Re: Crown groups

[Tim Williams <twilliams_alpha@hotmail.com>]

Jonathan R. Wagner wrote:

> Obviously, crown clades ARE useful to talk about them, because
> they are usually what neontologists ARE talking about. But, ultimately, the
> choice of which taxa to name is *arbitrary*.

I agree that crown groups are useful, especially to neontologists (who 
massively outnumber paleontologists) since the 'survivor' lineages are the 
basis for their disciplines.  However, I was questioning the wisdom of 
constructing naming conventions around these crown clades, especially the 
use of the Pan- prefix.  For example, just how useful is the term 
'Panlissamphibia', which is essentially equivalent in content to the 
time-honored 'Amphibia'?  How comfortable are you or anyone else referring 
to _Eryops_ as a 'panlissamphibian' rather than simply an 'amphiban'?  Or, 
to give another example, why is 'Panmammalia' necessary when the traditional 
name 'Synapsida' is available for essentially the same clade?

> I've seen some very savvy phylogeneticists slip on
> this sort of thing quite regularly, including a frog systematist who
> insisted that we should use Amphibia instead of Lissamphibia (I agree), and
> apply it to the crown clade, then turned around two lectures later and
> called Eryops an "amphibian." I think that paleontologists, by applying the
> name outside the crown clade, have confused the neontologists, and they 
> seem
> to be just trying to keep up.

There is a lot of truth to this.  But this example may be due more to 
vernacular versus phylogenetic definitions.  _Archaeopteryx_ will still be 
called a bird irrespective of whether the clade name 'Aves' ends up at the 
_Archaeopteryx_ node or much higher up, at the base of the crown group.  
SimilarIy, having the name 'Mammalia' anchored to the node of the crown 
group will not change the imprecise and often subjective usage of the word 
'mammal' in the scientific literature.  I have a feeling that _Morganucodon_ 
will continue to be called a mammal, even if it lies well outside the crown 
group.  Ditto for _Eryops_ being an amphibian.  Vernacular terms are more 
elastic and connotative than phylogenetic terms, and hence a little murky in 
their limits.  The ambiguity of such terms as 'bird' and 'mammal' will not 
change if and when the phylogenetic terms Aves and Mammalia are applied to 
the crown clades.



Tim

_________________________________________________________________
Stop worrying about overloading your inbox - get MSN Hotmail Extra Storage! 
http://join.msn.click-url.com/go/onm00200362ave/direct/01/