Re: dino-lice

[Tim Williams <tijawi@gmail.com>]

Dann Pigdon <dannj@alphalink.com.au> wrote:

> I've always wondered whether alvarezsaur forelimbs were attrophied from 
> general lack of utility
> (as in Carnotaurus), with the only function left being that of intraspecific 
> kangaroo-style wrestling
> matches.


I've wondered something similar.  Forelimb reduction is a recurring
theme among theropods (even the non-avian ones).  Carnotaurines
represent an extreme example, in which the forelimbs were
non-functional.  By contrast, tyrannosaurids probably used their tiny
didactyl forelimbs for some purpose - I'll go with Carpenter and
Smith's (2001) view that they were used to help secure large,
struggling prey while it was dispatched by the jaws.


I have no doubt that alvarezsaurids used their truncated, monodactyl
forelimbs for *something* - and as with the tyrannosaurids, it was
probably a trophic function.  But unlike David M., I associate
forelimb truncation in alvarezsaurids with a lack of day-to-day usage,
rather than being an optimization for digging.  I also have a
suspicion that the compact arm-folding mechanism (semilunate carpal,
etc) of maniraptorans was evolved for the same reason - it represented
an alternative to forelimb truncation, rather than being associated
with a specialized function per se.  I know many will disagree with me
on this...




Cheers

Tim