Re: pteros have lift-off

[Michael Habib <mhabib5@jhmi.edu>]

David Peters wrote:

> Also, did basal short-metacarpal pterosaurs create a Z-fold in the 
> forelimb?

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 
average).

> 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 
launching.

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