RE: Ceratops (was RE: Pterosaur diversity (was: Re: Waimanu))

[mike@miketaylor.org.uk (Mike Taylor)]

Tim Williams writes:
>> Sometimes it's too late.  By the time we had enough new genera that
>> _Titanosaurus_ was no longer uniquely diagnosable, it was 125 years
>> old.  By the time we figured out that procoelous caudals are not
>> synapomorphic for "titanosaurids", Titanosauridae had been
>> established for the best part of a century.  For that
>> century-and-a-bit, _Titanosaurus_ and Titanosauridae were good,
>> useful taxa.  That they are now rightly deprecated doesn't change
>> the fact that they were historically useful.
> 
> I agree - but the word "were" is the crux of this argument.  When a
> taxon is no longer useful, it is probably better to discard it -
> instead of resorting to heroic efforts to keep it alive.

I only half agree.  Remember, we are dealing with three four of name
here: species, genera, family-and-related, and clade.  Let's take them
one by one.

1. I think everyone agrees that, based on the type material,
   _Titanosaurus indicus_ is not diagnosable from other titanosaurs,
   so that species, which it was once valid, is now a nomen dubium.  I
   think it's important that this change has happened not because of a
   change in attitude to the original material, but a change in the
   context in which it's evaluated, i.e. we now have dozens of
   sauropods with procoelous caudals, so that this character is no
   longer diagnostic.

2. I think everyone also agrees that since _Titanosaurus indicus_ is
   the type species of _Titanosaurus_, that genus is no longer valid.
   There is not much choice in the matter: since the ICZN is the only
   code that even attempts to govern genera, its rules can hardly be
   overlooked.  (The only way out for someone who was really set on
   retaining the name Titanosaurus would be to define a clade of that
   name govered by the PhyloCode.  I trust we don't need to go into
   all the reason why that would be a bad idea :-)

3. If we consider names ending -idae (etc.) to be "family-level" and
   therefore governed by the ICZN, then Wilson and Upchurch (2003) are
   right that Titanosauridae must also die; but of course that same
   name could equally well be read as a clade-name, in which case it
   is governed (if at all) by the PhyloCode; and as Salgado (2003)
   points out, the name is probably still OK under phylocode rules,
   since the _T. indicus_ material is still diagnostic to the level
   that it is safely included in the Titanosauridae as traditionally
   conceived (and therefore also in Titanosauridae as it would be
   phylogenetically defined by someone who was careful to approximate
   traditional content in her definition.)  I still feel queasy about
   this, though: if the genus _Titanosaurus_ is gone, then the
   PhyloCode article governing clades that are named after genera does
   not strictly apply; but I think it's clearly in the spirit of the
   code that the name is for that reason better avoided.

4. Finally, we consider clade-names that do not end with -idae (and by
   the way, what a stupid category that is.  A clade may be above,
   below, or slap in the middle of "family level" but still end with
   -idae or similar.  Oh well).  It is clear that no article of the
   draft PhyloCode prevents us from continuing to use Titanosauria.
   But I still feel a bit queasy about it -- maybe because I am
   offended that different rules seem to govern Titanosauria and
   Titanosauridae.

In my fantasy world, the ICZN continues to govern species and genera,
and the PhyloCode foreswears all intention of messing with them.  In
return, the ICZN gives up families and the related ranks, leaving the
PhyloCode free to govern all clade-names without interference,
irrespective of their endings.  But, hey, that's just _my_ fantasy.
Yours might be completely different, and involve warm butterscotch
sauce.

> This could be harder to prove.  After all, unless an explicit
> etymology is provided for each clade, it is open to interpretation
> whether it is named *after* a given genus.  For example, we know
> that when Titanosauria was first named (was it by Bonaparte and
> Coria, 1993?) it was ultimately named after _Titanosaurus_; but
> unless this is explicitly stated in the paper, the name could just
> be a descriptive term in its own right ("titan lizards").

Good point -- I've not seen it made before.  Sadly, the draft
PhyloCode seems to be silent on the subject of etymology.  It might be
worth proposing a change to that?

>> That says to me that it's bad PhyloCode practice, too, to make a
>> name based on a genus whose affinities can't be rigorously
>> established.
> 
> Yes.  After all, rigorously establishing the affinities of taxa is
> the main purpose of PT.

Hahahahahahahaha.

Oh, sorry.  That wasn't a joke, was it?

:-)/2

 _/|_    ___________________________________________________________________
/o ) \/  Mike Taylor  <mike@miketaylor.org.uk>  http://www.miketaylor.org.uk
)_v__/\  "Can't someone act COMPLETELY OUT OF CHARACTER without arousing
         suspicion?" -- Bob the Angry Flower, www.angryflower.com