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Re: bauplan convergence



Ken Kinman wrote:

>I believe protofeathers first evolved for...(snip)...(t)hen the aerodynamic
developments followed.<

The fossil record suggests that the sequence leading up to flapping avian
flight was that the "folding wrist" came first; then feathers, then flapping
flight. I say this based on my understanding that some form of a semilunate
carpal block (which allows the avian "folding wrist" motion) sems to be more
inclusive than the Maniraptora (possibly also within the Allosaurids), that
feathers are found only within the Maniraptora and that the "flapping
shoulder" joint is found only within the Eumaniraptora.

Since we know from living birds that the wrist motion is more important for
thrust production than the flapping shoulder joint, it seems reasonable to
assume that the presence of feathers and a folding wrist somewhere among the
basal Maniraptora(?) introduced aerodynamic advantages for cursorial
manueverability and forward thrust >before< the evolution of flapping
flight.  Enhanced thrust "unloaded" the animal aerodynamically and increased
the potential importance of adaptations that contributed to lift, such as
development of secondary lifting feathers and a flapping shoulder joint.

PTN