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Re: pteros have lift-off
David Peters wrote:
Also, did basal short-metacarpal pterosaurs create a Z-fold in the
Sure, to an extent - the "Z-fold" just refers to the amount of joint
excursion possible in the limb. Pterosaur forelimbs are rather
"stiffer", as it were (less excursion), than something like a frog or
galago, but there's still plenty of motion there to leap, and using the
forelimbs still adds a lot of power. Heck of a lot better than trying
to biped launch.
Mike H. wrote: > Ground effect doesn't help quite that much.
Then why does every big bird launch I've ever seen include it?
It seems like a good way to accelerate AND fly. Such a system requires
a less powerful takeoff.
Because if you're climbing at a shallow angle, with less anaerobic
power, then ground effect is helpful. But it isn't required nor as
helpful as you seem to expect. Ground effect just means that there is
reduced drag flying near the fluid-surface boundary (i.e. the ground,
in this case) - that reduces power requirements a bit, but doesn't do
much for a burst takeoff nor does it have much impact on the actual
launch. Vultures and herons, for example, tend not to use ground
effect when launching (especially in escape launches), while water
birds tend to do so more often (open habitat and slower climb rates, on
Mike H. wrote: > Besides, a biped launch doesn't get many pterosaurs
even close to cruise speed
And with ground effect acceleration, it doesn't need to. That's the
point, I think...
It still needs to get into the launch window, which need not be cruise
speed, but is still sufficiently fast that a little ground effect isn't
going to help a launching pterosaur very much. Ground effect is not
nearly so influential so as to make a bipedal launch feasible for most
pterosaurs, nor would it explain the relatively weak hindlimb scaling
rate in pterosaurs (and correspondingly high forelimb structural
scaling exponent). Ground effect makes certain maneuvers more
efficient, but it doesn't vastly drop the power requirements for
Michael Habib, M.S.
Center for Functional Anatomy and Evolution
Johns Hopkins School of Medicine
1830 E. Monument Street
Baltimore, MD 21205
(443) 280 0181