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Re: Pterosaur wing membranes (a couple of short questions)



Just back from the excitement in Italy I found:


----- Original Message -----
From: <ee555@freenet.carleton.ca>
To: <dinosaur@usc.edu>
Sent: Thursday, November 06, 2003 5:38 PM
Subject: Pterosaur wing membranes (a couple of short questions)


> I have been thinking about Pterosaur wing structures (and aerodynamics
during the flapping motion), ever since a study that used CAT scans of
pterosaur skulls suggested a quite a different brain structure in pterosaurs
which seemed possibly to indicate a very different form of flight control
from living groups.
>
> So I have a few questions:
>
> Do you have any idea how flexible the outer wing bones are, is it possible
they could be bent or moved independently?


It is generally accepted that almost all pterosaurs had lost the capability
of voluntary motion of the interphalangeal joints.  The articular surfaces
have a large radius and the ligaments presumably could have stretched some
to provide some flexibility so as to prevent fractures of the wing
phalanges.  I discussed this some in the functional morphology part of my
monograph on Pteranodon (Bennett, S. C.  2001. The osteology and functional
morphology of the Late Cretaceous pterosaur Pteranodon.  Palaeontographica,
Abteilung A, 260:1-153).  The wingfinger thus would be somewhat flexible as
a result of the design of the interphalangeal joints and minor flexion of
the phalanges themselves, but could only be flexed and extended voluntarily
at the metacarpophalangeal joint.  There was paper that looked at wing
flexibility some years ago (Sneyd, A. D., M. S. Bundock, and D. Reid. 1982.
Possible effects of wing flexibility on the aerodynamics of Pteranodon.  Am.
Nat. 120 p. 455-477), but it has so much math in it that my eyes just glaze
over and my mind wanders.



> Do you know if there is much evidence of torsional muscles near base of
wing?

The glenohumeral joint of pterosaurs was a somewhat bent saddle joint that
would have allowed considerable rotation of the humerus about its long axis,
and presumably fine control of that rotation as well.  Regarding pectoral
musculature, my reconstruction of pterosaurian pectoral musculature using
the EPB technique has just appeared in the pterosaur symposium volume
(Bennett, S. C.  2003. Morphological evolution of the pectoral girdle of
pterosaurs:  Myology and function.  Pp. 191-215 in Buffetaut, E. and J.-M.
Mazin, eds.  Evolution and Palaeobiology of Pterosaurs. Geological Society
Special Publications 217.  Geological Society of London); watch out, there
is so much dull anatomy in there that there is a good chance that your eyes
will glaze over and your mind will wander!


> Is their any evidence of muscle attachments further along the wing bones
that could either control wing shape through directly flexing the outer wing
bones or directly bending the wing membrane, using muscles built into the
wing?


There is evidence of muscle attachments to move most everything out to and
including the metacarpophalangeal joint.  There is no evidence of muscles to
move interphalangeal joitns of the wing.  It is certainly logical to assume
that there were intrinsic muscle fibers within the wing membrane that could
have controlled its shape.  I discussed this possibility in my paper on
actinofibrils (Bennett, S. C.  2000. Pterosaur flight:  the role of
actinofibrils in wing function.  Historical Biology, 14:255-284).  If I
remember correctly, Unwin and Bakhurina (1994.  Sordes pilosus and the
nature of the pterosaur flight apparatus.  Nature 371:62-64) described small
fibers in the wing of Sordes that in my opinion are not actinofibrils and
might be muscle fibers, though they also might be elastic or collagen
fibres.


>
> It seems clear there is a possibility of wing fibres providing enough
strength to allow the pterosaur to form a somewhat independent shape to
parts of the wing and also allowing different areas to have different levels
of strength. Is this correct?
> Also could it possible for such structures to be used to produce tension
only in some directions, possibly allowing the wing to change shape slightly
if muscles put pressure in at one angle as opposed to another?


See my actinofibril paper cited above.



> Would the wing fibres be springy?


Elastic and collagenous fibers would be springy to varying extents, but
according to my interpretation of actinofibrils they would have functioned
in compression, would have been essentially inextensible, and would not have
been stiff enough to have significantly effected wing camber by themselves.
For alternative view of the pterosaur wing, see also:   Frey, E. and J.
Reiss.  1981.  A new reconstruction of the pterosaur wing.  Neues Jahrbuch
für Geologie und Paläontologie Abhandlungen, 161(1):1-27; and Padian, K. and
J. M. V. Rayner.  1993.  The wings of pterosaurs.  American Journal of
Science, 293-A:91-166.


>
> And most imporantly would the wing taste good?
>

Absolutely, though you've got to get the sauce just right.

Chris


S. Christopher Bennett, Ph.D.
Assistant Professor of Basic Sciences
College of Chiropractic
University of Bridgeport
Bridgeport, CT  06601