Eurypterus lacustris Fauna
The Eurypterus lacustris Fauna replaced the Euryptrerus remipes Fauna.  It is younger,  but still occurs within the Bertie Group (as redefined by Ciurca, 1990) of Western New York and Ontario, Canada.  The faunas are are not comingled, the occurrence of the Eurypterus lacustris Fauna in  the rocks
Lyman Child Wooster
(1849-1947)
Naturalist (at what is now Emporia State University, Emporia, Kansas) holding a specimen of Eurypterus lacustris Harlan which he collected from near Buffalo, New York in the early 1900s (Williamsville Fm. of the Bertie Group, Late Silurian age).
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HISTORY OF GEOLOGY
by James S. Aber
Above photo: Copyright Emporia State University
of Western New York and Ontario, Canada excludes earlier forms (because of evolution).  While many differences may appear to be slight, detailed observations show that most of the misidentifications are due to preservational features.
OCCURRENCE OF THE
EURYPTERUS LACUSTRIS FAUNA
Eurypterus lacustris is a common form.  Since Harlan (    ) described this animal, thousands of specimens have been found by collectors,  and many specimens are still being found to this day.  This arthropod has found its way into many of the museums of the world, but the largest collection is in the Buffalo Museum of Science.  Around the turn of the last century, about the time Lyman Child Wooster (at right) collected his specimen, workers at a quarry in Buffalo, N.Y. were paid to keep their eyes open for specimens that were then given to the museum at Buffalo.  Apparently, many of the specimens found their way to museums around the world via exchanges of fossils with the Buffalo Museum.
   I have calculated, based upon specimens being found at a large quarry in Ontario, that about 1,000,000 essentially complete
E. lacustris specimens occur per square mile of the Williamsville Formation. The concentration of specimens in the Fort Erie to Buffalo region leads to a figure of several million specimens.  Specimens are not rare, they are just difficult to access due to heavy overburden of glacial de- posits and bedrock.  Collection depends only upon access via quarry operations, excavations and construction sites. Natural outcrops are few, but even these still yield material.
The geographical extent of the occurrence of this fauna is truely amazing.  Westernmost occurrences are from the area of Haggersville in Ontario, Canada.  From Buffalo and eastward, occurrences become fewer--
Eurypterus lacustris is replaced by the Paracarcinosoma scorpionis Fauna and only rare fragments of E. lacustris are found. Currently, the easternmost occurrence of the P. scorpionis Fauna is near Jamesville, New York (Oxbow Waterlime of Rickard).
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Eurypterus lacustris (Harlan) from the Late Silurian Williamsville Formation (Bertie Group).
The structures seen on the carapace are the coxae--these meet in the middle--the 'mouth'.
The final segment is the 'tail'-actually the TELSON-of the eurypterid, analogous to the ter- minal spine of the extant horseshoe crab,
Limulus, common to our Atlantic coastal waters. All Bertie eurypterids are MOLTS--there is no evidence that these eurypterids lived where we find them.  They are usually found in WINDROWS, collections of animal and plant debris.
SPECIMEN IN PHOTOS ABOVE IS 7 1/4 INCHES IN LENGTH - FROM CIURCA COLLECTION
SPECIMENS OF EURYPTERUS LACUSTRIS (HARLAN)
THIS SITE COPYRIGHT 2001 - SAMUEL J. CIURCA, JR., ROCHESTER, NEW YORK
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AT LEFT: A very small specimen of the eurypterid, Eurypterus lacustris. Note that the operculum, bearing the medial sex appendage, is well preserved in this ventral view of the specimen.  The animal is about 15 mm in length. This is a rare specimen from the Williamsville Waterlime, Bertie Group, Ridgemount Quarry of Fort Erie, Ontario, Canada.
Larger specimens are the norm, up to about 15 inches in length.  Structures that are also prominent are the telson, walking legs (with spines), metastoma and the swimming legs. Matrix is a very fine-grained dolostone (waterlime).
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