[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index][Subject Index][Author Index]

Re: a rose by any other name(was fish & dogs)




Kendall,
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.
-----Ken Kinman
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 <k.clements@auckland.ac.nz>
Reply-To: k.clements@auckland.ac.nz
To: Dinogeorge@aol.com
CC: dinosaur@usc.edu
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...

Dinogeorge wrote:

> "Fish," for example, may be unambiguously defined as all vertebrates that are
> not tetrapods. It is not at all the "mishmash" group that cladists would have
> one believe it is. Defined this way, lampreys, sharks, rays, and teleosts are
> 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
slippery slope.

Kendall

----------------------
Kendall Clements
k.clements@auckland.ac.nz
_____________________________________________________________________________________
Get more from the Web.  FREE MSN Explorer download : http://explorer.msn.com