[Taxacom] Minimum dates

Michael Heads m.j.heads at gmail.com
Wed Jun 7 21:57:23 CDT 2017


That's right - we should say *at best* they provide a minimum clade age.

On Thu, Jun 8, 2017 at 2:39 PM, Rob Smissen <SmissenR at landcareresearch.co.nz
> wrote:

> Dear John and all
> While the age of the oldest known fossil of a taxon provides a minimum age
> for that taxon (if correctly assigned and correctly dated), it is simply
> not true that all dates extrapolated from that fossil through molecular
> dating are also minimum dates. Other sources of error in the process can
> result in dates of exaggerated antiquity. These sources of error include
> accelerated rates of sequence evolution in some lineages and sorting of
> ancestral polymorphisms.
> Many molecular systematists may well misrepresent their dates, and I
> personally take them all with a large pinch of salt (and preferably some
> lime and a shot of tequila). However, no matter how many times it is
> repeated, the claim that all dates extrapolated from a fossil of one taxon
> to the age of another taxon are also minimum dates is simply not true. I
> could, through deliberate naivety and misapplication of methods, "show"
> that one herbaceous plant diverged from its paternal parent several million
> years ago. Such a date would not be a minimum date.
> Please think a bit harder about this, you have a point but it is not quite
> the one you keep making.
> Best wishes
> Rob
>
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-- 
Dunedin, New Zealand.

My books:

*Biogeography and evolution in New Zealand. *Taylor and Francis/CRC, Boca
Raton FL. September 2016.
https://www.routledge.com/Biogeography-and-Evolution-in-New-Zealand/Heads/p/book/9781498751872


*Biogeography of Australasia:  A molecular analysis*. Cambridge University
Press, Cambridge. 2014. www.cambridge.org/9781107041028


*Molecular panbiogeography of the tropics. *University of California Press,
Berkeley. 2012. www.ucpress.edu/book.php?isbn=9780520271968


*Panbiogeography: Tracking the history of life*. Oxford University Press,
New York. 1999. (With R. Craw and J. Grehan).
http://books.google.co.nz/books?id=Bm0_QQ3Z6GUC
<http://books.google.co.nz/books?id=Bm0_QQ3Z6GUC&dq=panbiogeography&source=gbs_navlinks_s>


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