Re: CLADISTICS AND PALEONTOLOGIST(S) OF THE CENTURY

[Jonathon Woolf <jwoolf@erinet.com>]

Tetanurae wrote:

> SCROLL DOWN IF YOU HATE CLADISTICS
>
> Jonathon Woolf wrote:
>  <<Very good.  That's my exact question.  Unfortunately, you haven't given a
> good
>  answer yet.  No matter what alternatives, evasions, exceptions, riders, and
> other
>  1040-grade complexities you introduce, you cannot get away from the fact that
>  ultimately, organisms are classified based on physical characteristics,>>
>
> This is surprising to you?  Did you think that cladist told people they had
> some magical way of deciphering the relationhsips of organisms?

Sure looks that way to me.  Look at the messages I got today claiming
that
cladistics is simply a method of recognizing the existing evolutionary
relationships between organisms.  

> Of course
> not, they use characters to decipher the relationships.  Here is an
> explanation on how to construct a cladogram in three easy steps that I give to
> my non-scientist friends:
> 1) construct a spread sheet with species on the Y axis and character numbers
> on the X axis
> 2) examine specimens to determine the proper character state for each of the
> species and fill out the spreadsheet
> 3) plug the data into cladistic analysis program that will make trees based on
> the statistically most likely distribution of characters

Hm.. Programs?  As in, sets of instructions that run inside a computer? 
Are you
familiar with the acronym GIGO?  Are you familiar with the computer
analyses that 
show a bird-mammal grouping because endothermy is assigned a high
weighting in 
the analysis?

> That is completely different from naming clades, which is obviously what you
> are bungling up with.  Clades are defined on ancestory because they are stable
> as opposed exclusive membership based.

Which is a pretty useless way of doing it, since you don't _know_ what
organisms
are ancestral to what other organisms, and never will.  Call me
old-fashioned, but
I think a method of classification should be useful in telling you
whether a
specific organism belongs to a specific group or not.


> No matter how the topology changes, at
> least some part of the classification stays intact.
>

Which you seem to think is a good thing, even if the part that stays
intact is the
one part that shouldn't.

> I believe your original gripe had to do with nothing more than the fact that
> Arctometatarsalia - named after the arctometatarsus - was a bad name since the
> arctometatarsus evolved more than once.  So what?  Bird-like feet have evolved
> at least three times, yet we keep the name Ornithopoda.

And maybe we shouldn't keep it.  Likewise the other examples you name --
in
ceratopsids, it always struck me as illogical to call something that
doesn't have
either horns or head frill a "ceratopsid."  Ceratopsids are _horned_
dinosaurs --
and for the sake of simplicity, anything descended from a horned
dinosaur, like
_Pachyrhinosaurus_.  Even protoceratopsids could be reasonably called
horned
dinosaurs, since the male _Protoceratops_ has an incipient horn on its
nose.  But
_Psittacosaurus_ isn't a horned dinosaur and shouldn't be placed in
Ceratopsia.

> Even within
> Ornithopoda, only hadrosauroids, dryosaurids and Gaspirnirsaura have even
> remotely bird-like feet and the vast majority retain the primitive dinosaurian
> pattern, yet we keep that name....

Why was Ornithopoda expanded to include dinosaurs without birdlike
feet?  And who
did it?  Some evangelical cladist on a crusade?

> You are confusing diagnosis with definition.  Arctometatarsalia is DEFINED as
> "Ornithomimus and all animals that share a more recent common ancestor with
> Ornithomimus than with modern birds."  It is DIAGNOSED however by the
> arctometatarsus (which, in fact, differs quite substantially from other forms
> of arctometatarsaly), D-cross section premax teeth etc etc..

If that's how it's defined, then it should be named in a way that
reflects the
definition.  It's not me that's confusing the two -- it's the guy who
named the
group, because he gave it a name that implies any member of the taxon
will have a
certain diagnostic feature.  Names have meaning.  Names have power. 
Anyone who
sees the _name_ Arctometatarsalia is going to automatically conclude
that the name
relates to a feature common to all members of the group, just like with
Arthropoda
(joint-feet), Osteichthyes (bone-fish), Diapsida (two-holes),
Echinodermata (spiny
skin), Diptera (two wings), Hemiptera (half wings), Mammalia (milk
giver),
Ichthyosaurid (fish lizard), and so on.  Good names are names that tell
you
something about the group they refer to.  The definition is included in
the name.
Even if a specific member of the group doesn't have the feature
indicated in the
group name, as in pandas and Carnivora, the feature (meat eating) is
plesiomorphic
within the group, so you know the ancestor had the feature even if the
descendant
does not.

The name "Arctometatarsalia" tells you nothing about the organisms that
belong to
the group, because the feature indicated by the name is neither common
to all
members of the group nor plesiomorphic within the group.  IT DOESN'T
MATTER if
OTHER features are common to all members of the group.  Those features
aren't
included in the name.  You need to add the definition to get useful
information.

Oh, and if you think there are a lot of group names that don't meet my
criteria
for good group names, you're right.  I like things to make sense.  Maybe
that's
where we really differ.

-- JSW