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Re: Pterosaur arm supination (getting long)



This is getting good...don't send him...send us..

>(to cut to the chase, please let's not continue this argument anymore  

>with words. Send me diagrams and lists of real extinct pterosaur  

>precursors. Not hypothetical chimaera cartoons).



Cheers
Lucas


>DP



>On Jan 12, 2008, at 1:55 PM, jrc wrote:



> Comments inserted.

> JimC

> ----- Original Message ----- From: "david peters"  

> <davidrpeters@earthlink.net>

> To: <dinosaur@usc.edu>; <rccea@bellsouth.net>

> Sent: Saturday, January 12, 2008 10:17 AM

> Subject: Pterosaur arm supination

>

>

>> Jim C wrote:

>>

>> In other words, pterosaur arms, while flying, where completely  

>> supinated (radius and ulna parallel in every view) in this model.

>

> No to both points.



Then your model is different than that shown in John Conway's image  

and his description of it. Your model matches mine. That's the  

neutral position. The neutral position is like clapping hands when  

the elbows are angled out slightly. That's good. What you described  

earlier was complete suppination (elbows lateral, palms together over  

the head).



> Sorry, but if I were a pterosaur, when I did that maneuver the  

> palms would be facing one another, not in the begging position.  I  

> have to suppinate my own palms to make them face one another when  

> over my head.



Exactly. Which is how you described it.

>

>>

>

> When the humerus is still oriented within 20 degrees of distally,  

> the hyperextended fingers are oriented outboard, with the minor  

> exception that digit three is also shifted somewhat aftward since  

> it is pulled in that direction by the hyperextended, folded digit  

> four.



Jim, all the fingers in all reconstructions always are oriented  

outboard. What we're looking for is the direction the claw tips are  

facing. I say toward the ground in flight. John Conway and Chris  

Bennett say in the direction of flight. Right? Perhaps a good drawing  

would help. I'll send one under separate cover.

>

>

> Again, articulatin
 

> coracoid doesn't match your descriptiion.  The saddle-shaped  

> shoulder glenoid isn't all that saddle-shaped, and while it does  

> allow far more motion up and down and back and forth, it also  

> allows the humerus roughly about 20 degrees of rotation about the  

> long axis when the pterosaur's arm is extended in flight position  

> and a much larger range of rotation about the long axis of the  

> humerus when the distal end of the humerus is raised well above the  

> glenoid (the humerus pointed almost vertically). In that position,  

> the lip on the upper side of the glenoid is supported by the lip on  

> the proximal humerus, and the lip on the distal end of the humerus  

> is supported by the r/u.  This lowers the torso so that it is  

> pretty much parallel with the ground.  I don't know if pterosaurs  

> (or, at least, azhdarchids) ever used this posture for walking, but  

> their skeletons and muscle attachments were capable of doing so.



Interesting, but probably better suited for the highest portion of  

the upstroke during flight. We were talking about terrestrial  

locomotion.

>>

>> Elbows back (30 degrees from the parasagittal plane), neutral  

>> pronation/suppination, medial fingers in standard tetrapod  

>> orientation, a s90 degree torsion of the wing metacarpal work  

>> great for walking, flying, wing folding, tree grasping, etc. Ah,  

>> parsimony!

>

> In all honesty, parsimony isn't always correct -- neither is  

> Occam's Razor.....



Okay. The ball is in your court. Show me. You know where to send the  

blueprints.

>

>> Mike Habib mentioned that Chris's scenario does not depend on  

>> phylogeny: it could have happened just as easily with an iguana- 

>> like lizard or a proterosuchid-like archosaur. This is a magic  

>> trick designed to seduce you into thinking phylogenetic analysis  

>> is unimportant when it comes to certain taxa. Chris has had seven  

>> years to simply drop the characters he sees or he has read of  

>> Sharovipteryx, Longi
us  

>> into his existing cladogram and to accept or dismiss from his  

>> results subsequent claims. Such avoidance of cladistic analysis is  

>> exactly the same as tactics used by Jones, Rubens, Feduccia and  

>> Martin, Padian, Unwin, among others, which DMLers always rally  

>> against.

