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TETRAPODS, PHYLOGENETIC TAXONOMY, AND CLEAR DEFINITIONS
Jonathon Woolf wrote:
<<True. I didn't understand what Wagner was getting at with that bit either.
always seen "Tetrapoda" used as the name for the group consisting of all
land-dwelling vertebrates. Until the cladists got hold of it, anyway.>>
Tetrapoda was defined cladistically as a phylogenetic taxon and became just
about the same as it always had been: amphibians, reptiles, mammals, birds.
The only difference here is that we get a clear deliniation of what an
NOT a paraphyletic smear of animals that link fish to amniotes, but a
monophyletic taxon with its own set of synapomorphies etc that are distinct
from those of non-tetrapods ss and distinct from those of the amniote stem.
There is a problem deliniating between "fish" and "tetrapod," there is no real
difference between some taxa, and they do seem to show a continuum of
creatures. A similar thing happens with non-avian theropods and birds.
ESPECIALLY with the new taxa coming to light? Is Rahonavis a bird? Is
Unenlagia? How about Protarchaeopteryx and Caudipteryx.
We need to have clear definitions so that we won't have the ambiguity that can
be involved. How tetrapodish do you have to be to be a tetrapod?
<<True enough, within limits. However, scientific names are nearly always
manufactured from pieces of words in some language or other -- usually Greek
Latin, but more and more often they're from other languages. So the name
has a meaning in whatever language it's taken from. That meaning is part and
parcel of the name.>>
So what? If everyone agrees on what the name refers to, then there is no
reason for it to mean anything. Sometimes they are cute, sometimes they are
neat (as in the case of Einiosaurus' etymology) but no where does it say, no
where has it ever said, and no where has anyone ever suggested that the named
NEED to mean something useful.
<<If the thing has all the diagnostic features for
the group, it should be included in the group. What could be simpler?>>
If it has all the diagnostic features of the group it has to be included
within the group.
<<_Seymouria_ has all the diagnostic features for being a tetrapod, so how
not be in Tetrapoda?>>
If Seymouria is not a tetrapod ss then it DOESN'T have all the diagnostic
features of being a tetrapod. If you mean that Seymouria has four legs, thus
has all the dignostic features of being a tetrapod, then you are just being
foolish. I could just as easily say that the cactus genus Mammalaria must be
a mammal because it has breast-like protrusions, or that Andre tthe Giant is a
member of the genus Titanus cause he is big.
<<_Morganucodon_ has all the diagnostic features (all the
skeletal ones, at least) for being a mammal, so how can it not be in
Because it doesn't have all the diagnostic features of being a mammal. Is
there something you are not getting here? Mammalia was defined as a crown
specifically so there would be clear deliniations on what was and wasn't a
Since when you enter all the data into a matrix and come up with a tree,
Morgonocudon isn't either a monotreme or a therian, then it is not a mammal.
It is a synapsid very close to the ancestory of mammals, but it is not a
<<On the other hand, as far as I know _Marasuchus_ and _Psuedolagosuchus_
have all the features used to diagnose Dinosauria.>>
Morgonocudon does not have all the features that define mammals (you said it
yourself in the previous paragraph).
<<Therefore, they aren't dinosaurs and chouldn't be included in Dinosauria.>>
Exactly the same thing with Seymouria and tetrapods and Morgonocudon and
<<> 2) there is no reason to have 'reason' applied to it, as long as everyone
> agrees to what something means, then that is what it means
I think that statement just might make my case all by itself, but no
Huh? Weren't you the one who suggested we abandon Arctometatarsalia even
though everyone agreed what it was because not all arctomets had an
<<The fact that it's widely accepted doesn't mean it's right. Remember,
years ago everybody thought dinosaurs were big, dumb, slow lizards and birds
descended from some other archosaur.>>
Yes, yes, blah, blah. I know things change. The point is that almost
EVERYONE has abandoned Linnean (subjective) clasification syestems in favor of
Phylogenetic (objective) classification systems, or at least have started
using cladistic analyses to aid in their quest for objectivity.
This is almost becoming a first grade argument. Why is it better to be
objective? You should know he answer to that.
<<Did you hear about the molecular trees that
place birds and mammals in a clade with dinosaurs as an outgroup?>>
I didn't know dinosaurs had any molecular data to enter into a matrix. Where
was this done? Or perhaps this is the same old thing you were talking about
last time when you were so anoyed at Arctometatarsalia. The neontological
tree that added in paleo stuff later.
Well Jonathon, I hate to break it to you, but even if you find this hypothesis
patently absurd IT IS MORE OBJECTIVE THAN YOUR SUBJECTIVE STATEMENT THAT IT IS
ABSURD since an analysis was done.
<<Robert Carroll almost got lynched at a conference a couple of
years ago because he dared to point out that cladistic methods were not
How dare he!!! Whatever.... This statement seems a little exagerated, much
like the claims of certain unmentionables when they talk about disagreements
in science. You remember that rumour of a fistfight between Sereno and Holtz
at SVP 96?
In any case, no one ever said that cladistic methods weren't infallible, just
that they are more objective than pick and choose taxonomy.
<<"Most of the time" isn't all the time. So why do people treat phylogenetic
taxonomy as being infallible, and either ignore or rationalize away the
You still are not understanding the difference between phylogeneric taxonomy
CLADISTICS has to do with entering data into a matrix and coming up with a
tree. When people make said trees, they can still apply Linnean ranks and
have paraphyletic taxa etc just like in Linnean systematic.
PHYLOGENETIC TAXONOMY is a different kind of taxonomy that does not rank taxa,
has clear unambiguous definitions for taxa, and does not allow paraphyletic
<<So why do people treat phylogenetic taxonomy as being infallible,>>
Why are you treating pick and choose Linnean systematics as infallible? All
anyone is saying is that the cladistic method is more objective than pick and
Concerning crown clades, Woolf writes:
<<It makes them useless because they can't be relied on to do what they're
to do: identify a _diagnosable_ monophyletic evolutionary group.>>
Yes they can. How is a crown clade different from any other node-based clade?
You can see how Marasuchus and Psuedolagosuchus fall outside the node
Dinosauria. Why is it different for Morgonocudon falling outside the crown
<<If you can't tell what organisms belong to a group, then the group has no
If the group is undiagnosible, it would never have been named. It can't have
been named in fact...
<<If Hopson is right that monotremes and placentals share a MRCA in the Mid
then nothing earlier than that can be a mammal>>
<<-- including such animals as the morganucodonts, which have every feature
that could reasonably be used as an apomorphy for mammals.>>
That is the problem. You put in the word "reasonable." Since Morgonocudon
does not share all the features that Monotremes and Therians do, they are NOT
mammals. Same example as before, Marasuchus is very similar to dinosaurs but
lacks some features that link Saurischians and Ornithischians.
<<Uh-huh. In other words, the cladists want me to ignore the evidence and
their word for it.>>
Ignore what evidence? This is the same argument as some certain
<<Sorry, I don't work that way. I know "experts" who worship
cladistics. I know other "experts," just as qualified if not more so, who
that cladistics and phylogenetic taxonomy as paleontologists use them are
A very unmentionable argument indeed. Have you read de Quierez and Gauthier
90 and 92? Anything by Hennig? I thought not....
<<When I hear conflicting opinions from two different groups of "experts," I
throw away all their opinions and go back to the facts. And the facts, to my
eyes, say that the cladists are wrong. >>
So you throw away objectivity in favor of pick and choose gut feeling