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Re: Wilkinson's new pterosaur paper, J. Headden




On Jul 13, 2007, at 12:45 PM, Jaime A. Headden wrote:

Tracing is biased, however, as it is based on perception of what blur means
what. Viewing a slab and sampling the material is the only way to KNOW what is
what on the slab. In the case of unpreserved membrane, in examples like
*Sordes*, you have heavy carbonaceous remains on the slab that in some places
are not fully preserved. But you do not have ONE slab, you have TWO, and
furthermore slabs are not all exposed or even buried in a single plane, as has
been explained before rather more than a few times. Missing material from just
behind the elbow can be solved by somewhat of a simple technique, if there are
aktinofibrils which disappear before they reach the elbow, but would seem to
extent to the elbow's "vanishing point". As these have been hypothesized to be
evolved muscle tissue, I doubt they are NOT attached to the limb itself in any
way, 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.



Jaime,

1. If other Sordes material is on a counter plate, why has it received no mention in the literature? or online? If you have any data other than hopeful imagination, please share it.

2. re: solving the riddle of the missing material behind the elbow: the pattern of aktinofibrils is such that there are no fibers inboard of the elbow. 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 – with a twist. - Historical Biology 15: 277–301). If you can make the Zittel wing do more than I showed it could do, please do so and send me the results. In the case of Sordes, a smooth and gradual curve can be drawn from wing tip to just aft of the elbow encompassing all of the aktinofibrils. Any other interpretation involves making a sharp unwarranted turn, jumping over blank spaces and these Unwinish 'membranes' contain no aktinofibrils.

That H.B. paper was published in 2002 and David Unwin's pterosaur book came out a few years later. Don't you think that Dr. Unwin would have taken the opportunity to negate my hypothesis with some high resolution data in the form of published photographs if he had the evidence? I submit that he did not. There is nothing a pterosaur paleontologist loves to do more than squash opposing hypotheses with evidence. Given the chance, what did he do? He passed. In a book that otherwise referenced every last paper ever devoted to pterosaurs he omitted every peer-reviewed and published paper I wrote. That should tell you something. He doesn't have an opposing argument or evidence.

3. Aktinofibrils are not evolved muscle tissue. They are parts of extradermal membranes, as in the hind limbs of Sharovipteryx or the crests of Basilisk. They are bounded by vascular and muscle tissue as others have shown.

4. I wonder why you attempt to build a 'straw dog' with this argumentative statement, "I doubt they are NOT attached to the limb itself in any way," because everybody, including me agrees with you. The inboard fuselage fillet, as I said earlier many times, is attached at mid thigh aft of the elbow, as shown on all specimens in which this is preserved.

David Peters
St. Louis