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Re: Fate of Protoarchaeopteryx(Pygostyle origins?)
From: "Jaime A. Headden" <firstname.lastname@example.org>
Related ness of type of pygostyles depends on use; we can
posit that the tails of ankylosaurs and *Nomingia* are not
comparable, but can we posit the same for *Nomingia* and birds?
What is the evidence that the classical avian pygostyle evolved as a
locomotor adaptation. Currently this hypothsis has not been tested. It is
clear that though Archaeopteryx lacked a pygostyle it could fly. Now both in
the avian lineage and the oviraptorosaur lineage we observe the same same
pattern- earlier less derived forms with long tails and feathers on them. In
some latter derived forms we see the pygostyle supporting a feather fan.
Given that all current phylogenetic analysis strongly suggests that origin
of flight was merely an oppportunistic sideshow of the insulation problem.
Further two fairly distinct early forms like Protopteryx and Confuciusornis
show long tail feathers. Thus an equally likely scenarios is that pygostyles
had nothing to do with flight to start with but with intraspecific display.
This intraspecific display fuled much of the evolution flight through
recycling. Looking a something as big as Unenlagia with all its bird like
features of its pectoral region does it even make sense that flight was the
principle selective force? So we may have the following 'exaptive' scenario:
Insulation selects for hair formation->selection for better insulation:hairs
branch->downy feathers->feathers recylced for display: various long feathers
formats emerge like the Caudipteryx variety and the Protopteryx
variety->Long features provide a selective advantage in provinding lift in
leaps->leaps to flight. The pygotysle independently emerges for display->
recycled in avian theropods for flight.
Finally thanks to Mr. Mortimer for his clarifications on PA
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