[Taxacom] Defining polyphyly
jgrehan at sciencebuff.org
Wed Dec 15 07:09:33 CST 2010
There's the hinge of it all - whether paraphyletic groups are any more 'natural' than those that are polyphyletic.
From: taxacom-bounces at mailman.nhm.ku.edu [mailto:taxacom-bounces at mailman.nhm.ku.edu] On Behalf Of Kenneth Kinman
Sent: Tuesday, December 14, 2010 6:56 PM
To: taxacom at mailman.nhm.ku.edu
Subject: [Taxacom] Defining polyphyly
As I said in my last post, I agreed with how
Chris defined a paraphyletic group (specifically, a singly paraphyletic
group). However, I think that he misspoke in defining a polyphyletic
group as "clade A minus clades B. C., etc." Actually that defines a
paraphyletic group with multiple exgroups (doubly paraphyletic, etc.).
But if you then combine those exgroups together, you do get a
polyphyletic group. Creating a paraphyletic group is a subtractive
process, while creating a polyphyletic group is an unnatural additive
For instance, Class Reptilia is a
doubly paraphyletic group: Clade A (Amniota) minus Clades B and C
(exgroups Aves and Mammalia). However, if you combine the two exgroups
(B plus C), you do get a polyphyletic taxon (namely Haemothermia).
Polyphyletic taxa are unnatural, while paraphyletic and holophyletic
taxa are natural.
Chris Thompson wrote:
Not exactly as a paraphyletic group is merely clade A
minus clade B. A polyphletic group is merely clade A minus clades B, C,
etc. So, it is not argument by authority.
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