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Re: vaulting pterosaur launch, questions



Jim pretty much covered the bases already, and given that he and I are in agreement on this particular issue, I've only inserted thoughts that he didn't mention/get to:

There's no doubt that the forelimbs are more powerful in pterosaurs, but that has never been the question.

Fair enough, but then ask yourself: why are they so much more powerful? After all, that's not the case in large birds.


The question has always been: Can you line up the vectors in ALL pterosaurs so that the hands are a wee bit behind the shoulder glenoid during the launch phase?

Yes, during launch, just not as a stable phase - it's a transient pose, but that's not a problem. The primary method is actually pushing the torso forward before unloading the forelimbs.


Mike, have you considered running while flapping, gooney bird style? When you put your project together, consider and reconstruct this possibility then knock it down. Too many papers start with a preconception and never explore alternatives.

I have considered it, and duly knocked it down. Actually, the degree to which most paleontologists (and even just biologists in general) misunderstand running launch has been quite surprising to me. It is not really a method of improving launch speed or power - running launch mostly shows up in birds as a method of dealing with take off from compliant surfaces (ie. water). Of course, many seabirds are also large, and hence the apparent link with size. Running launch does also allow a partial solution to launching with extreme spans (presuming the animal is constrained to a bipedal launch), which would apply to pterosaurs, but that still leaves the power problem - big pterosaurs simply couldn't take off by running any more than they could launch by bipedal leaping.


(Sidenote: Running launch in birds also allows the hindlimbs to be absolutely very short, because it shifts the requirements from excursion length to short-distance acceleration. However, the limbs still have to be stout, which conflicts with pterosaur anatomy).

Are the Q. hindlimbs able to sustain the forces required for bipedal walking or running with wings folded and off the substrate? Hopefully a simple yes or no will do. 

Yes, but I'm not sure the power generation from the hindlimbs would be sufficient. They'd run better using all four limbs, and probably canter as obligate pacers, incidentally.


Jeepers, Mike. Let me go back and insert: (without MUCH hind limb assist). It's not like they were crippled and of course I'm not arguing for that matter. That would be indeed foolish, as you kindly point out. 

Sorry if that was a bit overpowering: my long response was largely there for the edification of other readers, because the basics of launch are very often misunderstood. In any case, even the insertion of the "much" only helps a little: most of the power for launch needs to come from the leaping impulse. After all, for birds, the hindlimbs are producing 85-90% of the impulse.


Power is not the question. Vectors are.

Both are important - power is always a question in these sorts of problems. Hindlimb power alone is insufficient, while quad power is quite sufficient. I find that quite telling.


-- BTW, I don't think you'll get a greater forelimb/hindlimb disparity than in those early Rhamphorhynchus longicaudus with tibia about the length of their short metacarpus. Unbelievable until you see it. Make sure that that species is in your x by y cloud. Too often certain pterosaurs are omitted from research.

Sounds pretty wicked - I'll check it out (thanks!) I do doubt, however, that the disparity would be greater than in aquatic birds and the like. After all, there is more than just length involved in the total geometric disparity. Nonetheless, that animal is worthy of further investigation.


Let's follow your theory in our imaginations. Like a pole-vaulter (see your comments below), Nyctosaurus plants its long metacarpal into the substrate (ouch! if that's a rock)...

It only starts with a vault, the main power comes from a forelimb push. Incidentally, planting the long MC shouldn't be any more hazardous than planting a hand (which it's still doing, just minus fingers).


Note that Desmodus has a strong terminal lever at the tip of its folded wing, the thumb, to provide the final contact lever with the ground. It acts like the toe of a kangaroo. Nyctosaurus does not have such a terminal lever.

No, but it has a catapault storage mechanism (I'm gonna make everyone WFTP on this one - but it's cool).


Does your model depend on the strength of the fingers during the final phase of the launch?

Not especially.

Does your model depend on the whipping of the skull skyward then downward during any phase of the launch?

Nope.

Does your model depend on the rapid extension of the wing finger in contact with the substrate during the final phase of launch?

Not at all, though it does extend quickly after launch is initiated to begin the stroke cycle - and the inertia of the distal wing helps it do so.


I also note that the humerus of Desmodus is more than half as long as the antebrachium + metacarpus. Not so in Q. or Nycto. So the lever is smaller. Much smaller. 

Proximal lever is shorter, distal levers are long. Having a short, stout humerus is key: it allows for massive bending and torsion resistance, which is pretty key for a massive quad launching animal. Note that big birds have short, stout femora for the same reason (but, again, the role is moved to the hindlimb because birds are obligate bipeds).


Remember that during such a polevault, the pole (the wings) would be detached and left behind to launch the vaulter (the torso) -- unless the momentum of the torso were sufficient to drag the wings into the air.

The push of the arms is sufficient to propel the entire animal, including the arms themselves, into the air. Even a human can push themselves off the ground a little with their arms, without dislocation - imagine if your forelimbs had the relative power of a pterosaur.


Is this so in pterosaurs? Where do they get they're final kick?

The final kick comes from the forelimbs unloading: in other words, pushing hard. Given the muscle mass driving them, and the likely anaerobic muscle fraction in large pterosaurs, it's a pretty mean kick (nod to Nathan Myers).


Just wondering what the numbers say. The wings seem awful doggone big compared to the torso and head in some taxa, too big to drag into the air IMHO. 

They don't have to "drag" them: the arms push off the ground just as you might leap using your legs. They just act as a vaulting pole, first.


Cheers,

--Mike


Michael Habib, M.S. PhD. Candidate Center for Functional Anatomy and Evolution Johns Hopkins School of Medicine 1830 E. Monument Street Baltimore, MD 21205 (443) 280 0181 habib@jhmi.edu