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Re: "wing muscles"

Larry Febo wrote:  generally thought that pterosaurs

> ...... to adjust the camber of their wings (as noted in previous
> discussions)? How do you know they didn`t? They had actinofibrils to
> maintain stiffness and wing shape, but, were these passive structures, or
> could they be modified by wing muscles? Is there any evidence for or against
> this?

First, the aktinofibrils were slender enough that their internal stiffness was
negligible.  So they functioned in tension, and if there were also diagonal
internal muscles that could slightly translate the intercalated aktinofibrils
relative to one another, then they could locally modify the relative spanwise
and chordwise tension, and this would affect the camber, which would, in turn,
provide a degree of geometric stiffness to the wing structure.  There is some
very sketchy evidence  to back this up, but not enough to really hang your hat
on.  My personal opinion is that the aktinofibrils were probably  located near
the lower surface of the membrane and that there was probably a sheet of crossed
diagonal internal muscles that attached between/to the aktinofibrils  to serve
this function.  I don't consider this to be proven, though.  If it is true, then
even with rather widely differing assumptions about visco-elastic properties,
the wings could be expected to assume quite similar airfoil sections under load.

> Perhaps I should have stepped in and asked earlier when Jim Cunningham was
> also taking part in this discussion,

I didn't know I wasn't.

All the best,