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2013/3/5 Tim Williams <tijawi@gmail.com>:

> I think a distinction has to be made between "striking a pose", and
> how a theropod habitually stood, walked, or ran.  When running, the
> trunk was possibly held closer to the horizontal (i.e., at a shallower
> angle) than when walking, and (especially) when standing.  That's if
> modern terrestrial birds are any guide (e.g., guineafowl, re Gatesy,
> 1999).  There are exceptions - such as the plains-wanderer
> (_Pedionomus torquatus_), which habitually adopts an upright stance
> (mentioned by Ron Orenstein), and of course penguins, which are an
> extreme example.

Even we humans lean forwards at running (and at a lesser degree, in
walking). Never as much as horizontal, of course. I am not entirely
sure of the reason, but think that it may be that displacing forwards
the center of mass may help "falling forwards" faster, thus helping
acquiring higher velocity. The posture also looks more aerodynamic. If
the center of mass shifting idea is right, one may expect different
leaning angles at different velocities (including 0 km/hour) in other
bipeds. However, this variation may have been minimal.