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Re: FLIGHTLESS BIRDS




Greg Paul wrote:
<<A running theropod evolving flight should have a tail no shorter and a
sternum no longer than Archaeopteryx, lack ossified sternal ribs, have
arms longer than other theropods, aerodynamically asymmetrical arm
feathers, and be an insectivore

> Matthew Troutman wrote:
> Can you give us some reasons for this?  I am as skeptical of the
> 'ground-up' notion as you are, but I see no reason for some of these
> features.  If anything a running protobird such have a shorter tail than
> Archaeopteryx to reduce drag; a longer, larger sternum for the
> attachment of large pectoralis and supracoracoideus muscles; and I see
> no reason why it should lack sternal ribs, which are one of the things
> that help raise and lower the sternum for lung ventilation (can you
> illuminate me?). Speaking logically, these features make no sense.  I do
> think that the 'ground-up' idea is nearly impossible to achieve, but
> these features make little to no sense.

I agree with Greg on this, with the exclusion of ossified sternal ribs,
which I haven't given any thought. Quantitatively, Archie's tail drag isn't
terribly significant. Re difficulty of getting off the ground, keep in mind
that pre-launch airspeed is the sum of running velocity + wind velocity +
transient gust velocity + any velocity due to motion of the wings, and that
lift increases with the SQUARE of airspeed.  With the aid of gusts, getting
off the ground is dead easy.  This is why we tie airplanes down on the apron
(they are prone to leave without us). It's flight control once off that's
difficult. I suggest that you guys apply a conservative running velocity and
a reasonable gust velocity combined with a moderate coefficient of lift and
calculate how much wing area is required to pop the animal up several feet
off the ground, even without flapping, so that he can convert the potential
energy gained back into airspeed, then groundspeed and range.  The answer
will be a stunningly small wing area, even with the reduced density of the
modern atmosphere.
All the best,
JimC