Specimen of the Month
Samuel J. Ciurca, Jr., Rochester, New York           by
Searching the famous Bertie Waterlimes for Eurypterids
JUNE 2009
Will we ever know the true habitat of the eurypterids? Through hundreds of feet of strata, from the base of the Vernon
Formation (Salina Group) up into the Early Devonian limestones and dolostones of New York and Ontario, Canada,
distinct eurypterid faunas punctuate the sequence. One fauna occurs and is replaced in the vertical section by
another very distinct fauna and on right into the Early Devonian. Even with all of the eurypterid faunas now known,
there are still more to be discovered within this great geographic expanse. Why?
When I found my first eurypterid, within a glacial erratic, only a few years out of high school - who (including me) would
have ever thought that that single event would lead to over forty years of constructing an enormous collection of
these extinct creatures from known occurrences and newly discovered horizons. The thousands of hours I spent
amassing the collection are history. I did not simply collect objects (like the beer cans I started to collect once, in my
early years I might add), I 'collected' field experience, an increasing knowledge of strata and the sediments comprising
them. Stratigraphy became at least as interesting as finding another fossil and many of the rock layers I encountered
exhibited unusual lithologies - most, little understood. There are many eurypterids I would not have found, and new
horizons I would not have recognized, if I had neglected stratigraphy.
I'm not sure about other parts of the world, especially Siluro-Devonian sections, but 'our' eurypterids occur within an
evaporite sequence having commercial deposits of halite and gypsum and at least relict structures of salts when the
actual deposits are not present. Many of the eurypterid-bearing waterlimes of the Salina and Bertie Groups contain
fantastic salt hopper structures (perhaps a good topic for August 2009) and other manifestations of evaporite
sedimentary structures. The structures have been found on eurypterid integument itself and on what are interpreted
to be 'algal' clasts ripped up from microbialite mats often found in eurypterid beds.
ABOVE: The Williamsville Waterlime,
(Late Silurian Bertie Group) is a very re-
sistant, fine-grained dolostone and is
the repository of countless eurypterid
specimens. Unfortunately, it is rarely ex-
posed natually and when encountered in
a quarry is relatively difficult to work.
When fresh, the eurypterid-bearing beds
are about 18 - 24 inches thick in one
solid mass. A little weathering, however,
begins to weaken the layers and the
rock can begin to be split. In the photo
above, an eurypterid collector takes ad-
vantage of natural joints in the strata and
works his way into the beds - notice the
narrow block of waterlime he has just re-
moved. Shortly after I took this photo, an
eurypterid was encountered and the
problem of extricating the animal from
the rock, began.
Collectors try their best to remove a
specimen as best they can, but the way
waterlime often breaks causes many
problems in recovery. Waterlimes are
brittle and usually exhibit conchoidal
Anatomy of a 'Dig'
ABOVE: Eurypterus lacustris Harlan, found shortly after the block of waterlime was removed from the bedrock (see
photo above). Water was sprayed on the specimen to improve contrast for photographing the specimen in situ. The
collector will assemble and glue the pieces together after the specimen is removed from the excavation.
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It takes a little work!
and a little bit more!
and a pile of rock!
RIGHT: A relatively large
carapace I found (050809-1A),
Eurypterus lacustris. Width (at
base) about 7.5 cm., dorsal up.
There were no other remains
nearby, suggesting an isolated
occurrence, i.e. the carapace
was not part of a windrow.
As part of a larger study, orien-
tation is taken of many of the
various specimens collected to
ascertain current direction of
deposition and whether material
is dorsal up or down. Since all
material collected appears to be
molted, it is assumed that the
integument floated into the re-
during storm activity revealed in
distinct layers within the relative-
ly unfossiliferous (lagoonal)
waterlime. Eurypterid carapaces
are among the most commonly
encountered remains.