Eurypterus is by far the most well-studied and well-known eurypterid and its fossil specimens probably represent more than 90% of all known eurypterid specimens.
About two dozen families of eurypterids “sea scorpions” are known from the fossil record. Although these ancient predators have a superficial similarity, including a defensive needle-like spike or telson at their tail end, they are not true scorpions. They are an extinct group of arthropods related to spiders, ticks, mites and other extant creepy crawlies.
The first fossil of Eurypterus was found in 1818 by S. L. Mitchill, a fossil collector. It was recovered from the Bertie Formation of New York, near Westmoreland, Oneida County. Mitchill interpreted the appendages on the carapace as barbels arising from the mouth. He consequently identified the fossil as a catfish of the genus Silurus. In 1825, American zoologist James Ellsworth De Kay identified the fossil correctly as an arthropod. He named it Eurypterus remipes and established the genus Eurypterus in the process. The name means "wide wing" or "broad paddle", referring to the swimming legs, from Greek εὐρύς (eurús, wide) and πτερόν (pteron, wing).
However, De Kay thought Eurypterus belonged to branchiopods, a group of crustaceans that includes water fleas. Soon after, Eurypterus lacustris was also discovered in New York in 1835 by the palaeontologist Richard Harlan. Another species was discovered in Estonia in 1858 by Jan Nieszkowski. He considered it to be of the same species as the first discovery (E. remipes); though it has since been renamed Eurypterus tetragonophthalmus.
|Jan Nieszkowski's 1858 dissertation|
More fossils were recovered in great abundance in New York in the 19th century, and elsewhere in eastern Eurasia and North America. Today, Eurypterus remains one of the most commonly found and best-known eurypterid genera, comprising more than 95% of all known eurypterid fossils.
Eurypterids hunted fish in the muddy bottoms of warm shallow seas some 460 to 248 million years ago before moving on to hunting grounds in fresh and brackish water during the latter part of their reign. Their numbers diminished greatly during the Permian-Triassic extinction, becoming extinct by 248 million years ago.
Image: Dorsal and ventral aspects of Eurypterus tetragonophthalmus, from Jan Nieszkowski's 1858 dissertation; By Jan Nieszkowski (1833-1866) - Nieszkowski J. De euryptero remipede: dissertatio inauguralis. Dorpat: H. Laakmann, 1858, Public Domain, https://commons.wikimedia.org/w/index.php?curid=11225856