Re: Forelimbs of "Terror Birds"

[Graydon <graydon@dsl.ca>]

On Tue, Dec 11, 2001 at 04:58:45PM -0600, Steve  Brusatte scripsit:
> On Tue, 11 Dec 2001 13:15:23  Williams, Tim wrote:
> >It reminds me of one current suggestion for the mini-forelimbs of
> >tyrannosaurids: that they were used to clasp large prey close to the
> >predator's chest, after the jaws and feet had subdued the prey.  
> >
> >There is also Newton's suggestion (not mutually exclusive) that the
> >forelimbs were used by males as claspers during copulation.
> 
> Although I can't say I know for certain, I think the prey-clasping
> function of tyrannosaurid forelimbs seems the most logical, at least
> judging by what literature is available.  Check out Carpenter and
> Smith's paper in Mesozoic Vertebrate Life.  It's full of some
> intriguing calculations on the subject.

I thought the calculations were convincing; T. rex arms are meant to
take considerable load.

What I now want someone to explain is what possible _use_ clasping the
juvenile hadrosaur in the positions available to the arms would be to a
predator whose primary killing tool is a bite that it can't apply to the
area of what it's holding.

The only thing that I can picture that begins to make sense is
orientation control; grap the prey from behind, over the hips, and hold
on, so that the neck stays lined up for biting, but that doesn't work
ideally well, since the desired bite angle is going to be _across_ the
neck, rather than parrallel to it.  (and indeed IIRC the few healed
tyranosaur bite marks do apply 'across' as the angle of attack.)

Has anyone got a better idea about this one?

-- 
                           graydon@dsl.ca
               To maintain the end is to uphold the means.