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Re: Pterosaur wing - Part 2

Chris Bennett wrote:
> Hah!  The original subject line was "a couple of short questions" and look
> what it turned into.

Yes, but it's most interesting -- to me, at least.

> > Again, I think we may be using different terminology for the same
> > motion.  I see the vertical bending of the IP joints as being similar to
> > that in humans with their arms and hands held in the same position.  I
> > would call that flexing, but recognise that my terminology is likely
> > non-standard.  My take is that you are calling it adduction?
> >
> >
> No, we are not using different terminology for the same thing.  IN Part 1 we
> agreed that flexion and extension of the wing phalanges was essentially not
> possible, but that that movement would have been flexion and extension.

At the time I wrote the above (prior to your part 1, I think), I believe
we were using different terminology for the same thing.  After reading
your part 1, I rotated the skeleton in my mind and started using the
same terminology that you are (I think), and we should now be on the
same page in that regard.

> The active addutcion in the vertical plane that you see as desireable is a
> 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 way
> 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
> > > Note that I have sent an
> > > accompanying e-mail message to the dinosaur and vertpaleo listservers to
> > > see anyone knows of any animal that can do it.

A conservative procedure to be sure (and I approve), but I have no doubt
that you are correct in that no other is known at the moment.  How many
other animals need to do it?
> >
> > Good idea.  Humans can do it, with the exception of that proximal swing
> > at the palm, parallel to the palm.  But that isn't the motion we are
> > discussing.
> No, humans cannot actively adduct or abduct the interphalangeal joints.

Again, my post above was written prior to your part 1, and I have since
changed my terminology to match yours, so now agree with you in that
regard.  Humans can flex the interphalangeal joints vertically when the
palm is held down (at 90 degees to the flight position of the 'palm' of
pterosaurs, which is the direction of motion that I was trying to
express, and I agree that humans cannot adduct the IP joints.  They can
however actively adduct the MC/Ph joints (pterosaurs [at least quetz]
don't appear to be able to adduct the MC4/Ph4-1 joint).  I don't know
about the other pterosaur MC-Ph joints (oops - insert.  I just read your
sentence below -- am now interested going back and examining the
original materials for parts of the hand other than the wingfinger.  I
don't have casts of them here and am just looking at photos.

> All
> adduction and abduction takes place at the metacarpophalangeal joints and in
> Part 1 we agreed that the pterosaurian metacarpophalangeal joint did not
> permit adduction and abduction.

True re pterosaurian metacarpophalangeal joint, at least for the
wingfinger -- you're likely right re the others too, since you've
examined them more closely than I have.

> > > 2.  In typical non-pterosaurian tetrapods the metacarpophalangeal joints 
> > > are
> > > provided with interossei muscles, whose action is to adduct and abduct the
> > > digits.  The fourth metacarpophalangeal joint of pterosaurs, the
> > > wing-knuckle, seems to be highly modified so as to essentially lock the
> > > joint in an extended position spreading the patagium.

I agree.  And if I remember correctly part of the modification, the
front flange on Ph4-1 is actually a fused sesemoid (I think that
probably originally came from you, but memory partially fails me).


> I think that I have been aware of that and may even have commented on it in
> my non-aeronautical-engineer kind of way.

I don't remember for sure, but expect you did.  I don't think you would
have missed that.
> > I'm not sure that that gets described as often since it is
> > a vector effect.
> >
> >
> > > Given that
> > > pterosaurs seem to have lost the ability to adduct and abduct the
> > > wing-knuckle even though they presumably inherited muscles to do just
> that
> > > from their non-flying ancestors, it seems unlikely that they would have
> > > evolved other muscles to adduct their IP joints when typical non-flying
> > > vertebrates have no such muscles.
> >
> > But those joint articulations are now at right angles to one another.
> No, the joints are not at right angles to one another.  In the typical
> non-pterosaurian tetrapod flexion and extension of the metacarpophalangeal
> and interphalangeal joints all takes place in the same plane.  For example,
> if you place your hand flat on a horizontal surface flexion and extension of
> the metacarpophalangeal and interphalangeal joints would occur in a vertical
> plane, and the metacarpophalangeal joints could adduct and abduct in a
> horizontal plane.  In the pterosaurian wing digit the situation is the same
> except that the entire digit has been rotated roughly 180 degrees about the
> long axis of the metacarpal.  That rotation does not change the fact that
> the metacarpophalngeal and interphalangeal jonts all move in the same plane.

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.

> > 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.  It
> 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). I
> > think that if this joint were allowed to bend or rotate substantially in
> > 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? 

> > 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.

> 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.

> We have
> always known that Quetzalcoatlus was living pretty close to the limit with
> rather slim margins of safety.  Is this just one more place where they were
> really close to the limit, which most other pterosaurs were safely further
> away from?

Yes, though Quetz isn't really that close to the limit yet (nor all that
far).  Off the top of my head, I think the skeleton could probably be
morphed to allow another couple of meters of wingspan before using up
all the margin (13 meters vs. 11 meters).  That would probably coincide
with a mass increase on the loose order of 50% to 60%.

> I took probability and statistics in college rather than calculus, and it
> has served me well for most things I have wanted to do.  I have once or
> twice attempted to work my way through books that offered "teach yourself
> calc at home the easy way for fun and profit" and I just couldn't handle it.

Chris, I know you well enough to know that you can handle anything you
wish, once you decide you might actually need to or want to.  Calculus
is actually pretty simple, and if I say that, it must indeed be simple,
because I'm a pretty simple-minded guy.  As an aside, I took probability
and statistics too.  Hated every minute of it.  But it came back to
haunt me, because I make a good bit of my living out of probabilistic
stuff. Yuck.

> That's enough for the moment.

Me too.  Little as I want to, gotta work.