Re: Pterosaur structure, good job JC

[David Peters <davidrpeters@earthlink.net>]

Dear John and David M.,

re: adductors on the prepubes, well, without modern analogs, there's  
just no telling, is there? I would suggest as a hypothesis that since  
bones serve as anchors for muscles -- and we first see prepubes on  
Sharovipteryx, a creature with hyper-elongated legs and without all  
the presacral mass exhibited by pterosaurs -- that prepubes probably  
developed to assist that sprawl-legged biped to maintain its  
configuration. The logic is: if the prepubes are new, then what is  
else nearby is new that it developed in association with? Answer:  
elongation of the legs. Perhaps it's not the only explanation, but it  
seems parsimonious.

Your reconstructed pteroid is indeed on the medial side of the  
preaxial carpal, and I apologize. Seemed to be in the cup. I checked  
out:

http://palaeo.jconway.co.uk/object.php? 
title=Anhanguera_piscator&objectid=53

then realized that the articulating surface is near the cup of the  
preaxial carpal and that may be the cause of the confusion.

Here's a solution. It should also be noted that in situ the pteroid  
tucks into a vacancy distal to the radiale (Bennett 2007, JVP 27:885)  
as it does on Eudimorphodon and all manner of other pterosaurs.  
That's because it is not a new bone, but a former centralia. The  
migration to the anterior surface can be traced beginning with  
Macrocnemus, which, like Cosesaurus, has a poorly ossified carpus  
(for whatever reason). The predecessor of Macrocnemus,  
Huehuecuetzpalli, likewise has a poorly ossified carpus, so it's  
phylogenetic situation over a series of taxa. These migrated carpals,  
in my opinion, need to remain in association with the carpus in your  
reconstruction.  On page 888 of the same issue, Bennett's  
reconstruction, like your's, places the preaxial carpal on the  
prominence of the distal syncarpal, which acts to separate the  
pteroid from the radiale. This situation is remedied by going back to  
the insitu specimen on p. 885. You can see that Bennett has labeled  
the disarticulated right preaxial carpal (pc) with the sesamoid in  
place, but he did not label the articulated left preaxial carpal  
still attached to the left distal syncarpal (ds) behind and below.  
The in situ specimen maintains all elements in close association and  
everything articulates as it should. Adopting this configuration  
dramatically closes the gap between the radius and pteroid, as in all  
other pterosaurs.

re: the articulation of carpals I-III with the carpus, again on page  
885, I'm looking at the insitu specimen and I understand what you're  
saying about aligning dorsoventrally. Since this case is different  
from that of all other complete and articulated specimens in which I- 
III align in the plane of the wing, it may be more parsimonious to  
consider the case of AMNH 22555 as one in which the elements have  
moved during taphonomy. Clearly there is movement of the right  
preaxial carpal and the left metacarpals seem to have followed the  
drift.

re: the absolutely tiny fingers on AMNH 2255: They appeared to be  
rather standard in terms of size to me, similar to those of A.  
piscator and other ornithocheirids. If you could, please send me your  
photos so I can update my reconstruction.

re: getting into the walking position. I have to ask, do you follow  
Wellnhofer's (1991: p. 156) in which the fingers point anteriorly? Or  
do you follow Unwin (The Pterosaurs From Deep Time: 201) in which the  
elbows are in anterior to the shoulder glenoids? Or Robodactylus (The  
Pterosaurs From Deep Time: 207) in which the elbows are in and the  
fingers are not included? Or (redrawn from Lockley in The Pterosaurs  
from Deep Time: 217) in which the fingers are right for the tracks,  
but they do not point anteriorly, as you and Bennett suggest? Or the  
one I'll send you in a separate email from my own collection. All are  
reconstructions of a walking Anhanguera in different configurations  
(Unwin seems to prefer all of them).

re: awkward scenario for muscle attachments. John, I will attempt a  
muscle reconstruction, as you suggest. Hopefully it will not be  
awkward. I wonder if the problem stems from the problems you and  
Chris are having with that Anhanguera skeleton?

re: Compromising on the hind limbs: Don't backslide. You had it right  
the first time. Legs out, like Sharovipteryx.

Again, many compliments on your work. If I'm wrong, I need to know.  
The most important thing is to get it right.

Best,
David Peters
St. Louis


On Jan 11, 2008, at 10:53 AM, John Conway wrote:

> David Peters wrote:
> > Dear John and dinolisters,
> > excellent restoration of pterosaur anatomy is well worth the look.  
> > His artwork, I think, places him as the heir apparent to Doug  
> > Henderson.
>
> Thanks Dave.
>
> > John has envisioned the big traps and lats that so many artists  
> > miss. But I notice John does not put adductors on the prepubis.
>
> As David Marjanovic says, should I? (Genuine question.) But then  
> you know, I've probably missed a lot of stuff that isn't forelimb  
> related. The hindlimbs are rather schematic too.
>
> > I would like John to comment on his placement of the pteroid in  
> > the bowl of the pre-axial carpal, a placement that is not  
> > reflected in the fossil record, as recently shown by Chris Bennett.
>
> It isn't! - maybe the picture isn't clear enough to see.
>
> > 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. 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.
>
> I disagree, obviously. The base of the metacarpals (the  
> articulations of which can be seen on /Anhanguera/ wrists) are  
> aligned nearly dorso-ventrally. I don't think you've fully grasped  
> the position I have the fingers in, it's closer to your position  
> than you may think - I'll try to get some drawings together to make  
> it clearer.
>
> > I'm also looking for and having a hard time seeing the big unguals  
> > in fingers I-III.
>
> They aren't there. The fingers are absolutely tiny on AMNH 22555,  
> what's there is what I saw of the fossil.
>
> > When the wing fingers are placed into the standard tetrapod  
> > configuration and the radius is in the neutral position, the  
> > fingers face each other during tree trunk climbing and they  
> > hyperextend laterally during walking (with elbows oriented  
> > posterolaterally), matching ichnites. How can this happen in this  
> > configuration without some sort of strange humeral configuration?
>
> I don't see your problem to be honest. All you need do is swing the  
> arms down and bam! walking position, with the fingers aligned with  
> tracks.
>
> >  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.
>
> Ah, well, I think Chris provided a decent scenario for how that  
> might have happened at Flugsaurier. The paths required of the  
> muscles for flight-position to be extension are, well, crazy  
> spiralling.  Counter challenge: draw your own scenario of forelimb  
> musculature, I think you'll find it's awkward, to say the least.
>
> > 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. He mentioned examples of wing  
> > connection to the thigh or ankle. I'd be very interested in seeing  
> > those delineated.
>
> I actually prefer the hip-attachment for pterosaurs like this  
> myself, but variety is the spice of life and all that. I was  
> originally going to to draw this with several different attachment  
> versions, but I decided I'd spent too much time on it already, and  
> went with a 'compromise' position.
>
> > A tip of the hat to a great artist and visionary, Hope to see the  
> > same specimen walking one of these days.
>
> Cheers Dave, thanks for looking so closely! (... maybe too closely.)
>
>
> John
>
> --
> Palaeontography: http://palaeo.jconway.co.uk