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Re: Ceratonykus braincase described



On 28 April 2011 10:33, David Marjanovic <david.marjanovic@gmx.at> wrote:

> Regarding alvarezsaur arms, I have yet to catch up with the discussion, but
> the combination of proportionally tiny size (in parvicursorines -- not in
> *Patagopteryx* or *Haplocheirus*!), proportionally huge thumb claw, very
> restricted range of movement, and mind-blowing humongous muscle attachment
> sites leads me to support Longrich's hypothesis that alvarezsaur arms
> sacrificed speed and range of movement for power.

Power has a pretty specific definition:
http://en.wikipedia.org/wiki/Power_(physics), which short levers
(large output angular velocities for a given muscle contraction, so I
guess I disagree with sacrificing speed) and large muscles (high
forces output for a given muscle contraction) fit with quite well,
although the relationship of the moment arms to the fibre length of
the attached muscle would be critical. But in what proposed use of the
forelimbs would power, as distinct from the economical application of
force, be useful? If usage for breaking something stationary is
proposed, dramatic shortening of the limbs would shorten the muscle
moment arms and much as the outlever moment arms, meaning to exert
large moments you need to have large muscles, basically wasting
energy. Enhancement to the olecranon may correct for that somewhat.

Keeping the arms relatively long and moving the major muscular
attachments distally to enhance their moment arms make much more sense
if you are using the arm to break/dig stuff, as in fossorial mammals,
but that doesn't seem to be what they are doing. Shortening the muscle
moment arms and the outlevers and enlarging the muscles, which might
enhance power (as in rapid work application), suggests there may be a
time component to the task in hand - maybe breaking something that
requires a high impulse (force/time) to break, or as has been
suggested, use in some kind of display.