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

[David Peters <davidpeters@att.net>]

>> 
> 
> 
> 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.

Mike, you may be forgetting that the narrow chord we're talking about is in the 
vicinity of the elbow with the wing stretched between elbow and wing finger, 
not hind limb and wing finger, in which you would have a much deeper chord in 
the vicinity of the elbow gently curving toward digit V, or the distal tibia. 
> 
> 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.

The DML is a web-based arena that prohibits anything but words to be 
communicated. Having web-based info referenced gives everyone a chance to see 
for themselves. 
> 
> 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

My friend, nothing is ever perfect. 1) The stains follow and match impressions. 
2) There are no large muscles in tetrapods posterior to the elbows. 3) 
bacterial mats may be the very reason why the stains have a shape 4) It might 
be an artifact if it were a one time event, but I've given four examples all 
morphologically identical. That becomes a trend without exception. I'm still 
hoping to see an exception.
> 
> 
> 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?

No reference. Pure observation at this point. No paper that I am aware of. The 
ROM specimen simply follows the pattern of the other three. On the same point, 
the darkwing, the Vienna specimen  and the Zittel wing all preserve the wing 
membrane in entirely distinct fashions, yet the shape is the same. Same here. 
> 
> 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.

Agreed. But like I said, it follows one pattern, not the others. 
> 
>> 
>> 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.

If you're talking about the lowest part of the membrane (in the picture), 
that's the inboard membrane, etc. It's a little loose after being ripped off 
the torso and femur. 

With regard to "narrow wing" I'm restricting my meaning, as always, to the 
vicinity of the elbow. Such a wing is essentially decoupled from the hind 
limb.Yes the attachment is broad proximmaly, but much less so than if the tibia 
or toe were involved.

> 
> 
>> 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.

Understood. The "ing" was a goof. Chord is the same overall to the elbow in my 
model. However, in the deep chord-hind leg attachment model, the chord should 
deepen considerably in the vicinity of the elbow. 

What sort of material was that lateral to the tibia? Was it possibly tibial 
(non-wing) material? If the wing were to open, would the wing tip pull that 
material open as well? There's no vector that would pull that membrane out with 
wing extension.

Back to the Hone image: There is obviously a big hole in the wing membrane  
posterior to the elbow, anterior to the knee, (to the left of the yellow arrow) 
which essentially divides the wing membrane in two, an inboard to the elbow 
portion and a distal to the elbow portion. When the wing finger unfolds, which 
it must do, that hole does not go away and suddenly fill with wing material. 
Those are the nuts and bolts of this model. Every pterosaur that preserves wing 
material in the vicinity of the elbow has some evidence of this vacant area 
posterior to the elbow (whether noticed by the original workers or not). Such a 
hole is not predicted by the hind-leg attachment model. 

When Wellnhofer 1978 discussed the Vienna wing, one image showed the insitu 
specimen with a hole behind the elbow, another showed the wing at full 
extension with the hole miraculously filled! Peters 2002 did the same thing but 
without the miracle.

David 


> 
> 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
> 
>