[Taxacom] Defining polyphyly

Stephen Thorpe stephen_thorpe at yahoo.co.nz
Tue Dec 14 20:11:04 CST 2010

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 ...


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
            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. 


Taxacom Mailing List
Taxacom at mailman.nhm.ku.edu

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

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

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


More information about the Taxacom mailing list