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Eurypterina is one of two suborders of , an extinct group of chelicerate commonly known as "sea scorpions". Eurypterine eurypterids are sometimes informally known as "swimming eurypterids". They are known from fossil deposits worldwide, though primarily in North America and Europe.
Seventy-five percent of eurypterid species are eurypterines; this represents 99% of specimens. The superfamily Pterygotioidea is the most species-rich clade, with 56 species, followed by the Adelophthalmoidea with 43 species; as sister taxa, they comprise the most derived eurypterines. Pterygotioidea includes the , which are the only eurypterids known to have a cosmopolitan distribution.
Though more numerous both in specimens and taxa, the eurypterines have the shorter temporal range of the two eurypterid suborders. They first appeared around the same time as the Stylonurina in the Middle Ordovician. The suborder faced a slow extinction during the Middle Devonian and Late Devonian, possibly tied to the emergence of jawed vertebrates. Every Eurypterine genus and lineage went extinct before the Carboniferous save for Adelophthalmus which would go extinct in the Early Permian, millions of years before the Permian-Triassic extinction event that ended the stylonurines.
Swimming eurypterines represent the absolute majority of both known eurypterid species and known specimens, though the morphology of the walking Stylonurina is almost as diverse in appearance, and the fossil record of the eurypterines may therefore simply be more complete than that of the stylonurines, possibly due to varying habitat preferences.
The Megalograptoidea were likely the first major successful group of eurypterids, evidenced by a Late Ordovician radiation. All known members of the Megalograptoidea are from the Middle to Late Ordovician of Laurentia, though potential records from the Silurian of Baltica are known in the form of the genus Holmipterus (though its classification as a megalograptoid is questionable).
Eurypteroidea are known from Laurentia and Baltica, with one known species from Avalonia. Eurypterus and other eurypteroids appear to have been unable to spread beyond waters. The genus Eurypterus in particular dominated many Silurian eurypterid faunas of Laurentia. Despite its abundance, it appears to not have originated in Laurentia, the earliest records of the genus are from Baltica and Eurypterus was thus likely an Invasive species in Laurentia, albeit one that managed to adapt well to the new habitats.
The majority of carcinosomatoid taxa are also known from Laurentia, Baltica and Avalonia. Isolated and fragmentary fossils from the Late Silurian of Vietnam and the Czech Republic show that the of Annamia and Perunica were within the geographical range of the carcinosomatoids. Only a few basal carcinosomatoids (e.g. Carcinosoma and Paracarcinosoma) have been found in deeper waters whilst the more derived forms, such as Mixopterus and Lanarkopterus have not. Basal carcinosomatoids (Carcinosomatidae) are likely responsible for the fossil remains in Vietnam and the Czech Republic and may have had a distribution similar to the cosmopolitan distribution of the Pterygotioidea, though were not as common nor as successful.
Adelophthalmoids were the longest lasting clade of eurypterines, becoming extinct in the Middle Permian, this is in part due to the survival of Adelophthalmus beyond the Middle Devonian. The earliest records of the genus are from the Early Devonian of western Germany, but following the amalgamation of Pangaea during the Carboniferous and Permian, the genus gained an almost cosmopolitan distribution. The basalmost species in the entire clade are from Baltica and most of the evolution within the basal members took place in Laurussia. By the Devonian, representatives were found in both Siberia and Australia long before the formation of Pangaea.
Although the Pterygotioidea only existed for a period of about 40 million years during a time when most continents were widely separated, the clade is the eurypterid clade with the most cosmopolitan distribution. Like other eurypterines, they are most common in Laurentia, Baltica and Avalonia, but are also found commonly in other . Fossil remains have been recovered from Australia, Libya, Algeria, Morocco, Florida, Saudi Arabia, Iberia, South America, vast swaths of Gondwana, Bohemia and Siberia. The earliest pterygotioids are from the latest Llandovery of Scotland, Laurentia and South China and this mobility makes it difficult to pinpoint the geographical origin of the clade, though it is speculated to have been close to or in Laurentia like the Adelophthalmoidea.
In contrast to the Megalograptoidea, the Eurypteroidea is a rather well-known clade that contains around 90% of all known eurypterid specimens. They were closely related, supported by numerous similarities, to the Carcinosomatoidea. The Carcinosomatoidea have a poorly resolved internal phylogeny, though can be easily recognised by scorpion-like appearance and heavily spinose appendages.
Pterygotioidea and Adelophthalmoidea are the two most derived clades as well as the most taxonomically diverse ones. Adelophthalmoidea contains 43 species, whereas Pterygotioidea contains 56. The superfamilies classified as part of Eurypterina contain the following families:'', a Pterygotioidea. At a length of 2.5 meters, it is one of the largest to have ever lived.]] Suborder Eurypterina Burmeister, 1843
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