Message 2004-10-0044: Re: Panstems

Mon, 13 Sep 2004 11:10:19 -0700

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Date: Mon, 13 Sep 2004 11:10:19 -0700
From: [unknown]
Subject: Re: Panstems

Kevin de Queiroz wrote-

> This is true in the sense that some non-Pan names have already been
defined as referring to total clades;

Indeed, have any major total clades of vertebrates NOT been defined a=
by non-Pan names?

> however, the names have a much longer history than this, and they h=
also been associated with non-
> total clades (even after their first phylogenetic definitions), so =
is no disruption of continuity in the
> sense of loss of the names.

Currently defined crown clade names generally have a much longer hist=
ory and
have been associated with more non-crown clades.  Look at the crown c=
equivalents to the total clades I listed before (dates quickly compil=
ed from
the internet, some may not be accurate; number listed is amount of ye=
crown clades were named before total clades)-

Lissamphibia 1866 < Amphibia 1758. -108
Anura 1820 < Salientia 1768.  -52
Caudata 1777 < Urodela 1825. 48
Amniota 1866 < Reptiliomorpha 1934. 68
Mammalia 1758 < Synapsida 1903. 145
Marsupalia 1811 < Metatheria 1880. 69
Placentalia 1837 < Eutheria 1872. 35
Reptilia 1768 < Sauropsida 1867. 99
Testudines 1758 < Anapsida 1903. 145
Sauria 1984 < Romeriida 1988. 4
Lepidosauria 1839 < Lepidosauromorpha 1988. 149
Archosauria 1869 < Archosauromorpha 1946. 77
Aves 1758 < Avemetatarsalia 1999. 241

Crown clades contain some of the oldest names (Caudata, Mammalia, Rep=
Testudines, Aves), on average 70 years older than their total clade
equivalents.  Seven of the above total clades were named in the 1900'=
s, and
only two in the 1700's.  Yet five of the above crown clades were name=
d in
the 1700's and none in the 1900's.
Crown clade names have been associated with more non-crown clades tha=
n is
true of total clade names and total clades.  Which names have been
associated with more clades than Mammalia, Reptilia and Aves?  Archos=
been a non-crown node too, and I'm sure some of the other crown clade=
s have
similar histories that I'm unfamiliar with.

> Obviously, adopting a universal convention for a particular type of=
will not be without some negative > consequences.  These consequences=
to be weighed against the benefit of making it a lot more easy to >
recognize the names, especially for people who work on other taxa (su=
ch as
plants) and are familar with
> names such as Aves and Mammalia, but not with Ornithosuchia (or
Avemetatarsalia) and Synapsida.

Amphibia, a total clade, is aguably one of the ten most well known cl=
names, being one of Linnaeus' original vertebrate classes everyone le=
arns in
school and possessing a commonly used vernacular equivalent.
If you argue "we could just redefine total clade names to equate to o=
more or less similar, clades", as in your Synapsida example, why not =
do that
for crown clades instead*?  Sure, more people know more crown clade n=
but they don't know they ARE crown clades and in most cases don't eve=
n know
what a crown clade is.  So the only important thing for them is to ke=
ep the
names they know in circulation, which would be accomplished just as w=
ell if
the crown clade names were redefined (e.g. Mammalia =3D the first tax=
on with
mammary glands homologous to Homo sapiens used for feeding young, and=
its descendents**).  Obviously, the only people who really care about=
definitions are us biologists who actually study the groups in questi=
on, and
I think the consensus is clear that we are all too happy to face the =
of memorizing different total and crown clade names for the price of =
currently named total clades (as exemplified by Laurin's excellent po=

* Not that I'm arguing we should, but I'm saying it's just as logical=
doing such for total clades.
** A terrible definition, I know, but there are instances where simil=
poor definitions have been proposed based on soft tissue and/or behav=

> More importantly, as I think was stated in some earlier version of =
PhyloCode preface or the webpage,
> the period of time between the first proposal of phylogenetic defin=
and the offical implementation of
> the PhyloCode is supposed to be treated as a period for experimenta=
If we decide that we could do
> some things better, given a second chance, we should not let our ea=
decisions (mistakes?) constrain
> us.

I don't think any of us want a period in history (be it the 1990's an=
d early
2000's, or the early 200n's) where phylogenetic definitions for any k=
ind of
clade were temporarily different.  That's why we've all been trying t=
consistantly define and use clade names, even though we know none are
official until 1-1-200n.

> Continuity is never 100% in terms of hypothesized composition.  I w=
as more
concerned with the total loss
> of certain names--i.e., if ALL of the names are given standard affi=

Once you factor in the many 'orders',  'families' and 'genera' in cur=
use, most of which contain some stem taxa in addition to their crown =
least in vertebrates), continuity of hypothesized composition will be=
greater without Pan-stems.  So much greater, in fact, that I have a h=
time expressing it.

> I wasn't suggesting that names associated with total clades have be=
associated with more alternative
> definitions than those associated with other types of clades.

That's how I interpreted "In the case of total clades, one could argu=
e that
most names that have been associated with these clades have also been
associated with other clades."  I suppose you just mean they've been
associated with more alternate non-PT concepts/compositions in the pa=
Which I also dispute, as argued above.

> More importantly, if neonotologists (i.e., the majortiy of biologis=
acutally used the proposed crown clade > names (e.g., Neotetrapoda,
Neornithes) when talking about traits that can only be assessed in li=
> organisms (and not in fossils), then I agree that it would be logic=
al to
use the widely known names (e.g.,
> Mammalia) for apomorphy-based clades and coin new names based on st=
affixes for the crowns (e.g., > AcroMammalia).  Unfortunately, they d=

I honestly never saw this as a problem.  Our language is such that it=
 can be
assumed one means "the members of group X that can be examined for th=
trait have it" whenever one says "members of group X have this trait"=
.  And
since neontologists talk about recent 'orders', 'families' and 'gener=
a' a
LOT, to solve this "problem" would require that huge disruption in
continuity of composition I mentioned earlier.  Is it worth it to hav=
thousands of taxa removed from clades they've always been included in=
, just
to ensure people who are ignorant don't think genetic or behavioral t=
are known to be present in extinct stem lineages of crown clades?

Mickey Mortimer
Undergraduate, Earth and Space Sciences
University of Washington
The Theropod Database -


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