[Taxacom] Defining polyphyly

[Stephen Thorpe]

another way to understand it is this: 
a polyphyletic group is defined by homoplasies (or even just characters shared 
by virtue of parallel evolution), but a paraphyletic group, while defined by 
true synapomorphies, excludes a subgroup(s) which lack the synapomorphies due to 
reversal or other transformation ...

Stephen





________________________________
From: Kenneth Kinman <kennethkinman at webtv.net>
To: taxacom at mailman.nhm.ku.edu
Sent: Wed, 15 December, 2010 12:55:57 PM
Subject: [Taxacom] Defining polyphyly

Dear All, 
         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
process.            
            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. 
                    ----------Ken            
---------------------------------------------- 
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. 


_______________________________________________

Taxacom Mailing List
Taxacom at mailman.nhm.ku.edu
http://mailman.nhm.ku.edu/mailman/listinfo/taxacom

The Taxacom archive going back to 1992 may be searched with either of these 
methods:

(1) http://taxacom.markmail.org

Or (2) a Google search specified as:  site:mailman.nhm.ku.edu/pipermail/taxacom  
your search terms here