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Re: dino-lite

On 4/21/2011 11:30 PM, Tim Williams wrote:

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.

As anyone who has done any digging knows, teeny little arms poking out of your chest are NOT the tools you need, as Jason and several others point out, especially when range of movement is limited.

OTOH, it is consensus that the anatomy shows the presence of significant physical stresses while alive.

Those who have crawled around in tight places in caves or culverts can readily imagine that teeny but powerful arms poking out of your chest could be very useful indeed -- especially when backing out of a constricted or dead-end passage, where the hind limbs are nearly useless or even a hindrance.

With a nod to Pigdon and the "Cloaca Speculation" -- assigning these short but strong limbs a locomotive function that involves assisting the narrow head and neck in accessing and retreating from burrows, hives, nests, hollow logs and/or the nooks and crannies of large animal carcasses while in search of insects, small animals, or even small eggs is the best speculative fit in my view to the general morphology of alvarezsaurids.

Also, the locomotive function offers a clear path of incremental evolution from the basal Haplocheirus to the highly derived Shuvuuia....