Latin names versus scientific names [was: So much fornomenclatural stability]

[Curtis Clark]

on 2005-03-11 09:06 Richard Jensen wrote:
> I'm not sure I follow what Curtis writes below.  Just to make sure we're
> all on the same page, a monothetic set is one for which the possession
> of a single characters state (or a unique combination of character
> states) is both necessary and sufficient for membership in the set.
> This is not the same as monophyly and cladistic classifications are
> rarely monothetic (most have too much homoplasy to recognize strictly
> monothetic sets).

A good point that I did not sufficiently consider. Let's take the
contrived example of the snakes as members of the tetrapods. If the sole
apomorphy "defining" the tetrapods were four limbs, the snakes could not
be a member of a monothetic Tetrapoda if we focused on the lack of
actual limbs, but they could if we instead talked of the "essence" of
limbs. Monothetic groups work much better if you are an essentialist.

> Now, I can see how apomorphies "below" a node might be used to support
> monophyly - as we are moving up that part of the tree, all taxa share
> these apomorphies (which are equivalent to synapomorphies).  However,
> apomorphies above a node provide no basis for declaring that all taxa
> arising at that node are monophyletic.  If they did, they would be
> synapomorphies at that node, right?

You're basically right about this, but what I was thinking of was that
the apomorphies above a node aren't found *outside* the group. That
provides an additional level of support to the node (since every node is
a hypothesis, the sequence of nodes is also a hypothesis). But it
doesn't really have anything to do with monothetic groups.

--
Curtis Clark                  http://www.csupomona.edu/~jcclark/
Web Coordinator, Cal Poly Pomona                 +1 909 979 6371
Professor, Biological Sciences                   +1 909 869 4062