[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index][Subject Index][Author Index]
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
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
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
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
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 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
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:
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.