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Re: Ceratopsian jaws

Robert J Meyerson (Rob Meyerson) wrote:

> Nick Longrich writes;
> >  Longer muscles can contract over greater distances, but
> >the strength of a muscle is directly related to it's cross sectional
> >area. This is why modern herbivores tend o have short, broad sheets of
> >muscle to pull on the jaw; because it develops much more force.
> This is a good point.  I'll have to think things over during Christmas
> break.

You're both right!  Longer muscles don't pull harder, but they can apply
more turning force to a joint.

Turning force (newton-meters or foot-pounds) is the product of muscle
force and the normal distance from the line of force to the pivot.  I
understand the muscle-attachment points on ceratopian jaws were on bone
extensions to increase this distance.  That might be called leverage.  I
think it's also called a bell crank.

Moving the attachment point away from the joint would increase the
biting force.  It would also increase the distance the muscles would
have to contract.  

I understand a muscle must be about four times as long as the distance
it must contract.  Measuring the distance the attachment point had to
move would allow you to estimate the minimum distance between that point
and the attachment point on the skull.

- Stephen Throop