Re: Who says dromaeosaurs can't fly?

[Ronald Orenstein <ornstn@rogers.com>]

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:ornstn@rogers.com