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Re: questions for Witton & Naish: Azhdarchid Pterosaur Functional Morphology

I've not read the paper yet (Darren sent it to me this morning, and I've been busy -- will get to it this afternoon or evening) so, I'm only going to make a few general comments herein. See below.
JimC

----- Original Message ----- From: "Mark Witton" <Mark.Witton@port.ac.uk>
To: <davidpeters@att.net>; <dinosaur@usc.edu>
Sent: Thursday, May 29, 2008 9:57 AM
Subject: Re: questions for Witton & Naish: Azhdarchid Pterosaur Functional Morphology


The mesotarsal ankle of pterosaurs dictates that the knee joint has to be perpendicular to the long axis of the body

The quetz ankle doesn't indicate that. However, on the ground, the knee would be a lot closer to anteriorly oriented than laterally (doesn't sprawl).

and the tibia has to be orientated more-or-less subvertical.

On the ground when walking, I agree. With some emphasis on the 'sub' part of subvertical. The tibia can be moved well away from the vertical, but likely not to the extent of a sprawling gait.

With this in mind, we can see from the orientation of the Haenamichnus footprints that the trackmaker was walking with its knees facing forward, not laterally.

I haven't seen those tracks (or, if I have, I've forgotten), but based on the pterosaurs I'm familiar with, I would not expect the knees to face laterally when walking.

If this is the case, the femora cannot be splayed out to meet them, or else the trackway would need be much wider to maintain a vertical-ish tibia.

This seems to imply that the femora cannot be splayed out in flight, and I strongly disagree with that, but am likely misreading the sentence above and will withold any real comment till after reading the paper and discussing it directly with Darren and Mark

Azhdarchids have long femora, after all: they would need a considerable case of rickets to stick their femora out, strut around with a splayed gait, and bring them back into Haenamichnus territory.

I think they can stick their femora out more than you may credit them with, but probably not to the extent of splaying the feet on the ground.

"W&N illustrate: pteroids in the anterior orientation and a deep chord wing membrane. Is there any evidence for either?"

I can stick my hand up and admit that the pteroid orientation is probably not correct: the drawing and science behind the drawing were done pre-Bennett's 2007 efforts. If I re-did this bit now, I would go with Bennett's medial orientation. Just for the record, though it only has a minor effect on wing area and therefore doesn't change our conclusions.

I haven't read the conclusions yet, so can't comment on conclusions right now -- but, the pteroid articulation does have a pretty substantial effect on wing performance. That said, I too agree with Bennett's medial orientation. However, the range of motion that is available from that medial orientation is capable of generating substantial aerodynamic effects.both locally and throughout the wing, since among other functions, it is capable of changing the spanwise tension and camber of the wing all the way to the wingtip.

The evidence for broad wing membranes is discussed in the paper, and I'm not going to go through it all again. I know some folk have their reasons for not buying broad chords, but I (along with Darren and, I think, a healthy chunk of the pterosaur community) reckon it's the way the evidence points.

I'd say ya'll are in the majority. Since all three major configurations will work after a fashion, my bet has always been that over the eons, all three have existed at one time or another. I wish the fossil evidence were better. Till better fossil materials turn up, we're all speculating to some degree.

Firstly, Fig 9 is a effectively an elaborate sketch and should not be taken as gospel: it has scientific backing, but, as with any bit of palaeoart, there's a certain amount of artistic licensing. The folding of the membrane is something I've always struggled with, so and I really wouldn't put to much faith in my restoration on that issue. 

That's candid, and I'd cut Mark some slack on that.

"But didn't Kellner and Langston show with Q. sp. that the dentary is shaped much like a flattened and squared-off yardstick?"

All jaw tips refered to Azhdarchidae, including Azhdarcho, Bakonydraco, Quetzalcoatlus and some scrappy bits from Morocco, have flattened occlusal surfaces and steadily tapering lateral margins. 

That's not true of the lateral margins of the quetz anterior lower mandible

Not sure about Jidapterus: the mandible is preserved in dorsalvental view, sure, but it's also squashed flat.

and I've been called stupid in several comment sections on newspaper websites in the last few days.

You know, that's one source of insults that should roll off us like water off a duck's back.

"Is this the only possible configneck could have risen more vertically? Should a range of motion be provided?"

Yeah, it should be, but there aren't many azhdarchid cervicals around that articulate properly: they're all squished and deformed in the wrong places.

I woudn't say that they all are, but I would agree that it would be better if fewer were..... :-)

Hence, while we can get a sense of the neck's immobility, actually quantifying it is easier said than done. 

Well said.

We reckon there's more dorsoflex than ventral because the condylar articular surfaces face posterodorsally, suggesting the vertebrae did not regularly arc downwards significantly. There is, however, more flex apparent at the anterior end: the posterior is locked up pretty tight. No actual figures for you on this though, I'm afraid. Maybe Wann Langston will have had better luck with his studies on Quetzalcoatlus sp. 

He did.  But, I'm going to leave comments about it to him.

"I would also suggest a range of motion for the knees. For if the knees bent more than indicated then the posture changes."

Y-e-s... but we're basing our posture on footprints.

I think the footprints may say more about effective orientationsthan they do about possible orientations. Without the cartiledge, its hard to tell what the range of knee articulaton was, but based on the skeleton alone, it is obviously substantial.

Pterosaur femora are also, if you come from our school of pterosaur wing membrane construction, integral to the wing shape. Hence, their functional roles are twofold: supporting a pterosaur on the ground _and_ in the air. Hence, their articulation is not necessarily going to be straightforward.

Femur orientation in the air for both scenarios would have been much the same most of the time, whether the wing membrane attached to the hindlimb or not. There are scenarios where the orientation would be different, but in either event, the articulation is NOT straightforward.

"As above, sprawling femora, when combined with knees bent at 90Â still place the feet beneath the torso." 

But not with the feet oriented as per trackways evidence.

Still not with you on the sprawling thing. Besides, pterodactyloid pelves and limbs are not really built to support a sprawling limb:

I agree. When you direct the femur outboard, the tibia is directed aft or laterally in the horizontal plane, not down.

..... Such a structure is noticably absent from sprawlers. Pterodactyloids have the same kind of anteriorly projected illiac blade as birds and mammals, and therefore probably didn't sprawl.

I agree, though there is also another reason that you don't mention. The iliac blade defines the camberline of the wingroot.

"The illustration (Fig. 6) fails to show individual toes. And if the toes are considered as a whole, they are aligned parallel to one another, not much wider than the metatarsal set. So I was wondering how webbing was discovered? If it could not be confirmed by the authors, shouldn't they have questioned it?" 

Gotta read the paper before I can comment.

Well, maybe. To our shame, neither Darren nor I could afford a trip to Korea to see the Haenamichnus prints, 

Darn, I thought I was the only one who had that problem  :-)


I disagree. With the possible exception of the Chaoyangopterus-like critters from China, there's nothing else really like an azhdarchid out there. 

I'm not sure that I would agree with that just yet.

No reason for it: just got carried away. Too much fuzz. The pterosaur, not me.

Oh. In that case, I won't send you a razor.
All the best,
JimC