[Taxacom] Invisible evolution, paraphyly

[Ken Kinman]

Curtis,
     I look at it differently.  The general cladistic viewpoint seems to be 
that there aren't ANY taxa Reptilia which are real.  My point is that there 
are actually a large number of them, each slightly different, especially for 
Reptilia which (being doubly paraphyletic) requires three cladistic cuts 
(beginning of Amniota, beginning of Mammalia, and beginning of Aves).

     Where you make those cuts is arbitrary, but this fuzziness at the edges 
doesn't make ANY of the resulting pieces (of the tree of life) any less 
real.  My goal for classifiying Class Reptilia is to make those three 
cladistic cuts at the most useful places so that a consensus might be 
reached (at least among people who will formally recognize paraphyletic 
taxa).  Out of all the various REAL taxa we could attach the Reptilia (all 
of which would contain the same living groups), we can pick one which is as 
maximally useful and stable as we can make it, although new fossils could 
blur the edges even further.

     Cladistic cuts on the real tree of life will result in real taxa, and 
the arbitrariness of where to make those cuts doesn't make the resulting 
taxon any less real.  And as Rob Smissen noted, extinction and a poor fossil 
record have left gaps which thankfully limit the possible choices and 
eliminate most of the fuzziness.  The gaps are now smaller, but I believe a 
consensus is still possible and desirable, resulting in a Class Reptilia our 
predecessors would easily recognize (albeit with some new fossil taxa at the 
edges).
    -----Ken Kinman

**********************************
>From: Curtis Clark <jcclark-lists at earthlink.net>
>To: taxacom at mailman.nhm.ku.edu
>Subject: Re: [Taxacom] Invisible evolution, paraphyly
>Date: Mon, 11 Jun 2007 21:36:46 -0700
>
>On 2007-06-11 07:58, Richard Zander wrote:
> > Maybe there's a problem with species definitions, Curtis. Could you tell
> > us, in short, what the difference is between paraphyletic species and
> > paraphyletic higher taxa.
>
>Reptilia is a paraphyletic higher taxon. Its existence depends on a
>classification decision by people, not by the mode of speciation of the
>first bird or first mammal.
>
>Speciation by peripheral isolation ordinarily results in a paraphyletic
>ancestral *species*. As has been pointed out repeatedly, systematists
>often disagree about the circumscription of species. But anyone who
>claims that the amniotes minus the mammals and birds constitutes a
>*single species* is clearly not using any of the plethora of definitions
>to come out of my generation of systematists. I continue to maintain
>that anyone who uses the existence of paraphyletic species as a
>justification for the Reptilia isn't interested in evolution as a process.
>
>--

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