"...the large size, great length, and unconventional arrangement such that it swung backward in flight position enabled digit IV to spread and support the wing yet fold it out of the way when the animal was not flying.
Such an arrangement of fingers with one swinging away from the others is unique among vertebrates."
Let's consider this "uniqueness".
Whenever an explanation requires a characteristic that is "unique among vertebrates" we have to question whether this explanation is correct.
After all, if someone says to you - okay here is how it worked. It worked in a way that is found NOWHERE ELSE IN THE VERTEBRATE WORLD. Then you have to think that perhaps that explanation is not correct.
So I think we can put such an explanation to the side.
In case people are having trouble visualizing what I am proposing, work with your own hand.
Hold your hand out, palm down. Your index finger is the wing finger so it is very long. Bend your index finger toward your palm. Now imagine that you could continue bending it in that direction so that the index finger would point back toward the elbow.
That is what I am suggesting.
Now the question arises as to how that could be accomplished, given the length of the index finger.
I can see how that could be accomplished but if anyone would like to offer up a suggestion please do.
Hold your hand out, palm down. Your index finger is the wing finger so it is very long. Bend your index finger toward your palm. Now imagine that you could continue bending it in that direction so that the index finger would point back toward the elbow.
That is what I am suggesting.
Now the question arises as to how that could be accomplished, given the length of the index finger.
I can see how that could be accomplished but if anyone would like to offer up a suggestion please do.
Here is how it could work:
Begin with the pterosaur on all fours (or standing) with the index finger bent (toward the palm and then toward the elbow).
The unfolding of the index finger is a combined motion of lifting the arm, rotating the arm slightly backward (palm back) and unfolding the finger. Then at the top of the arm extension, rotating the arm back again.
What I am saying does not require a vault launch method but it would work with that method as well.
See video:
http://www.newscientist.com/article/dn19724-did-giant-pterosaurs-vault-aloft-like-vampire-bats.html
I should make it clear that when I say the INDEX finger I am proposing that the huge finger that is considered the "4th finger" is actually the index finger and is positioned where index fingers are usually positioned.
ReplyDeleteThe three little fingers are behind it when in flight*, with the index finger on the leading edge of the wing.
* During the forward downstroke phase of the wing motion. See earlier posts on the phases of the wing motion.
http://bigcat.fhsu.edu/biology/cbennett/flotsam/Bennett-2008-forelimb-myology.pdf
ReplyDelete"The reconstruction suggests that during the evolution of the pterosaur wing, digit IV did NOT rotate about its long axis such that extensor muscles spread the wing and flexor muscles folded it, but rather the range of motion of the metacarpophalangeal joint
of digit IV migrated posteriorly so that flexor muscles spread the wing and extensor muscles folded it. Thus the function
of the flexors and extensors of digit IV may be thought of as having been reversed."
Bennett shows that the wing finger was not turned 90 degrees. That is progress.
However Bennett's alternative is that flexor muscles spread the wing and extensor muscles folded it.
In other words the function of the flexors and extensors of digit IV may be thought of as having been reversed.
In case people are having trouble visualizing what I am proposing, work with your own hand.
ReplyDeleteHold your hand out, palm down. Your index finger is the wing finger so it is very long. Bend your index finger toward your palm. Now imagine that you could continue bending it in that direction so that the index finger would point back toward the elbow.
That is what I am suggesting.
Now the question arises as to how that could be accomplished, given the length of the index finger.
I can see how that could be accomplished but if anyone would like to offer up a suggestion please do.
Oudenoida posted:
ReplyDelete"Having the second digit point towards your feet (downwards for humans, posteriorly for a flying pterosaur) and attached to the body with the wing membrane in that position, leaves you with the forearm fully pronated, without the ability to supinate it again."
I am not sure if we are visualizing this the same.
Why do you say "without the ability to supinate it again"?
Are you questioning how the long bent index finger could be straightened out again?
I am not sure what problem you are visualizing. Can you describe the problem in more detail?
Can anyone else contribute on this?
Oudenoida posted:
ReplyDelete"To have your second digit point backwards, you need to fully pronate the forearm. In that position, you can freely flex or extend the finger- but if the flexed finger is attached to the body with a membrane, then you cannot *supinate* the pronated forearm (unless you roll, stretch and twist the entire membrane). Feel free to visualize it. Like you described, imagine that you have a membrane extending from the backwards-pointing finger of your pronated forearm to the side of your body. Now try to supinate the forearm, and you'll find that the bent second finger HAS to turn, first down, then FORWARD. How would the pterosaur do that? It would rip the wing.
Can anyone visualize the situation I am describing?
ReplyDeleteCan you see how the index finger straightening out movement can occur?
If anyone wants to see how a creature can manipulate a membrane I recommend this:
http://www.youtube.com/watch?v=YTKNZDjSaXQ
(I am not suggesting that the pterosaur movement is the same. Just that a membrane can be manipulated in quite extraordinary ways).
Begin with the pterosaur on all fours (or standing) with the index finger bent (toward the palm and then to the elbow).
