Re: Apomorphy-based definitions - who needs them?

["Ken Kinman" <kinman@hotmail.com>]

    Generalized typological thinking is what I am trying to eliminate from 
the scientific definition of Aves.  There is nothing wrong with a precise 
"typological" definition, and even PhyloCode allows apomorphy-based 
definitions.  Two years ago the manuscript of a new high school biology 
textbook had a cladogram, and the synapomorphy for birds was "feathers".  I 
told them that their book would be out of date before the book even got 
printed, and they changed it.  I don't like that kind of typological 
imprecision either.
    The other word that gets carelessly tossed around a lot is "arbitrary". 
 If apomorphy-based definitions are so arbitrary, better tell the 
PhyloCoders to forbid them.  But I simply have never understood why cladists 
can't see that node-based and stem-based definition are just as arbitrary.  
They seem to cause a lot more headaches than the apomorphy-based Mammalia 
(which we might have to refine slightly ever few decades).
     Eclecticists and strict cladists alike establish boundary nodes that 
are ultimately based on characters.  The only real difference is that strict 
cladists forbid the truncation of a clade under any circumstances.  A 
paraphyletic group is just a truncated clade that has an upper boundary as 
well as a lower boundary.  Therefore, there is nothing unnatural or 
unscientific about a paraphyletic taxa.  Cladists keep saying they are, but 
that will never make it true.
     Cladists declaring that their system is superior to eclecticism is 
nothing more than semantics, which is used to justify the conditioning of 
the next generation to hate paraphyly.  Paraphyly is a real evolutionary 
phenomenon, while Hennig's convention (of a mother species giving rise to 
two "matricidal" sister species) is just that----a convention that makes 
cladistic analysis more useful.  Sister groups don't really exist in nature, 
and those who teach cladistics should be giving their students both sides of 
the story.  I was lucky, because I had a systematics professor like Peter 
Ashlock who taught me both sides.
    Anyway, I obviously won't be adopting "pygostyles" for any 
apomorphy-based definitions, or anything else that is imprecise and likely 
to arise convergently.  The "true" semilunate seems to have enlarged rather 
suddenly (geologically speaking) between ornithomimes and maniraptors.  And 
as far as I know, the semilunate is always a fused single bone in adult 
maniraptors, but since the more primitive "semilunate" (of non-maniraptors) 
is sometimes fused as well, I didn't put the word fused in the definition.  
I tried to be very careful about the wording to avoid any possible confusion 
with the evolutionary homologs that preceded "true" semilunates.
              ------ Ken Kinman



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