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Re: was: Pterosaur.net now: pteroid



I agree with Mark. It was capable and sound. I'm looking at a left Qsp pteroid placed in the pteroid facet on the inboard face of the preaxial carpal, and it is obvious that although the primary direction of articulation is along the camberline (the camberline passes through the radius), the pteroid is also quite capable of being raised or depressed to some extent at will, which will shift the position of the anterior camberline. I agree with Chris that the muscles which do so are attached to the preaxial carpal and it is also possible that some may in addition, attach to the radius and to the anterior face of proximal metacarpal IV (as far as I know, those latter two attachments are unproven at the moment, but they would help modulate wing swing, pitch orientation, and energy storage and recovery if they do exist).

These orientatons are as would be expected, partially to accomodate the shift in the orientation of the proximal carpal as the elbow is extended or flexed, and partially to adjust the pressure jump between the upper and lower surface of the wing (depressing the pteroid slightly will increase the pressure jump and increase both spanwise and chordwise tension in the inner wing, thereby inhibiting inner wing flutter). It doesn't require much depression to accomplish this, and the pteroid didn't depress very far. The 'line' of the pteroid will remain aligned fairly well with the delto-pectoral crest. When depressed, it does not form a sharp Vee in the leading edge of the propatagium and does not severely stress the propatagium. In quetz, the D-section of the pteroid cross section is structured to accomodate substantial bending in the caudo-ventral direction (mostly caudal), while resisting bending transverse to that axis. It is not fragile, but this might be a good place to mention that Matt's reconstruction showing the pteroid directed forward and down had a rather scruffy preaxial carpal placed upside down on the distal carpal and the pteroid socketed into the sesimoid 'A' facet instead of the pteroid facet.

Note that increasing the camber of the inner wing will increase lift on the inner wing while simultaneously reducing camber and lift of the outer wing (due to the increase in spanwise tension and the corresponding increase in chordwise tension of the outer wing). This means that inner wing lift will increase while the outer wing lift is reduced. Since there are also other mechanisms in play to simulataneously modulate both lift and drag of the wing, the pterioid depression can be used to either facilitate a turn or to inhibit it, at the animal's discretion.

To give another example of the rather odd interplay between wing positioning and forces produced by a membrane wing, a slight retraction of the right wing will create a left roll and left turn. A somewhat greater retraction will create a right roll and right turn. The pteroid can be (and is) used both to create and modulate these and other interactions.
JimC

----- Original Message ----- From: "Mark Witton" <Mark.Witton@port.ac.uk>
To: "David Peters" <davidpeters@att.net>
Cc: <pterosaur.net@googlemail.com>; "Mike Habib" <habib@jhmi.edu>; "dinosaur mailing list" <dinosaur@usc.edu>
Sent: Friday, January 15, 2010 8:36 AM
Subject: Re: was: Pterosaur.net now: pteroid


....it seems to me, therefore, that the weight of evidence indicates that the pteroid was both capable of depressing the propatagium and biomechanically sound enough to do so.

Mark

--

Dr. Mark Witton

Palaeobiology Research Group
School of Earth and Environmental Sciences
University of Portsmouth
Burnaby Building
Burnaby Road
Portsmouth
PO1 3QL

Tel: (44)2392 842418
E-mail: Mark.Witton@port.ac.uk

David Peters <davidpeters@att.net> 15/01/2010 14:04 >>>
Okay, given the grooves, and given the muscles attached to the grooves, which bone did the other end of the muscles attach to and does that attachment provide a ventral vector when pulled? Most reconstructions place the pteroid anterior to the radius while in flight. So... if the pteroid is [somehow] pulled ventrally, how does that affect the sometimes sharp tip that WAS pointing at the deltopectoral crest? Does that produce a V-shape (in anterior view) in the propatagium? And if so, doesn't that put a lot of stress on that fragile point?

I see the anterior propatagium as a straight line providing an inboard leading edge to the wing. It changes shape only when relaxed, when the elbow is flexed during wing folding, as in birds and bats. Those grooves, in my opinion, anchored the pteroid to the rest of the wrist because there was precious little else to anchor it at its articular surface.

David Peters



On Jan 15, 2010, at 7:46 AM, Mark Witton wrote:

Dave,

There are grooves and rugose protuberances on the proximal ventral surfaces of pteroids (see Unwin et al. 1996) : these, presumably, anchored musculature that, because of its insertion on the ventral pteroid face, would have to depress the pteroid if contracted.

Mark

--

Dr. Mark Witton

Palaeobiology Research Group
School of Earth and Environmental Sciences
University of Portsmouth
Burnaby Building
Burnaby Road
Portsmouth
PO1 3QL

Tel: (44)2392 842418
E-mail: Mark.Witton@port.ac.uk

David Peters <davidpeters@att.net> 15/01/2010 13:27 >>>
Mike,

What tells you the pteroid can be depressed? Which muscle depresses the pteroid? What bone anchors that muscle? There's nothing out at the tip to pull it up and down. If you're attempting to manipulate the pteroid near its articulation, then you've got a very short lever to work with. And finally, are you articulating the pteroid principally on the radiale?

At present, your answer doesn't appear to have any evidence to back it up.

David



On Jan 14, 2010, at 1:28 PM, Mike Habib wrote:

On Jan 14, 2010, at 11:42 AM, David Peters wrote:

"The additional membranes (especially the front one) controlled by a special bone called the pteroid would have helped with steering." The pteroid was inboard and would not have been such a great steering aid.

Because depression of the pteroid (and hence the propatagium) changes entry angle of the inboard wing, the pteroid would be a very good "steering aid" - flying taxa turn by altering the fluid force production between the two wings, such that they differ, which forces a roll and therefore a turn. A little change in entry angle goes a long way, so the propatagial position is, in fact, a factor in maneuverability.

Cheers,

--Mike


Michael Habib
Assistant Professor of Biology
Chatham University
Woodland Road, Pittsburgh PA  15232
Buhl Hall, Room 226A
mhabib@chatham.edu
(443) 280-0181