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Re: OCCAM'S RAZOR & THERIZINOSAURS



In a message dated 98-08-02 13:59:30 EDT, cbrochu@fmppr.fmnh.org writes:

<< At present, the phylogenetic pattern recovered by multiple independent
 analyses over the past decade does not support secondary flightlessness.
 Secondary flightlessness is an additional assumption placed on the pattern
 a posteriori.  Is it a bad assumption?  Not necessarily - but it is
 secondary, and hence not parsimonious. >>

Actually, secondary flightlessness is the simplest and most parsimonous way to
describe the relationship between birds and theropod dinosaurs. In BCF, the
wing does not go through a state in which it is a short forelimb before it
once again becomes a long forelimb (as in primitive archosaurs); it starts out
as a long, grasping forelimb in quadrupedal tree-climbing archosaurs and it
remains a long forelimb in dino-birds and birds. The short forelimbs of
theropods are >derived< proto-wings, just as the short forelimbs of extant
flightless birds are derived neo-wings. In BCF, birds do not go through a
state in which they become large, heavy, ground-dwelling cursorial bipeds
before once more becoming small; they start out as small, lightweight,
arboreal forms (probably as far back as the Permian) and remain so. The large,
unflightworthy size and bipedal cursorial lifestyle of theropods are derived
relative to the common ancestor of birds and theropods.

And so on with features of the feet, tail, and skeleton. There are no miracles
in BCF, no magic moments when flightless, ground-dwelling theropods suddenly
find themselves with exactly the right mix of features they need for flight
where before there was none. Just good old plodding evolution, acting
incrementally over tens of millions of years on dozens or hundreds of
different arboreal dino-bird lineages until finally recognizable avians
appear. This is the whole point of BCF.