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

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

Tim Williams writes:
>> To play devil's advocate, both Ceratops and Titanosaurus were very
>> distinctive when they were first found.  It's only with hindsight
>> that we know strongly procoelous caudals and large brow horns have
>> wide distributions.
> 
> I agree.  It is not the fault of either the _Ceratops_ or
> _Titanosaurus_ type material that their significance was eclipsed by
> later discoveries.  But if we want stability in phylogenetic usage,
> then we should be anchoring our clades in the genera that we name
> them after.  (This only applies to family-level clades.)  And if a
> certain taxon is too poorly-known to be used as a specifier, then we
> should name the clade after a taxon that can be used as a specifier.

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 don't think there's much that can be done about this, beyond just
accepting that things change.

Tim Williams writes:
>> Is the parenthetical statement to suggest that higher clades like
>> Titanosauria should be kept?
> 
> Yep.  These higher-level taxa do not come under the purview of the
> ICZN, although co-ordinated family-level taxa do.

... but the draft PhyloCode also, of course, also requires that taxa
(i.e. clades) that are named after genera include those genera:

        11.8. In the interest of consistency with the preexisting
        codes, it would be desirable for a clade whose name is
        converted from a genus name under a preexisting code, or is
        derived from the stem of a genus name, to include the type of
        the genus name. Therefore, when a clade name is converted from
        a preexisting genus name or is a new or converted name derived
        from the stem of a genus name, the definition of the clade
        name must use the type species of that genus name at the time
        of establishment as an internal specifier.

        Example 1. If the preexisting name Magnoliales, which is based
        on the genus name Magnolia, is converted to a clade name, its
        definition must use the type species of Magnolia as an
        internal specifier.

        Example 2. If Ajugina, which is not a preexisting name but is
        based on the preexisting genus name Ajuga, is adopted as the
        name of a clade, the definition of Ajugina must use the type
        species of Ajuga as an internal specifier.

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.

 _/|_    ___________________________________________________________________
/o ) \/  Mike Taylor  <mike@miketaylor.org.uk>  http://www.miketaylor.org.uk
)_v__/\  "You know you're getting older when your music heroes begin
         playing benefits for prostate cancer" -- Globe & Mail's Paul
         Simon article, 2nd October 2000.