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

[Chris Campbell <sankarah@ou.edu>]

Ronald Orenstein wrote:
> 
> >> How, then, do you explain Pachyrhinosaurus?  I can't see whatever it had on
> >> its snout being much use except in shoving matches.
> >
> >Well, yes, but what's on its snout isn't a pokey horn.  More of a
> >callous or something.  That's fine for shoving, but I don't think you'd
> >get the same behavior in the rest of the family, do you?
> >
> >Chris
> 
> Perhaps not - but I presume Pachyrhinosaurus wouldn't have ended up the way
> it did if some form of shoving hadn't existed in its immediate precursors
> at least.  In antelopes, smaller species such as steenbok use their horns
> for intraspecific contests that are sometimes fatal; as antelopes grew in
> size there appears to have been a shift towards less lethal weaponry, but
> the focus started with intraspecific competition.  It would not surprise me
> to learn that the same or something similar happened in ceratopians.  

I agree; I think it likely that as the horns grew longer behaviors
shifted from the relatively safe head butting and horn locking to more
of a predator-defensive mode.

> I find it hard to imagine how the hornless Psittacosaurus or Protoceratops
> could have used their head armour offensively except in shoving matches
> (and is it not now accepted that the sister group of ceratopians are the
> pachycephalosaurs?).  As ceratopian evolution proceeded some lines may have
> shifted from direct head-butting to non-contact displays (possibly so in
> the long-frilled forms?), with the horns serving, perhaps, an antipredator
> function as you suggest - but other lines, such as those culminating in
> pachyrhinosaurs, may have (I suppose) begun as head-butters and stayed that
> way.

I think you're right; the use of horns for display alone has an awful
lot going for it, and brings to mind the extinct _Megaceros_, the Irish
elk.  

Chris