Taxacom: Dating biogeographic events from "Early Permian" angiosperms... real or not real taxa/names?

[John Grehan]

Hi David. You make some interesting points (some have also been made in the
literature). Some comment below:

"There are also several difficulties with using such dates - not
necessarily insurmountable, but requiring significant caution. "

There are always 'difficulties' with any approach, so yes in principle.

"Plate tectonic events are lengthy and complex."

As a generalization this is hard to assess. Some tectonic events are longer
than others. 'complex' is context related.

"For example, the first terrestrial mammals to reach South America from the
north had arrived by 10 Ma, whereas the last coastal marine species would
have been able to get through about 2.5 Ma."

Need analysis to judge this. But what seems to be different here is that
you are relating the origin of a distribution to a geological event,
whereas the Dianella example is a correlation between a distribution and a
tectonic structure. Very different approach.

"Terrestrial plants with limited dispersal ability were able to
reach Iceland from North America and Europe in the mid- to late Miocene,
though the North Atlantic began to open much earlier."

Need the analysis to comment.

"Many different events can happen in the same general region over time."

Agreed, and one has to take care. Heads has given examples where
distributions attributed to formation of the Panamanian isthmus show
biogeographic-tectonic correlations that indicate a different tectonic
relationship.

" The Appalachians were built by collisions in the Ordovician through
Carboniferous.
However, several lines of evidence point to the occasional chunk of lower
plate from the collision zone breaking off the bottom of the plate and
sinking into the mantle, causing rebound and elevation changes above from
time to time up to the present."

There are various examples of sequential tectonic events given attention by
Heads. But the issue here is of tectonic correlation - i.e. correlation of
distributional patterns and tectonic structure - not just with a historical
model in isolation of that relationship.

"The problems apply also to studies that have come up with a date and are
hunting for a matching event."

Agreed - which is why panbiogeographic approaches involve matching
biological and geological PATTERNS, not just matching a biological pattern
(distribution) with a hypothesized event in isolation. The Dianella example
is a correlation of the distributional boundary with a tectonic structure -
the Mwenetzi monocline . It is that spatial correlation that gives a basis
for inferring a historical evolutionary relationship between the geological
process and history of the monocline and the origin of the biological
distribution.  So this is not just a matter of coming up with a date and
hunting for a matching event (You appear to be referring to those fossil
calibrated divergence dates where indeed authors go hunting for matching
events). Heads has also pointed to the value of multiple tectonic
correlations for different clades within a group that are consistent with
sequential vicariance. So in principle I agree with the caution, but note
that there are numerous and detailed analyses of tectonic correlation that
are open to analytical critique and further evaluation.

Cheers, John Grehan

On Wed, Jun 8, 2022 at 7:47 PM David Campbell via Taxacom <
taxacom at lists.ku.edu> wrote:

> > >But
> > fossils are not the only form of evidence for the age of taxa. Take for
> > example the distribution of  the angiosperm genus Dianella. Its western
> > boundary lies on the Mwenetzi monocline which formed along the split
> > between Africa and Antarctica beginning about 185 Ma. This puts the
> > existence of this genus well into the Jurassic.
>
>
> There are also several difficulties with using such dates - not necessarily
> insurmountable, but requiring significant caution.  Plate tectonic events
> are lengthy and complex.  For example, the first terrestrial mammals to
> reach South America from the north had arrived by 10 Ma, whereas the last
> coastal marine species would have been able to get through about 2.5 Ma.
> Terrestrial plants with limited dispersal ability were able to reach
> Iceland from North America and Europe in the mid- to late Miocene, though
> the North Atlantic began to open much earlier.
>
> Many different events can happen in the same general region over time.  The
> Appalachians were built by collisions in the Ordovician through
> Carboniferous.  However, several lines of evidence point to the occasional
> chunk of lower plate from the collision zone breaking off the bottom of the
> plate and sinking into the mantle, causing rebound and elevation changes
> above from time to time up to the present.
>
> The problems apply also to studies that have come up with a date and are
> hunting for a matching event.
>
> --
> 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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