds have pygostyles?  

Could this be due simply to preservation bias and we had not as yet
found any primitive/more basal birds with pygostyles?  
So we could perhaps add another far reaching effect (conclusion?) you
did not mention:

g) the pygostyle is not diagnostic of advanced birds if later non-avian
birdforms have retained it from this earlier state.


dbensen wrote:
> I disagree here.  Things like that DO mean something because it seems that
> ONLY ADVANCED BIRDS have pygostyles.  If the oviraptor was taken alone, then
> that would work out; the oviraptor is a flightless bird that hasn't lost a
> feature of its ancestors.  However, less advanced (more basal, whatever)
> oviraptors than this one DO NOT have pygostyles, and so we know that the
> feature is not  something from its ancestors.  This fossil has very far
> reaching effects as I see it.  Either
> a) GS Paul (and other's) hypothesis that the oviraptors are flightless birds
> is wrong (I certainly hope it isn't), or
> b) the pygostiles are convergent (is such a feature useful enough to be
> evolved independently?  Do regular pygostiles and the oviraptor's share enough
> features that we know they are actually the same, not just superficially
> similar structures?)
> c) Caudipteryx and all the other dinosaurs we consider more basal than this
> unnamed one are actually more derived and have lost this pygostyle (doubtful,
> since they were earlier than the unnamed one and we more primitive in many
> respects)
> e) This thing isn't an oviraptor at all (I don't think so, but how much do we
> REALLY KNOW about this creature.  "So mister Oviraptor, if that _is_ your real
> name . . .":)
> f)The pygostyle was glued on by a Chinese farmer or a graduate student (You
> know those farmers:)
> As I look at this list, I think that a or b is the most probable solution
> (given Occam's razor, a is the best), but I really like Dr. Paul's theory
> about flightless birds and it makes sense in every other instance.  I hope
> that there is just a simple answer that I haven't thought of.
> Dan

Flying Goat Graphics
(Society of Vertebrate Paleontology member)