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Date: Wed, 02 May 2001 15:21:38 -0600 (MDT)
From: kinman@usa.net
To: phylocode@ouvaxa.cats.ohiou.edu
Subject: Re: subscribers
Chris,
In the case at hand, if cladistically-defined and "precise"
Lophotrochozoa turns out to be a synonym of Bilateralia, the cost of that=
precision is going to be pretty steep.
The contents and characteristics will expand considerably (with the
addition of all deuterostomes and ecdysozoans). Numerous trees and clado=
grams
in the intervening literature will be incorrect, and the accompanying tex=
t
confusing as well for those unaware of the whole story. Lots of confusio=
n and
inaccuracy in the name of precision (no thank you).
And what a waste of a name. Couldn't call the paraphyletic group
lophotrochozoans any more. Would be stuck with an explanation like:
Lophotrochosozoa was formerly erroneously restricted to the
"non-ecdysozoan, non-deuterostome bilateralians", but then later more com=
plete
cladistic analyses showed this clade to be a heterodefinitional synonym o=
f
Bilateralia.
But in the meantime, what I fear most is that some workers, assumin=
g
that Ecdysozoa and Lophotrochozoa are really sister groups, might begin u=
sing
ecdysozoans as outgroups in cladistic analyses of groups in the supposed =
clade
Lophotrochozoa (as we see it in the literature from 1995-2001). This wou=
ld
produce an even bigger mess. =
My main warning on this issue is that neither ecdysozoans (nor
deuterostomes) should be used as outgroups to the presently constituted
Lophotrochosozoa. I can see how workers would be tempted to do this, sin=
ce
outgroup selection was one of the criticisms levelled by Conway Morris et=
al. =
That is one criticism I definitely wish they had not made, because it co=
uld
have workers cladistically jumping out of the frying pan and into the fir=
e
(making the outgrouping problem worse rather than better). Better to use=
a
cnidarian outgroup than to use an ecdysozoan (which I believe is really a=
n
ingroup). =
That's my advice, Ken
*****************************************
chris brochu <cbrochu@blue.weeg.uiowa.edu> wrote:
>Ken Kinman wrote:
> Why not just call them lophotrochozoans, and let them remain an
informal
>taxon, at the very least until we can demonstrate whether or not it is b=
ased
>on symplesiomorphies rather than synapomorphies.
OK, I should probably keep my mouth shut (or my fingers still), but I'm
addicted to making an ass of myself, so here are some thoughts.
One of the purposes behind phylogenetic nomenclature (or any kind of
nomenclature) is precision. It does us little good if the names we use=
have fluctuating meanings. Informal names will always have imprecise
meanings.
The classic example, of course, is "Dinosauria" - one common objection to=
formally defining Dinosauria in a way that might include birds is that a=
standard, colloquial, informal meaning already exists for "dinosaur."
Any survey of children's books on dinosaurs or kits of toy "dinosaurs"
should dispel that myth rather quickly. "Dinosaur" can mean "nonavian
dinosaur," "big extinct reptile," "big extinct animal," or "any extinct
organism." I have seen plesiosaurs, mammoths, Dimetrodon, sabertooth cats=
,
and even trilobites listed as "dinosaurs." If the informal meaning is so=
precise, why is it so hard to find a consistent lower bound for the grou=
p
in the media?
Another example (closer to my heart) is "crocodile." I am always being
asked how old the oldest "crocodile" is. The answer is, "it depends on
what you mean by 'crocodile.'" Do you mean crown-group crocodylian?
Member of the "genus" Crocodylus? A crocodylid? Mesoeucrocodylian?
Crocodyliform? Crocodylomorph? All of these have, at one time or
another, approximated the informal term "crocodile," and all of these hav=
e
very different temporal, geographic, and morphological properties as
currently understood. But when I say Crocodylus, or crocodylian, or
mesoeucrocodylian, my meaning suddenly becomes much more precise.
I could go on with "plant," "bug," or "rat."
I am aware that the contents and properties of formally-defined taxon
names will fluctuate over time. This is not the same as having an
imprecise meaning - the meaning of a taxon name will remain precise, ev=
en
if our understanding of its membership, diagnosis, or any other propert=
y
changes.
chris
------------------------
Christopher A. Brochu
Assistant Professor
Department of Geoscience
University of Iowa
Iowa City, IA 52242
christopher-brochu@uiowa.edu
319-353-1808 phone
319-335-1821 fax =
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