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Re: How did dromaeosaurs use their arms?



Jaime "James" A. Headden wrote about the mechanics of a dromaeosaur arm:

>   How does this work?
> 
>   Movement of force along an arm when being swung in
> an arc will result in the force attempting to move the
> arm in any direction it can; the more flexible the
> joints, the less likely it is the arm was useful for
> "snapping" or "swapping" at something and actually be
> able to grab it. The loss of a great deal of
> supination/pronation in the maniraptoran arm results
> in an increase of force transmitted towards the tip of
> the arm (or lever, since we're talking force here) and
> an increase in the resistance at the joints (elbow,
> wrist, axial [md1, major] digit) that would force the
> arm to behave in particular ways when force acts along
> it. Thus, the arm, when pulled into forward extension,
> would still have nearly all the force transmitted into
> the hand, rather than acting on the wrist or elbow

I think I didn't quite get this. The force that bends the arm acts on a plane 
and has two components, the x and the y, for example. If a force bends an arm 3 
newtons to left and 6 newtons down, for example, stiffening the arm so that it 
moves only between left and right doesn't make it excert forces an ounce 
greater in those directions than it would in a more mobile arm. Well, that's 
what I think.
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