RE: JFC-Bloodiest Battle ??

[Tim Williams <twilliams_alpha@hotmail.com>]

Dan Chure wrote:

> I remain agnostic on the myrmecophagus habits of Mononykus. The
> forelimbs are very short and I can't see how that would work
> functionally with the long neck. 


The alvarezsaur bauplan is certainly unlike any modern myrmecophagous mammal.  
However, between them I think Senter (2005) and Longrich & Currie (2008) 
present a strong case for considering alvarezsaur forelimbs as being 
specialized for breaking into insect nests.  The combination of a long neck and 
short forelimbs might make sense if (as Longrich & Currie propose) alvarezsaurs 
fed on wood-nesting termites.  So as the claws tore into rotting trees, the 
alvarezsaurid jaws would snatch up the termites scurrying up the surface of the 
trunk.  A long and flexible neck would help in this case.


Nevertheless, the shortness of the alvarezsaur forelimbs is especially weird.  
Even if the forelimbs were used for digging, why were they so short?  It's 
possible/lilely that alvarezsaurids evolved from theropods in which the 
forelimbs were already reduced (as in compsognathids - or maybe compsognathids 
themselves were the ancestors of alvarezsaurids).  Perhaps alvarezsaurids 
inherited forelimbs that were on the way to being vestigial?  Then, for one 
reason or another (maybe to do with the shift to a myrmecophagous diet), the 
forelimbs acquired a new function in digging.  But by this point the 
alvarezsaurs were stuck with their puny forelimbs, and had to make the best of 
them.  And, for some reason, the forelimbs could not be re-enlarged - although 
fortunately a strong upper arm musculature was retained.  Carnotaurines have 
tiny forelimbs that were probably useless, but the scapula and coracoid are 
still very large and (presumably) well-muscled.  So alvarezsaurid ancestors may
 similarly have drastically shortened the forelimb (associated with loss of 
function), but left the arm musculature mostly untouched (?to promote ribcage 
and pectoral girdle mobility, as suggested for _Carnotaurus_).  This gave the 
alvarezsaurid forelimb 'wiggle room' to take on a novel function, although in a 
less-than-ideal way given how short the forelimbs had become.  



Cheers

Tim
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