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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).
>On Jan 12, 2008, at 1:55 PM, jrc wrote:
> Comments inserted.
> ----- Original Message ----- From: "david peters"
> To: <firstname.lastname@example.org>; <email@example.com>
> 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
> 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
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
>> 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,
> 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
>> 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
>> 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
> 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
>> 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
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
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
>> 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
>> 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
>> 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
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.
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
In conclusion: Send me pictures or drawings. I'm sending you mine
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