Re: Croc classification (was Re: Sarcosuchus and Dumbing things down)

[chris brochu <cbrochu@blue.weeg.uiowa.edu>]

I'm going to prune sections of this to save bandwidth.



> > > Contrary to the assertions of several cladists, Owen did not use the term
> > > 'Crocodylia' (with a 'y' instead of an 'i') when he emended Gmelin's
> > > Crocodili in 1842 to additionally encompass fossil taxa.
> >
> >  I don't recall cladists (including myself) referring to Owen for taxonomic
> >  principles;
>
> Well maybe you should.


Why?  We're working in an evolutionary framework, Owen worked on a 
typlogical  framework.  Different frameworks.


> >    Up until 1973,
> > > Crocodilia was broadly equivalent to what most cladists now call
> > > Crocodylomorpha.  About the only point of contention prior to 1973 (and
> > > indeed for about a decade after) was whether Sphenosuchia should be placed
> > > in Crocodilia or Thecodontia.
> >
> >  Crocodylomorpha = "sphenosuchians" + crocodyliforms.  I think you mean "in
> >  the older usage, Crocodilia meant "Crocodyliformes."
>
> No.  Some poeple considered spenosuchians members of Crocodilia (hence the
> comparison to Crocodylomorpha), whereas others excluded them, placing them
> in Thecodontia instead, hence making Crocodilia broadly equivalent to
> Crocodyliformes.


Isn't that what I just said?  Leave out the "sphenosuchians," and you 
had relatively broad agreement over content - that's Crocodyliformes. 
Add the "sphenosuchians" and you get Crocodylomorpha.





>  > I think some posters to this list have the misimpretion that "Crocodilia"
> >  had a stable meaning before the crown-group definition was published in
> >  1988 - and Ken, you'd be VERY surprised at who the senior author of that
> >  paper was.  If it did, there'd not have been a need for a revised
> >  definition. Most people agreed that things like dyrosaurids and
> >  notosuchians should be "crocodilians," but what about Gracilisuchus?  or
> >  Terrestrisuchus?  Were these "crocodilians" or "thecodonts?"  The lower
> >  bounds of "Crocodilia" in the former usage were absolutely unclear and
> >  ambiguous.
>
> Is it any different now?  Just compare the works of Clark, Wu, Sues,
> Brinkman, Parrish, Sereno and Wild.


Yes.  Details of phylogeny among, say, the "sphenosuchians" are in 
dispute, but the range of the tree between Crocodylomorpha and 
Crocodyliformes is stable.  That's why the stability sought for in 
phylogenetic nomenclature is meaning, not content.

> It's not what I propose; I'm just going along with Owen and Huxley.
> Taxonomic stability is an unachievable Holy Grail.  In any case, it makes
> systematics more enjoyable.


See  a previous post of mine - there are different kinds of 
stability.  I think you're  thinking about stability of content, and 
we're more interested in stability of meaning.


>  >
> >  In the context of the Linnean system, perhaps.  But we no longer use the
> >  Linnean system (or shouldn't), so whether one spelling or the other in the
> >  Linnean system has priority is irrelevant to the crown-usage currently in
>  > place.
>
> Whose 'we'?  Not me.  I'll use which ever system I think is most
> appropriate.  And for purely taxonomic purposes, the Linnean system wins
> hands down.  Phylogeny is something else.

If the Linnean system were so great, why are we eliminating it?  Just 
to be a bunch of annoying persons?


chris



--
------------------------
Christopher A. Brochu
Assistant Professor
Department of Geoscience
University of Iowa
Iowa City, IA 52242

christopher-brochu@uiowa.edu
319-353-1808 phone
319-335-1821 fax

www.geology.uiowa.edu/faculty/brochu