Polyphyly, etc

Ken Kinman kinman2 at YAHOO.COM
Wed Nov 10 23:06:11 CST 2004

     Although this view may be correct most of the time, I doubt that is ALWAYS true (strictly speaking).  Mother nature can always throws us a few curves.  That said, however, in the river dolphin case, I think that it probably is correct.  The preponderance of the evidence does point toward river dolphins being polyphyletic.  And although the title of the PNAS article calls them paraphyletic, they do refer to the grouping as polyphyletic in the text.  The ONLY tree that shows river dolphins as paraphyletic (Figure 1c), which is based on morphology alone, is most likely due to homoplasies.  River dolphins seem to have evolved (at the very least) twice independently from marine groups, and I would therefore call it a polyphyletic group.
                ----- Ken Kinman
Don Colless wrote:
   George Esterbrook's notion of "convex" groups is surely the neatest way of distinguishing between paraphyly and polyphyly.  It can be easily illustrated on a tree, where (as James Adams points out)  a paraphyletic group is convex - its members are all connected on the tree without passing through ancestor(s) of any other group.  Members of a (concave) polyphyletic group can only be connected via ancestors of some other group.

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