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Re: Another example of narrow chord pterosaur wing on the 'net



On Mar 21, 2010, at 7:35 AM, David Peters wrote:


This link, or simply googling images for "Ctenochasma elegans" will get you there.

http://images.google.com/imgres?imgurl=http://upload.wikimedia.org/wikipedia/commons/8/8c/Ctenochasma_elegans.png&imgrefurl=http://commons.wikimedia.org/wiki/File:Ctenochasma_elegans.png&usg=__7GDhp3WU1u9p0TxN9jpjoEewVjA=&h=2040&w=2238&sz=10207&hl=en&start=1&um=1&itbs=1&tbnid=yX67GIU6Q0q1FM:&tbnh=137&tbnw=150&prev=/images%3Fq%3Dctenochasma%2Belegans%26um%3D1%26hl%3Den%26safe%3Doff%26sa%3DN%26tbs%3Disch:1

Two immediate thoughts/questions:

1) Aren't we discussing the inboard attachment, not the overall chord? You keep using the title "example of a narrow chord pterosaur wing", but the narrow chord of the overall wing isn't in question.

2) While searching the web for photos might be a great start, isn't working with specimens for which we have direct observation a better approach? Wouldn't next best be looking at what is reported in the peer-reviewed literature. Drawing conclusions from blurry photos of specimens we haven't seen up close is not altogether robust.


This is an ROM specimen attributed to Ctenochasma elegans, but that's dubious and irrelevant. Again, a wee bit of camera shake here. Resolution is 2000+ pixels square.

With the camera shake, the relatively high resolution just gives us more blurry pixels. Besides, this specimen requires examination with a lens or microscope to interpret, because otherwise we can't tell if various stains are: 1) membrane 2) muscle impression 3) bacterial mats 4) some other form of artifact


Here some (not all) of the wing membrane is preserved, either as orange colored material or as impressions of a trailing edge that continue in its place. The wings are folded. A distal membrane trails m4.2 and a continuing line trailing m4.3 is nicely folded in, but that's not what we're looking for.

Is there a reference confirming your interpretations of the material? I'm not confident that it's all membrane. Was that discussed in the paper describing the specimen?


The bright orange membrane with a distinct trailing edge posterior to the upper elbow is narrow. Darn it, it terminates just where it gets interesting on a bulge in the matrix. Both wings cross the femur (the one ventral to the torso) at the presumed (in the narrow chord model) point of attachment. This patch is inboard (anterior) to both distal wing membranes. It covers the deeper elbow. It has a concave bend at the predicted turn toward the femur.

Presuming the orange stains are, in fact, membrane and not where bacteria munched some muscle, it still leaves us with a mangled, shredded membrane. I wouldn't be confident using this specimen to argue for any specific membrane attachment. There is barely any wing left.


ALSO ~

The famous Zittel wing (with narrowing toward the elbow) is here:

http://science.nationalgeographic.com/science/enlarge/reptile-wing-fossil.html

Actually, the trailing edge is arcing away from the elbow, but it could be an artifact. The area behind the elbow is indeed narrow, as is the overall wing. Again, we're not talking about whether or not the wing has an overall narrow chord; this issue is the nature of the inboard attachment of the wing. A narrow wing can have a broad attachment.


AND ~

David Hone provides the Vienna specimen (with narrowing at the elbow and a distinct line to the femur) here:

http://archosaurmusings.wordpress.com/2009/04/13/where-is-the-pterosaurian-5th-finger/

The wing does not narrow at the elbow - it's just that there is less membrane behind the spar at the elbow. Chord is about the same overall (remember, chord of the wing is from the leading edge to trailing edge, regardless of what components make up each at any given location). I used to think that the membrane ran to the femur in that specimen, as well - in Munich I noticed that some membrane seems to exist lateral to the tibia (albeit partially folded under the leg). Therefore, I am currently ambivalent regarding what attachment it preserves. If there is a specimen that could be argued to show a femur attachment, that would be the one. Just about everything else is shredded inboard. Oh well.

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