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Re: giant birds



In a message dated 11/11/99 3:36:52 PM EST, k.clements@auckland.ac.nz writes:

<< I'm afraid I can't agree with George that "BCF and cladistic analysis 
 are not opposed; they work together. I use available dinosaur 
 cladograms to trace the evolution of avian features." I can't put it 
 any better than Luis Chiappe, who said (Nature 378: 349-355 1995): 
 "assumptions about evolutionary processes or adaptational scenarios, 
 such as these, are misleading when identifying historical 
 relationships. Phylogenetic reconstruction should be based exclusively 
 on the hierarchical distribution of homologies among taxa, and a given 
 phylogenetic hypothesis can only be rejected by providing an 
 alternative hypothesis for which supporting evidence outweighs that of 
 the original hypothesis." >>

Sorry, Chiappe is wrong. There are many ways to reject cladograms other than 
by building bigger cladograms. You can check them against stratigraphy and 
biogeography, and you can check them against functional anatomy. You can even 
reject cladograms on the basis of common sense, if you like. There are still 
too many holes in cladistic analysis itself for it to be granted this kind of 
authoritarian philosophical position. Nobody has to accept any cladogram just 
because its author can provide statistical arguments, for example, that show 
how good it is.

But suppose for the moment that Chiappe is right, and that only by winning a 
synapomorphy war--that is, only by building a cladogram from a larger, more 
inclusive character matrix--can you reject a previous cladogram. This 
paradigm will eventually render cladistics untestable, unfalsifiable, and 
thus unscientific by producing the Final Cladogram, one that is done from the 
largest possible character matrix by the best possible algorithm. This 
cladogram--by construction--cannot be tested against other cladograms, 
because it already includes all the information from which the other 
cladograms could be produced. Since Chiappe admits no >other< way to test the 
Final Cladogram, it is untestable, and therefore unscientific. Too bad, 
that's the way it works. We haven't reached the Final Cladogram in 
dinosaurology yet (although the way Tom Holtz is scavenging characters these 
days, we soon will :-), but if we do, how will we know it really is the True 
Phylogeny? Or do we enter the fool's Paradise and simply >declare< it to be 
just that?

You still haven't figured out BCF and its relationship to dinosaur 
cladistics. I did not produce a phylogeny from the idea that dinosaurs 
originated as arboreal archosaurs. I >arrived at< this idea from examining 
numerous published phylogenies and then extrapolating the likely features of 
the various common ancestral forms from them. Phylogeny leads to BCF, not the 
other way around.