Eurypterids
Specimen of the Month
Samuel J. Ciurca, Jr., Rochester, New York         by Eurypterids.net
ABOVE: (CIURCA 063208-1) Beautifully preserved pincers (rami) of the pterygotid, Acutiramus cummingsi. This
specimen is from the Williamsville 'A' Waterlime, Late Silurian Bertie Group, RQS in Fort Erie Township (Bertie),
Ontario, Canada (specimen has been donated to the Peabody Museum of Natural History at Yale University in New
Haven, Connecticut. The fixed ramus is about 4.8 cm long. While rarely encountered, this pterygotid is known
(mostly from molted parts) from similar rocks as far east as Jamesville, New York. Complete specimens are known,
but extremely rare. Pterygotids punctuate the Late Silurian strata at many intervals within New York State, from near
the base of the Salina Group to the Early Devonian Manlius Group (Helderbergian).
Pterygotids were undoubtedly the 'sharks' of the Siluro-Devonian seas. Their prey could likely have been the
smaller eurypterids, e.g.
Eurypterus, which is preserved in countless numbers in the various units of the Bertie
Group. A wholesome predator/prey ratio exists if this were the case. A streamlined body, large anterior eyes and the
great claws makes for a monstrous, swift and agile predator. It is noteworthy that no remains of 'fish' have been
recorded within our eurypterid-bearing rocks, but the association does occur in other regions and, especially, in
Devonian rocks.
ABOVE: Ukraine Eurypterids  Several years ago, the fossil 'market' was flooded with eurypterids from the Ukraine.
In more recent years, many specimens became available on Ebay and, at more reasonable prices, I purchased
much material. Most of the specimens are labeled
Baltoeurypterus tetragonophthalmus (a real mouthful) and as
can be seen in the example shown above are quite like the common
Eurypterus species (Eurypterus remipes and
Eurypterus lacustris) found in the waterlimes of New York and Ontario, Canada.
What is evident from all the specimens I have seen to date is that they are most like the Bertie Group lithologies in
preservation, and hence my interest. The animals (most likely molts) are often collected together in windrows or
gyres initiated by Silurian storms. The likely setting is shallow, offshore lagoons as in the type areas of New York.
What I don't know at this time is whether the Ukraine eurypterid material is found in hypersaline deposits that are so
characteristic in the New York evaporite sequences (Salina and Bertie Groups).
NOVEMBER 2008
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