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Re: Re: Sterna, Whales, and Evolution



On Thu, 15 Feb 1996, Ronald Orenstein wrote:

> >Which is exactly why trying to break the monophyletic Dinosauria up into a
> >paraphyletic Dinosauria and a monophyletic Aves is such an unuseful idea!
> >(Which was how the discussion began).
> 
> This is certainly true if you are trying to say something about phylogeny.
> However, as I noted earlier, it is certainly "unuseful" to reduce all bird
> families to tribal level to make them consistent with a dinosaurian taxonomy
> if you happen to be an ornithologist - 

Since Linnaean ranks are meaningless, phylogenetically speaking, you can 
certainly keep all bird families as families and squish more nodes in 
between family and whatever rank Aves would assume.

Or, as I pointed out in an earlier post, you can retain the traditional 
class Aves, make Maniraptora a superclass, Coelurosauria a hyperclass, 
Tetanurae a megaclass, Theropoda a gigaclass, and so forth...

In case anyone out there missed the point this is another subtle argument 
for abandoning Linnaean ranks (above, perhaps, superfamily).


> just as I assume it would be
> "unuseful" for you to treat dinosaurs as a subgroup of Crossopterygian
> fishes 

Not at all!  Especially not if you phrase the assertion in a different 
form:  Tetrapods and "Crossopterygians" are members of a single 
monophyletic taxon.


> I am still puzzled as to how to construct a taxonomy that is
> phylogenetically accurate and practical for use.

Aren't we all!  I still say that you gotta throw out the ranks to make 
any sense of it.

> 
> Anyway, isn't calling Dinosauria "paraphyletic" dependent on where you start
> looking?  I assume that all animals normally called dinosaurs, no matter how
> many lineages they produced, form a monophyletic group within Archosauria at
> some level.

I'm not positive, but you may be confusing "paraphyletic" with 
"polyphyletic" here.  "Paraphyletic" means that a group contains animals 
which are all descended from a common ancestor--but that not all the 
animals descended from that common ancestor are included in the group.

Does this help?


> Now - is the base species of the new radiation excluded from the genus with
> the other ten species?  Must the whole of the new radiation, no matter how
> differentiated and diverse it becomes, be included in the stem genus of
> which it forms a nested subset?  If not, why not?

Ooh!  Good question!  Tough...  On a practical level, I'd have to say 
that the base species goes with its descendants and that each of the other 
ten original species gets its own genus (just to avoid allowing these 
species to run around without generic names).  All of these groups would 
then be grouped together in the next-higher-level taxon.

If the base species is different enough from the other ten that we can 
tell that it is the ancestor of the subsequent radiation, then it should 
have its own genus anyway.  

If this is just a hypothetical question and 
the base species is not actually different from the others, then we will 
never know that the scenario you outlined was, in fact, the situation, and 
we will be free to classify all eleven original species in one genus--which 
will technically be paraphyletic, but we won't know the difference!

I sure hope everyone can understand what I'm saying here...


> --
> Ronald I. Orenstein                           Phone: (905) 820-7886 (home)


Nick Pharris
Pacific Lutheran University
Tacoma, WA 98447
(206)535-8204
PharriNJ@PLU.edu

"If you can't convince them, confuse them." -- Harry S Truman