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Re: four-winged dino -- ptero homology?



David Peters wrote:

> Pterosaurs, and especially Sharovipteryx, apparently ran bipedally on
> hind limbs encumbered(?) by flight membranes and glided with them as
> well.

While I agree re Sharovipteryx, I have some trouble with a bipedally
running pterosaur.  As an aside, it would appear that the Sharovipteryx
overall body plan is superbly suited for flapping flight if the hip
articulation and associated muscle attachments allow the appropriate
flapping kinematics. I would expect that Sharovipteryx would generally
launch by leaping rather than running.

> certain basal pterosaurs
> (dimorphodontids) in which uropatagia are present yet the femoral head
> is strongly angled to the femoral shaft. In my opinion the hind limbs
> were held in an inverted V in these cases.

This is an extremely high drag position, very good for increasing the
descent rate and reducing the gliding range.  Sort of like extending the
flaps on aircraft, but without the lift increment.

> Later pterosaurs improved
> this situation, bringing the hind limbs into the plane of the wing by
> increasing the angle between femoral head and shaft, reaching an acme in
> the soaring taxa of the Niobrara and Santana formations.

Yes, if one considers the acme to be a plateau that continues on.  Yaw
command authority can be established by dropping one of the two hindlims
into the inverted V position while maintaining the other in a
semi-horizontal position (also takes a few other simultaneous
adjustments, easily accomplished).