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



Another try, as apparently my iPhone is not sending in plain text:

On Mar 21, 2010, at 3:23 PM, David Peters <davidpeters@att.net> 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 impressions.

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

Indeed.

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, etc.


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 elbow.

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 life.


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.

Cheers,

--Mike