Re: Cursorial adaptations (was T.rex and elephants)

[Dann Pigdon <dannj@alphalink.com.au>]

Chris Campbell wrote:
> 
> That makes sense, and fits with most of the data presented.  However, as
> George points out the frills came before the horns.  I think this can be
> explained, though; if the frills and proto-horns were used for shoving
> matches and defense, the growth of horns can be explained.  We have to
> keep in mind that the horns and frills wouldn't serve only one function;
> the frills might start off as defensive, but then be combined with horns
> for intraspecific competition.  As the horns get longer (possibly in
> response to predation pressures) the intraspecific uses become more and
> more dangerous, so the display functions take over.  The horns remain
> nice and long, though, because they're great as defensive items.
> Meanwhile, those who stuck with nose horns would go on with their
> wrestling and respond to threats with head butts, bites, and short
> charges.  Makes sense, but I dunno how well it'd stand a rigorous
> analysis.
> 
> Chris

        Frills certainly had more than one function. Originally they
probably developed to increase the surface area for the jaw muscles.
Neck protection was almost certainly secondary, but since evolution
works by co-opting old features for new purposes the defensive
function was eventually emphasised. They were probably co-opted for
display purposes as well, perhaps as the display function of the
bill-board tail of protoceratopsians was lost in larger descendants.
        In some species perhaps the display function was
more important than a solid protecting frill. I can't see that the
increase in protective properties of torosaurus frills would have been
worth the inconvenience of such a large encumberance if it were for 
protection alone. If styracosaurus / centrosaurus is anything to go by
then there may have been a degree of sexual dimorphism as well,
with the males (?) of the species sporting ornate displays, while
females had more physically functional arangements (much like
many modern ungulates).
-- 
____________________________________________________
        Dann Pigdon
        Melbourne, Australia

        Dinosaurs Reconstructions:
        http://www.geocities.com/capecanaveral/4459/
        The Australian mirror:
        http://www.alphalink.com.au/~dannj
____________________________________________________