RE: Sereno's (2005) new definitions

[Tim Williams <twilliams_alpha@hotmail.com>]

Mickey Mortimer wrote:

> A nomen dubium cannot influence a topology except to create a polytomy 
> which covers its potential placements.  Only taxa with unique combinations 
> of characters can influence topologies, but nomina dubia by definition lack 
> those.

Depends who you ask.  :-)  I would say that a unique combination of 
characters is enough to uphold the validity of a taxon - and I'm sure you 
would too.  But there is another (more stringent) view that a taxon must 
have autapomorphies in order to be deemed valid.  That seems a little harsh 
to me.

> > In other words, we could put a nomen dubium into a matrix - but why would 
> > we need to?  Why, when we could just replace the nomen dubium with an 
> > unquestionably valid taxon?
>
> To tell what the nomen dubium's phylogenetic relationships are, of course.

But by definition, a nomen dubium does not represent a discrete organism.  
Because a nomen dubium has no unique characters (or combination of 
characters) it cannot be differentiated from other taxa.   For example, 
_Antrodemus_ might be _Allosaurus_, or it may not be; we're never going to 
know.  Therefore it is weird (for want of a better word) to include a nomen 
dubium in a matrix.  I think this is what Jaime is also driving at: a nomen 
dubium has nomenclatural standing (in the sense that the name is valid) but 
no taxonomic standing (in the sense that we don't know what organism it 
pertains too).

> Why view -idae and -ia clades differently if we're ignoring the ICZN?

Because -idae clades should at least be assured of containing the eponymous 
genus.  This goes way beyond the ICZN: the suffix -idae represents a 
tradition going back thousands of years.  The ancient Greeks used '-idae' to 
designate a dynastic lineage or family: Atreidae, Heraclidae, Achaemenidae, 
Seleucidae, Arsacidae, etc.  Each lineage/family had the eponymous ruler or 
hero as a member - in these cases, this was the founder (real or alleged).  
So, to answer your question, -idae and -ia should be viewed differently 
because -idae actually denotes something in its own right.

Cheers

Tim