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Re: Pterosaur take-off movie on the NG site

On Sep 8, 2009, at 11:17 AM, Mike Habib wrote:

David Peters wrote:

Actually, no fossil shows the inboard wing clearly at all;

Not true. See Peters 2002. Unfortunately, no one else since then has shown any different.

Actually, a *lot* of people have shown differently in the literature. Just for starters: Wild 1993; Unwin and Bakurhina 1994; Wang et al. 2002; Lü 2002; Bakhurina and Unwin 2003; Frey et al. 2003 and Bennett 2007

Actually: no. Wild showed patches but no pattern. Unwin and Bakhurina 1994 tried to follow Sharov 1970, but got completely different lines. My 2002 paper showed those lines to be geological faults. Wang et al. sketched what I did in 2002 so we found the same things. They simply described it differently to fall in line with the paradigm. Lu found patches but no pattern. Bakhurina and Unwin 2003 is an abstract without illustration. Frey et al. 2003. traced no wing membrane but concentrated on veins and such details. What they describe near the thigh of the darkwing is thigh material. The tight curve at the anterior femur was ignored. Bennett 2007 ignored his own sketch , which also showed the tight little curve aft of the elbow, when recreating his wing diagram.

Well, to really do this, we would need to be in the same room, with the specimen. This was the case in Munich, which actually convinced me of a hind limb attachment (of some sort) in many specimens (though it by no means suggests that this was the case for all taxa). It also demonstrated just how difficult it actually is to follow the inboard wing on even the best specimens. I know that you can supply photo outlines that seem suggestive of a more narrow wing. I do not find them conclusive, in and of themselves. Some of Helmut Tischlinger's UV photo work really seems to indicate that there is some mesopatagium lateral to the tibia in some of the specimens. I find his work to be somewhat more convincing, at this time.

specimen number? paper?

We can eliminate certain gaits because they don't provide propulsion.

Perhaps - have you done a biomechanical power and propulsion analysis to constrain the potential ground-walking gaits? I've done some, but not enough yet for publication.

I can tell when the fingers can't get behind the elbows. This occurs only in certain cases, and in no beachcombers.

Two ornithocheirid tracks are known:

1. Purbeckopus pentadactylus (DORCM G 6664; Delair, 1963; Wright et al. 1997) an early Cretaceous ichnite.

2. TATE 0049-06 (Southwell and Conneley, 1997) a late Jurassic ichnite.

I can send you pdfs if you don't already have them. Neither has the single deep indention you describe. Just enough room for three fingers.

They might not be ornithocheirids,

They match specific ornithocheirid pedes. Part of my studies. Don't go by the published sketches of either. They both have errors. I can send you revisions by request, but I only did the feet.

actually, but putting that aside: note that they are not "hollowed" at the base of the fingers. I said explicitly that it would not be a single, deep indentation. Instead, the mcIV/phIV joint impression is apparent as the middle of the manus track. The bases of the "free" fingers are confluent with the sides of MCIV. Their bases cannot touch the substrate. Therefore, the "thing in the middle" is not the base of the free fingers. It is the MCIV/PhIV impression.

If finger 1 provides a complete impression, not just an ungual, as is the case, then the the fingers are being hyperextended 90º. That they all join at the base supports that reconstruction. Yes, there's a roundness medial to digit II. That must be digit IV. Key here is: the fingers all surround digit IV and have plenty of floorspace alotted to them. They are weight-bearing and get pushed into the substrate. They were not raised as your illustrator and animator show.

It need not be especially deep. I think you presume that more details of weight support are evident in tracks than is usually the case. Sometimes a weight shift can be seen, but the tracks need to be especially well preserved, and substantial weight shifting needs to occur. Tracks are often counter-intuitive, especially if the substrate was deep and soft (see Steve Gatesy's work with avian tracks).

seen it.

There is a deepening of the manus impression in some East Coast tracks (as yet unpublished, so I won't say more on the identity), in what appears to be a launch sequence. That's not surprising, as it would amount to about 2 or 3 times body weight, which is a substantial increase and can be see in the ichnite with some clarity.

I'm looking forward to seeing those tracks when they become available. Remember the old snowshoe example. The broader feet don't sink as deep as the narrow ones. The fingers are smaller in area, typically, than the feet are, so they sink in deeper. Simple as that.

