I assume you mean ectothermy rather than endothermy and symplesiomorphies instead of synaplesiomorphies. If so, then you are on the right track. Personally I can't figure out why anyone would want to recognize either para or polyphyletic taxa. Neither reflects phylogeny, and I find that taxonomy based on phylogeny is the most informative. Cking seems to think there is something "natural" about paraphyletic taxa, but I don't see it.

Here is an example of what can happen when you consider paraphyletic groups to be valid taxa. Let's say there are 4 species in genus X, and each member of the genus possesses some autapomorphy in a different character (while the other species are plesiomorphic). Let's use an example based on DNA for simplicity.

For gene X:
Position 10: species A has the nucleotide T
Position 11: species B has the nucleotide A
position 12 species C has the nucleotide G
position 13 species D has the nucleotide C

Let's assume the real relationships among the species are (A,B)(C,D). We could exclude any of the species from the group by their autapomorphy, just like birds are excluded from reptiles for their autapomorphies. So what is the "best" paraphyletic taxonomic grouping based on plesiomorphies.

A,B,C as one taxon?
How about A,C,D?
Maybe A,B,D?

I see no objective answer. If I asked you to name every monophyletic group, anyone who understands the definition of monophyly can do that. So besides the fact that peraphyletic goups do not reflect phylogeny, they can also be quite arbitrary.

What is the point?

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