Re: Definitions

["T. Mike Keesey" <tmk@dinosauricon.com>]

On Fri, 17 Aug 2001, Mickey Mortimer wrote:

I'm being very picky here, but....

> A node-based definition is-
> "all descendents of the most recent common ancestor of A and B"

I prefer, "The most recent common ancestor of A and B [and C, etc.], plus
all of its descendants." The above formulation does not include the
ancestor of the group, a vital component in order for the taxon to be a
clade.

> Basically, anything in the smallest clade containing both A and B.

That is another good way to put it.

> A stem-based definition is-
> "all taxa more closely related to A than to B"

This formulation I really dislike, since people use "closely related" in
different ways.

A better one would be, "The earliest ancestor of A which is not also an
ancestor of B [and C, etc.], plus all of its descendants."

Or, "The most inclusive (largest) clade containing A, but not B [or C,
etc.]."

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