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

[David Peters <davidpeters@att.net>]

Thank you, Mark, for the reply. A few notes follow yours.


> 
> 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.

BTW, I knew that. I just needed your further thoughts. Not restricted to 
tupuxuarids either. 
> 
> 
> 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. 

Splayed does not mean horizontally opposed, either in pterosaurs or iguanids. 
Move the knees to about 45º. 3-D skeletons manipulated into a variety of poses 
will show you that with all the restrictions at the ankle and knee, the feet 
will fit the prints. And speaking of the ankles, all that's holding the 
proximal metatarsals to the tibiotarsus are a tiny pair of ball bearings, the 
centrale and the 4th distal tarsal. While restricted, this is not a lock-downed 
joint with tibial flanges and such.
> 
> 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 reco
 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.

I applaud you for your pteroid pturnaround. 

With regard to the deep wing chord situation, you cited a number of references, 
for the record, none are substantial. In Wild 1993, you've got wing tips and 
uropatagia. In Unwin & Bakhurina 1994, you've got ephemera with lines of 
demarcation that continue beyond the wing indicating their geologial origin. In 
Frey & Martill 1998 you have a wonderfully folded wing, but no evidence for an 
ankle connection. The Wang et al. 2002 Jeholopterus paper was covered by me in 
2002. When you put the plate and counterplate together, you get a very clear 
shallow chord. The Lu 2002 paper on BPM 0002 (Beipiaopterus chenianus) has bone 
and skin, but no one has determined the connections. Finally, in Frey 
Tischlinger, Buchy and Martill 2003 you have the darkwing Rhamphorhynchus, 
which purports to have wing material extending to the ankle (but that could be 
drumstick meat) because if you pull the bones back into a living configuration, 
you'll find the connection to the
 ankles disappears and is replaced by a small tight curve anterior to the 
femur. Plus in the same issue the narrow-chord Zittel wing (from another 
Rhamphorhynchus) says it all with a tight little curve, torn abit, anterior to 
the femur. The Zittel wing is good solid evidence. Still the best we have. 
>
> 
> 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. 

The key is the angle between rami. In one camp the angle produces a 
Pteranodon-like, Tupuxuara-like, Germanodactylus-like point. In the other 
clade, it produces a very gradually widening yard stick. 
Clade Az has a fused tibia/fibula in which the fibula essentially disappears. 
Clade Q has a distinct fibula. The prepubis has the shape of a modern putter 
with a posterior process in the Q clade, but a fan or an excavated fan in the 
Az clade. The pubis and ischium meet, nearly meet or fuse in the Az clade. 
Widely separated in the Q clade. The terminal wing phalanx is considerably 
shortened in the Q clade. Not so in the Az clade. And there's more of course. 
Granted, the two clades are remarkably convergent otherwise.
> 

> 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.

Kellner and Unwin did not include Eoazhdarcho, Eopteranodon and dozens of other 
taxa that split the long-necked pterosaurs into two clades (see below). The 
Andres and Ji paper I haven't seen
l is out. If anyone has 

Andres, B. & Ji, Q. 2008. A new pterosaur from the Liaoning
Province of China, the phylogeny of the Pterodactyloidea, and
convergence in their cervical vertebrae. Palaeontology 51, 453-469. Please send 
it.

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

Ouch! Wow. With so much data, why go with so little? 

> 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.

So.. you're saying... the old 'straightforward' rules are out? The irony is, 
when you follow _all_ the rules, includng lining up the axes, you get ideal 
configurations for land and air. 


> 
> 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. 

Sharovipteryx would beg to differ with you. A what great evidence it offers! 
Plus it's related! In pterosaurs, only the angle of the femoral head determines 
angle of sprawl. In many cases its negligible. In many others, quite distinct. 
Go with the evidence. In certain pterosaurs, you're right. The limbs are 
oriented dino like. In others, like ?azhdarchids and ornithocheirids they are 
not.

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.

Please, let me direct you to 
. Very enlightening. After you've seen this, tell me how wrong I am. In detail. 

http://www.biology.uc.edu/faculty/jayne/videos.htm

If certain living lizards can do these wonders. Sharovipteryx, Cosesaurus and 
pterosaurs could do them because they are better equipped to do them. 

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

Really? I can think of lots of critters: 
Biepiaopterus, SOS 2179, Huanhepterus, SOS 2428, Wellnhofer's No. 42, AMNH 
1715, Chaoyangopterus on the Q side, 

Wellnhofer's No. 13, Eopteranodon and you mentioned Eoazhdarcho on the Az side. 
Did Andres consider these taxa as well? If not, someone needs to.

I understand your need to focus. Hope you don't mind a little heat, all for the 
good of science. When I blunder, I want someone to tell me. And I love a good 
defense, but it must include evidence.

Best, Mark and way to go.

David Peters