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Re: The Papers That Ate Cincinnati




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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