[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index][Subject Index][Author Index]

Re: aktinofibril intercalation, JCunningham



Jim, 

I am familiar with the intercalation. But I don't recall hearing the 
hypothesis, until now, that the fibers moved longitudinally. Who is that author 
of that hypothesis and where is the paper? As a percent of resting length, what 
is the maximum lengthening one may expect in a chord? 2%? 200%? If the former, 
why bother mentioning it? If the latter, nothing like that has been documented 
in a dead pterosaur. If some figure in between, that's not been documented, to 
my knowledge, either. 

I can imagine some minimal longitudinal movement, but only passively to 
facilitate folding. Not during flight without any other movement of the wing 
finger. According to this new hypothesis, must all the aktinofibrils in a wing 
trailing edge move the same way? Or do sections operate independently, as in 
modern airliners? 

Finally, if true and substantial, this might have some consequence in the 
outboard wing, does it have any relevance whatsoever to the inboard wing? 
That's where the argument lies. And that's where the fibers are shorter to 
absent.

>

With regard to J. Headden's reliance on the observations of Unwin and Sharov 
for Sordes, I remind readers that both observers also made the mistake of 
considered the twin and overlapping uropatagia (in the style of Sharovipteryx) 
to be a single membrane stretched between the posterior rims of both legs 
(medial in the knees out flight configuration) binding the legs in such a way 
that ordinary tetrapod location would have been impossible. Such a bat-like 
configuration was considered reasonable prior to 1995 because we had no 
consensus on pterosaur tracks. But now we do. Now we know the hind limbs of 
pterosaurs operated like those of most tetrapods, excluding bats. The 
interpretation of a single uropatagium is invalid. And so is the observation of 
'membranes' attached to the ankle. 

As always, I'll change my mind when shown evidence.

>

With regard to J. Headden's dismissal of blurring to capture details, I remind 
readers that halftone dots and pixels are similar in that they both represent 
units of color and tone that, when seen in the company of thousands of other 
dots or pixels create a picture. When Photoshop blurs a halftone (created by 
only black or  overlapping cmyk dots)the spaces between the dots are provided 
with pixels that average the tone and color of adjoining dots. In this way a 
few to many pixels may be added between halftone dots creating the illusion of 
a continuous tone. In this way, and only to a limited extent, do you get more 
out of 'blurring' a photo, not less. Usually you'll want to blur no more than a 
dot width. 


David Peters
St. Louis



-----Original Message-----
>From: jrc <jrccea@bellsouth.net>
>Sent: Jul 14, 2007 9:19 AM
>To: davidrpeters@earthlink.net, qilongia@yahoo.com
>Cc: dinosaur@usc.edu
>Subject: Re: Wilkinson's new pterosaur paper, J. Headden
>
>The actinofibrils are intercalated.  They do not run full length.  They can 
>be longitudinally lengthened (and shortened) by shifting relative to one 
>another along their lengths.  This is one of the primary mechanisms for 
>controlling the aeroelastic number and inhibiting flutter.  It can also be 
>used for roll control.
>JimC
>
>----- Original Message ----- 
>From: "David Peters" <davidrpeters@earthlink.net>
>To: <qilongia@yahoo.com>
>Cc: <dinosaur@usc.edu>
>Sent: Saturday, July 14, 2007 5:11 AM
>Subject: Re: Wilkinson's new pterosaur paper, J. Headden
>
>
>> Fibers beyond the elbow can be rotated to show their  maximum chord 
>> length. They cannot be longitudinally lengthened as I  demonstrated with 
>> the Zittel wing (ref.   Peters, D. 2002b. A New  Model for the Evolution 
>> of the Pterosaur Wing â with a twist. -  Historical Biology 15: 277â301).
>
>