Bipedalism in the trees

[James Norton <JNorton@MAILBOX.UNE.EDU>]

Bipedalism evolving on the ground and moving into the trees or bushes
seems reasonable, more so to me than bipedalism evolving in the trees in
the first place.  I think the arguments about extant tree-dwellers and their
use of all four limbs are good ones.

Ground-originating bipedalism would provide the putative creature with
the coordination and balance necessary to be able to perch on a branch
as a biped. The forelimbs, which may have evolved for prey capture,
could have been modified to preserve prey capture but also provide
additional balance, in the same way that a tightrope walker uses arms or
a pole.  In this scenario, lengthening the arms would be good for balance.
 The lengthened arms, possibly covered already with feathers or
proto-feathers, could then have been used not just for balance but to
provide a controlled descent (pouncing on prey, jumping to another
branch), lift (for gliding from one perch to another), and eventually thrust.

JM Norton