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Jason Brougham <firstname.lastname@example.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
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.