[Taxacom] minimal estimates?

[Rob Smissen]

Hi all

John Grehan and co-thinkers point to a very important limitation of molecular dating exercises - that the first appearance of a clade in the fossil record provides only a minimal age for that clade.

However, it does not follow from this that molecular clock dates for clades calibrated on the basis of such fossils are necessarily minimum estimates.

Why? Because there are many potential sources of error to be considered. Some of these, such as misspecified substitution models, ancestral sequence polymorphism, incorrectly estimated phylogenies, hemiplasy, and among lineage rate variation can all result in over-estimates of clade ages. If errors leading to age-estimate exaggeration are greater than any fossil record related error causing age underestimation, then the age-estimate be to old.

It is not helpful to seize on one source of error alone, we need to consider all the potential sources of error, and preferably quantify them.

Not all of these estimates are of equal reliability, and in general I do agree with John that they need to be treated with scepticism. However, to label them minimum estimates is incorrect, even if it does tend to favour panbiogeographer's eccentric ideas about the age of taxa.

Cheers
Rob

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