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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, qilongia@yahoo.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 
necessary.