Re: Bird arms

[twilliams@canr1.cag.uconn.edu]

Alvarezsaurids have truncated, coossified forelimb bones because they 
evolved from volant birds which had a fused carpometacarpus.  A fused 
carpometacarpus is (presumably) useless for predation, but it may have been 
co-apted as a digging instrument by alvarezsaurids.

(I should point out that this is just one theory on the function of 
alvarezsaurid forelimbs.  It's also been proposed that they were used 
to strip bark off trees, or to smash open dino eggs.  I'm sure there 
are others.)