[Taxacom] Taxacom Digest, Vol 68, Issue 8

John Grehan jgrehan at sciencebuff.org
Wed Nov 9 15:53:50 CST 2011

-----Original Message-----
From: Sergio Vargas [mailto:sevragorgia at gmail.com] 
Sent: Wednesday, November 09, 2011 4:08 PM
To: taxacom at mailman.nhm.ku.edu; John Grehan
Subject: Re: Taxacom Digest, Vol 68, Issue 8

> by theoretically claimed you mean hypothesized?

If you like.

> well... if you had empirical evidence for the maximal/actual age of a 
> clade you would not need molecular dating. 

Or any other dating

> I would like to know what the empirical evidence for the maximal age of a 
> clade could be? 

So would I

> There is no way to demonstrate that a fossil is of maximal age, you can 
> only approximate the maximal age of a clade hypothesizing that there is no 
> fossil of taxon A that is older that the oldest known fossil of taxon A, 

Yes, and even then its just a guess

> or using molecular dating to provide a credible interval for the maximal 
> age of the clade given the calibrations (minimal ages) and prior 
> distributions for the node ages (to model the maximal age). 

Another guess

> Most authors agree that fossils provide only minimal ages, I don't think 
> they ignore this but they base their conclusions on the credible region 
> obtained from the analysis, and treat this credible region as an 
> approximation to the maximal age of the clade. 

Transforming a minimal date maximal according to some 'credible region' sounds more like voodoo.

> Of course some authors really want to have The Date of cladogenesis, but 
> with bayesian methods this is getting less common.

A minimum is a minimum is a minimum.

John Grehan



Sergio Vargas R., M.Sc.
Dept. of Earth&  Environmental Sciences
Palaeontology&  Geobiology
Ludwig-Maximilians-Universität München
Richard-Wagner-Str. 10
80333 München
tel. +49 89 2180 17929
s.vargas at lrz.uni-muenchen.de
sevra at marinemolecularevolution.org

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