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Re: Yet more on pterosaur quad arm posture



Greg,

"Do not know what the "Paul (2011) reconstruction of Q. n." is"

The one from the spring edition of Prehistoric Times where you were,
again, moaning about my work and giraffe-sized azhdarchids? The
humerus of that sticks out at 90 degrees from the body which is
extremely unlikely for reasons mentioned by myself and Mike H.

I don't have time to run through this message point by point, but the
asymmetrical nature of the wing finger/metacarpal joint, which you
seem convinced is not there, is very well established in pterosaur
literature. You can see it illustrated very clearly in several papers:
Wellnhofer 1978, 1985, 1991 (his Anhanguera monograph), Young 1964,
Eck et al. 2011 and so forth. The wing finger can fold very neatly
along the metacarpal: see work by Bennett (2001) and the recent paper
on Noripterus by Junchang Lu and colleagues. This latter, 3D specimen
in particularly nice, as it shows the wing folded along the metacarpal
and clearing the elbow. The suggestion, therefore, that the wing
finger stabs the body if the animals stand parasagittally is
unfounded.

The orientation of the pterodactyloid glenoid is rather broad, and it
is open posteroventrally. The fact that the arm can be folded against
the body while being ventrally deflected is well established, not the
least by a number of pterodactyloid fossils preserved in lateral
orientations which show this arrangement (check out Wellnhofer's
monograph on Solnhofen pterodactyloids for numerous examples). The
supraglenoidal buttress extends posteriorly further than the ventral,
which probably helped support the standing limb while permitting
movement in the ventral plane. I really cannot understand why you
think there are so many problems with this posture.

"What should happen is
that I should be the reviewer of all papers on the subject of archosaur
articulation since I have been at this so long and have a better ability to
mentally visualize functions in 3-D than most it seems (have already shot down a
couple of bad articulation papers in peer review for major bio journals). That
would eliminate a lot of nonsense. Seriously, send the manuscripts to me
and I'll determine if they make sense or not."

This comment will certainly affect my consideration of you as a future referee.

