Wonderful stuff. I should add a bit more about my guess regarding the bone spurs on the leading edge of the wing. They are called the pteroid bones and are actually somewhat of a puzzle to scientists. The three competing explanations for its existence seem to be that the pteroid bone is either:
A.) Held pointed in towards the head as shown and used to support a flap of wing membrane connected to the base of the neck or shoulder.
B.) Pointed nearly straight forward and used to extend the leading edge of the wing to create additional lift for landing and takeoff (just like the slats on the leading edge of an airplane wing). Some researchers have done wind-tunnel tests which show this would be very effective.
C.) Used as part of a mechanism for holding the wing open against drag forces during flight.
As for my guess, the bone is definitely not a thumb, but it may be an altered wrist bone (carpal). While hypothesis B would agree with me, the musculature and tendons in the area do not appear to be rigged for using the bone this way, and the bone itself was probably not strong enough to withstand the stresses involved in this arrangement. After reading this wonderfully illustrated explanation, it would appear that A or C is more likely, though this assumes that small and large pterosaurs had the same mechanisms involved in the pteroid. I question this assumption because (as you can see in my photos compared to some of the images in the link above) some pterosaurs had very different lengths of metacarpals, and the pteroid sat at the base of this extended wrist/palm bone while the fingers sat at the end. I wonder if the mechanisms were the same for long and short hand bones.
I point this out because it's a great illustration of how enveloping and interesting the scientific point of view can be. From noticing a strange bone on a fossilized wing and questioning its function, I'm already asking questions to which no one seems to have a definitive answer as of yet. The research has led me to learn more about anatomy, biomechanics, and biology, and only adds to the sense of wonder that I get when I strain my neck to look up at the enormous flying reptile suspended above the Great Hall at the Texas Memorial Museum. All it takes is a bit of inquisitiveness to lead you down a trail of investigation that never stops forking and narrowing as it winds its way into the unknown.
If curiosity killed the cat, the cat died happy.