Okay, let's say your resistance and recoil hypothesis worked on hard, unyielding surfaces. Would it work on soft mud or wet sand at all scales for all pterosaurs? Or would the substrate slip? And along with it, the wing finger under tension?

Show me some pterosaur tracks in which digits I-III are -not- taking the weight. They -are- structural capable. Ichnites show it.

Not true; see above. You cannot glean as much about weight support from the tracks as you might think, though you can see a fair bit. Again, if MCIV/PhIV was not contacting the ground, then the tracks would have a more pronounced concave crescent.

Why are you turning this argument around? No one said mc IV is not taking weight. I only said it is not taking -all- the weight.

This applies to essentially any trackway at all. But just for starters, let's look at the very nice trackway just published by Mazin et al. (the possible landing track). Look at figure 1b: note that the manus prints are all *convex*, not concave. If you were correct, the tracks would lack any impression in the area of MCPhIV joint, but there is a very nice impression of it in each track.

I asked you to show me tracks in which I-III were NOT taking weight. You have twisted the query.

Keep in mind that digits 1-3 are rooted, as it were, to MCIV. Thus, the area in the "middle" of each track where the fingers seem to come together must be MCIV.

Granted. Never an issue.

It is leaving an impression, and a rather large one, actually.

Actually no. When you subtract digits I-III from the "runway" tracks, you are left with a very slender minority of the print.

As for structural capacity, a quantitative analysis of bending strength is more informative.

No, deep impressions of tracks are more informative because they take in all the factors including the exact weight bearing down from above.

My quick calculation indicates failure for the small digits in a large azhdarchid trying to stand on them alone. Of course, this is just illustrative, because what would actually happen is that the animal would simply sink down onto the MCPhIV joint, given that the fingers are not single rigid structures.

That makes sense. There would be failure in the human hand were we to try to do the same thing.

I also note that articulating many specimens, especially large pterodactyloids, into a walking posture forces the MCPhIV joint to touch the substrate. Personally, I have been unable to find any articulation in which digits 1-3 touch the ground and the MCPhIV joint does not. They all touch together, except in things like Nyctosaurus, which just seems to walk on the hind limbs and MCPhIV.

I never argued otherwise, my friend.

It's also a coincidence that the pteroid fits into the cup of the preaxial carpal and look at what trouble that has brought to those who move it there in reconstructions. Mike, I am following your logic. In the end though, there's too much trouble for me to accept this "click beetle"-like launch mechanism.

I don't see any trouble. If you wish to refute it, however, then I am all ears. However, you will need to supply stronger evidence. Preferably a quantitative, biomechanical analysis of structural load capacities. If nothing else, you would need to demonstrate that an ornithocheirid cannot place the MCPhIV joint on the ground. I argue that it did so nearly all the time, and that the free fingers in some taxa could barely touch the substrate.


I make this argument based on finger proportions and trackways. However, even if my assertion is incorrect in this regard, the catapult storage mechanism is still plausible and consistent with morphology so long as the tendon *can* be compressed, even if it was not locked during walking.

And you made a great presentation. Don't consider this the end, though. Fix the problems by making them more reflective of the reality. Your best friends in this regard are your worst critics. If your hypothesis is real you'll be able to handle any detractors with evidence. If you're right, you'll be able to show it. You'll be able to handle their objections to the satisfaction of your detractors and ultimately bring them along to your hypothesis.

I appreciate that the numbers are working on one side and not the other. Not sure what the solution is if not gooney-bird- or pelican- like.

Well, I've given a plausible alternative. Actually, there is really nothing in any pterosaur suggestive of a gooney-bird or pelican-like launch. We have no reason to assume such a gait, and it turns out to be impossible for all large pterodactyloids. In fact, all of the morphological traits we would presume to exist in a bipedal, running- launching species are not only absent in large pterodactyloids, they trend in the *opposite* direction of what we see in water-launching birds. The femora in large pterosaurs are proportional more gracile than in small species, not more robust. The feet in many of the largest pterosaurs are small, not large. The proximal forelimb is robust, not gracile. The list goes on for a while.

Understood. But notice you're talking about increasingly derived taxa. They are solving various locomotion and mass problems in several ways and different from birds. I just found a pterosaur with a pelvis half the torso length. Now that pterosaur has issues!