ReplyDeleteThe unfolding of the index finger is a combined motion of lifting the arm, rotating the arm slightly backward (palm back) and unfolding the finger. Then at the top of the extension, rotating the arm back again.
What I am saying does not require a vault launch method but it would work with that method as well.
See video:
http://www.newscientist.com/article/dn19724-did-giant-pterosaurs-vault-aloft-like-vampire-bats.html
So we see how the long index finger could be unfolded.
ReplyDeleteHow would it be folded to begin with?
It would follow the steps I listed in reverse order. Starting with the arms up.
Does anyone have trouble visualizing that?
Bennett proposed that:
ReplyDeletehttp://bigcat.fhsu.edu/biology/cbennett/flotsam/Bennett-2008-forelimb-myology.pdf
"..the range of motion of the metacarpophalangeal joint of digit IV migrated posteriorly so that flexor muscles spread the wing and extensor muscles folded it".
Concerning this, Peter's said:
http://pterosaurheresies.wordpress.com/2011/08/22/which-way-did-pterosaur-fingers-flex/
"The supination of the hand envisioned by Bennett (2008) ultimately included reversing the flexion and extension of digit 4 such that hyperextension folded the wing in his view. No other tetrapod has ever done this. Also note there is no space for the large wing extensor between the attached metacarpals (1-3 back-to-front with 4) in the Bennett (2008) configuration."
Please note that we are dealing with two things here:
ReplyDeleteWhich finger was the wing finger? And how did the wing finger fold?
I am proposing that the index finger was the wing finger and that it folded toward the palm and then toward the elbow.
After all is said and done, it may be as simple as this:
ReplyDeleteThe index finger was the wing finger and bent toward the palm and elbow when the creature was alive. In the first fossils that were found the index finger "rotted, disarticulated [separated] and fell" (see reference* below) in a twisted direction from its normal position.
And the later fossils that were found (that were ambiguous or appeared like the first ones) were interpreted on the basis of the incorrect idea from the first fossils.
Some researchers in this field have theorized that the pterosaur wing finger was turned 180 degrees. And other researchers have theorized that the pterosaur wing finger was turned 90 degrees.
That should have given us the clue that the wing finger was just fossilized in different twisted positions.
*http://pterosaurheresies.wordpress.com/2011/08/22/which-way-did-pterosaur-fingers-flex/
"YPM 49400 – a Rare Anterior Burial and Posterior Exposure in Pteranodon
Here in a Pteranodon specimen YPM 49400 metacarpus was preserved anterior face down. This is a very rare burial. The manus was preserved intact and in its natural orientation, fingers 1-3 palmar side down and metacarpal 4 palmar (flexor) side now posterior for wing folding. The claws here pointed ventrally as in other tetrapods. The metacarpals lined up as in other tetrapods. Buried like this there was no chance for them to wave around or become disarticulated in the bottom currents. The proximal wing phalanx would have stood vertically erect (essentially the Z-axis) in this configuration, but it rotted, disarticulated and fell on its dorsum, exposing its ventral face."
Concerning the differences of opinion - whether it was a 90 degree turn or a 180 degree turn we can see the following:
ReplyDeleteThose who opt for 180 degrees show that it cannot be 90 and those who opt for 90 show that it cannot be 180.
In other words it cannot be either.
The most parsimonious conclusion is that the wing finger simply disarticulated in different positions during fossilization.
http://en.wikipedia.org/wiki/Disarticulation
In medical terminology, disarticulation is the separation of two bones at their joint, either naturally by way of injury or by a surgeon during amputation.[1]
For reference:
ReplyDeletehttp://www.bioone.org/na101/home/literatum/publisher/bioone/journals/content/vrpa/2007/02724634-27.4/0272-4634(2007)27%5B881:aafotp%5D2.0.co;2/production/images/medium/i0272-4634-27-4-881-f01.gif
and
http://www.port.ac.uk/media/Media,113467,en.jpg
An oddity:
ReplyDeletehttp://pterosaurheresies.wordpress.com/tag/pterosaur-wings/page/2/
The Wellnhofer (1991) Twist
Wellnhofer (1991) lined up the metacarpals anteriorly, but also twisted the unguals anteriorly. Of course, this could be a problem in pterosaurs with fingers of similar lengths and does not take into account the various disarticulations at several finger joints.
See Figure 16-3 Drawing F.
ReplyDeletehttp://books.google.ca/books?id=JySAELseRlAC&pg=PA273&lpg=PA273&dq=Wellnhofer+(1991)&source=bl&ots=f2WIpJezNb&sig=Qmy7zEnn16xNyj1zH3vFSIG4fOc&hl=en&ei=je7CTuWpGOTg0QH58d2JDw&sa=X&oi=book_result&ct=result&resnum=3&ved=0CCoQ6AEwAg#v=onepage&q=Wellnhofer%20(1991)&f=false
Did Wellnhofer twist the unguals anteriorly?
If so, then suddenly the drawing makes sense!
The unguals actually pointed in the opposite direction.
See Figure 16-2 Drawing A.
