[Taxacom] more science nonsense

[John Grehan]

Some comments on David's observations (in quotes) below:

“The fossil indicates that the clade was present in the southern hemisphere
at the time.”

Agreed. This is empirically evident

“Lacking a corresponding northern hemisphere find, it very weakly supports
a southern origin”

This is not empirically evident. It is an inference that comes from one of
a multitude of criteria invented for recognizing an invented center of
origin, of which some are contradictory (As noted by Camp long ago).

“But this depends a lot on the dispersal abilities”

It has been shown that dispersal abilities have little to do with the
geography of allopatry.

“Large seabirds can easily travel almost anywhere, so finding one in a
particular place is not particularly informative”

Agreed, although even for birds that travel widely (and some perhaps almost
anywhere), various bird taxa show patterns of allopatry and tectonic
correlations, particularly for nesting location.

“and the avian fossil record is rather patchy.”

Rather - as with most taxa (most not having any record at all).

"Thus, it is extremely weak evidence.  In contrast, extensive records of a
shallow marine invertebrate clade with hard shells and high abundance in
one region but not another would be much better evidence of a region of
origin.”

Like the occurrence of fossils, the location of highest diversity is
evidence only of highest diversity. Center of diversity is another one of
those made up criteria for recognizing a made up center of origin.

“Most taxa will originate in a particular region, simply because that's
where a particular mutation first occurred (although gradual replacement
with interbreeding with other groups
is possible, making the identification of a specific point in time or space
of origin difficult.)”

I would suggest that the identification of a specific point in time or
space of origin is not so difficult where allopatry is intact.

John Grehan

On Thu, Oct 3, 2019 at 11:35 AM David Campbell via Taxacom <
taxacom at mailman.nhm.ku.edu> wrote:

> The fossil indicates that the clade was present in the southern hemisphere
> at the time.  Lacking a corresponding northern hemisphere find, it very
> weakly supports a southern origin.  But this depends a lot on the dispersal
> abilities, the level of knowledge about the group, and other factors.
> Large seabirds can easily travel almost anywhere, so finding one in a
> particular place is not particularly informative, and the avian fossil
> record is rather patchy.  Thus, it is extremely weak evidence.  In
> contrast, extensive records of a shallow marine invertebrate clade with
> hard shells and high abundance in one region but not another would be much
> better evidence of a region of origin.  Most taxa will originate in a
> particular region, simply because that's where a particular mutation first
> occurred (although gradual replacement with interbreeding with other groups
> is possible, making the identification of a specific point in time or space
> of origin difficult.)
>
>
> > --
> Dr. David Campbell
> Associate Professor, Geology
> Department of Natural Sciences
> Box 7270
> Gardner-Webb University
> Boiling Springs NC 28017
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