[Taxacom] Thought experiment

[Richard Zander]

Okay, let's consider all ancestors extinct, as in gradualistic evolution of two sister groups away from their joint ancestor. Then all the exemplars are apomorphic with respect to their immediate ancestor though perhaps not with respect to, what? ancestors of taxa in long lineages?
 
How about a pectinate tree with one surviving ancestor that gave rise to all the others? One exemplar is then pleisiomorphic, the remainder apomorphic.
 
How about a zigzag tree with each taxon (but, necessarily, one) giving rise to a daughter taxon but surviving to the present. All exemplars except one are then surviving taxa and thus pleisiomorphic.
 
A fully pleisiomorphic tree might be, what, all fossils? The zigzag tree with the one nonancestor being atavistic through reversals?
 
_______________________
Richard H. Zander
Missouri Botanical Garden
PO Box 299
St. Louis, MO 63166 U.S.A.
richard.zander at mobot.org
 

________________________________

From: taxacom-bounces at mailman.nhm.ku.edu on behalf of Curtis Clark
Sent: Sat 3/28/2009 9:54 AM
To: TAXACOM
Subject: Re: [Taxacom] More precise sound bite



P.P.S. An interesting thought experiment: Could we have a classification
  formed of only paraphyletic groups? At first that seems absurd, but
remember that the apomorphies of a clade are also plesiomorphies with
respect to hypothetical derivative clades not yet evolved. In a sense, a
lot of the grade-organized early evolutionary classifications were this,
without the terminological trappings.