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re: AT LAST!! WAIR (in pterosaur too?)



The ancestral condition of the flight membrane in pterosaurs is the
subject of

Peters, D. (2002) A New Model for the Evolution of the Pterosaur
Wing?with a twist. Historical Biology, Vol. 15, pp. 277?301

A close sister taxon of pterosaurs, Sharovipteryx, has only one digit
(IV) preserved, but not in its entirety. The humerus, ulna, radius and
phalanges 4.2, 4.3, 4.4, and the ungual 4.5  are present either on the
left or right or both. In proportion to the body, digit IV is no bigger
than in a typical prolacertiform. In proportion to the humerus, the
finger has pterosaurian proportions ~ which suggests that Sharovipteryx
has a vestigial forelimb, having given up flapping with its forelimb for
running and gliding with its hind limbs chiefly. I say chiefly because
the forelimb may have been provided with a small (unpreserved) membrane
and if so would have functioned as a small canard wing. In addition, or
alone, the wrinkled neck skin, already more than five times wider than
the slender cervicals as preserved, could have been stretched further
laterally by the elongated hyoids and ceratobranchials which invade it.
In this way the cobra-like neck skin could have served as a strake, an
aerodynamic device seen in a number of modern jet aircraft. Because the
neck is highly maneuverable in the sagittal plane, such a strake would
have made a highly effective elevator to help control angle of attack at
the main wings, the hind limbs.

What this means concerning pterosaurs, is that evidence for the
ancestral condition in pterosaurs is demonstrated in Sharovipteryx in
which the hind limbs  and fore limbs are not incorporated, but rather
the fore and hind limb membranes has separate origins and complete
independence.

But the real novelty of pterosaur wings (as far as traditional dogma
goes) is that the wing membrane probably developed distally first and
proceeded proximally. In this way, perhaps, it found homology in bird
wing development.

David Peters
St. Louis