RE: true semilunates & carpometacarpi (was Caenagnathiformes)

["Williams, Tim" <TiJaWi@agron.iastate.edu>]

Ken Kinman wrote:

>     I'm not sure exactly what Mickey means by non-semilunate form in 
>Caudipteryx and Protarchaeopteryx, but assume it is the shape.  

I think Mickey has very articulately outlined the difficulties (potential
and real) of using the semilunate carpal as the "key apomorphy" that defines
the Aves.  You're pouring all your taxonomic eggs into one basket - and what
we get is an omelette.

>So to 
>account for that, perhaps the  definition should say: "usually" has a 
>distinctive semilunate shape.  

"Usually".  Oh dear.  This definition is already dead in the water.  Poor
Sisyphus hasn't even had a chance to push that boulder up the mountain.  :-)


>I listed the size criterion first, since
>the relatively large size seems to be a little more diagnostic than >shape
anyway.

"Relatively large size" as a diagnostic character?  I can see it now...

Aves: Defined by the presence (usually) of a carpal block that is fused
(most of the time) and large in size (relative to the carpus of non-avians,
anyway) and of a distinctive semilunate shape (more or less, since it may be
block-like or ovoid, or perhaps other shapes too).  

Yes, I can see just how clear-cut apomorphy-based definitions are.  ;-)



Tim

>     What *does* concern me is the possibility that the fused carpals
>found in some non-maniraptors could be mistaken for one of these >fused
"true" semilunates (i.e. carpometacarpi).  

Now I'm confused.  I thought alvarezsaurids and avimimids *were*
maniraptorans.


Tim