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Re: Vestigial Arms (was: Theropod limbs - how mobile?)



On Sun, May 19, 2002 at 11:49:46PM +0100, Michael Lovejoy sent:
> Sorry if I seem to be labouring this point, but I'm still having
> trouble with it. While I'm not disputing that it is physically
> possible, why is it better to do this rather than deliver a big bite
> and back off? As I understand it, theropods can't take falls and
> knocks the way for example big cats can. So why risk grappling with
> prey about as heavy as they were? 

Thing that comes to mind is that being able to use the kill was location
specific; if you give the hadrosaur time to run, it gets into a
thicket/over the stream bank/etc, in the wet sort of lowland environment
we know a little bit about, so there may have been a selection pressure
for speed of kill.

There may also have been a selection pressure for, not being able to
hold on, but for having a mechanical linkage position sensor; many
dinosaurs appear to have had a lot of lateral flexing ability over the
whole length of the body, and hadrosaurs -- which didn't have that --
would have been able to turn hard; the idea is not to hold the prey, but
to hold the T.  rex to the prey's motions as a sort of feedback sensor.
It would take body muscle to match the heaving, but knowing where it was
would be worth something.

-- 
graydon@dsl.ca   |  Hige sceal þe heardra, heorte þe cenre,
                 |  mod sceal þe mare þe ure maegen lytlað.
                 |   -- Beorhtwold, "The Battle of Maldon"