paraphyly and polyphyly
kinman2 at YAHOO.COM
Thu Nov 11 20:28:00 CST 2004
Ah, there's the rub: "using a given, fixed topology". The problem with some groups (e.g. reptiles) is that the topology is still very uncertain and controversial (the placement of turtles is today even more uncertain and controversial than it was 20-30 years ago). Therefore, a fixed topology had never existed and there isn't one anywhere in sight (not even close).
A paraphyletic Reptilia (with exgroup markers for Mammalia and Aves) therefore remains the best approach and will probably remain so for decades to come. It can be characterized as any amniote (i.e., possessing amniote synapomorphies) that lacks the synapomorphies which characterize the exgroups Mammalia and Aves. It's as SIMPLE as that! We might quibble about exactly where we should draw the lines between reptiles and their two exgroups, but this is minor stuff compared to the excalating taxaonomic confusion caused by trying to completely cladify the Reptilia. Premature cladification is chest-beating hubris that should be strongly condemned and discouraged, and reptiles are just one such case.
----- Ken Kinman
Kelly Miller wrote:
Steve Farris wrote a paper attempting to formalize the
definitions of paraphyly and polyphyly using a given,
fixed topology and group membership variables rather
than actual character information. In this way he was
able to construct operational definitions allowing
arbitrary groups in a specified phylogenetic
hypothesis to be distinguished as monophyletic,
polyphyletic and paraphyletic without referencing any
real characters or their evolution. The solution
converges on something very like Hennig's or Nelson's
earlier definitions, but decides operationally whether
an ancestor belongs to a particular group or does not.
Farris, J.S. 1974. Formal definitions of paraphyly and
polyphyly. Systematic Zoology 23: 548-554.
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