Message 2004-10-0190: Re: crown clade convention (long)

Wed, 20 Oct 2004 12:08:01 -0400

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Date: Wed, 20 Oct 2004 12:08:01 -0400
From: [unknown]
Subject: Re: crown clade convention (long)

David Marjanovic wrote:

- Neotetrapoda is not widely known. I am certain that by far most of =
neontologists simply don't know it exists.

>That's exactly the problem!  They're not going to use poorly known n=
ames =3D
if they want people to read their papers.<

- Tetrapoda has occasionally had a rank (superclass), while Neotetrap=
oda =3D
never had one, as far as I know or can imagine. When Neotetrapoda was
coined, almost everyone was still concerned with ranks, and preferred=
that had ranks over such that lacked them. This practice still has =
even proponents of phylogenetic nomenclature often prefer using widel=
y =3D
names over using less widely known but more precise names when they j=
sketch the outlines of a tree in their texts.

>I doubt that many more people would have used the name Neotetrapoda =
just =3D
because it had a rank.<

- Neotetrapoda was coined at a time when very, very little was known =
tetrapod phylogeny. There was no perceived difference between the
traditional group and the crown-group -- except for *Ichthyostega* (f=
people knew the two or three others), about which neontologists simpl=
didn't care.

>The number of known taxa outside of the crown is not what's importan=
t.  =3D
Ichthyostega was recognized as being outside of the crown, and that's=
 the =3D
reason that the name Neotetrapoda was proposed.  Moreover, neontologi=
sts =3D
still largely don't care about fossils outside of the crown, even tho=
ugh =3D
that number has increased in recent years.  The problem does not have=
 to =3D
do with the number of such fossils but with the fact that the charact=
ers =3D
of interest to neontologists often cannot be assessed in those fossil=
s.  =3D
This is exactly the problem:  Neontologists don't care about the foss=
ils =3D
but they do want to use the well known names.  Therefore, they common=
ly =3D
use those names as if they apply to the crowns.<

I don't quite understand why we should canonize forever the casual =
used by many neontologists. The PhyloCode presupposes evolution, afte=
r =3D
To talk about evolution while ignoring fossils is not a good idea.
Neontologists are stuck on the 3-dimensional surface of 4-dimensional
biology. They usually don't even _need_ the precision that paleontolo=
need when talking about a phylogenetic tree.

>History has already shown that neontologists often ignore the fossil=
s =3D
even though the names they use supposedly refer to clades that includ=
e =3D
various fossil taxa outside of the crown, so it doesn't seem that =
perpetuating that use of names is going to get them to pay attention =
to =3D
the fossils.  The fact that neontologists don't _need_ the precision =
that =3D
paleontologists do is precisely the reason that they are unlikely to =
adopt =3D
the unfamiliar names proposed by paleontologists to make those precis=
e =3D

This is a good argument [about justified inferences], but perhaps not=
 as =3D
good as it first seems. The real
problem, what's really going on here is, I think, the tendency to =
=66rom a small subset to an entire clade _with a well-known name_. Th=
ere are
incidents when features found in living birds, or only in _some_ of t=
have been generalized to all of Dinosauria! Perhaps -- I'm just guess=
here -- the pompous introduction of specific new names for certain (!=
crown-groups would make the abovementioned neontologists more aware o=
f the
need to be precise -- in those rather few cases where it is a need in=
first place.

Besides, I think that statements about the expression of a gene are =
not going to lead to a noticeable misrepresentation of the
larger-than-crown-croup with the name in question.

>History has already shown that this isn't how it works.  Names such =
as =3D
Neoterapoda and Neornithes have already been proposed for crown group=
s, =3D
but the neontologists don't use them.<

(Less important... Tetrapodomorpha is preoccupied by the panstem, the
sistergroup of Dipnomorpha which includes the lungfish. Both names ar=
widely used. Like Tetrapoda, Dipnoi has been used for something large=
r =3D
the crown-group since the 19th century... oops... fossil lungfish wer=
e =3D
before living ones were recognized... so perhaps this isn't a good =

>First, earlier defiinitions of Tetrapodomorpha have no status under =
the =3D
PhyloCode, but even they did, I'm sure we could come up with another =
name =3D
that made reference to the relevant apomorphy:  Tetrapodiformes, Tetr=
ia, Holotetrapoda, Acrotetrapoda, or some other name.<

I wouldn't say so [about whether paleontologists or neontologists hav=
e =3D
been more willing to change their use of names]. Lacertilia vs Sauria=
seems to be a case of widespread
change in the neontological community, like Carinatae vs Neognathae, =
abandonment of Pisces, Anamnia and now even Agnatha, or the surprisin=
widespread use of Archosauria (which, outside of phylogenetic nomencl=

includes only the crocodiles among the living, so it is redundant for
neontologists; in PN it also includes the birds).

>These examples are not comparable in that they don't have to do with=
changing the reference of a widely used name from a more inclusive gr=
oup =3D
to a crown.< =3D20

This could bear a certain risk that phylogenetic nomenclature is bein=
adapted to what neontologists are _perceived_ to be doing, not what t=
really _are_ doing... I fear. I'm concerned because very few neontolo=
have weighed into this debate -- not just on this list or in Paris, b=
ut =3D
(to my limited knowledge) in the literature. It's certainly not good =
if my
fears are true and WE (paleontologists) are talking about THEM.

>Well, I am primarily a neontologist, as are Cantino and Donoghue, an=
d we =3D
also favor the crown convention.<
I would say that there is rather little neontological literature that=
with crown-group Mammalia as a whole. The monotremes are much too oft=
either ignored or regarded as curiosities; this has far-reaching
consequences because far fewer internodes separate them from the trad=
beginnings of Mammalia than from the last common ancestor of marsupia=
ls =3D
placentals. It's sort of the opposite of the situation with the birds=
. :-)

>No comment (tangential).<

The other way around neontologists wouldn't so much have to _change_ =
usages as to make them more precise. Do they mean "Tetrapoda" when th=
write it? Do they mean "living land vertebrates"? Do they mean anythi=
ng in
between? I think in many cases they haven't thought about this themse=
But in many other cases they have -- and write phrases like "must hav=
e =3D
present in the common ancestor of living tetrapods", note "living".

>This is certainly possible, though it remains to be seen whether mos=
t of =3D
them would actually state things more precisely.  If the widely known=
names refer to the crowns, they will automatically be precise without=
having to make an extra effort.<

20 Oct 2004


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