Re: The Papers That Ate Cincinnati

[Tim Williams <twilliams_alpha@hotmail.com>]

Mike Keesey wrote:

> It depends on the definition. (And it's not a matter of classification, but 
> of changing phylogenetic hypotheses.) If a clade is defined with 
> _Opisthocomus hoazin_ as a specifier, then that species shifting around in 
> different cladograms may affect our understanding of the clade's content. 
> But I don't think anyone's ever used _O. hoazin_ as a specifier for any 
> clade, and, given its uncertain position, I'm not sure anyone would want 
> to. (Except in case the genus _Opisthocomus_ or any eponymous taxon is 
> converted as a clade name, of course.)

A stem clade "Panopisthocomiformes" could be erected for all birds closer to 
the hoatzin (_Opisthocomus hoazin_) than to any other modern bird.  It might 
include such fossil taxa as _Hoazinoides_ and _Foro (if not a 
musophagiform), though probably not the highly dubious _Onychopteryx_.

Given the highly uncertain relationships of the hoatzin, a node-based or 
stem-based definition of Opisthocomiformes would be highly problematic.  I 
don't see any easy solution, except by resorting to a long list of external 
specifiers.  The alternative is to make Opisthocomiformes apomorphy-based, 
as Clarke et al. (2003) suggested for Sphenisciformes.

Evelyn Sobielski wrote:

> Then, anything that is unicellular and reproduces clonally. In these cases, 
> ontogenetic genetic changes (eg by HGT) *are* possible phylogenetic 
> changes. Howto define clades in these?
>
> Or try Woese
> (http://www.pnas.org/cgi/reprint/97/15/8392 and
> http://mmbr.asm.org/cgi/reprint/68/2/173).

These days, higher-level classification of prokaryotes (bacteria and 
archaea) is based on 16S phylogeny.

Cheers

Tim

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