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Re: Platecarpus tympaniticus - how to analyze a nomen dubium



On Tue, Sep 21, 2010 at 10:34 PM, Anthony Docimo <keenir@hotmail.com> wrote:
>
>
> I think this is what confuses me the most:
>
>> Such arguments over absolute ranks are pointless. We all know
>> Archosauria includes Dinosauria, which includes Saurischia. All three
>> of these taxa are the same however we rank them. So why bother ranking
>> them?
>
> Âbut by maintaining the sequence  (Archosauria - Dinosauria - Saurischia, in 
> that order), doesn't that continue to (legitimize?)(justify?) the ranks? Â
> We're still using the framework for everything.

It does justify *relative* rank. E.g., we can say Archosauria is
bigger than Dinosauria because it includes Dinosauria. But it does not
justify *absolute* ranks, like Class or Infraorder. Dinosauria is the
same taxon whether it's a tribe, suborder, class, or not ranked at
all.

> its like if I decide to grow grapes, and the vines completely blanket the 
> trellis so I can't see what metal or wood is holding it in place and in that 
> shape...but even if I never say "trellis" again in all my life, it's still 
> there, holding the grapes.

The trellis in this instance would be the hierarchy, not the ranks.
The hierarchy is still there (and, indeed, nowadays many researchers
base it on phylogeny, an actual phenomenon which can be discovered,
rather than taxonomic opinion).

(Mathematically speaking, the relation of inclusion can be used as the
basis for a partial order on the set of all taxa. Absolute ranks would
imply a total order, which is not really useful in this situation.
Saying Archosauria > Dinosauria is meaningful; saying Order Primates >
Infraorder Theropoda isn't.)

-- 
T. Michael Keesey
Technical Consultant and Developer, Internet Technologies
Glendale, California
http://tmkeesey.net/