[Taxacom] Defining polyphyly

[Stephen Thorpe]

>But hominids do share the synapomorphies that encompass great apes and hominids

Yes, obviously, but hominids don't have the synapomorphies that define great 
apes (or rather they do, but they have been transformed)

a better example is fish ... to simplify the example somewhat: fish are not just 
non-tetrapod vertebrates, they have positive features of their own, e.g., fins, 
which tetrapods don't have. However, 'vertebrates with fins' is 
paraphyletic because tetrapods have lost their fins ...

My point is just that paraphyly of this kind should always be considered ...

Stephen




________________________________
From: John Grehan <jgrehan at sciencebuff.org>
To: taxacom at mailman.nhm.ku.edu
Sent: Thu, 16 December, 2010 2:14:16 AM
Subject: Re: [Taxacom] Defining polyphyly

No, the excluded subgroup still have the synapomorphies of the node that 
includes that and the others that are made paraphyletic by their exclusion. For 
example, great apes exist as a group by virtue of excluding hominids (living and 
extinct humans and fossils more closely related to humans than any great ape). 
But hominids do share the synapomorphies that encompass great apes and hominids.

John Grehan

-----Original Message-----
From: taxacom-bounces at mailman.nhm.ku.edu 
[mailto:taxacom-bounces at mailman.nhm.ku.edu] On Behalf Of Stephen Thorpe
Sent: Tuesday, December 14, 2010 9:11 PM
To: Kenneth Kinman; taxacom at mailman.nhm.ku.edu
Subject: Re: [Taxacom] Defining polyphyly

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. 


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