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Re: Say this slowly: theropoda is paraphylitic, theropoda is paraphlyitic.....
In a message dated 6/26/00 3:01:59 PM EST, email@example.com writes:
<< Polyphyletism is what Mr. Lurio agreed his theory
represented: a multiple series of evolutionary
sidelines being grouped into a whole, rather than
representing a monophyletic whole. Whereas
paraphyletism is two convergent lineages grouped into
a monophyletic whole. >>
Whoa, here. A group is >polyphyletic< if it includes at least one subgroup
that does not share a common ancestor within any other subgroup in the group.
A group is >paraphyletic< if it includes the single common ancestor of the
group but excludes at least one descendant subgroup with an ancestor within
the group. A group is >monophyletic< if it has the single common ancestor and
excludes no groups descended from that common ancestor.
You can always make a polyphyletic group monophyletic by extending the
lineages back at least to their most recent common ancestor (which always
exists, according to present evolutionary theory) and including that ancestor
and all its descendants. You can always make a paraphyletic group
monophyletic by including any excluded descendant subgroups. This is why
cladists like monophyletic groups; the messy choice of which groups to
include or to exclude in a group is--theoretically, anyway--no longer