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Re: Crown clades a-frikkin'-gain [was Re: Tetrapod note]



Jonathan R. Wagner wrote:

> >c), as you point out, is the cladistic one, and the cladists can have it
> >for all I care.  Any definition that says _Seymouria_ isn't a tetrapod has no
> >rational basis as far as I can tell..
>         We've been through "rationality" and taxonomy before. Please check
> the archieves under "Arctometarsalia".

So we have, and you're still wrong. Without some reason applied to it, any
"classification method" is simply a recipe for manufacturing meaningless
collections of random syllables.  Since reason is something that's noticeably
lacking in the way many alleged experts in the field apply cladistics, the 
method
itself is effectively worthless.  _Homo sapiens_ is supposed to be a thinking
animal -- so why not think instead of mindlessly following the rules?

>         The idea behind crown clades (at least in part) was to restrict taxa
> based on extant animals to the most recent common ancestor of all extant
> froms and all of its descendants. The purpose was to "clean house".

A noble purpose.  Too bad some people insisted on throwing the baby out with the
bathwater.  If membership in a group can't be diagnosed, the group is 
effectively
useless -- and in a number of cases there is no known way to distinguish members
of a crown-based clade from their immediate ancestors.  Early mammals, for
example.  There is a long, long string of fossil forms from the latest Triassic 
up
through the mid Cretaceous that look mammalian in every detail -- but can't be
called mammals because they date from before the last common ancestor of
Monotremata and Theria.

>         Now, for crying out loud, lets get back to dinosaurs!

Fine with me.  What do you make of the fact that _Eubrontes_ footprints can
apparently be used to mark the Triassic-Jurassic boundary in eastern North
America?  _Grallator_ is found in both Triassic and Jurassic rocks within the
Newark Supergroup, but _Eubrontes_ has only been found in Early Jurassic rocks
there.

-- Jon W.