Mark

On 1 July 2013 00:30,  <GSP1954@aol.com> wrote:
> In a message dated 6/27/13 3:26:25 AM, mark.witton@port.ac.uk writes:
>
> << Pterodactyloid trackways show that their limbs are held in parasagittal
>
> poses, and those of azhdarchids seem to drop almost vertically from the
>
> body, as depicted in my 2008 illustration and subsequent works. I'm not the
>
> only person to illustrate and describe their postures in this way: Chris
>
> Bennett (1997), David Unwin (1997, 2005), Hwang et al. (2002), Mazin et al.
>
> (2003) and many others have done the same. Presumably, the skewed joint at
>
> the end of the metacarpal deflects the distal wing laterally when the arm
>
> is folded up. Thus, I'm happy that my reconstructions are more-or-less
>
> consistent with this idea. The idea that pterodactyloids had sprawled
>
> forelimbs, akin to the Paul (2011) reconstruction of Q. n., is not
>
> supported by any trackway data.
>
>  >>
>
> This is a remarkable statement. Including how citing a list of persons as
> doing a particular thing is useless if it is none of them or others have
> backed up with proper documentation. And as is becoming increasingly clear 
> they
> have not come close to doing.
>
> Do not know what the "Paul (2011) reconstruction of Q. n." is refering to.
> Aside from not remembering publishing a pterosaur illustration that year, I
> restore azhdarchids with narrow trackways.
>
> There seems to have arisen a strange opinion that a narrow trackway
> precludes a sprawling humerus. This is of course long been known to be 
> incorrect,
> including the Gambaryan & Kuznetsov paper this year in J Zool illustrating
> the combination of a sprawling humerus and narrow trackway in echidnas. And
> that in an animal in which the humerus makes up around half the arm length. In
> azhdarchids the radius-ulna+metacarpal length ratio is about 4. So with the
> humerus sprawling, just flex the elbow about 95-100 degrees ventrally and
> medially and you get as narrow a trackway as you want. Duh. Seriously, this
> is obvious, what is this argument about? If Witton etc saw an echnidna
> trackway they would insist it is erect limbed, but it ain't.
>
> To determine limb posture trackways are important, and when the trackway
> gauge is very wide it must be sprawling, but when it is narrow joint
> articulations etc must be examined to determine humerus posture.
>
> We know quad dinosaurs had erect arms not just because of their narrow
> trackways, but because the shoulder glenoid faces predominantly
> ventro-posteriorly, with the scapula component often facing a little 
> medially, precluding a
> sprawling humerous posture (as I have published in the technical
> literature). It is not an exactly parasagital gait, the elbow is bowed out 
> some (as is
> common in mammals), and the hands are more widely separated than is common
> in mammals. But it is erect, not sprawling.
>
> The primary function of the super specialized pterosaur arms was flight.
> That was what they were mainly adapted for. Ground locomotion was a secondary
> function that had to be accomodated to the flight adaptations.
>
> We have no doubt that the pterosaur humerus could sprawl because that is
> what it had to do in flight, and becasue the shoulder glenoid faces laterally
> as in sprawlers, not postero-ventrally. So far no one has shown that any
> pterosaur could position its humerus in an erect posture. Vague armchair
> assertions that a laterally facing shoulder joint will also allow an ungulate
> posture will not do. Until someone publishes a detailed diagram showing it can
> be done, or mounts a cast based on well preserved bones -- anyone want to
> point out an example? -- it is very dubious speculation at best, and very
> likely wrong.
>
> No to "the "skewed joint at the end of the metacarpal deflects the distal
> wing laterally when the arm is folded up." The flexion at the joint of the
> base of the wing finger had to operate in the horizontal plane during flight,
> so the outer wing could be swept back during say diving flight. If the wing
> finger base acted as W suggests then sweeping the outer wing strongly back
> during flight would also cause it to arc upwards, partly flat on to the air
> flow, which would be aerodynamic madness. That's why nothing like that
> happens with the outer wing of birds. Wellnhofer 1991 says something obscure 
> about
> the wing finger base joint causing the outer wing to twist for folding the
> outer wing so its top side faces laterally, but that does not match his own
> figure on the previous page, or on p 137.
>
> Take a look at that last figure. And p 156 of the Wellnhofer books. Those
> quad poses get the articulations of the joints and orientations of the wing
> elements right -- except for the short fingers. Humerus. Sprawling (as also
> in flight, same as in birds). Humerus condyles for radius and ulna. Directed
> ventrally (so rest of wing can be downstroked in flight at elbow because
> humerus cannot depress much below horizontal -- the lack of down flexion in
> Wellnhofer 87 p 153 is way off, as is the flexion at the wrist -- also
> streamlines joint, same as in birds). Radius anterior and maybe a little 
> medial to
