[Taxacom] burn out (was: classification of Class Rosopsida)

Richard Zander Richard.Zander at mobot.org
Tue Apr 14 10:00:14 CDT 2009

Okay, using the paraphyletic method (where paraphyly implies ancestry of
the autophyletic taxon (or taxa), the basalmost paraphyletic taxon in
Aves is the bird ancestral to all the rest, at the resolution of the
lowest grade inclusive of all the exemplars in the paraphyletic taxon.
The ancestor of Aves would be the closest paraphyletic taxon to Aves in
a molecular cladogram, that is, closest being the best resolution given
the data. 

Thus, if mammals had two branches below Aves, then mammals would be the
ancestor of Aves: (((Aves) mammal) mammal)... If you could name the
mammals more accurately, you would have higher resolution. E.g.:
(((Aves) hairy shrew) hairy shrew) then hairy shrew would be the
ancestor of Aves (an example, just an example). The trouble is that if
there are few molecular analyses of multiple exemplars of, say, hairy
shrews, then there is no data on paraphyly at that taxonomic level.

The metric is absolute patristic distance, an instance of paraphyly
supported by molecular data at 95 percent credibility or more. 

Criticisms of parsimony? It's a good clustering method, and gives
general groupings that are commonly supported consiliently by molecular
analysis. It is not terribly good in resolving power because (1) equal
weighting is nonsense, (2) traits if selectively linked confound
parsimony (3 synapomorphies if linked may be equivalent to only one,
evolutionarily, (3) punctuated equilibrium may allow a taxon terminal on
a lineage to be the surviving ancestor of all the lower branches, and
thus pleisiomorphic, (4) the multifurcation in morphological cladograms
expected in punctuated equilibrium may not obtain since daughter species
peripherally derived from a surviving ancestor may have some convergent
traits that falsely are evaluated as synapomorphies, and (5) there is
morphological convergence (doubtfully total except in cases of extreme
reduction) that is not dealt with by molecular analysis since the latter
only infers genetic continuity and isolation, not speciation.

Richard H. Zander 
Voice: 314-577-0276
Missouri Botanical Garden
PO Box 299
St. Louis, MO 63166-0299 USA
richard.zander at mobot.org
Web sites: http://www.mobot.org/plantscience/resbot/
and http://www.mobot.org/plantscience/bfna/bfnamenu.htm
Non-post deliveries to:
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-----Original Message-----
From: taxacom-bounces at mailman.nhm.ku.edu
[mailto:taxacom-bounces at mailman.nhm.ku.edu] On Behalf Of Curtis Clark
Sent: Monday, April 13, 2009 10:28 PM
To: taxacom at mailman.nhm.ku.edu
Subject: Re: [Taxacom] burn out (was: classification of Class Rosopsida)

On 2009-04-13 06:50, Richard Zander wrote:
> The ancestor of Aves is the closest paraphyletic taxon.

What's your metric for "closest"? For all your criticisms of the
weaknesses of parsimony analysis, this seems rather vague. Do you mean
number of generations, phenetic similarity, or what? I assume Aves had
to descend from it. Do you mean at the same rank (whatever that means 
analytically), or what?

I can think of analytical approaches to grade taxa (I have mentioned
them, but no one seemed interested), and I don't find grade taxa
valuable. It seems to me that their proponents should either be able to
do as well or else explain why analysis is unnecessary and what
substitutes for it.

Curtis Clark                  http://www.csupomona.edu/~jcclark/
Director, I&IT Web Development                   +1 909 979 6371
University Web Coordinator, Cal Poly Pomona


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