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