Re: Pterosaur structure, good job JC

[Michael Habib <mhabib5@jhmi.edu>]

> I also note that the radius and ulna are not in the neutral position, 
> but are suppinated. To move the radius to the neutral position 
> requires not more than about a quarter of an inch move distally closer 
> to the medial edge of the ulna and another look at the carpals 
> orientation.

Any reason that we should expect neutral positions?  I've noted, at 
least in some other species, that the slight supination seems to yield 
a better wing position given the articulation at the elbow, and the 
manner in which the radius fits against the ulna distally.

> With wings extended that places metacarpals I-III in the plane of the 
> wing, as in other tetrapods and basal pterosaurs, not pasted against 
> the leading edge as it appears in John's drawing.

What do you mean by "in the plane of the wing", in this context?  
John's configuration technically has them in the plane of the wing, 
just palmar surface forward.  While this may seem a bit 
counterintuitive, pterosaurs seem to be derived from the typical 
tetrapod condition.

>  I cannot agree with John's hypotheses on wing folding = extension and 
> wing deployment = flexion. I'll await a further explanation that is 
> more parsimonious than the torsioned wing metacarpal hypothesis. 
> Hopefully it will include a phylogenetic demonstration using nonvolant 
> sister taxa of how flexion was prevented and extension became 
> hyper-extension. I also don't understand why palmar flexors can't flex 
> (fold) the torsioned fourth digit.

Chris Bennett independently came to the same conclusion, and detailed 
it in his Munich talk (which I''m sure you recall).  It is apomorphic, 
and the primary evidence comes from anatomical landmarks.  
Phylogenetically, the condition is apomorphic within pterosaurs, no 
matter which sister taxon you recover for them, so the bracket is 
currently somewhat uninformative (though I always support putting a 
character in its phylogenetic context).  Essentially, there is no 
evidence that the flexor or extensor tendons wrap on the antebrachium.

> I also liked John's earlier version of hind limb configuration during 
> flight in which the hind limbs were more laterally oriented forming 
> horizontal stabilizers.

Those are quite cool, I agree.  That position would not be for cruising 
flight, though; the limbs would reach that position (if it was used) 
during specific maneuevers where aft-support or extra lift was needed.  
Stabilization, per se, was probably not too important (as animal flyers 
generally use unstable flight).

> A tip of the hat to a great artist and visionary, Hope to see the same 
> specimen walking one of these days.

I second that!

Cheers,

--Mike H.



Michael Habib, M.S.
PhD. Candidate
Center for Functional Anatomy and Evolution
Johns Hopkins School of Medicine
1830 E. Monument Street
Baltimore, MD 21205
(443) 280 0181
habib@jhmi.edu