Those dredging where micros occur can end up with an extensive list
as the result of a single trawl. For instance, a list from a canyon
at 600m depth off Dunedin, NZ can be pretty long, though live
specimens are thehuge  minority. Presence of empty shells of
shallow-water species (and even a freshwater hydrobiid) can be reason
for caution... not every species in the haul may be from the dredged
locality... some may have washed-in from shallower water and they or
others may be relicts which have been lying there since a time of
lower sealevel. This obviously applies to fossil deposits as well.

The richest single locality I can think of is one in the middle
Eocene of the Paris Basin, with over 1000 species. In 7 hours in a
latest Pliocene Caloosahatchee shellpit (Pit #5, DeSoto, Arcadia,
Florida) I collected over 487spp, many of them micros. In repeated
visits I have collected a similar number of species from a latest
Oligocene limestone quarry in southern NZ, where many of the spp are
new; this total does not include micros, which I have not sampled yet
due to necessity of disaggregating the soft but not
totally-uncemented rock.
--
Andrew Grebneff
Dunedin
New Zealand
Fossil preparator
<[log in to unmask]>
Seashell, Macintosh, VW/Toyota van nut

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