Eurypterid - Eurypterus lacustris


March’s Fossil of the Month is this exquisite Eurypterid, which was discovered in the 1950s — and the original photograph is still with it in our museum!
We chose to highlight this “sea scorpion” because this month was supposed to be the Buffalo Gem, Mineral, and Fossil Show in which we would have had a display on Eurypterids for all to see. (However, due to the spread of COVID-19, the Gem Show has been cancelled. So you will just have to visit our Eurypterids in our museum!)

Although they look similar to today’s lobsters, the Eurypterid’s closest living relatives are actually horseshoe crabs, spiders, and scorpions. Their bodies are divided into three parts: the prosoma, or head; the opisthosoma (body); and the telson (tail). The paddle-like limbs were used for swimming in a probable up and down rowing motion.
The Eurypterus lacustris averaged at 6 to 9 inches in length, and is one of the most common Eurypterus found. This “sea scorpion” is very similar to the Eurypterus remipes, however its eyes are placed farther back on its hard upper shell, or carapace.
Most fossils of Eurypterids are not of the actual animal, but of the molts of the exoskeleton because it had to shed its hard shells frequently in order to continue growing. However, we believe our Eurypterus lacustris is of the animal itself because of the complete nature of the fossil (among other reasons). Our fossil also contains another smaller Eurypterid that is turned on its side with its legs in view and two eyes present.

When you come to see this specimen, tell us what you think!

Silurian (~430 million years ago)
Bertie Group
Western New York

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