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Re: more cladistics



On Thursday , 6 September 1995, Tom Holtz wrote:

>>           Yes, the position of a taxon on a tree determines its status.
>>What determines the position of a taxon on a tree? SHARED DERIVED
>>CHARACTERS that are inherited via common ancestory.  You said so, yourself.

>This is a point a lot of people miss.  In cladistic taxonomy, the DEFINITION
>of a taxon is based on position: nothing more, and nothing less.  If, with
>further discovery, a derived character previously used to *diagnose* (but
>not define) a taxon is found to have a different distribution (e.g., if
>feathers are found on Coelophysis), the definition of the taxon DOES NOT
>CHANGE.  In the example above, the taxon Avialae will retain the same
>defintion regardless of the discovery of feathers on Coelophysis.  The
>character diagnosis will change, but the defintion will remain the same.

EXACTLY!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
That's the beauty of cladistic taxonomy.  It allows you to argue about
characters and their distribution, not the definition of taxa - the thing which
people who don't confer to it seem to get so worked up about half the time :o)

Cheers
Steve Salisbury
Vertebrate Palaeontology Laboratory
School of Biological Sciences
University of NSW, Australia
P2158753@vmsuser.acsu.unse.EDU.AU