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Re: Dinosaur Web Pages' Re-Opening



In a message dated 97-09-04 18:31:02 EDT, jconrad@lib.drury.edu (Kevin James
Dracon) writes:

<< I am not a professional, but I would like to mention that it does seem
 that once a digit is gone, it's gone.  Look at all mammals, birds,
 reptiles, and amphibians.  Also, see Gould's wonderful report "Eight (or
 fewer) little piggies." (Nature magazine, not sure what month or year
 right now.)  As the autopodia become more and more specialized it has been
 seen time and time again that tetrapods lose digits, never gain them (the 
 closest possible thing is the false thumb of the panda, which is not
 really a thumb or digit, just a specialized carpal). You are right that
 this does not prove that it absolutely cannot happen, only that the
 potential to do so has never been shown in any group of tetrapods ever.   >>

This is EXACTLY my point. I am >not< willing to accept the regaining of a
functional digit from a vestigial one >just because it makes somebody's
cladogram come out "better."< If your cladogram indicates that a digit must
have reappeared at some point in a phylogeny, I think it is up to you to show
how or why this occurred, functionally. Otherwise you should entertain the
possibility that your cladogram is incorrect.

The crux of the problem with cladistics is the assumption that the cladogram
>must< take precedence over issues of biogeography and functional anatomy. I
assert, to the contrary, that if the phylogeny presented by a cladogram
contradicts our understanding of the biogeography or functional anatomy of
the group, then there is quite as good a chance that the cladogram is >wrong<
as there is that the biogeography or functional anatomy is wrong. Why is this
so difficult for cladists to grasp?