Eurypterids
Specimen of the Month
Samuel J. Ciurca, Jr., Rochester, New York           by Eurypterids.net
ABOVE: Eurypterus lacustris (2 specimens) on posters showing size attained during the Late Silurian based upon
study reported below.
DECEMBER 2008
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THE SIZE THAT COMMON EURYPTERUS SPECIES ATTAINED
(LATE SILURIAN BERTIE GROUP OF NEW YORK
AND ONTARIO, CANADA)
Poster Session presented before the Rochester Academy of Science Fall 2008
Scientific Papers Day hosted by Nazareth College, Rochester, New York
BELOW: Text of Abstract:
Across New York State and southwestern Ontario, Canada, the 'common' eurypterids occur in countless numbers
within a sequence of rocks termed the Bertie Group. Within the lower portion of the group, i.e. the Fiddlers Green
Formation, the eurypterid
Eurypterus remipes is the characteristic taxon found within the preserved biota.
Stratigraphically higher, the common form is
Eurypterus lacustris. Generally, E. remipes is found in a small/medium
size (~5 - 8 inches), while
E. lacustris occurs in a medium/large size (~6 - 9 inches). Interestingly, in the Niagara
Peninsula of Ontario, Canada, some of the smallest (~0.5 - 2 inches) eurypterids (
E. remipes) are found in the
Fiddlers Green Formation (Ellicott Creek Member). Whether size-sorting, i.e. segregation according to the size of
individuals or fragments, is the principle reason for the distribution observed is not known at present, although
size-sorting has often been obsrerved within these eurypterid-bearing units not only in the case of eurypterid
material, but also associated animal and plant remains (cephalopods, gastropods, horseshoe crabs, etc.).
Regionally, it appears that storms frequently carried or floated all kinds of organic debris, much as they do today,
into widespread areas of shallow water deposition that existed shoreward of stromatoporoid banks/shoals and bands
of microbialite mounds. It is suggested that much sorting took place as material moved shoreward and currents
distributed molted eurypterid remains in bands (windrows) within the fine dolomitic muds.
The Peabody Museum of Natural History contains one of the largest collections of eurypterid material ever
assembled (Ciurca Collection) with a very wide assortment of ranges of size and preservation. Specimens of
Eurypterus sp. indicate, by extrapolation of preserved parts, that the common eurypterids attained a size of about 16
- 18 inches in length, a condition not recorded by complete material reported from the waterlimes of New York and
Ontario.  
A new specimen proves that these eurypterids attained an even greater size. A telson discovered in the Williamsville
'A' Waterlime is an exceptional 6 inches in length, the largest found to date, and was recently added to the
invertebrate collections of the Peabody Museum in New Haven, Connecticut. Two large specimens of nearly
complete
E. lacustris, with telsons measuring 3 inches in length, were photographically enlarged to a size where the
telsons became 6 inches in length. This photographic enlargement indicates that a eurypterid with a 6-inch telson
reached over 2 feet in length from the tip of the carapace to the tip of the telson. It also shows that the carapace of
the animal (
E. lacustris) reached approximately 7 inches in width.
This study is being extended to a 'common' fossil found in the Pittsford Member of the lower Vernon Formation
(Salina Group), viz.
Eurypterus pittsfordensis, as a very large collection of 'Pittsford Shale' material is now available
for study.
LEFT: One of the actual specimens used
in the study. The telson measures about
3 inches in length. Note that the anterior
portion of the specimen is dorsal and the
rest the ventral aspect (the cast having
been removed). The arrow points to
magnetic north and the specimen was
found preserved dorsal up.
Some of the very best preserved
Eurypterus fossils originate in the
waterlime of the Williamsville Formation of
western New York and Ontario, Canada.
This region has yielded thousands of
specimens over the past century.
Specimens are found in museums
throughout the world, and an especially
good collection of
Eurypterus lacustris is
to be found in the collection of the Buffalo
Museum of Science in Buffalo, New York.
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Text of abstract also printed in the Rochester
Academy of Science BULLETIN, August, 2009,
Vol. 63 #7.