> ulna (presents minimal profile to airflow when flying, same as in birds).
> Slender metacarpals anterior to stout one (also maximizes streamlining by
> keeping leading edge of hand directed anteriorly as in birds). Folded outer 
> wing
> directed posteriorly to clear body, and in same plane as
> radius-ulna-metacarpus (basically same as in birds).
>
> Some of you may be bouncing off walls saying but the trackway gauge is wide
> in the figures. Stop, calm down, and think about it. Be Zen. Note how the
> wide hand gauge is because the humeri are directed somewhat dorsally (as
> during the beginning of the flight upstroke), while the elbow flexion is about
> 90 degrees, so the arms slope down and out, placing the hands laterally for
> no particular reason. Here's how to solve the problem. Simply depress the
> humerus about 20 degrees until it is horizontal, and/or flex the elbow more as
> needed, swinging the hands medially until they are nearly on the midline.
> There you go, a sprawling humerus with a narrow trackway. Ta-da! While at it,
> rotate the humerus along its long axis so the rest of the arm is more
> vertical rather than directed strongly forward as shown in both figures, and 
> it is
> ready to walk, baby.
>
> Also change the orientation of the fingers. They are shown directed
> forwards, but that cannot be correct because the distal line of the small
> metcarpals runs antero-posteriorly (this is like trying the wrench the 
> fingers of
> your left hand hard to the right, on the same plane as the metacarpus and 90
> degrees relative to their true extension-flexion arcs - ouch!). With the
> fingers correctly extending dorsally relative to the plane of the metacarpals
> they will splay laterally.
>
> Here's another way to look at it. Take the two sprawling quad figures. Keep
> the radius-ulna-metacarpus complex articulation and orientation realtive to
> the body exactly the same. But depress the humerus a little until it is
> horizontal. And extend the wing finger. You now have the flight downstroke
> (with the elements presenting minimal frontal profile). Which we know worked
> just fine (do the same with the bones from your handy dandy bird wing, they
> have the same articulations and orientations in the downstroke). Now, refold
> the wing finger, and you have the basic quad pose, except flex the elbow a
> little more (remember, it can flex until the radius-ulna are nearly folded
> against the humerus as in birds and us, so getting the walking posture is 
> easy)
> to get that narrow trackway we all know and love. Neat, isn't it. All that
> has to then be done to walk on the arm is to rotate the humerus on the
> shoulder joint (presumably rolling it along its long axis [also used to vary 
> the
> wing's angle of attack relative to the body in birds and pterosaurs according
> to Wellnhofer] and perhaps fore and aft horizontally some [used to help
> vary wing sweep]) to achieve a stride, pretty long because the
> radius-ulna+metacarpal is so long so only a little motion of the humerus will 
> do it. There
> is little action at the elbow. It's all so easy, no fuss, no bother, using
> the same basic bone posture and muscle actions as in flight for quad walking,
> no strange if not impossible articulations or rotations. Because the same
> muscles are used for walking as for flapping, no need to have distinct walking
> versus flying muscles that add weight.
>
> If we instead try swinging the humerus back approaching 90 degrees (in
> dorsal view) into an ungulate posture, aside from probably disarticulating the
> shoulder joint, the outer wing is going to be directed right into the body,
> unless there is the improbable rotation at the elbow or along the long axis
> of the radius-ulna that look locked together along their shared plane (these
> are not feasible in birds, chances are low that pterosaurs could do them)
> that is undocumented arm chair speculation. The erect arm idea is directly
> self contradictory. The wing finger cannot collapse less than about 25 degrees
> tight on the metacarpus. So the more tucked in the eblow, the more the outer
> wing jabs into the body. And what for? Why have the arm for some mysterious
> and illogical reason going all erect what with the outerwing banging into
> the body and adding weight for muscles that work the humerus fore and aft and
> what all. That when keeping the humerus parsimoniously exploits the flight
> posture and avoids also those problems. Anatomically probably impossible and
> does not make functional sense.
>
> Take a gander at the photo of the complete Santanadactylus wing p 125
> Wellnhofer. It shows the arm in flight posture in dorsal view. If the winger
> finger is swept back nearly 90 degrees it will remain in the same plane,
> pointing directly down in the photo, no? The photo also shows the arm in 
> close to
> posterior view if the humerus is assumed to be in an erect walking posture
> (particularly the ulna-radius-metacarpus, there would be some flexion of the
> elbow). So what will happen to the wing finger when it is folded? It pokes
> right smack into the middle of the body, doesn't it. Anatomical nonsense,
> agreed? And there is no way to swing the folded outer wing outwards to clear 
> the