ReplyDeletehttp://books.google.ca/books?id=JySAELseRlAC&pg=PA273&lpg=PA273&dq=Wellnhofer+(1991)&source=bl&ots=f2WIpJezNb&sig=Qmy7zEnn16xNyj1zH3vFSIG4fOc&hl=en&ei=je7CTuWpGOTg0QH58d2JDw&sa=X&oi=book_result&ct=result&resnum=3&ved=0CCoQ6AEwAg#v=onepage&q=Wellnhofer%20(1991)&f=false
This shows the index finger as the wing finger.
For reference:
ReplyDeletehttp://pterosaurheresies.wordpress.com/tag/pterosaur-wings/page/2/
Here’s Where the Trouble Started
In many crushed fossils, like Shenzhoupterus (Figure 1) and the left hand of Eudimorphodon (Figure 5), the claws point anteriorly because they are crushed broadside down. In order to do this, some finger joints must disarticulate and this is always observable.
But look what happens in the right hand of Eudimorphodon
In the same Eudimorphodon (Figure 5) the right hand has the palmar surface exposed. The metacarpals were lifted and flipped over the palmar surface of metacarpal 4, but metacarpal 3 remained attached to metacarpal 4. Moreover the unguals pointed posteromedially. According to Bennett (2008) this should not have been possible if metacarpals 1-3 were bound to the anterior face of metacarpal 4 and pointed anteriorly. Digit 1 should have been buried first and deepest, but it was not.
Could it be that the unguals for the 3 non-wing fingers were crushed in some of the fossils to artificially point in the opposite direction?
ReplyDeleteIt may also be that the unguals for the 3 non-wing fingers were disarticulated and the researcher placed them in the wrong direction.
ReplyDeleteIt is ironic that all the incorrect ideas about the wing finger may trace back to an incorrect interpretation of the metacarpals (and particularly the unguals) of the 3 tiny non-wing fingers.
ReplyDeleteWe do not need to believe in magical wing-finger rotations (found nowhere else in vertebrates).
We can chalk it up to incorrect interpretation of the 3 non-wing fingers.
It seems there are 4 different explanations that have been proposed concerning the wing finger:
ReplyDelete1. Wing finger rotated 180 degrees (previously proposed by Bennett).
2. Wing finger rotated 90 degrees (Peters)
3. Wing finger hyperextended (Bennett currently)
4. Wing finger bent toward palm and then toward elbow (this is what I have proposed).
I think this is a correct summary.
Concerning #1, Bennett has shown that this is not workable
Concerning #2, I think that Bennett has also shown this is not workable (but I am not sure on this point)
Concerning #3, Peters has made the point that this option is not workable
Concerning #4, there has not been any analysis showing this not to be feasible.
Why, in all the articulated and uncrushed specimens do the claws and phalanges point towards the body? How does "crushing" achieve this? #4 is clearly not workable either.
ReplyDeleteHello A Nonny Mouse.
ReplyDeleteIt looks like you are in agreement that the others are not feasible.
When I say that the proposal I am making is feasible, I mean that it will work from the point of view of muscles, tendons etc.
The others fail from the point of view of muscles, tendons etc.
Concerning the claws and phalanges can you be more specific please?
I have already said a few things about them so you will need to be more specific about your concern.
By specific, I mean pointing to some actual evidence. Not just expressing your opinion using more words.
ReplyDeleteWhich specific fossils are you talking about and how do you see those fossils?
Please give references and point us to exactly the parts you are talking about.
Treat this in a scientific way.
http://archosaurmusings.files.wordpress.com/2011/10/aaz.jpg
ReplyDeleteIn this fossil, the wing finger (whether it be the index finger or the 4th finger) is not bent backwards, as the three other alternatives would have it.
This fossil (two versions) is also found here:
ReplyDeletehttp://pterosaur-net.blogspot.com/2011/11/aurorazhdarcho-jurassic-azhdarchoid.html
It can be difficult to get a feel for this fossil from the picture. I recommend you print it and rotate it 180 degrees. Then you can easily see both hands and how all the fingers bend toward the palm.
ReplyDeleteThis fossil (known for some time but only recently published) could change people's ideas about the orientation of the pterosaur fingers.
There is no longer any need to believe in the magical backward bending of the wing finger idea.
The wing finger (along with the other fingers) bent toward the palm, which of course is how fingers normally bend.
This reference includes a picture of a pterosaur fossil:
ReplyDeletehttp://www.port.ac.uk/media/Media,113467,en.jpg
It is the picture at the bottom including distal syncarpal, proximal syncarpal, metacarpals etc. It has the title "Pterosaur wrist bones".
Can anyone give us the reference for this fossil?
It has a strong resemblance to this drawing:
http://www.bioone.org/na101/home/literatum/publisher/bioone/journals/content/vrpa/2007/02724634-27.4/0272-4634%282007%2927%5B881%3Aaafotp%5D2.0.co%3B2/production/images/medium/i0272-4634-27-4-881-f01.gif
Does anyone know if the two pictures are related? Perhaps the drawing was made from the fossil.