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Date: Mon, 13 Sep 2004 11:10:19 -0700
From: [unknown]
To: phylocode@ouvaxa.cats.ohiou.edu
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= lready by non-Pan names? > however, the names have a much longer history than this, and they h= ave also been associated with non- > total clades (even after their first phylogenetic definitions), so = there 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= lade 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= ars 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= tilia, 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= auria's 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= name will not be without some negative > consequences. These consequences= have 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= ade 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= ther, 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= ames, 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= all its descendents**). Obviously, the only people who really care about= the 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 = burden of memorizing different total and crown clade names for the price of = keeping currently named total clades (as exemplified by Laurin's excellent po= st). * Not that I'm arguing we should, but I'm saying it's just as logical= as doing such for total clades. ** A terrible definition, I know, but there are instances where simil= arly poor definitions have been proposed based on soft tissue and/or behav= ioral characters. > More importantly, as I think was stated in some earlier version of = the PhyloCode preface or the webpage, > the period of time between the first proposal of phylogenetic defin= itions and the offical implementation of > the PhyloCode is supposed to be treated as a period for experimenta= tion. If we decide that we could do > some things better, given a second chance, we should not let our ea= rlier 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= o 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= xes. Once you factor in the many 'orders', 'families' and 'genera' in cur= rent use, most of which contain some stem taxa in addition to their crown = (at least in vertebrates), continuity of hypothesized composition will be= MUCH greater without Pan-stems. So much greater, in fact, that I have a h= ard time expressing it. > I wasn't suggesting that names associated with total clades have be= en 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= st. Which I also dispute, as argued above. > More importantly, if neonotologists (i.e., the majortiy of biologis= ts) acutally used the proposed crown clade > names (e.g., Neotetrapoda, Neornithes) when talking about traits that can only be assessed in li= ving > 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= andard affixes for the crowns (e.g., > AcroMammalia). Unfortunately, they d= on't. 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= is 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= e 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= raits 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 - http://students.washington.edu/eoraptor/Home.= html