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

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

Just realised my replies only went to Mike and Jim. Whoops.

--

I pretty much agree with everything Jim's said. Just a few things more
points to add:

"> 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)."

I mean when its orientated with the toes pointing forward, as shown by
Haenamichnus. 

"> 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"

Sorry - didn't explain that very well. It's more that sticking the
femora out laterally it affects the postture of the rest of the limb,
which then causes the feet to also face anterolaterally and the narrow
gait to disappear. 

"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."

I can almost guarentee that our discussion of flight performance will be
very basic to your ears, Jim. It's mainly basic wing ecomorphology:
comparing relative loading, aspects and that sort of thing. We mainly
use it to say 'azhdarchids would be fine flying around an inland
setting' rather than anything with real bite. Pteroid wise, once again,
I was a bit hasty. I mean that it doesn't affect wing area a great deal:
tucking it in a bit more doesn't suddenly transform azhdarchids from a
vulture into a duck, basically.

"Since all three major [wing] 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."

I agree to a point: with perhaps the exception of Sordes, there are no
fossils that unambiguously show an ankle-attachment (or any other
attachment for that matter). That said, I can think of at least seven
specimens that ambiguously show an ankle attachment (there may be more),
whereas a knee-attachment is only really supported by one (also
ambiguous), and the hip-attachment has no fossil support at all. It
seems to me that finding seven slightly dodgy examples is enough to
think that we might have the beginning of a pattern. And, sorry Dave
(Peters that is - lots of 'Daves' in pterosaur research), I think there
are enough pterosaurs specimens with proximal regions of the
brachiopatagia preserved to rule out an elbow attachment. 

"> 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"

True: it is a bit more parallel-sided than other azhdarchids, so it may
have had a blunter jaw tip. Still, there are no real 'blade-like'
azhdarchid mandibles (at least, not in my definition of 'blade-like' -
your Rynchops-type, I suppose. Not to be confused with the
Thalassodromeus-butter-knife-type).

"> 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."

Sorry: do you mean about the affinities of Chaoyangopterus and his chums
to azhdarchids, or that there are other azhdarchid-like pterosaurs out
there? 

"Oh.  In that case, I won't send you a razor."

Actually, I know several people who probably wish you would.

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