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not yet going offlist on Protista, bacteria (long, combined answer)



----- Original Message -----
From: "Tim Williams" <twilliams_alpha@hotmail.com>
To: <kinman@hotmail.com>; <dinosaur@usc.edu>
Sent: Saturday, March 03, 2001 10:01 PM
Subject: Re: going offlist on Protista, bacteria


>
> Ken Kinman wrote:
[...]
> >However, I think it is grossly unfair (and inaccurate) to >characterize
> >dinosaurs (and all the rest of the metazoans) as occupying a tiny twig
>on
> >the tree of life.  Such exaggeration will only confuse and >intimidate
> >students and everyone else.
>
> Or enlighten them as to the wondrous diversity of unicellular, microbial
> life.  This isn't taking anything away from the success of us
multicellular
> life-forms, just putting our success into perpective.  We are just one
> corner of the huge domain of Eucarya.  And the Eucarya is just one of
three
> domains of life on Earth.

That's it! The tree of life is so humongous that even the tiny twigs are
still so enormous that some are tempted to call them forests! And this
pattern continues into much lower levels... Passeriformes is just a tiny,
late-evolving branch among the much greater diversity of Neornithes,
Neornithes look all the same when compared to Metornithes as a whole, and
Metornithes are indistinguishable from one another if we look at all
Dinosauria at once. And so on.

> >    The number of Metazoan phyla has also gotten out of hand (I
>recognized
> >24, and even that is too many).
>
> "Phyla schmyla", as I once saw written on a T-shirt.  A lot of your
> irritation over what constitutes a phylum is resolved if you just abandon
> them altogether.  A taxon's position on the tree is all that really
counts.

yep

(What's that ?Yiddish schm- prefix meant to mean?)

> > Order Tullimonstrida (Tully monsters) is probably just an aberrant group
> >of sipunculans or molluscs.
>
> Then it's probably just an aberrant group within the Sipuncula or
Mollusca.
> Why agonize over whether the Tullimonstrida should be ranked as a phylum
or
> class or order.  The same problem surrounds whether the
black-smoker-loving
> Vestimentifera are just unusual pogonophorans, or whether the parasitic
> Pentastomida (tongue-worms) are just highly specialized crustaceans.
Should
> they be granted their own phylum?  Who cares?

Who can find out by anything else than _intuition_?

> It's their phylogenetic
> position that's important, so why bother weighing up whether these bizarre
> groups are "different enough" from their ancestors to qualify as a new
> phylum.  (I'm reminded of Tom's example of the wayward daughter who comes
> home one day sporting pink hair.  "She'll never be part of our family
again"
> rants the father.  "No," says the mother.  "No matter what she looks like,
> as our daughter she'll always be part of our family.")
>
> Again, you seem to be your own worst enemy Ken.  Your concern over the
> delineation of the Class Aves from the rest of the dinosaurs is rooted in
> the same preoccupation over whether certain groups deserve to be promoted
to
> higher ranks - whether it be Class, Phylum or Kingdom.

(Actually, I love to discuss about "cladobabble" -- but has any side brought
up any _new_ arguments since the last discussion in IIRC November?)

> I'm sorry to harp on this, but it concerns a very fundamental aspect of
> evolution.  One thing I've come across when discussing evolution with
other
> people is the misguided notion that the past 3-4 billion years of
evolution
> can be interpreted as a march of progress.  Vertebrates are not superior
to
> flatworms, any more than flatworms are superior to sponges, or any
metazoan
> life form is superior to any bacterium.  Each branch on the Tree of Life
> just does things differently.
>
> Ken, I'm not accusing you of you of subscribing to this view of evolution,
> but your "Kinmanian" classification perpetuates this myth - like the
> Linnaean hierarchial system which it draws upon.  Birds are not superior
to
> dinosaurs, so why give them a "Class" of their own.  Go way back to the
base
> of the Aves, and the differences between birds and dinosaurs resolves into
> one or two evolutionary innovations.  There's nothing so different between
> _Archaeopteryx_ and (say) _Sinornithosaurus_ that one deserves to be
raised
> into a "higher" class than the other.

HP "philidor11" answered:

> <Birds are not superior to dinosaurs, so why give them a "Class" of their
> own.>
> Easy:  because they are obviously different.

This is much more complex. You do agree that *Sinornithosaurus* is much more
similar (whatever superficial characters or apomorphies you choose) to a
bird, say, *Sinornis*, than to *Triceratops*? And then look at *Lagosuchus*.
It looks a lot more like *Sinornis* than *Sinornis* to *Triceratops*.
Repeating from some months ago -- who gets into a whole new class, while all
others are grouped with crocs, lizards and turtles???

> <Vertebrates are not superior to flatworms, any more than flatworms are
> superior to sponges, or any metazoan
> life form is superior to any bacterium.>
> These are examples of obviously different groups whose difference you are
> recognizing.

And indeed, vertebrates are not (descended from) flatworms, and flatworms
not from sponges.

> <Go way back to the base of the Aves, and the differences between birds
and
> dinosaurs resolves into one or two evolutionary innovations.  There's
> nothing so different between _Archaeopteryx_ and (say) _Sinornithosaurus_
> that one deserves to be raised into a "higher" class than the other.>
> Go far enough back in any group you choose to distinguish and the
> differences from an ancestral group will be small, by definition.  And,
> because the whole list of differences between the two groups appear over
> time, you also have to choose how many of those differences have to be
> present to say that a specific animal is part of one group or the other.

You have to choose? Why? If you abandon ranks, you don't have or need to.

If we could know all extinct species, hardly any node on a cladogram would
be supported by more than one single synapomorphy, and you _couldn't_
choose. Old sayer "natura non facit saltus". (More elaborately in the
"AMARGASAURUS SATTLERI" thread from ?September.)

The difference in approach being considered is:  are you emphasizing the end
result (bird/dinosaur) or the beginning of  the separation between the two
groups?  Doesn't it seem most reasonable to emphasize the end result when
deciding when differences are large enough to distinguish a group?

End? What end? Why should we choose 2001 AD as any end? Birds won't stop to
evolve this year. A case could be made for extinct clades to use their time
of extinction as such an "end", but then one would have to take what-if
questions into account for potential "end results". What if the K-T
extinction would have had a very odd selectivity, all (herbivorous at least)
mammals would have died out, all croc groups would have survived, crocs
would have had inherited the Earth and notosuchians would be the dominant
herbivores today? I'm sure users of the Linnean system would put them into,
say, at least an order apart from *Crocodylus*. So would you put real
extinct Notosuchia into an order of its own??????

HP Filippo Calzolari answered to this --

> Then you would have to consider Archie, and all the animals more "birdy"
than a dromie, but not "birdy" enough to be considered a true bird, as
something
between a bird and a dinosaur, but ....

...but Linnean taxonomy doesn't allow that. In cladistics, you can easily
put them into, say, Avialae, but not into, say, Pygostylia.

HP "philidor11" again:

> Many people start with the easy observation (That's a bird.) and don't
mind
> the difficulty that some early ancestors are hard to analyze.  I think
that
> this attitude should be acknowledged, even when disagreed with, and not
> criticized as the result of a presumption.

Again repeating from an older thread -- call whatever you want birds, but
"mind the difficulty that some early ancestors are hard to analyze" when you
want to know whether to put these into Aves, Avialae, Metornithes,
Pygostylia or whatever scientific group.