Real taxa => Ranking

Peter Stevens peter.stevens at MOBOT.ORG
Tue Sep 28 14:13:42 CDT 2004


>Certainly for flowering plants age is not a workable criterion for
>ranking - just read the vast literature on aging nodes, with
>estimates varying sometimes very considerably indeed.  But if we had
>a well-supported tree to the nodes of which we could assign ages in
>an unproblematic fashion, then we could arbitrarily decide on the
>ranks to be assigned to particular slices of time....  So the
>objectivity comes in the application of what is ultimately an
>arbitrary decision.


P.



>I was surprise to read:
>
>How to select the "appropriated" taxonomical rank (genera, tribe etc)
>for a
>group is a matter of debate, mainly because this issue is out of the
>scope
>of the formal methods of systematics (cladistics).
>
>====================
>
>When Willi Hennig himself clear proposed an objective method of ranking
>years ago as part of his "Phylogenetic Systematics" [= ? cladistics at
>one time, but today Willi would not recognize what we are calling
>"cladistics" has having any relationship to his idea, etc.]
>
>Hennig simply stated the proper criterion for rank was age of the
>taxon. And he suggested once one had their preferred cladistic
>hypothesis / tree, then there were various other methods which then
>could be used to date the taxa within the hypothsis / tree. He suggested
>various date for the categories of the Linnaean hierarchy, like 100 MYA
>or late cretaceous origin for the family category.
>
>Obviously Huxley who placed Homo sapiens in the Kingdom Psychozoa
>objected as did virtually everyone else. And apparently after that all
>was forgotten, but ...
>
>So, objective methods of ranking are only "out of the scope of the
>formal methods of systematics (cladistics)" for those who do not want
>them.
>
>Oh, well ...
>
>
>
>F. Christian Thompson
>Systematic Entomology Lab., USDA
>c/o Smithsonian Institution
>MRC-0169 NHB
>PO Box 37012
>Washington, DC 20013-7012
>(202) 382-1800 voice
>(202) 786-9422 FAX
>cthompso at sel.barc.usda.gov e-mail
>www.diptera.org  web site




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