[Taxacom] Snake garbage

[David Campbell]

Priors are not necessarily a minimum age; they may or may not have some
connection to the actual date of origination, given the lack of attention
to good calibration and uncertainty about molecular clock methods.  Some
common calibration errors (such as ignoring problems of paraphyly and
wastebasket taxa) tend to make molecular clock dates too old, for example.
Many analyses treat "first fossil record of clade X" as "date of the split
between the two Recent members of clade X that we happened to sample".

This particular paper has two major weaknesses.  One, as they state, the
results depend on the rejection of all records of crown group snakes from
the Cretaceous.  But that's rather circular, not deserving of big
headlines.  Two, realistic error bars for molecular clocks mean that a date
around the K/T (or any other particular event) is very unlikely to be
reliably determinable between before, after, or at the event.


On Fri, Sep 17, 2021 at 10:21 AM John Grehan via Taxacom <
taxacom at mailman.nhm.ku.edu> wrote:

> "Evolution and dispersal of snakes across the Cretaceous-Paleogene mass
> extinction" (https://www.nature.com/articles/s41467-021-25136-y.pdf )
>
> This paper carries on the time honored scientific tradition of just
> ignoring shortcomings of a method and ploughing on as if the ground was not
> already falling away beneath. In this case the representation or priors as
> some kind of empirically real source of estimating fossil calibrated clade
> ages as anything but a minimum ages, and the continued temptation of using
> an automated biogeography program as 'evidence' despite its
> inherent inability to distinguish between vicariance and dispersal where
> either can generate the same biogeographic pattern. I have been attacked
> for calling this stuff 'garbage' but I have not come up with a more
> accurate term - yet.
>
> John Grehan
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>


-- 
Dr. David Campbell
Associate Professor, Geology
Department of Natural Sciences
110 S Main St, #7270
Gardner-Webb University
Boiling Springs NC 28017