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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
Not at all! Especially not if you phrase the assertion in a different
form: Tetrapods and "Crossopterygians" are members of a single
> 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)
Pacific Lutheran University
Tacoma, WA 98447
"If you can't convince them, confuse them." -- Harry S Truman