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Pterosaurs and ABSRD (sensu Williams)
Just some thoughts.
There seems to be growing proof that pterosaurs are derived prolacertiforms.
If correct this would blast, sorry, move pterosaurs out of Archosauria and
Quite a distance phylogenetically. I think this underlines again the
importance of known basal members of a taxon. Without enough knowledge of
these "anchor" members a taxon may move relatively easily inside the
phylogentic tree. Reminds me of e.g. moving Tyrannosauria outside
Maniraptoriformes and Troodontidae into Maniratora (thus killing
Arctometatarsalia?). But Pterosauria is an extreme case.
Regarding the capability of development of hairy or feathery integument: if
pterosaurs did it and dinosaurs too, why not other archosaurs
phylogenetically in between these? Would be nice to find some fossil of e.g.
Euparkeria with some kind of integument.
If Dave Peters is right and Longisquama and Sharovipteryx are also derived
prolacertiforms then ABSRD has another problem. Feduccia wrote in his "The
Origin and Evolution of Birds" that Longisquama, Scleromuchlus and
Megalancosaurus were a disparate group of "avimorph archosaurs" from which
birds are descended. In "Nonavian Feathers in a Late Triassic Archosaur"
(Nature 2000, vol. 288) Longisquama's integumentary appendages were
interpreted as nonavian feathers propably homologous with avian feathers. So
now it's nonavian feathers in a non Archosaur.
But moving pterosaurs into Prolacertiformes is also a kind of BAND Aid. It
can be used as an example of how cladistics can go wrong. It can be argued
that characters used to unite dinosaurs and pterosaurs into Ornithodira are
due to a heavy dose of convergence. That's exactly what e.g. Feduccia says
about birds and nonavian dinosaurs.
On a lighter note,
Timothy Williams coined the term ABSRD (I like that) for
ABSRD = "Anything But a Small Running Dinosaur".
Perhaps this should be changed into
ABSURD = "Anything But a Small Undiscovered Running Dinosaur".
This is because according to ABSRD proponents any discovered non-avian
dinosaur fossil with some kind of feathery integument is either a secondarily
flightless bird or the integument is misinterpreted and anything else but
Heinz Peter Bredow