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Re: Silence of the new paper




I forgot to send the response below to the list.
JimC

----- Original Message ----- From: "jrc" <jrccea@bellsouth.net>
To: <mickeyprowe@gmail.com>
Sent: Saturday, December 12, 2009 8:00 AM
Subject: Re: Silence of the new paper

The reconstruction of an anteriorly directed pteroid that I'm most familiar
with had the base of the pteroid placed inappropriately in the preaxial
carpal's articular facet for Sesimoid 'A', and also had the preaxial carpal
itself turned upside down so that that facet was on the antero-ventral
surface rather than the antero-dorsal surface (it was not a particularly
well preserved preaxial carpal), thereby compounding the error.  On at
least one other species, the articular facet for the base of the pteroid is quite
well preserved on the inboard side of the preaxial carpal, thereby
eliminating the possibility of an anteriorly oriented pteroid and requiring
a medial orientation (with considerable mobility).  There is currently an
embargo on the release of previously unpublished information on that
particular species, so I am not at liberty at the moment to show a photo of
the pteroid facet.

As an aside, albeit somewhat speculatively, the robust pneumatic openings in
azhdarchids suggest that leading edge pneumaticity may have been extensive
and transiently pumped by the flight muscles.  That, taken together with the
shape of some pteroids suggest that such leading edge pneumaticity may have
been asymmetricly biased toward the ventral side of the leading edge so that
a powered downstroke would have transiently 'fattened' the leading edge
while the asymmetry simultaneously and transiently increased the leading
edge camber, so that the maximum lift coeffient could be substantially
increased during the downstroke (a little leading edge camber goes a looong
way)

In short, Palmer and Dyke are correct about the medial orientation of the
pteroid, as was Bennett's earlier analysis that demonstrated the medial
orientation.
JimC

----- Original Message ----- From: "Mickey Rowe" <mickeyprowe@gmail.com>
To: <dinosaur@usc.edu>
Sent: Thursday, December 10, 2009 9:21 AM
Subject: Silence of the new paper


Palmer, C. and Dyke, G.J. (in press). "Biomechanics of the unique
pterosaur pteroid", _Proceedings of the Royal Society Series B,
Biological Sciences_, doi: 10.1098/rspb.2009.1899

Abstract

Pterosaurs, flying reptiles from the Mesozoic, had wing membranes that
were supported by their arm bones and a super-elongate fourth finger.
Associated with the wing, pterosaurs also possessed a unique wrist
bone—the pteroid—that functioned to support the forward part of the
membrane in front of the leading edge, the propatagium. Pteroid shape
varies across pterosaurs and reconstructions of its orientation vary
(projecting anteriorly to the wing leading edge or medially, lying
alongside it) and imply differences in the way that pterosaurs
controlled their wings. Here we show, using biomechanical analysis and
considerations of aerodynamic efficiency of a representative
ornithocheirid pterosaur, that an anteriorly orientated pteroid is
highly unlikely. Unless these pterosaurs only flew steadily and had
very low body masses, their pteroids would have been likely to break
if orientated anteriorly; the degree of movement required for a
forward orientation would have introduced extreme membrane strains and
required impractical tensioning in the propatagium membrane. This
result can be generalized for other pterodactyloid pterosaurs because
the resultant geometry of an anteriorly orientated pteroid would have
reduced the aerodynamic performance of all wings and required the same
impractical properties in the propatagium membrane. We demonstrate
quantitatively that the more traditional reconstruction of a medially
orientated pteroid was much more stable both structurally and
aerodynamically, reflecting likely life position.

--
Mickey Rowe     (MickeyPRowe@gmail.com)