[Taxacom] Defining polyphyly

[Stephen Thorpe]

Ken,
Well, it can go either way. Perhaps reptiles appear to have no synapomorphies 
that birds and mammals don't also have? On the other hand, I suspect the other 
way is also common, i.e., suppose hypothetically that feathers and fur were both 
transformed reptile scales, and that the latter is a unique synapomorphy to 
reptiles, only it has been transformed to feathers and fur in birds and mammals 
respectively, so they (birds and mammals) appear to lack the synapomorphy 
definitive of reptiles (i.e., reptile scales). 
Stephen




________________________________
From: Kenneth Kinman <kennethkinman at webtv.net>
To: stephen_thorpe at yahoo.co.nz
Cc: taxacom at mailman.nhm.ku.edu
Sent: Wed, 15 December, 2010 4:45:45 PM
Subject: Re: [Taxacom] Defining polyphyly

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