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Re: Pterosaur structure, good job JC



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

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Palaeontography: http://palaeo.jconway.co.uk