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Re: Pterosaur Takeoffs (Under-rated Bats)
Jaime A. Headden wrote:
> are comparable in size to some
> larger bats, so they are probably capable of this
> feat, but definately not the larger forms, from
> pterodactylid size and up, because to my knowledge, no
> bird of that comparable mass (5ft+ wingspan) can do
> this, and certainly the biggest pterosaurs
> (pteranodontids and azhdarchids) could not just "jump
> up into the air." Jim, you may correct me on some of
> this, but from the little bit I've understood of
> large-body aerodynamics and the ground-up flight
> paradigm when dealing with dynamics for birds _or_
> pterosaurs, I think there's some fair assumptions on
> my part.
Birds can't. But Q apparently could, using a technique superficially
somewhat similar to the rotundus launch and the launch of some frogs.
This has been the only way I could find to get the big sucker off the
ground with reasonable accelerations and achievable power requirements.
It involves preloading the front leg in adverse mechanical advantage,
and then powering the leap first with the rear leg, and then during the
latter part of the launch -- the front leg. It doesn't bring the wing
into play till about midway through the first upstroke, when the pteroid
switches from the terrestrial to the flight position (both positions
point toward the shoulder). It even allows both Qsp and Qn to reach
cruise speed before running out of anerobic power, which opens up the
possibility that big pterodactyls may have been able to perform without
needing the high metabolic rate that birds require. That would also
substantially reduce food and oxygen (and consequently, respiratory)
requirements. See my previous post regarding my February talk at
SSA'99. I can't address the launch mechanisms in smaller pterosaurs,
not having worked on them.