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rudders and bipeds

        I had a discussion with an MAE major today (Mechanical and
Aerospace Engineering) showed him some of my origami pterosaurs (I
came up with a pretty nifty Pteranodon and Rhamphorhynchus this morning
out of the frog base)  and interrogated him briefly on the possibility of
tail rudders. He   said that a <>---------- tail would reduce the amount
of force  needed to turn, but that a shorter tail would not
necessarily make it  more maneuverable, it would just require that the
vane be larger.
        While the vane and the extreme stiffening may have evolved for
aerodynamic purposes, it seems possible that the tail itself was
originally there for bipedal movement, and as long as the animal needed a
big, long potential lever on which it could mount a rudder, this was taken
advantage of and exapted into a rudder structure.
        I saw a drawing of a print (I think it was taken from the real
thing and not just speculation) of a rhamphorhynchoid, with the
backturned fifth toe and everything, so it looks like those guys (some,
most or all) were bipedal, unlike the later pterodactyloids, in which
case anatomy and Pteraichnus seems to mark them mainly as quadrupeds,
albeit somewhat bizarre ones at that. The SVP poster I saw had some of
them walking like a man on crutches in a mostly-upright position. Quite
weird looking, but it's the first reconstruction I've seen that seems to
really fit with what Pteraichnus is telling us.

        -Nick L.