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Re: New AVES definition refined (more testable?)



philidor11 wrote-

> HP Mortimer observed:
> <"And at least one of these two characters"?!  That sort of definition
will
> never hold.  We're after shared derived characters, not characters that
have
> a greater probability of being present.>
>
> Please clarify this statement for me.

Sorry.  I meant that a definition including the condition that "at least X
number of Y characters are present" is invalid.  My short explanation was
meant to say that a valid definition would include the condition "character
Y present", which is valid because of inheritance through common ancestry.
We could make the argument that the taxon was monophyletic because it's
perfectly possible for something to develop character Y and pass it to the
next generation.  Having "at least X number of Y characters" is not
something passed down through generations though.  As far as I know, some
genetic agent that groups a certain number of characters together, then
expresses a random sampling of them in every generation, is not known.  This
would certainly not be a good character to use, as there is no reason the
two "and/or apomorphic states" should be grouped together (especially based
solely on fossil evidence).  It's like me saying "tyrannosauroids are those
theropods with D-shaped premaxillary teeth, unserrated premaxillary teeth,
or both."  It just makes no sense as an inherited character.

Mickey Mortimer