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Re: dino-lice

Jason Brougham <jaseb@amnh.org> wrote:

> In other words, how small would the arms have to be before we could all agree 
> that they couldn't be used for scratch digging? Right now we all agree 
> Shuvuuia would have to practically press its chest
>  against anything it touched with its arms, and that it couldn't see what its 
> arms were doing. Yet the bone shapes, alone, convince many that it was 
> digging with the arms.

I'm convinced that the forelimbs of alvarezsaurids were used for
*something*, and that *something* was associated with diet.  After
all, the forelimbs weren't THAT small.  Reduced though they were, they
certainly extended well beyond the body wall.  Plus, the arms were
operated by a powerful musculature.  I'm just not convinced the
forelimbs were used for digging into termite-mounds or ant-nests.

I doubt that _T. rex_ could see what it's arms were doing when it
grasped large prey.  That doesn't mean they weren't useful.  Also, an
alvarezsaurid could probably see its own arms - just not when it had
its body pressed against an insect-nest or tree.  I'm disputing the
hypothesis that alvarezsaurids were "dinosaur anteaters", rather than
dismissing the usefulness of the forelimbs altogether.

> What if the arms were a millimeter long and entirely embedded within the 
> skin? What if they were a micron long? Would the antebrachial anatomy still 
> persuade you that they were used for precision
> digging?

That's a leading question, so I'm going to duck it.  :-)  But I would
mention that it's possible (although so far we have no proof) that
certain alvarezsaurids lost their forelimbs altogether.  For example,
we don't know what size forelimbs _Parvicursor_ had.