Re: forams

Thanks, I didn't make that clear.

"Dr. David Campbell" <amblema@bama.ua.edu> wrote:> >And after Glenn Morton said that there are only about 150 foram
> species in toto, I rechecked those authors' list (see below) and
> found only 85 different species as candidates for their Miocene
> formation, not 150.
> I quoted the 150 from memory which is always a bad thing to do. I
> checked with Dan Georgescu's website. I was in contact with him when
> I made my page on forams. He told me that a new site was going up at
> that time. His site lists 212 total species of forams throughout all
> time--that is it. Just 212.

That's 212 species of planktonic forams. There are all sorts of
benthic ones. Perhaps the most famous benthic forams are the
nummulites that make up a large proportion of the limestone in the
Egyptian pyramids. Herodotus thought they were petrified lentils.

Some of the benthic species may be useful stratigraphically (notably
nummulites and fusilinids), but they have been used more as facies
indicators-they have strong depth, salinity, and oxygen preferences.

One factor in the limited diversity of planktonic forams is that almost
all of them went extinct at the K/T. There is a rapid radiation
afterwards, with the evolution of new genera readily traced in the
fossil record in a few places, but still such a drastic bottleneck will
tend to limit diversity.

A complication is that genetic work on living ones suggests that
some "species" as traditionally defined actually include several
species. I don't know whether the count of 212 takes that into
account.

Many other planktonic microfossils are important stratigraphic
indicators, including calcareous nannofossils, radiolarians, diatoms,
condonts, and pteropods. The only major difference between using
forams and using these is that the preparation and microscope
techniques vary. E.g., forams, nannos, and pteropods are acid soluble
but the rest can often be isoalted using acid to dissolve the bulk rock
or sediment; nannos are the smallest and require fancier scopes than
the others; etc.

-- 
Dr. David Campbell
425 Scientific Collections Building
Department of Biological Sciences
Biodiversity and Systematics
University of Alabama, Box 870345
Tuscaloosa AL 35487-0345 USA
glenn
http://home.entouch.net/dmd/dmd.htm
		
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