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

[David Peters <davidpeters@att.net>]

<Then specify the part of the chord you are referring to. When you say "narrow 
chord wing", I presume you mean the wing as a whole. >

I DO mean the wing as a whole. From wingtip to inboard of the elbow, sans 
fuselage fillet. The distal wing we agree on and is a none issue, case closed.



< Incidentally, the membrane passes behind the elbow, not to it.>

We all know this. We all agree on this. The fossils show this. Nevertheless, 
there is only one hypothesis that postulates the wing was stretched between the 
elbow (and its tiny trailing nacelle) and wing finger. ALL the others involve 
the tibia or beyond. 



<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.
Yes, but drawing firm conclusions from those web resources on subtle details of 
poorly preserved traces is ill advised.
My friend, nothing is ever perfect. 1) The stains follow and match impressions.>

<Really? Have you looked at the specimen in person to confirm?>

Please don't attempt to raise doubts with words alone. Please provide 
counteracting evidence. You said you saw the specimen. Either agree or disagree 
and provide evidence of same. 



<<<2) There are no large muscles in tetrapods posterior to the elbows.>>>

<<<The triceps and anconeus didn't get the memo, I guess. If there were no 
muscles behind the elbow then it wouldn't extend.>>>

:  )  Look again at your own elbow, Mike. That's air behind your elbow. In 
pterosaurs that's a trailing membrane.


<<<4) It might be an artifact if it were a one time event, but I've given four 
examples all morphologically identical.
You have given four examples all shredded in different ways; only one has the 
inboard wing preserved.>>>

One! Thank for accepting one!   [big smile here]   Now I'll remind you of the 
other three: 1. Vienna specimen   2. Zittel wing (both complete)  3. CM 
(partial, by thigh) 4. ROM (partial, by elbow). Now it's your turn. I'm still 
waiting for your one example. 


<<< That becomes a trend without exception. >>>

<<< "You keep using that word, I do not think it means what you think it 
means." --Inigo Montoya.>>>

Why play word games, raising doubt without providing evidence to support your 
doubt?  Mike, obviously you have evidence of thigh, ankle or toe attachment . 
Just circle it and send it! Why are you balking?


<<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.>>


<<<No, it is not decoupled. In fact, a wing making a sharp turn to the femur 
and one making a sharp turn to the tibia or ankle work basically the same in 
many respects: both allow hindlimb tensioning of the wing, both alter flow 
behind the elbow, both prevent bipedal running launch, etc.>>

Not so. At least not in the realm of the key word, "essentially". Neglecting, 
for the moment that the mid thigh and elbow are closer to the axis of flapping, 
it is because of the 90 degree bend in the membrane INBOARD to the elbow, that 
the wing and femur are essentially decoupled. When the elbow rises and falls, 
the remaining fuselate fillet acts in a minimal way to rotate the "essentially" 
transverse anterior femur up or down -- if at all. Large thigh muscles anchored 
on the long ilium would counteract that minimal tug. In all opposing candidate 
hypotheses there are force vectors starting at the wing tip acting to lift the 
knee, the thigh or the foot. With that essential bend between the membrane and 
the fuselage fillet, those pulling vectors are minimalized. Key difference. 

<<Yes the attachment is broad proximmaly, but much less so than if the tibia or 
toe were involved.
Sure, but that matters rather little.>>

On the contrary, it matters a great deal. 

Case 1: wing stretches between wing tip & knee. This gives freedom to the crus 
for unimpended motion, but the femur is pulled up and down with every flap, 
unless held rigid by muscle counteraction. 
Case 2: wing stretches between wing tip & ankle. The crus is pulled up or down 
with every flap, unless held rigid by muscle counteraction. Also the knee is 
extended in the direction of the wing tip, unless held rigid by muscle 
counteraction. No problem for bats, to your point, but not found in the fossil 
record.
Case 3: wing stretches between wing tip & lateral toe tip. All the above plus 
the typically hyperflexed (in situ) lateral toe would be extended and rotated 
to line up with the wing tip (ouch!!), then pulled up or down with every flap 
(how does it stay socketed?), unless held rigid by muscle counteraction (would 
that be possible given the size disparity?). 

Case 4: wing stretches between wing tip & elbow. This gives complete freedom to 
the entire hind limb and all of its parts to act as an independent aerial 
surfaces (uropatagia-provided) and landing gear (with hyperflexed digit V 
acting as a shock absorber in those that have it). 


<< 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.
Yes, but not in a narrow chord, broad attachment model - specifically one in 
which the membrane turns sharply to the hindlimb.  >>>

Can you provide a specimen that demonstrates this preferred model of yours? Can 
you provide a hypothetical drawing? Is Wellnhofer 1978 close to your concept? 
If so, note how much wing material he had to add to his illustration to make 
keep his paradigm intact. 


<<<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.
Sure there is - tension is transferred through the membrane.>>>

If so, please show it. Add a vector arrow from the wingtip, please.


<<<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.
The hole would be stretched and become long and narrow. It would also cause 
terrible flutter and result in the poor critter not flying. I am not under the 
impression that you consider Pterodactylus to have been flightless, so I am 
perplexed as to why you think the hole existed in life.>>>>

The "hole" (actually it becomes a hole only when the wing is folded to close 
off the outer opening) existed in life because the "hole" can be seen in the 
fossil (examples cited yesterday). In the hind leg attachment model, there 
should be no hole whatsoever. There should be no bend in the wing material 
inboard to the elbow. That bend or curve should have happened much more 
distally somewhere outboard of the elbow in your preferred model. That's the 
specimen example you need to provide. If you don't have such an example, why 
would you defend such a model?



<<<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.
It isn't predicted by any model that expects pterosaurs to fly. >>>


Not one aerodynamic paper has used the "wingtip to elbow membrane stretch, 
narrow chord, fuselage fillet model." However, such a wing model is used here: 

http://en.wikipedia.org/wiki/Glider_(sailplane)


<<<However, expectations from functional morphology and aerodynamics do predict 
that feature in the fossils: pterosaur elbows are quite deep, and therefore 
protruded outside of the contour if the membrane. As such, we should predict a 
soft tissue nacelle at the elbow and extending behind it. The nacelle could be 
fatty in nature, though work by O'Connor, Claessens, and others indicate that 
an air sac probably contributed to nacelle volume. Such structures would be 
expected to rot away quickly, so the hole is not surprising. Dead bats often 
develop holes in their membranes in specific locations during dessication and 
decomposition, as well.>>>

So... is this nacelle simply a blob in the middle of your wing? Or does it 
occur at that little nipple behind the elbow, outboard of the fuselage fillet 
in my model?

When we come to an agreement, we'll pop champagne~!  -- David


Cheers,

--Mike