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Re: Panstems



--- Christopher Taylor <ck.taylor@auckland.ac.nz> wrote:

> On 14/9/04 8:19 am, "T. Michael Keesey" <mightyodinn@yahoo.com> wrote:
> > http://dino.lm.com/keesey/documents/PhylogeneticNotation.doc
> 
>     One point which I've noticed in the exemplar definitions, which isn't a
> problem with Mike's proposed notation, but a problem arising from one of the
> definitions -'Panaves'. My question is - how are we to properly define crown
> clades? Simply defining them as node clades doesn't seem sufficient, as we
> should allow for the possibility that some of the living members may
> eventually be moved phylogenetically outside the proposed node.
>     Mike defines Panaves as the panstem clade of the node Struthio + Tetrao
> + Vultur.

Actually, de Queiroz and Gauthier did (in the Ostrom Symposium volume).

It should also be pointed out that _Tetrao_ is not a specifier. _Tetrao major_
is the specifier, and it has been given its own genus since its original
publication: _Tinamus_. I was merely citing the original form of the species
name.

> Under the current popular phylogenies, this wouldn't really be a
> problem - whichever the most basal branch of Aves is, most researchers would
> currently hold it to include one of these three. But among other taxa that
> have been suggested in the past to be the most divergent living birds are
> Mesitornithidae, _Opisthocomus_ and _Todus_ (!). Conceivably, we could get a
> situation where these are not Aves. By some older molecular phylogenies,
> Passeriformes would not even be Aves by the definition given. What to do?

You could use a stem-modified crown, e.g. "the first ancestor of all currently
extant organisms sharing more recent ancestry with _Vultur gryphus_ than with
_Archaeopteryx lithographica_, plus all of that ancestors' descendants". That,
or increase the number of internal specifiers.

There has been some discussion about the general topic of crown and panstem
clades on the PhyloCode Mailing List lately. Once again I urge everyone
interested in this topic to join. The instructions, once again, from
http://phylocode.org:

"If you would like to join an internet discussion group focusing on
phylogenetic nomenclature, send a message to listserv@ohiou.edu. The message
should read: 'subscribe PhyloCode' (without the quotation marks). Do not
include anything else in the message. In a short time, you should receive an
automatic reply explaining how to send messages to the discussion group."

=====
=====> T. Michael Keesey <http://dino.lm.com/contact>
=====> The Dinosauricon <http://dinosauricon.com>
=====> Instant Messenger <Ric Blayze>
=====


                
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