Silurian/Devonian Boundary
New York State and Ontario, Canada
Erieopterus microphthalmus
Manlius Limestone (Early Devonian)
Syracuse, New York
The occurrence of the eurypterid genus, Erieopterus, in the stratigraphic sequence generally marks the boundary between the rocks below ("Eurypterus Beds") and the Early Devonian strata of the region. Erieopterus, shown in the picture at the left, is a very widespread form.  I have traced Erieopterus from the Helderberg Escarpment near Albany, New York westward beyond Buffalo into Ontario, Canada. It is a very common eurypterid in the region from Byng westward (Clanbrassil, Cayuga, and Haggersville) in Ontario.  Occurrences continue westard into the Early Devonian rocks of the Michigan Basin, and southward in Ohio where it is a well-known form (Bass Islands).
   In general,
Erieopterus occurs in limestone sequences in the east, and dolostones in the west.  Typically normal marine units occur in the east.  Westward, stromatolitic biostromes and bioherms separate the marine regions from the backreef (hypersaline) regions formed from dolomitic muds.
AT RIGHT: Another example of Erieopterus, this specimen is preserved in fine-grained dol- ostone (waterlime), Honeoye Falls Dolostone south of the City of Rochester, New York. CIURCA 080379-1.  The Hon- eoye Falls Formation occurs only locally and is equivalent to the upper Chrysler Fm. and the Manlius Limestone of the Syracuse region to the east. Westward, this formation is correlative to the Erieopterus- bearing Clansbrassil Fm. in Ontario, Canada (Byng to the Haggersville region). Length of specimen: 8.8 cm.
AT LEFT: Large carapace of Erieopterus microphthalmus collected from the  Manlius Group near Syracuse, New York.  While most speci mens of this eurypterid are relatively small, it is obvious from this specimen that this eurypterid attained a great size.  Carapace at base, is 3 inches in width. Note the very small eyes.
ABOVE: Slab of Chrysler Dolostone with 3 carapaces of Erieopterus microphthalmus.  The Chrysler Formation in the Syracuse Region is rich in the remains of eurypterids, some associated with small thrombolites.  Eastward, at Clockville, Erieopterus occurs within the Chrysler Formation and the overlying (stromatolitic and thrombolitic) Thacher Limestone.  Associated fossils are, generally, the prolific brachiopod-Howellella vanuxemi, ostracods and a pelecypod. Eastward, more typical marine forms occur within the Erieopterus-bearing sequences (other brachiopods, tentaculites, bryozoans, etc.  Westward, all typical marine forms disappear and Erieopterus is the only fossil found (Honeoye Falls Formation (south of Rochester, New York), Clansbrassil Formation of the Niagara Peninsula of Ontario, Canada.  All of these units represent the earliest Devonian Period of the region. The entire region is underlain by the Late Silurian, Eurypterus-bearing Bertie Group. Note: Stromatolites, though not often obvious, are present throughout the eurypterid-bearing sequences of New York and Ontario