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Re: giant birds



In a message dated 11/9/99 8:15:10 PM EST, k.clements@auckland.ac.nz writes:

<< If nothing can be proved wrong in evolutionary theory, how 
 can BCF conclude which are "obviously wrong" parts of theropod 
 evolution and which are not? I'd much rather stick to an objective, 
 repeatable methodology that does not rely on ad hoc reasoning (although 
 I concede that character designation can be somewhat subjective). The 
 critical question is one of methodology. BCF adherents prefer an 
 incremental, functionally plausible narrative, while adherents of 
 phylogenetic systematics prefer a repeatable, testable methodology 
 based on character distribution. The latter requires that functional 
 narratives conform to, rather than dictate, tree topology. >>

I think you're misinterpeting BCF: I do not >prefer< a "functional plausible 
narrative" over "repeatable, testable methodology." Rather, I >use< the 
"repeatable, testable methodology" to arrive at a "functional plauisble 
narrative." This is what you're >supposed< to do, not the other way round as 
you seem to think I'm doing. BCF and cladistic analysis are not opposed; they 
work together. I use available dinosaur cladograms to trace the evolution of 
avian features; I do >not< fit the animals into some phylogeny contrived to a 
scenario depicting how I would >like< or >imagine< avian flight to have 
evolved. The fact that I have philosophical problems with cladistic analysis, 
such as questions about its testability and falsifiability, has nothing to do 
with BCF.

The term "obviously wrong" needs some clarification. When the "trees-up" 
ornithologists deny the dinosaur-bird connection by saying that the same 
specific sets of characters appeared simultaneously in birds and in 
dinosaurs, I regard this as having to accept a miracle. The chance of 
something like the same 120 characters appearing in two unrelated lineages is 
astronomically small. Hence, "obviously wrong": dinosaurs and birds >must< be 
intimately related phyletically.

And when the "ground-up" dinosaurologists present flight as evolving through 
an accumulation of characters in strictly ground-dwelling cursorial animals 
that just happened to make a lineage of flying archosaurs, I maintain that 
this is another miracle. The chance of this occurring is again astronomically 
small--something like the chance of dealing four royal flushes off the top of 
a randomly shuffled poker deck.

So, if you discard these "obviously wrong" elements of the "trees-down" and 
"ground-up" theories and synthesize the remainder into one scenario, you 
should see why dinosaurs must have an arboreal evolutionary history (for 
birds to evolve from them) and why many theropods were probably secondarily 
flightless--though their kind of flying was surely not as advanced as the 
flight of Archaeopteryx. Secondary flightlessness evolved repeatedly 
throughout avian evolution, and when birds were much less derived fliers than 
they are today, we may expect that it evolved even more frequently, leading 
to lots of theropod lineages.