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Re: Pterosaur structure, good job JC



Comments inserted.
JimC

----- Original Message ----- From: "Michael Habib" <mhabib5@jhmi.edu>
To: "dinosaur mailing list" <dinosaur@usc.edu>
Sent: Friday, January 11, 2008 10:28 AM
Subject: Re: Pterosaur structure, good job JC



Any reason that we should expect neutral positions? I've noted, at least in some other species, that the slight supination seems to yield a better wing position given the articulation at the elbow, and the manner in which the radius fits against the ulna distally.

Mike is correct. And keep in mind that in flight, the shoulder rotates the elbow rotated slightly to place the elbow near the camberline of the airfoil, not the chordline.


What do you mean by "in the plane of the wing", in this context? John's configuration technically has them in the plane of the wing, just palmar surface forward. While this may seem a bit counterintuitive, pterosaurs seem to be derived from the typical tetrapod condition.

All pterosaurs that I'm aware of, fly with the palmar surface forward. I believe that Chris Bennett was the first person to notice this, quite a few years ago.


I cannot agree with John's hypotheses on wing folding = extension and wing deployment = flexion. .......

Chris Bennett independently came to the same conclusion, and detailed it in his Munich talk (which I''m sure you recall).

If I remember correctly, Chris pointed it out to both John and me, several years ago. It was obvious at the time that he was right, as he generally is when it comes to pterosaur bone structure :-) That equates to digital extension folding the wing and flexion swinging it forward. The same holds for the other digits. Plus, I've seen a well preserved ornithocheirid wrist (unpublished) that preserves digits I, II, & III lying approximately spanwise and flat along the upper surface of the wing in cruise flight position (I don't remember offhand if that is the position that John uses in these current illustrations, but the fingers can be correctly placed in several orientations -- they were an active part of both flight control and launch; not static protrusions.


I also liked John's earlier version of hind limb configuration during flight in which the hind limbs were more laterally oriented forming horizontal stabilizers.

Those are quite cool, I agree. That position would not be for cruising flight, though; the limbs would reach that position (if it was used) during specific maneuevers where aft-support or extra lift was needed. Stabilization, per se, was probably not too important (as animal flyers generally use unstable flight).

I'm the one who suggested that orientation to John, as a transient position. It provides minimum drag when the aerodynamic tail structure is loaded. At the time, we were trying to get folks to accept that pterosaurs regularly and transiently use several leg positionings during flight, both symmetric and asymmetric. We showed that one to make the concept pop out at folks, in an effort to move folks away from the thought that pterosaurs always used a single mode of flight. During cruise flight, I'd expect the included angle between the two ankles and hips to subtend an angle of approximately 127 degrees (the minimum drag configuration for a moderately uploaded tail complex, supporting only the weight of the hindlimbs so that the hip musculature doesn't have to actively support them.


To be stabilizing in pitch, the hindlimb/tail structure would need to be downloaded and pterosaur hip musculature isn't aligned to support downloading for any significant duration. Downloading would be another transient, used only when needed and for no longer than needed. Like modern birds, pterosaurs seem to have evolved away from normally stable flight configurations.

A tip of the hat to a great artist and visionary, Hope to see the same specimen walking one of these days.

I second that!

Me three.

JimC