paraphyly/polyphyly

W.Wuster w.wuster at BANGOR.AC.UK
Mon Feb 7 16:31:18 CST 2000


On Mon, 7 Feb 2000, Philip Cantino wrote:

> There are cases, however, when it is much more difficult to decide whether
> a previously circumscribed taxon is paraphyletic or polyphyletic in light
> of a new phylogenetic hypothesis--i.e., by delimiting the taxon on a
> cladogram.  To make this decision using Farris's definition, one has to
> assess whether the immediate common ancestor of the group would be assigned
> to the group if it were known.  This assessment is based in part on the
> character states that the hypothetical ancestor is inferred to have (by
> parsimony-based mapping on the cladogram), but it also sometimes requires
> guesswork about whether the taxonomists who recognize the taxon would have
> included the ancestor in the group if it existed (alive or preserved as a
> fossil).  The latter is necessarily a very subjective decision.  In these
> cases, at least, I agree with de Jong that distinguishing paraphyly from
> polyphyly has little value, and we are better off just referring to such
> groups as nonmonophyletic.

Oosterbroek (1987) provided a better, operationally less ambiguous way
of looking at the problem:

Oosterbroek, P. (1987): More appropriate definitions of paraphyly and
polyphyly, with a comment on the Farris 1974 model. Systematic Zoology,
36: 103-108. 

Cheers,

Wolfgang Wuster

--
Dr. Wolfgang W├╝ster - Lecturer
School of Biological Sciences    Tel: +44 1248 382301
University of Wales              Fax: +44 1248 371644
Bangor LL57  2UW                 E-mail: w.wuster at bangor.ac.uk
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