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Re: pteros have lift-off

----- Original Message ----- From: "David Peters" <davidpeters@att.net

Zero for the largest ones.


Then how about the second largest ones?


I have a problem because in pteranodons, nyctosaurs and ornithocheirids the tiny fingers are far forward of the glenoid, so much so that the antebrachium is horizontal when terrestrial.

That's not a problem. The further forward the fingers relative to the glenoid at the initiation of launch, the lower the launch loads on the animal. Even when the antebrachium is horizontal, stretching of the muscles that fold it will drag it forward as metacarpal IV rotates forward relative to the manus. It will lag metacarpal IV, but the wingtip is still initially rising and moving forward as the wingfinger starts its inertial opening.

Short legs add to the problem.

If you mean hindlimbs, not in any substantial way, though it would be a good bit more difficult for the animal to launch if you amputated the hindlimbs. The primary function of the hindlimbs is to power the folding of the forelimbs into adverse mechanical advantage, thereby providing the power to 'push' the forelimbs into the 'Z' shape at the earliest stage of the launch. Secondarily, this also initially accelerates the torso, neck, head, and inner wing forward and it doesn't take a long hindlimb for that. A short one can actually help. As the force production of the hindlimb starts to tail off, the forelimb has already begun to take over power production for the leap.

Somehow, then, the fingers have to move behind the center of gravity so that the launch is in the anterior direction, following your need for a 30º launch trajectory.

There's no need for a 30 degree launch trajectory. It usually ranges from 25 to 35 degrees because that is the most efficient range. The fingers find themselves aft of the cg as the glenoid moves forward relative to the manus during that portion of the launch that precedes manus liftoff.

I think we talked about this earlier and the need for a pole vault scenario

I think you talked about the need for a pole vault scenario -- I don't recall that anyone else sees it as a requirement.

(run followed by a hind limb leap) to shift the fingers below or behind the shoulder glenoid.

Mike and I have always postulated a standing start, at least since late 1998. Personally, I don't see the need for a running start in any pterosaur. It seems like a terribly unnecessary waste of effort that would result in an inability to launch for most, if not all pterosaurs.