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Re: Evolution of tyrannosauroid bite power



On Sun, Dec 30, 2007 at 05:12:20PM -0800, don ohmes scripsit:
> Re-allocation of mass is what answers all three questions. The load
> had to be lightened somehow, and the arms were what could be spared,
> due to lifestyle. Just a cartoon, though, not currently testable (I
> think), other than with logic. Ask me what the arms were useful for, I
> promise a fuzzy answer neither critically involving, nor totally
> eliminating, predation. Getting up comes to mind ...

Bipedal dinosaurs are balance beams; if it's really important to have
the mass up forward, you can always accept being a bit slower and having
a larger tail to balance forward mass.  So the idea that there was
compelling selection for lighter forearms doesn't have obvious merit,
especially since T. rex arms are highly derived relative to the
ancestral tryannosauroid condition.

In the case of T. rex forearms, they're not, proportionately, strong;
very strong for their size, but not strong for the size of the animal or
the probable prey animals.

One probable reason for bite-and-leg dominance in T. rex predation is
that they *are* big animals; having forelimbs large enough to be useful
in direct predation would require very large and powerful forelimbs.

So instead they have dinky forelimbs that clearly underwent
proportionately high loads.  Could be mating related (but then we'd
expect to see disproportionate development/injury in males) or it could
be a prey position sensor.  It more or less couldn't be a 'hold the
prey' mechanism because even a thousand pounds of force isn't worth
anything when a five ton Edmontonosaurs thinks it's about to die.  It
can generate *lots* more force than that with its legs.  But it *could*
be a 'where is the Edmontonosaur I've just crashed into, bit once, and
which is now a)under my head/out of my direct line of vision and
b)vigorously concerned to get away.

-- Graydon