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

[David Campbell]

> >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