questions for Witton & Naish: Azhdarchid Pterosaur Functional Morphology

[David Peters <davidpeters@att.net>]

First of all, a well-written article. Brings up many good points. Rather than 
wax on with praise, I'll note these few questions.

W&N write: "Tapejarid feet show some of these characters but bear large claws 
on all digits [91], while tupuxuarids bear extremely elongate fifth digits." 

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

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])."

Is there a third alternative? Charlie Chaplin, Cosesaurus [one of the 
track-makers of Rotodactylus] and living lizards capable of bipedal locomotion 
on treadmills indicate that a tetrapod can have sprawling femora and produce a 
narrow-gauge trackway (more on this later).

W&N illustrate: pteroids in the anterior orientation and a deep chord wing 
membrane. 

Is there any evidence for either? 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? It should be extremely obvious in fossils. 
Rather, in reality the wing membrane all but disappears in all known fossils 
with folded wings. That can only occur with a shallow-chord brachiopatagium 
stretched between the wing finger and elbow. Arguments to the contrary will be 
gladly reviewed. 

W&N illustrate the azhdarchid with a narrow, pointed beak.

But didn't Kellner and Langston show with Q. sp. that the dentary is shaped 
much like a flattened and squared-off yardstick? As I recall, Jidapterus was 
similar. Zhejiangopterus is preserved in lateral view, so it cannot be used as 
an example. Azhdarcho and kin with narrow sharp beaks, were probably not 
related to these (see later).

W&N illustrate the azhdarchids with a stiff neck while walking.

Is this the only possible configuration? Or is it possible that the neck could 
have risen more vertically? Should a range of motion be provided? Again: 
functional morphology. I wo
gest a range of motion for the knees. For if the knees bent more than indicated 
then the posture changes.

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

As I recall, the femora would have sprawled in Q. if the axes of the acetabulum 
and femur were aligned. And if so, would that also change the posture? If the 
axes did not align, as C. Bennett asserts with Dsungaripterus, then why not? 
And why not explore all the possibilities and dispense with the illogical ones 
in a functional morphology paper? As above, sprawling femora, when combined 
with knees bent at 90º still place the feet beneath the torso.

W&N write: "The Haenamichnus pes prints show that the feet possessed soft
tissue pads on the digits, metatarsal heads and heel in the manner of
some tapejarids [91], [99]) with webbing between the digits [46]. 

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?

Were "azhdarchids" monophyletic? Has their phylogeny been tested to the genus 
level? Bakonydraco, Eopteranodon and Eoazhdarcho seem to be in league with 
Azhdarcho (sharp beaks and other characters), while Zhejiangopterus, Jidapterus 
and Quetzalcoatlus seem to be a different sort of creature (flat beaks and 
other characters), all sharing an elongated cervical series. For that matter, 
what genera are most closely related to azhdarchids? The key words "related" 
"phylogeny" and "ancestor" are not found in the text. Perhaps some clues as to 
functional morphology could have come from ancestral forms.

W&N write: "We therefore conclude that azhdarchid jaws were ill suited for
demanding feeding techniques or for subduing large, struggling prey,
and were better adapted for handling relatively small or immobile food
items."

I guess the baby sauropod in Fig. 9 falls under the latter category. And btw, 
is that a
 and substantial tail on Q?

All questions and disagreements swept away, I agree with W&N in their 
conclusions. The illustrations are first rate, although I would have attempted 
another tracing of Haenamichnus from the specimen because it needs it. 

 David Peters

davidpeters@att.net