>

> As you know, I leave cladistics and phylogeny to others who have  

> more time to mess about with it (not knocking c&phy, just  

> acknowledgeing that I have a limited number of years left, and my  

> time is better spent elsewhere).  I'm much happier just holding the  

> skeleton in my hands, manipulating the joints, and seeing how they  

> move against one another.

>

>> Even so, Chris's scenario also depends on hypothetical models,  

>> made-up creatures, and haven't we gotten beyond that? If not, wake  

>> up people!

>

> Naah, Chris has manipulated a lot of skeletons too.



You should have been there in Germany. Chris used a lizard outline to  

make his point. In any case, I'm not arguing that Chris hasn't pushed  

a few derived pterosaur bones. My point was, let's use real specimens  

to figure out the transition from some sort of reptile to basal  

pterosaur. All this business about hyper extending the wing finger  

takes place before or during the Late Triassic. If its Euparkeria,  

demonstrate using Euparkeria. If its Longisquama, demonstrate using  

Longisquama. No one should 'buy' hypothetical outlines anymore. We're  

beyond that.

>

>> Chris's scenario also asks us to believe that a lizard-like  

>> tetrapod with short limbs (that's the picture he used) would  

>> somehow evolve a suppinated forelimb, one incapable of grasping  

>> medial objects while still nonvolant and having posteriorly- 

>> pointed hands. That pterosaurs evolved as leapers (does anyone  

>> know any proterosuchid or lizard leapers?) that turned into  

>> gliders (does anyone know any gliders that turned into flappers  

>> without a bipedal phase?).

>

> Don't bet that pterosaurs didn't develop flapping s
nch.  Keep in mind that a largely forelimb  

> driven leap is very similar to portions of the flapping cycle and  

> it isn't a huge 'leap'  for them to go directly from leaping to  

> flapping.



No one said they didn't happen simultaneously. In fact I have a  

number of papers in review right now that support exactly that  

scenario. But, here again, you have to come up with a real creature  

capable of doing that. A creature that can be tested. One that is  

falsifiable. I have done that in past work. If you need to see it,  

I'll send you the images. Problem is: it has short arms and long hind  

legs.



I mentioned proterosuchids because that's where Bennett 1996 nested  

pterosaurs, if they weren't related to dinos. No one has suggested  

that any proterosuchids were leapers. I mentioned lizards because  

Bennett outlined a lizard without calling it a lizard. I don't know  

of any leaping lizards, other than maybe Draco and the ones I have  

promoted as pterosaur precursors. Sharovipteryx would make a great  

leaping lizard. But was it flapping. I think so. Certainly  

Longisquama was.

>

>> Chris's scenario does not include provisions for the development  

>> of an elongated ilium, a prepubis or a weird lateral toe. Is it  

>> better to conveniently ignore these? Or incorporate those taxa  

>> that also have them?

>

> I'll leave that to you and Chris.  What I do know is that he is  

> correct about the skeletal orientations and that the arm and  

> shoulder that I have here match his description.



You have to consider the pterosaur precursor in toto. That's the  

failing of previous cladistic analyses. They looked at only the  

antorbital fenestra and mesotarsal ankle and skipped over the rest  

while excluding lizards from consideration.

>

>> re: finger orientation. This is where it gets really crazy. I  

>> thought it was only artistic license that showed pterosaur unguals  

>> always pointing anteriorly so we could see them well in lateral  

>> view. Not so, according 
ls  

>> of early pterosaurs are clearly oriented in one plane, as in all  

>> tetrapods, the fingers flexed anteriorly, according to Chris's  

>> scenario. They didn't just get crushed that way, which is what I  

>> thought. Chris's scenario requires the evolution of all three  

>> medial fingers to rotate (torsion) themselves at the  

>> metacarpophalangeal joint 90 degrees.

