[Taxacom] Defining polyphyly

[Kenneth Kinman]

Hi Stephen:
          Are you sure about that definition of paraphyly?  Sounds like
you are saying that the excluded subgroup (exgroup) lacks the
synapomorphies of the mother (paraphyletic) group, which isn't
necessarily true [for example, the exgroups Mammalia and Aves still
retain the amniotic eggs which characterize their paraphyletic (mother)
group Reptilia].  It is actually the other way around---the paraphyletic
group lacks the synapomorphies of the exgroup.  Or am I misinterpreting
what you wrote?      
          -------Ken               
-----------------------------------------------------

Stephen Thorpe wrote: 
     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
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