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Re: 11th specimen of Archaeopteryx
On 10/27/2011 3:42 AM, Tim Williams wrote:
Yes, there are several lines of evidence that_Archaeopteryx_ was
incapable of sustained, flapping flight._Confuciusornis_ too; and
probably_Sapeornis_ as well. If this is true (and I'm sure not
everyone agrees!) all basal birds might have been gliders.
I am agnostic on the limits on upstroke amplitude in basal birds due to
limited data and skills -- I am just pointing out that if they were
severely limited in the manner that I have read is ascribed to Arch.,
then a path to powered flight that did not initially exploit gravity as
the primary energy source rather than muscle power is not clear -- at
least to me.
Nevertheless, it is possible that these gliders might have used simple
flapping motions in order to gain height or added forward momentum
during the glide.
Yes. Actually, I think that is a safe assumption, unless they were all
dead-enders -- and even then...
It is true that no modern glider engages in flapping behavior.
However, strictly speaking, no modern glider is "passive", because
while airborne they actively regulate aerodynamic forces by movement
of the glide surface(s) - especially towards the end, to shed velocity
prior to landing.
Braking motions could easily be the "basal flap', true -- but the basic
energy source is passive, as opposed to muscle-power.
Erik B. has pointed out the opportunities that accrue to
micro-environments wherein ridge-soaring is a daily or seasonal
phenomenon -- a very nice and possibly novel idea for expanding the
repertoire/habitat of passive glider, but I do not see a way that we
could ever confirm that one.
Again, that is a scenario wherein simultaneous control movements of the
wings could incrementally optimize the 'body and the mind' and lead in
straight-forward fashion to powered flight.