> body by radius-ulna rotation or other joint rotations in such a locked up
> system. How to get the outer wing to fold posteriorly? Easy. Flex the elbow
> about 90 degrees, swing the humerus laterally until it is sprawling, and the
> folded outer wing is clear of the trunk, right?
>
> Regarding Bennett's 97 restoration of pterowalking. It's wrong. Bill says
> he did not attempt to restore the actual joint action in the paper, so his
> posture is intuitive not scientific. The first clue that something is not
> right is that with the humerus erect the wing finger is folding on the
> outside(!) of the arm, which is opposite of what would actually happen. Why 
> the 180
> degree error? Because the proximal end of the radius in both pterosaurs
> figured is shown articulating with the ulna condyle of the humerus. (There is 
> no
> way to get the left radius so far medial with the left humerus in the erect
> posture shown. Get your bird bones and try it. To get the radius in
> something close to that position the humerus has to be nearly horizontal and
> directed very strongly anteriorly, with the distal humerus condyles directed
> medio-ventrally posteriorly, all of which is impossible. In the figure the 
> left
> elbow is also hyperextended well beyond the articulations. To get the right
> radius in the exact position and orientation shown requires having the humerus
> directed nearly vertically upwards. I'm not kidding, get your bird wing
> bones and ye shall see.) If the proximal ends of the radius and ulna are
> articulated properly the outer wing is directed inwards and banging into the
> belly. Also incorrect is the articulation of the short fingers, they are 
> rotated
> 90s degrees relative to their actual position on the metacarpus so the palm
> faces medially as in the trackways. With the orientation of the radius, ulna
> and metacarpus as shown in the fingers, the fingers would be splayed
> anteriorly. To actually get the fingers splayed out laterally as per the 
> trackways
> the radius needs to be anterior to the ulna, with the slender metacarpals
> leading the stout one. That happened automatically with, and only with, the
> humerus sprawling. Also incorrect is the orientation of the wing finger
> relative to the metacarpus. In the view shown in the figures we should be 
> seeing
> the leading edge directed laterally, towards the viewer. Instead it is
> directed posteriorly (which gives the illusion of proper outerwing folding 
> when
> walking), and that would again actually happen only with the radius and
> slender metacarpals on the leading edge during walking which requires a 
> sprawling
> humerus (in case you have not gotten the message yet).
>
> The fact is that most folks have not been paying into to the details. Some
> have posed the wing elements pretty much properly and have the humerus
> sprawling as it should be, but ignored the trackways so the elbow is too 
> extended
> and the hands separated too far (a common flaw of quad mounted skeletons).
> Many have been paying hardly any attention to  how the joints articulate and
> how the arm must work as a wing and assuming a narrow trackway demands an
> erect humerus when a little geometry and some modern animals proves
> otherwise. I would do something about this, but it is a major project that 
> would
> include obtaining casts of the Santanadactylus arms (cannot even get the
> Leonardi & Borgomanero 87 paper throught the JHU system). What should happen 
> is
> that I should be the reviewer of all papers on the subject of archosaur
> articulation since I have been at this so long and have a better ability to
> mentally visualize functions in 3-D than most it seems (have already shot 
> down a
> couple of bad articulation papers in peer review for major bio journals). That
> would eliminate a lot of nonsense. Seriously, send the manuscripts to me
> and I'll determine if they make sense or not.
>
> So if one wishes to continue to put ungulate posed arms on pterosaurs, get
> out there and show how it actually works with nifty detailed diagrams
> including of the joint articulations and/or a mounted cast. With the joints
> actually articulated as they should be. Preferably in the technical 
> literature.
> And when it does not work out and you instead publish a paper showing the
> humerus was sprawling as the hands were nearly on the midline, then be sure to
> credit my correct illustrations. There has been way too much failure to
> credit priority of late.
>
> By the way, as noted by Wellnhofer pterosaurs could not elevate the humerus
> vertically as is normal in modern flying birds. It is very likely that most
> if not all pterosaurs had good climbing flight abilities. So the inability
> of basal dinosaurian fliers like Archaeopteryx and Microraptor to fully
> elevate th humerus does not necessarily refute their ability to be good 
> powered
> fliers. Contemplate it.
>
> GSPaul
>
>  </HTML>



-- 
Dr. Mark Witton
www.markwitton.com
Palaeobiology Research Group
School of Earth and Environmental Sciences
University of Portsmouth
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Burnaby Road
Portsmouth
PO1 3QL
Tel: (44)2392 842418
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