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



On Mar 23, 2010, at 7:31 AM, David Peters wrote:


<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.

Well, the "sans fuselage fillet" would be a broad attachment. We're really arguing over that attachment, which you have not reconstructed as narrow - just more narrow than some of the alternatives.

< 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.

"Stretched between the elbow and wing finger" sounds like your giving the wing an insertion point on the elbow. I recommend different wording; this is what caused me confusion previously.


<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.

Sigh. What I'm saying is that the specimen is not clear - it does not provide much useful information on the inboard wing. I am arguing for uncertainty, not a specific alternative. I have provided possible wing configurations in the past, and consider them plausible, but they are just a few plausible attachments among many. I have seen the specimen; I disagree that it is clear or useful for answering the question of wing attachment. Not sure what "counteracting evidence" you want - even the blurry photo you provided indicates that the inboard wing is largely missing.


<<<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.

Okay... so when you said no muscle behind the elbow, I figured you meant close to the joint. So yeah, pterosaurs have wing after that - what's the point, exactly? [insert look of confusion].

<<<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)

The Zittel wing is not at all complete inboard (for one thing, it's only the wing), and the Vienna specimen is clearly not complete either, since it has a huge hole in the wing. However, I agree and accept that the Vienna specimen preserves enough inboard membrane to argue that it shows a thigh attachment, at minimum. What we can't tell is if the membrane traveled further down the hind limb from there. Let's suppose it does not. That still only tells us about the membrane on Pterodactylus. Sample of one. Even if you found one other decent example elsewhere in the tree, it'd be a pretty weak bracket. I know there are quite a few literature examples of two sample EPB usage, but that doesn't make it a good idea. (Robust usage of EPB brackets with multiple monophyletic groups). Again, I'm not saying a thigh attachment is wrong, I'm saying that the inboard attachment is unknown for the vast majority of pterosaurs, and that they may not all share the same attachment. Sordes seems to have a broader attachment, Pterodactylus seems to have a thigh attachment. We don't have any attachments from big marine pterodactyloids, but theory suggests that they might have hip attachments, etc.

3. CM (partial, by thigh) 4. ROM (partial, by elbow). Now it's your turn. I'm still waiting for your one example.

Well, seeing as my argument is "we don't know, there are multiple plausible attachments", both 3. and 4. work to my case - they are partial, and therefore uninformative. I have also cited several recent studies from the literature suggesting a broad attachment. I know you disagree with those manuscripts, but I don't think your arguments are definitive (that doesn't mean theirs are, either).

<<< "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?

David - it was a joke. That's a popular quote from "Princess Bride". The serious side of it is that you keep talking about "trends", when you have one specimen that kind/sorta shows a decent thigh attachment of some kind. And, as already indicated by Anthony, circling it on a slab of rock and shipping it to you is going to be very expensive. Sarcasm aside, I don't think photos are sufficient for most of these specimens. If you insist on having photographic examples, then I again point to the literature. My pictures aren't any better.

<<<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.

You make mention of force vectors on a regular basis, but I get the distinct feeling you haven't calculated any of them. Under none of the hind limb attachments would the hind limb be forced to move with the flapping wing, though it is quite plausible that the animals would actively move the hind limbs in phase to some extent (actually, they would move just out of phase, more on that some other time). Works fine for bats, incidentally. In any case, the sharpness of the turn has two effects: the dynamics of the translation of flutter to the inboard wing, and vortex shedding patterns. As it turns out, both the thigh attachment and the ankle attachments are going to require that the inboard wing be very elastic, which means it's going to be essentially aerodynamically inactive - which means that none of the differences in inboard motion that you just described actually have much impact.

That said, I do agree that the turn to the hind limb - wherever it turned to - was probably quite sharp. I expect this because the wing was narrow at least to the elbow, and because it improves vortex shedding behind the wing. A sharp turn/ankle attachment model was suggested as a *possibility* by myself some years ago; John Conway even was kind enough to illustrate it. Such a model has exactly the same aerodynamic advantages as a sharp femoral attachment. Which one is more accurate will be determined by better fossil information. Perhaps neither one of them are. I wouldn't be surprised, for example, if the first anhanguerid we find with a nice membrane shows evidence of a hind limb free of the wing altogether. I won't be surprised if it turns out your fillet to the thigh was common, either. But right now, we don't know.


<<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.

Wait, how do we know it isn't found in the fossil record? Isn't that the argument to begin with?

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?).

I don't particularly expect that the wing went to the toe tip, but for what it's worth, the pull is not nearly so powerful as you think. A couple of pounds of force in the big guys; nothing that couldn't be handled pretty easily.

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).

None of the differences you just described "matter a great deal" - essentially, in all cases, there is some pull on the hind limb, which resists easily, or can move slightly with the wing slightly out of phase to control dynamics on the trailing edge. Incidentally, the hind limbs act just fine as landing gear for bats, too.


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.

My suggested model (which is only given as a possibility) comes from the observation that the wings are narrow to the elbow in several specimens, that ankle attachments have been reported in several cases in the literature, that the inboard wing is known to have been more elastic than the outboard wing (Kellner et al., etc) and that a sharp turn would have aerodynamic advantages given those features (vortex shedding related). John Conway has illustrated the idea, which was kind of him. My model is largely hypothetical, but it is consistent with all of the above features, which was the point.


<<<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.

That doesn't make sense - are you familiar with the force translations inside elastic materials? (specifically, hetereogenous elastic materials). The force is translated to the trailing edge, which loads in tension and pulls the membrane laterally from the tibia and anteriorly (which puts it in tension). Also worth a reminder that DML messages don't take attachments, so the drawing wouldn't do much good unless I had the time to create a web location for it, which I do not.


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).

Wait, are you suggesting that anything we see in a fossil was present in life?


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?

There should be no hole in any model that suggests Pterodactylus could get into the air and stay there. The bend can happen very late, actually, at which point the shape in life is concave between the wing and hind limb. See above for the reasoning of the sharp turn to ankle model.


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)

A sailplane like planform would actually be most similar to a hip attachment, not a thigh attachment. But in any case, its the outboard chord that really matters for the pterosaur wings, and a narrow outboard wing gives an overall high aspect ratio, and thus a good glide ratio (like a sailplane).

Contrary to your assertion, several papers have used thigh attachment wing models in their calculations. Chatterjee and Templin did this, for example (but it was confounded by bad weight estimates, at least for large species). Pennycuick did a series where he tried a broad wing, mid-wing, and very narrow wing. The mid-wing had a thigh attachment. And, what's more every paper that has done a narrow wing with a fillet to the ankle has essentially done the model you prefer, because the difference in aerodynamic performance is tiny (see above). Again, I caution against the use of "wingtip to elbow membrane stretch" as your preferred wording, because it suggests that the wing is actually interrupted by the elbow (i.e. insertion at the olecranon), rather than passing behind it.



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?

The nacelle would be located at the elbow, extending behind it. In other words, the holes that show up at the elbow in several specimens indicate where the nacelle was located in life. I suppose that is just outboard of the fillet in your preferred attachment model.

Cheers,

--Mike