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Re: Pterosaur wing - Part 2 - cont'd.

Sorry about the delay, but I was actually working for a change!

----- Original Message -----
From: "James R. Cunningham" <jrccea@bellsouth.net>
To: "Chris Bennett" <cbennett@bridgeport.edu>; <dinosaur@usc.edu>
Sent: Friday, November 14, 2003 12:41 PM
Subject: Re: Pterosaur wing - Part 2

> ......
> > The active addutcion in the vertical plane that you see as desireable is
> > movement that as far as I know is not possible for any tetrapod, and one
> > that is my opinion was severely limited by ligaments in just the same
> > that flexion and extension in the horizontal plane is.
> I can't prove active muscle attachments at the moment, but the adduction
> in the vertical plane does appear to be articularly possible, at least
> in the skeleton I have here.  It sure would be desireable both
> aerodynamically and structurally, but I realize that that is not the
> same thing as being possible.  I do believe the possibility should
> continue to be investigated and the consequnces determined (some of the
> consequences are already pretty obvious, the ability to minimize the
> increase of spanwise tension during roll commands being one, and the
> minimization of the increase in spanwise tension during gusts being
> another.

I will keep your desire for active adduction in mind as I examine
interphalangeal joints in the future.

> ......
> > No, the joints are not at right angles to one another.  In the typical
> > non-pterosaurian tetrapod flexion and extension of the
> > and interphalangeal joints all takes place in the same plane.  For
> > if you place your hand flat on a horizontal surface flexion and
extension of
> > the metacarpophalangeal and interphalangeal joints would occur in a
> > plane, and the metacarpophalangeal joints could adduct and abduct in a
> > horizontal plane.  In the pterosaurian wing digit the situation is the
> > except that the entire digit has been rotated roughly 180 degrees about
> > long axis of the metacarpal.  That rotation does not change the fact
> > the metacarpophalngeal and interphalangeal jonts all move in the same
> Let me rephrase.  the IP joint lengths along the vertical axis of the
> wingfinger have now become long and relatively straignt so that the
> phalanges can no longer flex fore and aft.  I think we agree on that.
> The IP joints along the horizontal axis have now become relatively
> short, so that when the wingfinger is held horizontal, they provide
> little if any resistance to downward movements (they don't allow upward
> movements above the the horizontal, where by horizontal I mean beyond
> straight extension).  Again, I tend to think they may be able to
> actively flex in that downward direction because of the structural and
> aerodynamic advantages associated with the motion and because the joints
> appear to allow it.  I do not have proof in the form of muscle or tendon
> attachment markings.

What are the horizontal and vertical components of the load on the IP joints
in flight?  I would think that the vertical component from lift and down
flap would considerably exceed the horizontal component from tension in the
patagium, but I suppose it is possible the that might not be the case as
some of the vertical load on the patagium should be converted to horizontal
load on the wingfinger.  My knee jerk explanation for the shape difference
between IP joints 1 and 2 on the one hand and IP joint 3 on the other is
streamlining.  What would be the aerodynamic effect of a circular IP joint
with diameter equal to the greater diameter of the oval 1st and 2nd IP
joints?  Turbulence and flow disruption?

> > > Why would the muscles not have made the same adjustment that the
> > > articulations did?
> >
> > I assume they did, just following along with the rotation.
> >
> > > This is an area where you know far more than I do,
> > > but it appears to me that the orientation of the articulation between
> > > the MC & Ph1 rotated by 90 degrees, while the outer rotations remained
> > > unchanged.  This seems easier for me to visualise than the alternative
> > > that the MC/Ph1 orientation remained unchanged and all the outboard
> > > joints in all fingers rotated 90 degrees.
> >
> > I do not see any rotation of the phalangeal relative to the metacarpal.
> > is rotation of the metacarpal rotation the entire finger.
> Do you agree that the IP joints morphed so that they became broader and
> fixed in the fore-aft direction while becoming narrower in the up-down
> direction?  I may not have phrased it well, but it is a sincere
> question, not facetious.


> > > In quetz that joint looks like two golf tees crammed together head to
> > > head.  I don't think it was going anywhere in any direction or
> > > rotation.  It looks fixed to me. Phalange compressive stresses were
> > > substantial in this region due to the intense increase in membrane
> > > tensile stress at the tip (alleviated by the actinofibrils of course).
> > > think that if this joint were allowed to bend or rotate substantially
> > > any direction, it would have collapsed.
> >
> > What 'it'?  the IP joint or the distal phalanx?  If the joint, then why
> > would it be more susceptible to failure than the more proximal joints?
> 'It' the PhIV-3&4 joint.  It was in an area of greater surrounding
> tensile stress (not tensile force) and load offset than the more
> proximal joints and was in a location more prone to external impact.


> However, I'm open to input.  The joint is relatively far more robust
> both vertically and horizontally than the more proximal joints, to an
> extent that there must be a reason or reasons.  What might some of those
> reasons be?

No need to streamline?

> > > I agree that that did contribute, in the amount of about 15-18 degrees
> > > of rotation about the long axis.  But that rotation isn't always
> > > suitable for modulating gust loading.
> > >
> >
> > Good.
> Good that I agree, or good that the rotation isn't always suitable for
> modulating the gust loading? :-)
> Sorry, I couldn't resist that.  I never could pass up a straight line.

Good that you agree that I was right that it could contribute even though I
acknowledge that a contribution to a solution is not necessarily the entire

> > Well, can pterosaurs get by without active adduction of the joints?
> One of the things I'm working on now.  The need for active IP adduction
> becomes more important with increasing wingloading.  It wouldn't matter
> much to a small to mid-sized pterosaur, but may well matter to the
> giants, and may allow increased mass and wingspan.

Well you keep working on it while I look for evidence for or against active
adduction in IP joints.


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