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Re: Padian et al. 1999 (Was: New PaleoBios paper - diplodocoid phylogenetic taxonomy)



2005/10/4, Mike Taylor <mike@miketaylor.org.uk>:
> Anyway -- just because Sereno criticises something doesn't make it
> bad!  :-)

Surely it doesn't. I'm just saying that AFAIK (and I could be wrong)
there is some criticism elsewhere.

>  So I always try to be explicit about whether I mean stability of content or 
> of definition.

That is another problem that must be taken into account. What stability means?

A definition stability is reached by *any* definition - say an
apomorphic one: "avifilopluma is a group of dinosaurs that descend
from the first organism to have a hollow epidermic appendage
homologous to the bird feathers". One could say that it could comprise
only arctometatarsalian dinosaurs or the entire dinosaur group (if,
for example, the protoceratopsian caudal filaments was homologous to
avian feathers) - but *definitionally*  Avifilopluma don't change.

A content stability is *not* a prerogative of any definiton (in a
monophyletic grouping context). The Reptilia defined as the node clade
comprising turtles (or anapsids) and birds - could include Mammalia if
the diapsids ended-up being more closely related to the mammals than
to the turtles (or anapsids).

Node, stem, apomorphy, taxon-based definitions owe their content
stability to the tree stability.

I don't think that that kind of unstableness is a bad thing after all.
Maybe only linnean taxonomy could claim for stability.

[]s,

Roberto Takata