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Re: Sauropodz r kewl WAS: silly conversation on 2012 US presidential race



On Wed, Apr 18, 2012 at 12:23 PM, Anthony Docimo <keenir@hotmail.com> wrote:
>
>
>  But Sphenodon gets a number of (ranks?) above Genus to itself, was more my 
> point; apologies if anyone read my "separate" more in the vein of Darwin's "a 
> separate creation".

In that case, the dinosaurian version is surely Archaeopteryx
lithographica, which has often had a genus (Archaeopteryx), a family
(Archaeopterygidae), an order (Archaeopterygiformes), and even a
subclass (Archaeornithes) all to itself!

But note that A. lithographica's situation is very different from that
of Sphenodon! Sphenodon has all those to "itself" only if we limit
things to extant species. So in that case its "taxonomic distinctness"
is due to all its relatives dying out.

In A. lithographica's case, it has a lot of ranked taxa to itself
because it is very, very close to the ancestral node of a major clade
(with "major" being an arbitrary designation in this case). Every
species, even nearly-ancestral ones, has to have its full array of
supertaxa under the rank-based system. So its "taxonomic distinctness"
is due to it not being very derived.

In rankless phylogenetic nomenclature*, there is no such confusion
over what "taxonomic distinctness" means. We can see that Sphenodon
guntheri and Sphenodon punctatus are the only living populations of
Sphenodontia, and that they, along with fossil taxa, are also part of
various sphenodontian subclades. Archaeopteryx lithographica simply
goes in Eumaniraptora (or just outside, still within Paraves), and
perhaps forms a clade called "Archaeopterygidae" with a few other
populations.

* Phylogenetic nomenclature can be ranked, but most practitioners
don't see a point to that.
-- 
T. Michael Keesey
http://tmkeesey.net/