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Re: Some thoughts on AVES
On Fri, 2 Nov 2001, Ken Kinman wrote:
> Another (larger) gap should be chosen to mark the arbitrary line
> between Reptilia and Aves, but this time it should be based on osteological
> characters that are much more clear-cut (like those which divide therapsids
> and mammals). Yes, a character-based taxon---do I hear booing in the
> cladist camp? Sorry, but I think that is the best way to ensure relative
> stability of content in the long run (it did for mammals before the
> cladistic splintering messed it all up).
Ken, don't you see that any "larger gap" you choose is just going to fill
in as we make new discoveries? Evolution occurs through the accumulation
of minute changes, not the sudden appearance of radical changes. If you
try to pick a character you're just going to find that it arose gradually
and that there will be forms where it is debatable whether it has the full
character or not.
This is incredibly UNstable, because it decides ranks based on where the
largest gaps in our knowledge currently are, something which changes as
new discoveries are made.
T. MICHAEL KEESEY
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