[Taxacom] Snake garbage

[John Grehan]

For clarification, I was not meaning that priors were minimums. My
intention was to point out that all fossil calibrated ages are minimums.
Priors are just guesses, dressed up in numbers, as to how much older
authors believe a taxon might be. A sort of science fiction.

On Fri, Sep 17, 2021 at 10:32 AM David Campbell via Taxacom <
taxacom at mailman.nhm.ku.edu> wrote:

> 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
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> Nurturing nuance while assailing ambiguity for about 34 years, 1987-2021.
>