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RE: mass, momentum, & misc.



Nicholas Wren wrote:

>  I'm not just picking on the rex here, by the way.  Take a look at the
>Albertosaurus reconstruction.
>( http://tyrrell.magtech.ab.ca/tour/alberto.html ) 
>  What is going on here?  Does that look like an animal built to carry a
>heavy meal load up front?  From what I can tell, therapod experts don't seem
>to think huge meals would have posed a balance problem for these guys.  What
>do they (or you) know that I don't?

I have noticed the same thing with many, in fact most reconstructions/ 
restorations of bipedal dinosaurs and thecodonts.  They look unbalanced, 
with the centre of mass in front of or only just over the leading foot.  Am 
I imagining things?  Is balance carefully taken into account when mounting 
skeletons?  Do the artists on the list have rules of thumb for determining 
centres of gravity or, even better, use models?

>  What the hey??  I was under the impression that the horns and frills were
>so that the ceratopsians could mass together, in the fashion of musk-ox, to
>present a horny, armored barricade against any would-be predators.  Was I
>just completely out in left field on that one?  And did female ceratopsians

They may well have done, although I've not heard of any evidence (e.g. 
footprints) suggesting they did.  Can someone tell me if there's any 
evidence of herding at all in ceratopians?

In any case, herbivores' weapons tend to evolve for intraspecific combat, 
and only later are sometimes turned against predators.  This makes 
theoretical sense.  An incipient horn is no use against a predator: to use 
it you have to stop running, and then you'll easily be killed.  But even the 
feeblest beginning of a weapon may be useful in fighting off a rival similar 
to you.  Nearly all herbivores with horns and other weapons run from 
predators.  Only those which are substantially larger than their predators 
(elephants, rhinos, musk oxen) stand and fight.

>differ significantly from the males in armor and weaponry?  (My thinking
>being that sexual dimorphism would lend support to the notion that
>ceratopsians battled one another in contests much like deer and bighorn do.)

Your thinking is correct.  There are several places where ceratopians 
described as different species are now thought by many to be different sexes 
of the same species.  (BTW, in case you're wondering, it is alright to call 
them 'ceratopsians', rather than 'ceratopians'.)

                                                All the best,

                                                                Bill Adlam