This fossil is a nearly complete specimen of Acutiramus, a
pterygotid eurypterid, with its claws folded back towards the body when
the animal molted. Note the large eyes and the division of the body
into segments, named tergites.
YPM catalog no. 218956
Ridgemont Quarry, Late Silurian deposit near Niagara Falls, Fort Erie, Ontario, Canada
Eurypterids are an extinct group of chelicerates, arthropods whose
modern relatives include the horseshoe crabs, scorpions, spiders, mites
and ticks. Most common in rocks of Silurian age (444 to 416 million
years ago), they ranged from the Ordovician Period (approximately 480
Mya) until the end of the Permian (approximately 250 Mya), when they
They are aptly described by their common name, sea scorpions, because they look much like swimming versions of these living land animals. Yet, apart from living in water, they differ from scorpions in several important respects, most striking being their tendency to grow to enormous sizes!