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Re: Pterosaur take-off movie on the NG site

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

Now, you may disagree with their arguments, and that's fine, but to argue that the situation is clear and obvious is a bigger stretch altogether. If you are so confident that your interpretation is correct, while the above authors are confident in their interpretations, then at the very least, the mesopatagial structure is not obvious. It must be, at minimum, contentious.

the ankle/tibia attachment is a plausible reconstruction that several authors currently support.

IMHO twisting evidence to achieve an old paradigm. Several authors also support the weird pteroid placement and plantigrady for all pterosaurs. Evidence works, popularity without evidence doesn't have the same effect.

There is no need to draw ad hominem or political straws here. I'm merely stating that evidence has been presented in the literature for a broader inboard wing. Evidence is also very strong for a narrow actinopatagium, and from a flight mechanics standpoint, that is rather more important. The presence/absence of a hind limb attachment for the wing mostly matters for certain aspects of anchoring and inboard flutter control (i.e. how flutter is reduced - there are ways to do so under either attachment reconstruction). Furthermore, keep in mind that the original complaint was that Raul used a hind limb attachment for the wing. Given that many authors (most, in fact) support this model, it is completely reasonable for a paleoartist, searching the literature, to use such an attachment. The fact that your manuscript argues a different model need not change his mind (although I would be happy to see someone illustrate your version, too).

Where it goes from there is a matter of debate, because the more elastic mesopatagium is generally a mess (or missing) in most specimens, even those that have a nice outboard wing preservation.

List a specimen or two and I will show you that it's not a mess.

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.

Other positions can also be hypothesized, and also work. We don't know what the "ordinary" hindlimb posture is for any large pterodactyloid. The more vertical posture you prefer is quite plausible; it is not the only plausible posture, however, nor does it actually affect the overall launch sequence: if the starting posture is more vertical, then the animal can simply shift weight forward into a more horizontal posture first. This adds a small amount of time to the overall sequence. It is not of major consequence.

Which is why it stays in the "minor" category. If big pteros were different than little pteros than there should be some morphological marker that shows up in a cladogram to flag this change. I don't see it. Can you show it?

Why should there be some single "marker" in this manner? Stance and gait are the result of several different proportions. Furthermore, these proportions need not split according to size. If you wish to map gait and stance on a cladogram, then the traits of interest would be things like limb length, the relative lengths of each element in the limbs, robustness of limb elements, and the breadth, length, and depth of the thorax and abdomen. And yes, any one of us could show that these features differ between major clades. Reconstructing the effect on gait is something altogether, though I think it should be fairly obvious that something like an azhdarchid didn't walk and run the same way as an ornithocheirid.

They were probably there, yes - but we worked directly from the AMNH 22555 specimen, which doesn't have them.

It also doesn't have several other bones, which you added. You really need to add the prepubes.

I didn't add them - they had been estimated by the folks at the AMNH already. They didn't bother to estimate the prepubes. I didn't add them because it really isn't relevant to launch. Maybe some other time.

We don't know what the gait was in Anhanguera. There are multiple possible gaits. One of them is the near-bipedal gait you describe. A more thoroughly quad gait is also plausible, and is what we used. Contrary to your assertion, it is possible for the forelimbs to provide walking power in Anhanguera, albeit not a great deal of power because of their position. I agree it was likely airborne most of the time, and I would not expect it to be capable of a canter or gallop, as I suspect that most azhdarchids were.

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.

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, 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. 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). 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.

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?

Good questions. It would work on most substrates for most species. As such, there would be some taxa and/or some surfaces that would be harder to launch from than others. Again, the catapult mechanism is not required, it just helps.

Even presuming, for a moment, that this is the case, I can say with confidence that digits 1-3 did not take much of the weight not accommodated by the hind limbs, as these small digits are not structurally capable of doing so.

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. 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. 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. It is leaving an impression, and a rather large one, actually. As for structural capacity, a quantitative analysis of bending strength is more informative. 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.

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.

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.

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.

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. 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.

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. 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.

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.

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.

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