[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index][Subject Index][Author Index]

Even more on pterosaur arms

Notable how some are reacting to the posts by a paleoresearcher who 
publishes regularly in the peer reviewed literature and provides review 
services on 
these matters to editors not with a sense of scientific curiousity and 
careful debate, but in a reflexive angry manner along the lines of why is that 
uppity GP causing trouble with our consensus. As per MW complaining about GP 
"moaning about my work." What, my disagreeing on technical grounds is 
"moaning?" Does that mean that anyone who disagrees with MW is moaning? 

Because I lack the time and resources (including lots of casts) to do a 
paper am stuck with this not ideal venue (not a criticism of the list, a mere 
fact), so here's some more. 

MW says that the "idea that pterodactyloids had sprawled forelimbs, akin to 
the Paul (2011[Prehistoric Times]) reconstruction of Q. n., is not 
supported by any trackway data" and the "humerus of that sticks out at 90 
from the body [same illustration] which is extremely unlikely for reasons 
mentioned by myself and Mike H." Starting with the latter, how is a pterosaur 
humerus stuck out about 90 degrees in any way unlikely? They did that all the 
time while flying. It is the ungulate posture that has never been documented 
with proper illustrations in the literature. So we know the pterosaur 
humerus could sprawl as I show in the PT figure. The proximal radius is 
articulated with the lateral humeral condyle as it was, placing the radius on 
leading edge. We know that the elbow could flex ventrally 90 degress or more 
with the humerus sprawling as shown in the figure. We know that the hand would 
be almost on the trackway midline in this posture, as per the azhdarchid 
trackway. The articulations at the wrist and finger base are all normal, so 
there is no serious problem there. The wrist can flex (as researchers say it 
can) fore and aft, especially to help clear the hand from the ground in the 
recovery stroke. There is space left between the wing finger and metacarpus 
for the folded wing membrane. The fingers are splayed laterally as per the 
trackways (but I should have shown 3 directed posteriorly). The stride can be 
achieved by humeral rolling and/or rotation similar to the actions of the 
sprawling humerus used in flight. So why do WM and others think there are so 
many problems with this posture? More specifically, where, exactly, is there 
a problem that shows the basic posture is not viable? (Would not be 
surprised if some details are off a bit.)

Some are arguing that the wing finger could fold up tight against the 
metacarpus. Yet no artist has shown that, including MW. Why is that? As long as 
the angle between the wing finger and metacarpus is open as all artists show 
it, there is space for the wing membrane in between. The membrane is very 
scrunched up at the finger base, but all of the membrane is directed 
posteriorly relative to both the metacarpus and wing finger, forming a scrunced 
sheet in the same plane. There is little or no overlapping of the outer and 
inner membranes, and the trailing edge of the inner membrane outer membrane is 
protected from damage by the outer rim of the complex formed by the 
radius-ulna/metacarpus. If the finger is really tight against the metacarpus 
of the membrane will be crushed. And it is hard to envision how the wing 
would fold with all the twisting it would undergo. And something else very 
interesting happens if the wing finger is folded zero to just a few degrees 
the metacarpus. The wing membranes cannot fold entirely tightly against the 
wing bones, they will still project strongly posterior from the elements 
when even when the wing as maximally folded. The inner wing membrane will 
project beyond the leading edge of the wing finger if the wing finger is folded 
tight on the metacarpus, leaving it vulnerable to abrasive damage. And the 
trailing edge of the outer wing membrane will project beyond the leading edge 
of the metacarpus and radius, leaving it even more vulnerable to damge 
because it will be hanging out there to the front or side. And it would look 
really weird. These are reasons few if any have illustrated pterosaur wings so 
tightly folded, and if MW thinks this is a way to accomodate an erect arm 
posture he is going to have to start showing this in his pictures.  

Take a look at MW's ungulate armed pterosaurs in Fig. 9 in he and Naish 08, 
and the notorious frontal view of Q. n. towering like a colossus next to a 
giraffe. He has the folded wing distal to the elbow forming a fore and aft 
plane paralleling the body midline (with the wing finger posterior to the mid 
arm so it easily clears the body and inner membrane) at the same time the 
erect humerus is on the same plane as the rest of the wing. As I have 
explained earlier that requires that the radius and ulna be strongly crossed 
pronation that is truly unlikely, or the proximal radius articulating much 
more medially with the distal humerus than the condyle for the radius shows it 
did which is not possible, or the distal radius articulating more medially 
with the proximal carpals than the articulations indicate. I think(could be 
wrong) that MW now realizes that, and that if the humerus is parasagital, the 
wing finger is then medial to the metacarpus, which is way he is now 
suggesting very tight wing folding to avoid having the wing finger poke into 
body. But if, as I just indicated, such extreme wing folding is not 
practical, and instead there was about 15-20 degrees of angle between the 
finger and metacarpus as most articulated specimens with folded arms and that 
artists have all shown until now, then the outer wing ends up in the middle 
of the bodies in the WM illustrations. And the outer wing impinges on the 
inner wing membrane. 

