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Re: What Is Not a Dinosaur? (was re: Ankle Articulation in Pterosaurs)



In a message dated 97-01-24 14:40:22 EST, znc14@ttacs1.ttu.edu (Jonathan R.
Wagner) writes:

<< The new Novas article in JVP addresses this as well. >>

This reminds me to mention a philosophical problem I have with this paper, a
problem that seems to afflict phyletic taxonomy in general. Toward the
beginning of the paper, Novas DEFINES Dinosauria to be the monophyletic group
comprising the common ancestor of Saurischia and Ornithischia and all its
descendants. Later, however, he lists "17 characters (synapomorphies) that
SUPPORT monophyly of Dinosauria." But if he has already DEFINED Dinosauria to
be monophyletic, then there is no reason to list characters that "support"
its monophyly, as if its monophyly were something still in doubt, that still
needed to be established. When you >define< a group to be monophyletic, then
that's that. Its monophyly no longer is an issue requiring "support."

What Novas is really displaying are simply characters that seem to be common
to the monophyletic group Dinosauria as he has defined it. It seems to me
that making the diagnosis of a taxon subordinate to its definition puts the
cart before the horse: The devil with the characters; they're irrelevant.
Toss them out, even though they're the only handle we have on whether a
particular specimen might or might not belong to a particular clade.

Incidentally, I took some time to go over the characters that Novas lists.
Most of them are >really< minor--ill-defined tubercles and bumps on certain
bones here and there--and with such a poorly known distribution among
dinosaurian and pre-dinosaurian taxa (as Novas himself repeatedly
acknowledges) as to be practically worthless. Can't see why he bothered to
publish the paper.