The genus that gave the eurypterid group its name was relatively small and unspecialized. (Its close cousin, the Devonian Pterygotus, was one of the largest arthropods of all time at 2.5m/8 long.) However, Eurypterus was relatively widespread and common, considering the eurypterids' overall rarity. dolostone (waterline) containing 'salt hopper' structures, which indicate hypersaline (extra-salty) conditions.