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Re: Who says dromaeosaurs can't fly?
At 09:14 AM 13/09/02 -0400, Jeff Hecht wrote:
I think the problem may be that cladistics implicitly assumes that a
character should have evolved only once -- not many times as you suggest.
As I understand it, this is the base of creating a "most parsimonious"
tree that is considered the most plausible one.
Tom Holtz has answered this far better than I could, but I would add that a
lot depends on the nature of the character. Personally I would only use
analyses that are based on characters that are unequivocal. Thus, for a
fossil species, "asymmetrical primary feathers" could be such a character,
but "ability to fly" could not be because the character state can only be
implied (even with a high degree of likelihood) but not proved. Therefore,
if the morphological characters have been coded correctly the analysis
should not change merely because we assume that some species on the tree
could fly, unless what you are really doing is saying either that the
morphology has been described incorrectly or that new morphological
information, permitting addition of further characters to the analysis, has
come to light.
If Czerkas and Paul are correct. of course, there is still no reason to
assume that flight evolved more than once in maniraptorians - it may be
that it evolved much more basally than we had thought. As we know, loss of
flight can occur repeatedly even within modern birds. Flightlessness has
evolved at least a dozen times in rails alone, and yet no one is suggesting
that cladistic analysis is inapplicable to rails on that basis alone.
Ronald I. Orenstein Phone: (905) 820-7886
International Wildlife Coalition Fax/Modem: (905) 569-0116
1825 Shady Creek Court
Mississauga, Ontario, Canada L5L 3W2 mailto:firstname.lastname@example.org