follow up on paraphyly / polyphyly

Curtis Clark jcclark-lists at EARTHLINK.NET
Wed Nov 10 21:07:23 CST 2004


on 2004-11-10 13:42 Dr. James Adams wrote:
> On the other hand, if you were to group birds and mammals together in a
> classification, this would be polyphyletic, as there is no common ancestor
> for just these two groups that you can point at, without going into the
> reptiles.

A group of modern birds and mammals would be paraphyletic by exclusion
from the amniotes of modern turtles, lepidosaurs, and crocodilians
(ignoring of course all the extinct stuff). It would be a stretch to
justify such a group, but to me, the basic point is that polyphyletic
and paraphyletic groups can never be distinguished by membership, only
by the hypotheses used to form them. Of course, the same thing is true
of monophyletic groups.


--
Curtis Clark                  http://www.csupomona.edu/~jcclark/
Web Coordinator, Cal Poly Pomona                 +1 909 979 6371
Professor, Biological Sciences                   +1 909 869 4062




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