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I have read Lockley's paper on Pteraichnus prints and have correlated his
observations with moveable articulated pterosaur skeletons of various
specimens. It turns out that just as some (about 19) present-day lizards are
both quadrupedal and bipedal, pterosaurs were also quads and bipeds.
The catch is this, as quadrupeds, whether hanging on tree trunks, or wading
in shallows, the elbows were held in--not out. With elbows tucked in the
saddle-shaped glenoid permitted parasagittal movement of the entire arm--
basically it's a tucked-in flight stroke (try it yourself, but remember, no
twisting of the humerus within the shoulder joint is permitted). The
fingers, in this position, faced medially, which would have been ideal for
grasping a tree trunk of any diameter.
On the ground medially directed fingers extended laterally, as the fossil
shows, and as you can demonstrate with your own fingers. Most of the weight
is born by the big joint of the wing finger and digit one does not touch the
ground, again as the fossil seems to indicate.