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Re: bird arms



Gavin Rymill (gavin@gavinrymill.com) wrote:

<What is the correct position for the arms and hands of animals
such as Caudipteryx or Sinosauropteryx?

If the radius and ulna of these animals could not cross then
surely the birdlike posture with the arms tucked back is not
possible.>

  Birds cannot cross their radius over the ulna: facets for the
two long bones [ulna and radius] when articulated to the wrist
and humerus force the two elements to persist in a single aspect
of relationship to one another during their entire range of
motion.

<Which leads me to ask whether birds can cross their radius and
ulna to create rotational wing motion during flight, or to fold
them away.>

  This is done more at the wrist and humerus/glenoid
articulation than anywhere else, or at the manal digits which
allow the feather shafts to twist. I know when we try to
approximate arm torsion, it occurs at our elbow, however for
birds this is nigh impossible, and the torsion occurs at the
glenoid, which in us is much more difficult and only slightly possible.

=====
Jaime A. Headden

  Aaaaaaaaaaaaaaaaaaaahhhhhhhhhhhhhhhhhhr-gen-ti-na
  Where the Wind Comes Sweeping Down the Pampas!!!!

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