Re: Discovery Article On Pterosaurs

["James R. Cunningham" <jrccea@bellsouth.net>]

T. Michael Keesey wrote:

> Is this the technique bats use when taking off from the ground? (Or, e.g., a
> vampire bat taking off from a sleeping animal?)
> 
> Why the hands last? How would (?does) the order of events go?

Desmondus rotundus....  Well, no and yes.  The vampire bat goes out much
more vertically with a rather small zenith angle and the phasing of
force production is rather different.  Quetz seems to go out at about a
25-35 degree angle from the horizontal.  The bat doesn't appear to make
a special effort to preload the arms.  It would appear that Quetz does,
and that the arm motion is more elaborate in Quetz, more of a
preloading/folding/unfolding/unloading polevault sort of affair. 
There's not much visual similarity between the bat launch and pterosaur
launch, but there was enough similarity that I found papers on Dr force
production and phasing useful.  When cycling Quetz through flight
related kinematics, I find it interesting that the main skeletal
compression bracing seems to be aligned more with the launch scenario
than with flight loads, and that the 4-legged launch takes considerably
less total power than the 2-legged flapping launch. The 4-legged
technique has the advantage of requiring very little room for launch,
the ability to launch over low vegetation, and the perk of moving faster
than any likely predator can run by the time the hands (front feet)
leave the ground.  I spent a couple of months messing about with Qn
flapping launch scenarios before I finally decided I couldn't mount
enough muscle on the animal to power the required wing kinematics, and
even if I did it wouldn't explain the skeletal reinforcing alignment
(comparing now with Qsp because of the better fossil preservation). 
Which got me to thinking about what may have aligned with that bracing,
and why it was needed.  And that led to...., and so on.  John and I are
planning to do a Muybridge sequence of a Quetz asymmetric turning launch
as predator evasion for a poster we're doing for the 7th ICVM next
year.  Wish us luck.
Jim