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Re: Quick cladistics question



In a message dated 97-03-31 18:24:27 EST, jpoling@dinosauria.com (Jeff
Poling) writes:

<< One other question:  I carefully reread the definitions for stem and node
 based clades (and then did the requisite search of the archives).  It looks
 like the only difference between a node and stem based clade is how each is
 defined.  There has to be more to it than that ... what IS the difference?
>>

One way to visualize the difference is that the "node-based" clade includes
the node at its base and the "stem-based" clade does not include the node at
its base. If you're familiar with a little bit of basic set theory, the
"node-based" clade is >closed< at the base, the "stem-based" clade is >open<
at the base.

<< And one other one other question:  how is it decided when one definition
 has precedence over the other?  As part of my example, you mentioned that
 under those conditions Dinosauria would become synonomous with Archosauria,
 and Archosauria would be sunk.  I thought Archosauria had been named first?
>>

No, Dinosauria was named first, in 1842; Archosauria was named in 1869.
Priority by date of publication is the usual way of deciding precedence, but
there are no formal rules above the family level, and actually anything can
go. For example, Opisthocoelia and Goniopoda both have publication priority
over Sauropoda and Theropoda, respectively, but you know which names are
universally accepted.