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Re: a rose by any other name(was fish & dogs)
I don't think Dinogeorge is necessarily saying that we should go back
to recognizing a formal taxon Pisces (for fish). I think he's reacting the
same way I do when cladists claim the word "fish" refers to an unnatural
group. It is paraphyetic, NOT polyphyletic (as in your example of "humans
plus birds"). Before tetrapods evolved, fish (Pisces) was a perfectly good
holophyletic group, and the cladists want to retroactively say it's not a
real evolutionary group just because it's paraphyletic!? That's the point
that is being made. A natural group like "fish" didn't cease to exist just
because tetrapods evolved from one of them.
In my 1994 classification, I divided up gnathostome "fish" in a
cladistic manner, in a series of sister groups, successively splitting off
as Classes Placodermea, Chondrichthyea, Acanthodea, Actinopterygea, and
Sarcopterygea. But when I got to the last one, I made one of those
occasional paraphyletic cuts in the tree life. But I did leave a marker for
the exgroup (Tetrapoda) within Sarcopterygea, and coded it as sister group
to Order Panderichthyiformes.
Why strict cladists are not satisfied with such a middle ground
approach is beyond me. Do you think it might be peer-pressure that
perpetates this acquired distaste for paraphyly. I suspect this is part of
the problem. And it keeps cladists from seeing that "fish" (as Dinogeorge
is defining them) is a real evolutionary entity. Only polyphyletic groups
have no evolutionary meaning.
P.S. There is no slippery slope. One doesn't have to recognize every
paraphyletic group formally (there are so many of them, you couldn't even if
you tried). I didn't do it with fish as a whole (i.e. Pisces), but I also
realize Dinogeorge is correct that such a paraphyletic group is real and
natural, whether you name it or not. I think a good middle ground is to
reject a formal taxon Pisces, but "fish" is a natural group as long as
someone doesn't try to throw something like whales in with them.
From: Kendall Clements <firstname.lastname@example.org>
Subject: Re: a rose by any other name(was fish & dogs)
Date: Mon, 04 Dec 2000 09:57:26 +1200
I couldn't let this one go by...
> "Fish," for example, may be unambiguously defined as all vertebrates
> not tetrapods. It is not at all the "mishmash" group that cladists would
> one believe it is. Defined this way, lampreys, sharks, rays, and
> all "fish." Why would anyone have a problem with this?
Just what are the "benefits" of using a paraphyletic group such as
this in a systematic sense? Ichthyology textbooks usually cover all
aquatic vertebrates with fins that breathe water, but none pretend that
this grouping means anything in evolutionary terms. If you are happy to
use definitions like the one above we could place humans and birds
together (non-inclusively) in a group of amniotes that are not
quadrupedal. Would this be beneficial to anyone? Subjectivity is a
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