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Date: Tue, 04 Mar 2003 23:41:55 +0100 (MET)
From: David Marjanovic <firstname.lastname@example.org>
Subject: RE: Note 9.4.1
> Node- and stem-based definitions are most certainly useful tools in > taxonomy! This is especially true for those of us who work in fossil > forms and on large scale evolutionary biology issues. > > For example, complimentary stem-defined taxa have exactly the same time of > origination *by definition*; in contrast, node-defined taxa within these > stems could have radically different times of origins (as, similarly, > would apomorphy-defined taxa within these stems). To take another example, one that may have more relevance in practice: Usually in an interesting fossil exactly the part with the defining apomorphy is not preserved. In order not to take a stupid example like defining birds as having feathers, I'll take a very interesting apomorphy (or 2) that dinosaurs have: an asymmetric reduction of the hands, with fingers V and IV shrinking considerably (IV losing 2 of its 5 bones) but III, II and even I not changing or even growing. Nobody has, to my knowledge, tried to use it to define Dinosauria so far, because the _three or four_ closest outgroups (as of end 2002) don't preserve any hands whatsoever. (You see I'm talking of single specimens. "This bone is the proof that there is a connection between the dwarf brontosaurs and the giant brontosaurs", as a Disney comic put it.) We wouldn't be able to tell if they are dinosaurs or not, driving a good proportion of popular science book authors crazy, even though the phylogenetic positions of 3 of them are pretty certain (at the moment). Why would distance-based (isn't that phenetics?) phylogenies promote nodes & stems? > Thomas R. Holtz, Jr. > Vertebrate Paleontologist > [...] > > -----Original Message----- > From: peter a. cejchan [mailto:email@example.com] > Sent: Tuesday, February 25, 2003 8:35 AM > To: PhyloCodeList > Subject: Note 9.4.1 > > Do we really need node- and stem-based definitions? Perhaps molecular > phylogenies (seem to) force us to use these. However, adhering solely to > apomorphy-based definitions would simplify Art. 13. Are there other cases > for node- and stem-based d's than are the distance-based phylogenies? Just > my opinion, as usually... > > ++pac -- +++ GMX - Mail, Messaging & more http://www.gmx.net +++ Bitte lächeln! Fotogalerie online mit GMX ohne eigene Homepage!