Re: Wilkinson's new pterosaur paper, Cunningham, Habib

[jrc <jrccea@bellsouth.net>]

----- Original Message ----- 
From: "Jaime A. Headden" <qilongia@yahoo.com>
To: <dinosaur@usc.edu>
Cc: "david peters" <davidrpeters@earthlink.net>
Sent: Friday, July 13, 2007 11:45 AM
Subject: Re: Wilkinson's new pterosaur paper, Cunningham, Habib


> As these [actinofibrils] have been hypothesized to be evolved muscle 
> tissue,

They have also been hypothesized to be evolved scales on the lower membrane 
surface (Hall Train).

> I doubt they are NOT attached to the limb itself in any way,

They seem to tend to approach the posterio-ventral surface of the skeletal 
spar tangentially at roughly about the 4:30 position as seen looking 
outboard.  This makes some sense, as that approximate orientation would have 
an appropriate structural function.

> and perceiving an actual hole would tend to be viewed as a first
> impression improbability that would require testing (and proof) to 
> theorize
> about function from.

I think the holes are clearly demonstrable in a couple of specimens.  They 
appear to me to be post-mortem and seem to be consistant with the 
possibility of some 'padding' aft of the elbow -- think engine nacelle.

>  Moreover, reconstruction based on not artificially condensing the wing 
> when
> the finger is extended, or considering the ability to lengthen the chord 
> when
> the wing is in any shape, which the aktinofibrils suggest is possible.

The actinofibrils seem to work mostly in differential tension, capable of 
both shifting relative to one another along their intercalated lengths, and 
transversely.  They do have an ability to carry very localized, realtively 
small compression loads (limited by Euler buckling) that can inhibit and 
delay local wrinkling of the membrane (as does the ability to shift the 
membrane to replace local compression loads with tensile loads.  I think the 
important specifics of the mechanisms of their function are clear.

> Simply rotating the wing shape as preserved on the slab out and filling in 
> the lines
> based on a perceived narrowness proves very little.

Well said, Jaime.  So far though, I've seen no convincing evidence for a 
broad wing in any specimen and several bits of iffy evidence for a narrow 
wing.  I am a narrow-wing proponent, but as I've mentioned, I do not 
consider it to be proven unequivocably.  Wish we had more and better 
fossils.  All you diggers get to hunting....:-)

>  I wholeheartedly agree. See above. Practical experimentation and 
> first-person
> examination a must in this field, however. A good deal of people from Jim 
> to
> Conway to Unwin and Kellner are working on physical models under all 
> hypotheses
> to test aerodynamic shape and controls of wing planform and function.

Don't forget Matt.  I disagree with him about wing shape, but I strongly 
support his efforts to study the wingshapes that he prefers.  His hypotheses 
tend to be testable.

JimC