Re: pteros have lift-off

[jrc <jrccea@bellsouth.net>]

----- Original Message ----- 
From: "David Peters" <davidpeters@att.net
> > Zero for the largest ones.
> > JimC

> Understood.

> Then how about the second largest ones?

Zero.

> 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.