And there is something else I just realized. If an erect humerus results as 
it should in the plane of the rest of the wing being transverse to the body 
rather than fore and aft, we now have an awkward issue with the wrist 
posture and action. Now, if the plane of the wing is fore and aft during ground 
locomotion, then the wrist can operate as it normally does in animals with nar
row trackways. It might flex a little during the mid propulisive stroke to 
help keep the shoulder joint to ground distance more constant, and flex 
strongly fore and aft to help clear the hand of the ground during the recovery 
stroke (these motions are the same as varying wing sweep at the wrist during 
flight). WM and others show the wrist considerably flexed when quadrupedal. 
This may be correct, and is not a problem if the plance of the wing is fore 
and aft. But if the plane is transverse as an erect humerus very probably 
requires, then the wrist bulges awkwardly out to the side. Kind of like a bow 
legged person. Not impossible, but dubious. Avoiding this would require 
holding the wrist straight or very close to it. In any case, it would not be 
possible for the wrist to flip posteriorly considerably to clear the hand from 
the ground during recovery. Might not be critical, but inferior to the way I 
illustrate ptero arms when quad. 

To look at it another way, to get the bulk of the pterosaur arm to be 
parasagital when quadrupedal requires that the humerus be strongly everted, 
in birds. Making the humerus parasagital has the irony of rotating the wing 
well out of a parasagital plane, with all the adverse complications that 

MW said that he "really cannot understand why you[GP] think there are so 
many problems with this posture[MWs, CB's, etc]."

Here's the list -  

Sprawling humerus and erect arm from elbow down matches trackways, and 
works antomically (incl joint articulations, wing membrane) and functionally 
with no problems, using flight musculature to maximum efficiency. 

No joint articulation documentation that humerus can adopt ungulate 
posture. (Fujiwara & Hutchinson 2012 does not do this, and does not include a 
flying bird to see how it compares to pterosaurs using their method.)

Numerous dubious consequences that ensue from erect humerus. 

Different muscles are necessary to operate the arm when sprawling for 
flight and erect for walking, reducing efficiency and increasing arm muscle we
ight which is hardly likely in fliers. 

If entire arm including humerus work in a near parasagital plane then that 
requires improbabilites and impossiblities as follows. 

Proximal radius articulates medially with humerus (either between condyles 
as in MW as appears to be happening in Fig 1 in MW based figures in 
Averianov 13, or with ulna condyle as appears to be happening in Bennett 97) -- 
anatomically impossible. 

Or distal radius articulates medially with proximal carpals -- antomically 

Or radius and ulna strongly crossed permanently (which messes up wing 
posture in flight) or strong pronation from flight position -- both very 

Presuming none of the above are correct, then the plane of the folded wing 
below the elbow when quadrupedal is strongly transverse relative to the body 
midline. The problems with that are follows. 

The wrist is strongly everted, resulting in a dubious bow wristed posture 
and action. 

The short fingers are directed more posteriorly than the trackways ind

The wing finger is directed medially, so....

It impinges on the inner wing membrane, and projects into the body killing 
the poor animal. 

Or it is folded so tight on the metacarpus that the wing membrane is 
twisted in what is probably going to be a bad way at the base of the winger 
if not crushed, and the more proximal and distal membranes are overlapping 
so far that they are unduly exposed to damage. 

It looks like those who have been restoring pterosaurs with an erect 
humerus have not been paying close attention to each and every detail of how 
going to work. Seriously. They are showing the radius articulating too 
medially on the humerus, or speculating that the wing finger might fold tight 
the metacarpus without considering what will happen with the wing membranes 
-- and no one including MW illustrates that happening in their restorations. 
We should all be asking what is going on with this. It appears that some got 
so caught up in the trackways being narrow that they assumed that the upper 
arm must be parasagital, and then went for it without thinking matters 
through along the entire length of the arm, and without paying close enough 
attention to the details of their restorations. The real question is not why 
there is skepticism about the erect humerus, there should be. The real question 
is why is it being used without proper documentation that it will work with 
everything articulated properly, and without messing up the wing membrane, 
when the everted humerus works with no fuss or muss.