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Re: Polytomy question

On 10/26/05, Denver Fowler <df9465@yahoo.co.uk> wrote:
> This is in some respects a 'split lineage', but to
> think of a cladistic diagram as a 'family tree' is
> misleading. It's a statistical diagram, nothing more:

Well put.

> a split may indicate a shared <unknown> common
> ancestor between taxa, or that one of the taxa is
> infact, the ancestor of the other. it is not possible
> to determine which is which using this method, because
> cladistics makes no assumptions of time/age of taxa.

However, you can use a cladogram combined with data on the time ranges
of your OTUs to identify *potential* ancestors. If two sister taxa, A
and B, are scored identically except that A lacks certain derived
traits that B exhibits, and every member of A occurs earlier than
every member of B, then A *might* be ancestral to B (although this
can't be proven).
Mike Keesey
The Dinosauricon: http://dino.lm.com
Parry & Carney: http://parryandcarney.com