Plesions and plesiomorphons (not the same)
kinman2 at YAHOO.COM
Mon Mar 14 17:02:37 CST 2005
Oh my goodness no!!! ALL of my plesions are assumed to be holophyletic (usually fossil genera). Plesions are NOT supposed to be paraphyletic, although some workers have done so incorrectly, and Kluge has thus coined a new term (plesiomorphon) for what you are apparently talking about. After stating that plesions should NOT be paraphyletic, N.J. Kluge gives the following definition of plesiomorphon in his 2004 book (The Phylogenetic System of Ephemeroptera, p. 16):
Instead, here is suggested a new term "plesiomorphon" (in English plural "plesiomorphons", but not Greek "plesiomorpha"): plesiomorphon is a taxon characterized by plesiomorphies only; thus, its holophyly is not proven, and possibly (or probably) this taxon is paraphyletic, but its paraphyly is also not proven yet. Plesiomorphon can be a taxon of any size and systematic position in ranking or non-ranking classification, living or fossil, with any name (ranking, hierarchical, circumscriptional or other).
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