[Previous by date - Re: Panstems]
[Next by date - Nomenclatural Freedom IS the issue]
[Previous by subject - Re: Panstems]
[Next by subject - Re: Panstems]
Date: Mon, 13 Sep 2004 21:05:44 -0400
From: [unknown]
To: laurin@ccr.jussieu.fr, phylocode@ouvaxa.cats.ohiou.edu
Subject: Re: Panstems
Michel Laurin wrote: =09Here, I believe that Kevin is=3D20 disregarding a point that some of us tried to=3D20 make at the meeting and that is related to=3D20 Mickey's comment. Namely, systematists want to=3D20 keep these names for stem-based clades because=3D20 this is more or less the way that they have been=3D20 conceptualized (or at least delimited) by=3D20 generations of systematists. For about a=3D20 century, Synapsida has referred to the stem of=3D20 Mammalia, and in the last 20 years or so, it has=3D20 come to include mammals too, a necessary change=3D20 to make it monophyletic. It is because of the=3D20 long history of this name that many of us want to=3D20 keep it, not because Kevin and Jacques defined it=3D20 twelve years ago (although I agreed with the=3D20 definition that they provided at the time and=3D20 have used the name in that sense consistently).=3D20 Parenthetically, other taxa have a lateral=3D20 fenestra but were not included in Synapsida (at=3D20 least in the last 50 years), such as some=3D20 parareptiles. Indeed, the fenestra is so common=3D20 in early amniotes that Reisz raised the=3D20 possibility that it might be an apomorphy of=3D20 amniotes lost in the "anapsids", so redefining=3D20 Synapsida on the basis of the fenestra would be=3D20 a really bad idea. Similarly, when I proposed=3D20 (with Reisz) phylogenetic definitions of=3D20 Parareptilia (=3D3DPanTestudines) and Eureptilia=3D20 (=3D3DPanSauria), I used Everett Olson's terminology=3D20 (proposed in the 1940s), that had been used by=3D20 several other paleontologists (even in Russia).=3D20 If I want to keep these names, it is not only=3D20 (not even mostly) because we have used these=3D20 names in the last 10 years in PN but rather,=3D20 because these definitions reflect the use of=3D20 these names in the literature (rank-based and PN). >Of course, the reason that Jacques and I defined the name Synapsida = =3D phylogenetically as referring to the total clade of Mammalia is that = this =3D use "approximates" the way the name had been used for many years befo= re. =3D However, it's misleading to imply, as Michel does, that the name was = =3D uniquely associated with the stem, rather than with an apomorphy (or = a =3D node) for the approximatly one hundred years before Jacques and I = =3D formulated a phylogenetic definition for it. The name has been assoc= iated =3D with both, and in this particular case the exact association is ambig= uous =3D because the known composition of the two clades has been identical (i= .e., =3D there are no clear examples of taxa that lack the character but are = =3D clearly more closely related to mammals than to birds and turtles). = In =3D addition, potential homoplasy in the character is NOT a good reason f= or =3D avoiding an apomorphy-based definition (and in this case, Michel seem= s to =3D be disregarding comments that were made at the Paris meeting). If ot= her =3D taxa have evolved the character convegently, those taxa can be exclud= ed by =3D specifying that the condition has to be homologous with that in mamma= ls =3D (or Varanops). If instead the character arose earlier, then we would= =3D simply have to conclude that some other early amniotes that have not = =3D traditionally been considered synapsids are, in fact, synapsids (chan= ges =3D in hypothesized composition happen all the time). Moreover, even if = one =3D doesn't like apomorphy-based definitions, one could also make the arg= ument =3D that the name Synapsida has been no more clearly associated (at least= =3D prior to the first phylogenetic definition) with the stem of Mammalia= than =3D with the node representing the last common ancestor of Varanops, Eoth= yris, =3D and Cynognathus. In this context, it should be clear that I was not = =3D simply disregarding Michel's point made at the Paris meeting. Instead= , I =3D consider that argument incorrect. If one is going to argue that the = name =3D Synapsida was unambiguously associated with a particular clade, then = one =3D has to cite an explicit phylogenetic definition (e.g., that of Gauthe= ir =3D and de Queiroz). Conversely, if one is going to use the work of earl= ier =3D authors to establish usage, then one is not going to be able to assoc= iate =3D the name unambiguously with a particular stem as opposed to a node or= =3D apomorphy. The use of this name by earlier authors is highly ambiguo= us =3D with regard to these three different possible conceptualizations, bec= ause =3D the precise distinctions embodied in them generally were not made at = that =3D time. Consequently, the ambiguous association of the name Synapsida = with =3D the stem in question by earlier authors is not a good reason for reje= cting =3D PanMammalia as the name for the total clade originating from that ste= m, as =3D an equally good case can be made for a historical association of the = name =3D Synapsida with either an apomorphy or a node. Indeed, if one is goin= g to =3D follow the usage of earlier authors, Theropsida would seem to be a be= tter =3D choice than Synapsida, given that there is less reason to think that = the =3D former name does not describe an apomorphy and was originally associa= ted =3D unambiguously with thel clade in question (rather than with a paraphy= letic =3D group as in the case of Synapsida).< =3D20 =09One of the most common critique of the=3D20 PhyloCode is that it will generate many new names=3D20 and disrupt continuity with the literature; that=3D20 is certainly not true of the PhyloCode as it now=3D20 stands, but it COULD be true if the use of the=3D20 Pan- prefix for total clades is made mandatory=3D20 for most such clades. Let's not give critiques=3D20 of the PhyloCode such an obvious problem to point=3D20 out. >For the reasons given above, the argument about disrupting continuit= y is =3D false. Regarding new names, this compaint has been raised repeatedly= in =3D the history of taxonomy, yet the proposal of new names never ceases, = nor =3D does it cause any new problems beyond the general one of dealing wth = ever =3D increading information that characterizes all of human history since = the =3D invention of language. Neither of these concerns is well founded, an= d we =3D should not therefore allow them to constrain us.< Kevin de Queiroz Division of Amphibians & Reptiles Smithsonian Institution P.O. Box 37012 NHB, Room W203, MRC 162 Washington, D.C. 20013-7012 Voice: 202.633.0727 FAX: 202.357.3043 E-mail: dequeirk@si.edu