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

[Mark Witton <Mark.Witton@port.ac.uk>]

Hi all (and Dave),

To respond to Dave's questions:

"Rather than wax on with praise..."

Oh no, please do. We like praise.

"Tupuxuarids with long fifth toes? That's at odds with a big paradigm and the 
statement was not referenced."

Yup: Tupuxuarids have long-ish big toes. They're nothing like those of basal 
pterosaurs, but as pterodactyloids go, they ain't small. There's no reference, 
however, because it hasn't been published yet (guess we should've put a 'pers. 
obs.'). I'm not going to say too much because Alex Kellner has a paper on 
Tupuxuara on the cards, so we'll have to wait for the full assement from him.

W&N write: "It records a pterosaur moving with an efficient, parasagittal gait 
[46] rather than in a sprawled posture as suggested by earlier studies (e.g. 
[98])."

"...a tetrapod can have sprawling femora and produce a narrow-gauge trackway 
(more on this later)."

The mesotarsal ankle of pterosaurs dictates that the knee joint has to be 
perpendicular to the long axis of the body and the tibia has to be orientated 
more-or-less subvertical. 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. 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. 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. 

"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. 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.

"Fig. 9 shows what happens to the brachiopatagium in a deep chord configuration 
when the wing is folded. Why is it that no pterosaur preserves this?"

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. As for arguments to about the extent of pterosaur 
wing membranes, again, the evidence for broad chord wings is discussed in the 
paper and will not be repeated here.

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

"Azhdarcho and kin with narrow sharp beaks, were probably not related to these 
(see later)."

Um, not with you there. A monophyletic Azhdarchidae is one of the best 
supported and most stable groupings in Pterodactyloidea: Andres, Kellner and 
Unwin and other workers have all found it repeatedly in the last few years 
despite the increasing complexity of pterosaur cladograms and the introduction 
of long-ish necked edentulous forms from China. Heck, even I've managed to find 
it, and I've been called stupid in several comment sections on newspaper 
websites in the last few days.

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

"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.

W&N illustrate (Fig. 9) parasagittal hind limbs. 

"the femora would have sprawled in Q. if the axes of the acetabulum and femur 
were aligned."

The pterosaur acetabulum, being inperforate, facilitates a huge range of 
articulation. If memory serves, you can cross the legs of dsungaripteroids and 
keep the femora neatly in place. 

"If the axes did not align, as C. Bennett asserts with Dsungaripterus, then why 
not?"

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.

"And why not explore all the possibilities and dispense with the illogical ones 
in a functional morphology paper?"

Azhdarchids are certainly not the beasts to do this with: their remains aren't 
really up to the challenge (at least, as far as I'm aware). 

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

Still not with you on the sprawling thing. Besides, pterodactyloid pelves and 
limbs are not really built to support a sprawling limb: the hindquarters of a 
crocodile or lizard are significantly different from those of mammals or birds. 
Most obviously, upright walkers have long, dorsoventrally flattened, anteriorly 
directed illiac blades to anchor muscles that swing the leg forward. 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. Your suggestion that they did requires an explanation 
as to why three different approaches (comparative anatomy, ichnology and 
biomechanics) sharing the same solution is wrong.

"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?"

Well, maybe. To our shame, neither Darren nor I could afford a trip to Korea to 
see the Haenamichnus prints, so we had to go with what Hwang and chums told us 
in their paper. The take-home message is that the toes are the features you've 
pointed out: they're short, aligned parallel to each other and therefore add 
little to the footprint area, thus demonstrating their poor suitability for 
wading or swimming. Are they webbed? Well, I figure that Koo-Geun Hwang and his 
friends have probably got enough experience with fossil tracks to say so, but 
even if they're wrong, it doesn't change our conclusions one bit.

"Were "azhdarchids" monophyletic?"

See comments above. 

"Perhaps some clues as to functional morphology could have come from ancestral 
forms."

I disagree. With the possible exception of the Chaoyangopterus-like critters 
from China, there's nothing else really like an azhdarchid out there. We tried 
to stress the point that ptph group' only dilutes functional results. We wanted 
to do the opposite: focus specifically on one group and test their abilities 
regardless of what other pterosaurs were doing.  

"is that a rather long and substantial tail on Q?"

Long-ish, kind of...yeah...

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



Me as well.



Hope that adresses your points.

Mark

--

Mark Witton

Palaeobiology Research Group
School of Earth and Environmental Sciences
University of Portsmouth
Burnaby Building
Burnaby Road
Portsmouth
PO1 3QL

Tel: (44)2392 842418
E-mail: Mark.Witton@port.ac.uk