Re: Bird evolution (long)

["James R. Cunningham" <jrccea@bellsouth.net>]

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I'd like to add a couple of comments about about the potential
aerodynamic function of the half-moon carpals. JRC

> A half-moon shape is a sign that the animal rotates its hand extensively
> in a
> single plane.

In a flying animal, the expected motion would occur along a sector of
the surface of a large radius cone (or similar non-planar surface)
rather than in a single plane.

> In birds the bone enables the flight feathers to be
> tucked
> against the body when the wing is folded. 

It also enables the outer wing to be retracted somewhat in flight, which
enables significant lift and thrust production further into the recovery
stroke before having to reduce the lift coefficient to suppress adverse
thrust late in the recovery stroke.  In cruise, it allows higher speed
flight, providing a reduction in profile drag by decreased span, and for
a given airspeed, it increases the Reynold's number of the flow past the
outer wing by increasing the chord.  For smaller animals, during active
flapping it helps create unsteady effects which produce CL's over twice
those which can be maintained by a fixed wing (example, pidgeon CL ~ 3.4
flapping vs. 1.5 gliding). JRC

> In theropod dinosaurs the bone
> enables the hand  to be tucked against the body while running.

In birds with very high profile drag, it allows net drag reduction
through bounding flight. JRC

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