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Re: Polytomy question

This is well discussed by the excellent book by Smith:

Smith, Andrew B. 1994. Systematics and the fossil record: documenting evolutionary patterns. Oxford, OX; Cambridge, Mass., USA: Blackwell Science.

On 27/10/2005, at 2:36 AM, T. Michael Keesey wrote:

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

-- John S. Wilkins, Postdoctoral Research Fellow, Biohumanities Project University of Queensland - Blog: evolvethought.blogspot.com "Darwin's theory has no more to do with philosophy than any other hypothesis in natural science." Tractatus 4.1122