>

> No, it doesn't.



If it doesn't then set me straight. That's what he has said to me.

>

>> That's weird. But wait, now it gets really weird. In order to move  

>> the metacarpals into a dorso-ventral orientation, as John and  

>> Chris suggest for ornithochierids and Pteranodon,

>

> Azhdarchids match John's and Chris' suggestion too.  At least the  

> one on my desk does....



Be glad to see it. Send a picture. Then we can really talk.

>

>> the metacarpals have to rotate as a unit from the lateral plane to  

>> the dorso-ventral plane. Okay. In order to maintain the anterior  

>> orientation of the three medial fingers, they have to rotate back  

>> 90 degrees to their original untorsioned state. Isn't that alot of  

>> unnecessary voodoo?

>

> It would be if they had to do that.  Frankly, I have the impression  

> that your impression of pterosaurian r/u alignment is wrong and  

> that is causing you to think some unnecessary rotations are  

> required.  No offense intended.



John's own words and diagrams are what I'm working from.

>

>> Most damaging of all, Chris's and John's scenario

>

> Add me to that scenario as well.  To give credit where it is due,  

> Chris pointed the arm orientation out to both John and me several  

> years ago, and it very quickly became apparent to both of us that  

> he was correct.



Sounds like a wonderful epiphany. In which creature did that occur.  

Or between which two creatures did that occur? Nowadays you have to  

name names.

>

>> asks us to believe that a fully-functioning digit IV stopped being  

>> able to flex and started being able to hyper-hyperextend.

have no problem whatever with that.  Except that it didn't lose  

> it's ability to flex -- it just shifted the the center of rotation  

> of the articulation so that instead extending to straight, it  

> extends to about 160 degrees or so.  And instead of flexing to a  

> fist configuration, it flexes to nearly straight.



In other words, it did lose its ability to flex. If it can't make a  

fist, it can't flex, by definition, regardless of which muscles are  

being used. Now, I'll grant you, if the outside appearance of flexion  

and extension was maintained and only the muscles which controlled  

extension and flexion switched places then I would agree with you.  

But that is not the most parsimonious solution is it?

>

>> The transition is never explained, nor the transitional, pre- 

>> flight motive.

>

> One obvious pre-flight motive would be getting a progressively  

> elongated digit 4 out of the way when on the ground and  

> simultaneously placing it in an orientation where it is protected  

> from terrestrial damage.



Which creature is that? If unknown, which reptile was its closest  

relative?



My answer: At present there are obligate bipeds in the family tree of  

pterosaurs.  They weren't using their hands on the ground anymore, so  

they were freed up to become something else. The family tree of  

pterosaurs demonstrates that quadrupedality is secondarily acquired.  

That's why the hand prints are weird.

>

>> Chris's explanation is based on 'how do we get from here to  

>> there?' rather than letting the fossils guide us.

>

> I don't believe that.  In my experience, Chris always lets the  

> fossils guide him.



You should have been in Germany. He didn't use one fossil in his  

explanation for the origin of pterosaur wings. All cartoons.

>

>> If Chris and John's hypotheses depend on muscle scars, perhaps  

>> they have misidentified a few of them. After all, there are no  

>> modern analogs.

>

> Well....., actually crocs make a fairly good modern analog.



I 
ocs are not related. Try an iguana or a  

monitor lizard. You have to begin and end with phylogeny.

>

>> Certainly, their solution is not the most parsimonious.

>

> I think Chris has priority to the rest of us on the solution.  We  

> already know what I think about parsimony.  However, that said,  

> Chris' solution does appear to me to be reasonably parsimonious.



I would be very happy to change my mind, but you must have a  

convincing argument. Chris has been right about so many things, but  

wrong about so many things, too. Same with all of us. Let's get this  

right.



In conclusion: Send me pictures or drawings. I'm sending you mine  

right now.



David Peters

St. Louis









>

>













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