Re: Rapator,the giant alvarezsaur

["Tim Williams" <twilliams_alpha@hotmail.com>]

Dann Pigdon wrote:

> I like to imagine giant alvarezsaurids like huge Maribu storks (or
> Australia's Jabiru stork, with a confusingly similar name). Perhaps
> alvarezsaurids started off large, mainly using sharp stabbing beaks (or
> proto-beak structures), during which their forelimbs atrophied (similar
> to what may have happened in tyrannosaurs).

So the enlargement of the claw and strengthening of the forelimb musculature 
came *after* the forelimbs were downsized?  This hypothesis sounds similar 
to what transpired in the flightless bird _Titanis walleri_, which had tiny 
but apparently functional forelimbs tipped by a moveable claw.

> Later, if conditions
> favoured smaller alvarezsaurs, their forelimbs may have evolved into as
> functional a set of tools as was possible, given what they had to work 
> with.

But what was this "function"?  If the forelimbs did regain function after a 
period of atrophication, why did they remain so small?

> People seem
> to place a lot of emphasis on their forelimbs alone, as if their entire
> behavioural repatoir must have accounted for them. They had other body
> parts as well...

True, but the forelimbs represent the most apomorphic part of the 
alvarezsaurid anatomy.  The stubby forelimbs tipped by a single claw are 
highly specialized, and contrast with the gracile, cursorial proportions of 
the hindlimbs.



Tim

_________________________________________________________________
FREE pop-up blocking with the new MSN Toolbar ? get it now! 
http://toolbar.msn.com/go/onm00200415ave/direct/01/