[Taxacom] Minimum dates

Rob Smissen SmissenR at landcareresearch.co.nz
Wed Jun 7 21:39:38 CDT 2017


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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