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Re: tooth counts in systematics



Joshua Smith wrote:

>         and on the other hand I hope that it doesn't work, because then I
> can be vindicated in my visceral feeling that cladistics sucks and needs
> improvement at the very basic level of character selection.
> 
>         Hmmm...maybe back to the drawing board.\


Or, better yet, to the library.

What I'm sensing in this thread is the view that "if it's polymorphic,
then it really can't be used."  Neontologists have been dealing with
polymorphism for decades - in allozymes, scale counts, segment counts,
color ranges, even morphometrics.  But they *deal* with it - they don't
just toss it out.  .  

Polymorphism makes simple binary coding very difficult, but it does not
mean such characters are "useless."  We may be able to express the
variation in a step matrix, which is the standard method for coding
intraspecific variation in protein characters.  It works with
ontogenetic variation as well, as discussed in a near-classic paper by
Mabee and Humphries.  

As paleontologists, we'll be facing some additional challenges.  We
can't always get a handle on ontogeny, for example; and we usually don't
have a population to speak of.  But for more on polymorphism, a good
paper with lots of references is:

Weins, J.J., and M.R. Servedio.  1998.  Phylogenetic analysis and
intraspecific variation:  performance of parsimony, likelihood, and
distance methods.  Systematic Biology, 47:228-253.



chris





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Christopher A. Brochu
Department of Geology
Field Museum of Natural History
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