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More on formal paraphyletic groups (Was: Greg Paul's new (or newly named) iguanodonts)



Tim Williams writes:
 > BTW, I have no conscientious or ideological objections to naming
 > paraphyletic taxa, in principle.  But I suspect that in practice
 > these paraphyletic groups could become more trouble than what
 > they're worth.  By definition, paraphyletic groups could only be
 > 'diagnosed' by characters they *don't* have, rather than characters
 > they do have.

Ah, come on, who diagnoses any more?

(Just joking -- mostly.)

Yes, for sure: the diagnosis for a paraphyletic group would precisely
"is diagnosed by the diagnosis of the larger clade but not by that of
the smaller clade".

 > We could see a paper containing sentences like "Birds (Aves)
 > probably evolved from Thecodontia, given that primitive birds share
 > the following characters with thecodonts..."

Well, so?  Such confusion is just as possible now: "Birds (Aves)
probably evolved from thecodonts, given that primitive birds share the
following characters with thecodonts..."  The cure is clear thinking.
Yes, our choice of nomenclature can help, a little with that; but it
can't solve the problem.  (Not that I don't like the idea of a system
of nomenclature in which is impossible to make incorrect statements
:-)

 _/|_    ___________________________________________________________________
/o ) \/  Mike Taylor    <mike@indexdata.com>    http://www.miketaylor.org.uk
)_v__/\  "I have challenged the entire quality assurance team to a
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