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RE: Tawa hallae: everything you know about basal saurischians is wrong...
Mike Taylor wrote:
<Well, yes; the forelimbs of birds and bats are homologous; but the character
"forelimbs modified into wings" is NOT homologous in those taxa. So although
you're right that a character either is or not a homology with no intermediate
states, we do need to be a bit careful about exactly what we're saying is the
homologous thing -- in this case, the existence of the forelimbs, or their
modification for flight.>
Ah, an analogous function for nonhomologous structure deriving from an
homologous system (of bones).
Not only is the functional anatomy and behavioral use of the forelimb a host
of derived features, they are overlapping complexes of chaarcters that are hard
to fully disengage. The entire forelimb, shoulder, sternal complex, gastralia,
pelvis portions of the hindlimb, dorsosacral, and caudal vertebrae are all
involved in the avian flight apparatus, and appear to have been from very close
to the beginning of flight or wing-assisted movement, or the first organ to be
called a "wing" in dinosaurs. Bats, on the other hand, have a more
fundamentally involved system as it incorporates more of the hind limb
initially (apparently) while lacking many of the precursorial qualities that
birds developed from in regards to things like the vertebrae, the pneumatic
pelvic-driven gastric and forelimb-driven sternal/furcular pumps, etc.
Indeed, Gauthier's "forelimbs modifed for flight" feature that defined
Avialae in the beginning would almost certainly have to be abandoned due to
such a mess of applicability and comparability, not to mention the hundreds of
distinct traits involved in birds alone.
Jaime A. Headden
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