First of all, not all animals leap with the position you suggest. In fact, vampire bats, the living quad launchers, don't do so. But more to the point:

Figure 3 of The Journal of Experimental Biology 200, 3003–3012 (1997) THE DYNAMICS OF FLIGHT-INITIATING JUMPS IN THE COMMON VAMPIRE BAT DESMODUS ROTUNDUS shows this. Figure 2 stops short of becoming airborne. And the thumb tip is the last element to leave the ground. I also note that the humerus is more than half the length of the ulna and at maximum flexion the humerus and ulna are at 90º to one another in front view. This is where the leverage is in Desmodus. In some pterosaurs there are similar proportions. In others the humerus is much smaller and therein lies trouble.

Yes, the limbs extend and the thumb is last to leave the ground, but the leap is not frog-like, either, which was the gist of my earlier comment. In any case, much of the leverage in Desmodus actually comes from the thumb.

Then let's get those fingers involved in pterosaurs, too, at least to the extent that they are able.

There is some from the elbow and wrist, too, of course. While the longer humerus does increase the excursion length, it also limits the maximum stress that the humerus can take. The shorter humerus and antebrachium of pterosaurs gives them much greater power limits about the elbow. The excursion length of the limb is then increased by the long MCIV (relative to the bat). So, in both cases, there is a shorter, stouter element that sees a lot of stress, and some longer elements that help add excursion length. It's just that which elements are which differ between the bat and the pterosaurs. So once again, no trouble.

Mike, I don't have any trouble with pterosaurs leaping with their forelimbs. I only have trouble with the height that can be achieved when I see relatively little angulation (storage of energy) between the elements of the wrist. And I have trouble with the opening of the wing finger when its initial trajectory is straight down toward the earth at take-off.

1) the wing finger *is* forcefully extended - because of its shape, only the proximal end (the flexor tubercle itself, essentially) actually hits the ground. The rest of the finger does not "lay flat", as it were.

That doesn't show in the animation. If something is indeed forcefully extended it needs to be extended to the limits of its joint mobility. Not held back.

I already explained this: the limit of extension, in this case, is when the tubercle contacts the substrate.

Micromoments later the tubercle is not in contact with the substrate.

Incidentally, it is also not true that anything forcefully extended becomes ballistic in nature and goes to the limit of joint mobility. Actually, it almost never happens - antagonists usually fire even in powerful motions. For example, a person throwing a kick does not (generally) fully lock their knee. For more technical treatments, look at the myological literature - there are a lot of nice electromyograph papers out there.

Come up with an example that is similar to leaping from the substrate. Kicking is like eye-gouging or punching. Not similar.

2) the long flexors for the fingers also cross the wrist. Much of the stored power goes into mechanically extending (anatomically flexing) the wrist.

You say that, but the animation doesn't show any flexing of the wrist prior to launch. Only extension after launch.

Well, if it extends, then there is the power. We show a bit of flexing prior to launch, but not a great deal, as we have it starting in a highly flexed position.

If it's always 'cocked' is it really 'cocked'? Have your animator relax the wrist before cocking it. That will go over better.

I'm looking forward to seeing the evidence for implantation of digit IV in the substrate. Shoot it my way when you can. That's key. If you can't provide it, there may indeed be problems.

See above. Again, there are multiple ways this can work, which are all feasible. By contrast, I have yet to see any positive evidence for a biped launch, and I can supply a lot of negative evidence. The femur snapping in large species is a pretty good one, just for starters.

Femur snap? Well, that's not good. Surrounded by a massive thigh in perfect coordination with two of the limbs taking the weight off the femur? and it can't run? I'm getting a Whitfield and Bramwell deja vu. Remember, they said Pteranodon could not even walk on its hind limbs and would have been relegated to a small wheeled wagon, ala Porgy and Bess.

Thanks for the thoughts. I am your best friend. And you will have a fool-proof hypothesis when you're done.


Best regards, and congratulations on all the great PR.

Thanks very much; I appreciate it.



Michael Habib
Assistant Professor of Biology
Chatham University
Woodland Road, Pittsburgh PA  15232
Buhl Hall, Room 226A
(443) 280-0181