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



On Mar 20, 2010, at 2:51 PM, David Peters wrote:

I have described no technique here. And no reconstruction. This is pure observation.

You have described what you suppose the wing membrane extent was, even though much of it is missing in the specimen - that is a reconstruction, by definition.


There are many reasons why this could be misleading.

The term "many reasons" is way too open ended. Put your cards on the table. Be specific.

Okay, here's some examples of potential problems:

1) The membrane may be distorted, especially if the premature termination is a form of post-mortem tearing. 2) The arc of the patagium might continue at a consistent angle, in which case a tangent line extrapolation would be altogether inaccurate 3) The membrane might not follow a gradual arc, but may instead have a sharp turn or angle in it 4) The membrane as preserved may not be in its original plane, meaning that the torn (or unprepped) edge is not oriented in the z axis in the manner we expect.

Essentially, assuming we know where it was going just because the little bit of edge left on the inboard side kind/sorta points at the femur is premature. I am not going to claim that the CM specimen shows a broad attachment; I also am not going to claim that it shows a narrow attachment. It simply does not preserve an inboard attachment.


Are you sure you don't get a death spiral? Please, Mike, You can avoid it only for so long... Let's talk about that line leading off the tibia. And identical lines on the Vienna specimen.

Yes, I'm sure - a spline isn't that hard to do. My point is not that it aims at the tibia - my point is that there are many potential reconstructions, one of which happens to point that way. Others point towards different solutions. I could just as easily argue that the specimen suggests a hind limb completely free of the wing membrane. Point is, again, that the CM specimen just doesn't have an inboard wing, so there is little use in trying to make one up.


And, if you put the body back on the Zittel wing (see Peters 2002) another identical situation. I'm not the only one doing this. John Conway duplicates this here:

http://2.bp.blogspot.com/_VgcbfiMgVJA/S2hR_7lcyxI/AAAAAAAAAIQ/O3CQ0ZAf6rM/s1600-h/Pteranodon+longiceps-735463.png

and here:

http://palaeo.jconway.co.uk/dissecting_rhamphorhynchus.php

John also illustrates potential tibial attachments, ankle attachments, and wings free of the hind limb altogether. He acknowledges the uncertainty, and since he must pick a reconstruction for any given illustration, goes with what suits for a given image. It is not meant to imply any degree of certainty (yes, I know this is his take, because I talk to John on a regular basis).


But I don't think you can make either argument. The membrane isn't there, so making wild suppositions is no good here.

"The membrane" was described by Wellnhofer in 1970. I'm not the first to see it. Or are you talking about a membrane attaching to the tibia, no wait -- the fifth toe - that isn't there? Please be specific or send drawings. You are adding to the confusion. We need your finger to point to somewhere on the picture somehow.

"The membrane" in question is the inboard wing (i.e. proximal to the elbow), which happens to be missing in the CM Pterodactylus. Therefore, nothing to point to. I never claimed an attachment to the tibia or fifth toe - I claim that the inboard wing is not preserved. Full stop.


See above. "Does" -"does not" are closing arguments. We haven't gotten there yet. Time to provide the charts and graphs.

Charts and graphs of what? The inboard wing is not present in the specimen. I am not comfortable making one up, unless it is for purely artistic reasons (in which case I don't care which version you pick). That is honestly the extent of my argument; there is nothing to plot on a graph.

The opposing camp has given several examples.

Wrong. NONE have been delivered. You have only >cited< examples.

Citation of peer reviewed work is an important aspect of scientific procedure. I trust in the observations of those that have carefully looked at the original specimens, assuming they present documentation, unless I have looked at the same specimens in person and determined differently. Besides, I didn't say that *I* am the opposing camp; I merely suggested that the opposing camp has given examples, which they have.

You have dismissed them for various reasons, and while some of your arguments bear merit, others can say much the same about your narrow wing examples, leaving us eagerly awaiting a clear example of either one.

If you don't like this wing example show what >is< happening in the fossil.

I can't tell what is happening in the fossil because it does not preserve the detail in question. What I *can* do is run my calculations using a variety of potential wing attachments, constraining them according to the parts that we do have. As it turns out, the precise nature of the inboard wing has less effect on the results than we might expect, therefore I can make conclusions about locomotion within known confidence limits, despite the inboard wing being unknown.

Personally, I find several of the hindlimb attachment examples robust,

Send  just one  of your best.

I have done so a few times, and your consistent response is to dismiss the examples according to your digital tracings. I don't know that your reinterpretation is wrong, but I remain skeptical because I give greater weight to those that have seen the specimens in person. I don't particularly mind that you have a different interpretation, but it is a tad frustrating when you suggest no such potential examples have ever been produced.

but even then, we do not have attachments for the vast majority of clades, and attachment could easily vary.

If there was an alpha example and an omega example I would agree that we could have everything inbetween. But we have only one example over and over. Seriously, send one opposing example and I will be on your side.

I have done so, but even putting that aside, you don't have one example over and over - even if you are dead on, your examples still come from only a handful of the known clades. There are no inboard patagial extents preserved in any azhdarchids, pteranodontids, nyctosaurids, or ornithocheirids, for example. There is a shredded one from an azhdarchoid (potentially a tapejarid), but otherwise none from that larger clade altogether. It doesn't matter how you interpret everything else, that that is a lot of diversity for which we don't have any data - therefore, the attachment could be variable without our knowledge.

Fortunately, we have lots of good outboard wings, so we can reconstruct that much with relative confidence. It turns out that the specifics of the inboard wing don't make much of a difference when you work out the numbers, because a fillet is not very aerodynamically active.

Irrelevant at this point.

Not really - we care about the wing extent largely because of the implications for functional analysis. If the variation in potential wing extent has little effect, then the impact of uncertainty is reduced. This is handy.


Cheers,

--Mike H.


Michael Habib
Assistant Professor of Biology
Chatham University
Woodland Road, Pittsburgh PA  15232
Buhl Hall, Room 226A
mhabib@chatham.edu
(443) 280-0181