Re: the new pterosaur wing model

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

David Peters wrote:
> 
> The hind limb situation in the new art reminds me of the insitu
> Sharovipteryx.

Me too.
 
> A couple of questions.
> 
> 1.  Considering the new wing model, what do you artists think of the
> terrestrial or arboreal situation regarding the hind limbs? Is it
> sprawling (knees out) or erect (knees essentially beneath the hip
> sockets)?

Speaking as both an artist and as an engineer, it would usually be
neither.  The knees are very slightly out when in the terrestrial
position, with the angle of the ankle placement on the tibia
compensating so that the articulation of the foot at the ankle is
vertical. But I've only tested that on one species. Certainly not what
one would think of as sprawling, but not quite vertical either.
 
> 2. Does the tarsus in flight have its dorsal side up?

No.  But the differential aftward flexing does make the dorsal side
visible from above.

> Or anterior, in the plane of the wing?

Shifted somewhat from the plane of the wing because of hip rotation in
pitch to establish a truncated Rogallo on each side.
 
> 3. And if anterior, do the toes occasionally spread in flight as spoilers?

Yes.  The aftward flexing of some of the toes to form an airfoil would
be a variable and transient feature (as would the spoiler function).
Using the foot as a trim servo would greatly facilitate moving the
hindlimb about the roll axis, which would greatly facilitate use of each
hindlimb to generate auxiliary yaw command authority.  The hindlimbs
wouldn't have been primary for yaw command, but would have been able to
generate more yawing moment than the wings when such was needed.  You
can also create a spoiler function by simply lowering the legs somewhat
at the hips and or flexing the knees more while maintaining the original
loading.  For example, the Qn skeletal model hanging at the TMM has the
hindlimbs in a descent mode that would require about 4 horsepower to
maintain level flight, while placing the hindlimbs in the rogallo
positioning would require about 1.25 horsepower to maintain level
flight.  It's a good way to increase your sink rate when you want to
lose altitude.
> 
> 4. The tail in Anhanguera, as preserved, may not be complete. Some
> evidence suggests that an attenuated tail continued some distance beyond
> in many, but not all "pterodactyloids". Does the presence of a
> stingray-like tail, no longer stiffened by internal bracing, and
> trailing behind like a refueling boom have any aerodynamic effect?

Yes, but not much.  I don't have strong feelings about it.
 
> 5. What is happening to the fuselage fillet seen on most pterosaurs? It
> seems to disappear or become unnecessary in the present model in which
> the knees are brought anteriorly close to the elbows?

I don't think it is absolutely necessary, but it may still be there and
likely is in a number of species.  It could help with flow control.
> 
> 6. What is the situation in basal pterosaurs regarding digit V? Is it
> actively involved with any flight membrane? Or is it tucked away for
> some other use?

I think it may originally have been involved with the uropatagium and
then transferred more to the foot web in those later pterosaurs in which
it may have been preserved. Note that I don't know which species those
may have been.  That implies that uropatagium loads that were originally
accepted by digit V were transferred to MT V in order to free the foot
from the uropatagium loading and to keep the uropatagium free of the
effects of moving the foot.  May well have had other, terrestrial uses
too.  I dunno about that.
> 
> Any ideas? I'll ante up after others have played.
> 
> David Peters
> St. Louis