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Re: Another example of narrow chord pterosaur wing on the 'net
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- Subject: Re: Another example of narrow chord pterosaur wing on the 'net
- From: Mike Habib <email@example.com>
- Date: Mon, 22 Mar 2010 02:31:13 -0400
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Another try, as apparently my iPhone is not sending in plain text:
On Mar 21, 2010, at 3:23 PM, David Peters <email@example.com> wrote:
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.
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.
Incidentally, the membrane passes behind the elbow, not to it.
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
Really? Have you looked at the specimen in person to confirm?
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.
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.
You have given four examples all shredded in different ways; only one
has the inboard wing preserved.
That becomes a trend without exception.
"You keep using that word, I do not think it means what you think it
means." --Inigo Montoya.
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,
Yes the attachment is broad proximmaly, but much less so than if the
tibia or toe were involved.
Sure, but that matters rather little.
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
Yes, but not in a narrow chord, broad attachment model - specifically
one in which the membrane turns sharply to the hindlimb.
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.
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
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.
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.