Eurypterids, often informally called sea scorpions, are a group of extinct arthropods that form the order Eurypterida. The earliest known eurypterids date to the Darriwilian stage of the Ordovician period 467.3 million years ago. The group is likely to have appeared first either during the Early Ordovician or Late Cambrian period. With approximately 250 species, the Eurypterida is the most diverse Paleozoic chelicerate order. Following their appearance during the Ordovician, eurypterids became major components of marine faunas during the Silurian, from which the majority of eurypterid species have been described. The Silurian genus Eurypterus accounts for more than 90% of all known eurypterid specimens. Though the group continued to diversify during the subsequent Devonian period, the eurypterids were heavily affected by the Late Devonian extinction event. They declined in numbers and diversity until becoming extinct during the Permian–Triassic extinction event 251.9 million years ago.
Chasmataspidids, sometime referred to as chasmataspids, are a group of extinct chelicerate arthropods that form the order Chasmataspidida. Chasmataspidids are probably related to horseshoe crabs (Xiphosura) and/or sea scorpions (Eurypterida), with more recent studies suggest that they form a clade (Dekatriata) with Eurypterida and Arachnida. Chasmataspidids are known sporadically in the fossil record through to the mid-Devonian, with possible evidence suggesting that they were also present during the late Cambrian. Chasmataspidids are most easily recognised by having an opisthosoma divided into a wide forepart (preabdomen) and a narrow hind part (postabdomen) each comprising 4 and 9 segments respectively. There is some debate about whether they form a natural group.
Alkenopterus is a genus of prehistoric eurypterid classified as part of the family Onychopterellidae. The genus contains two species, A. brevitelson and A. burglahrensis, both from the Devonian of Germany.
Bassipterus is a genus of eurypterid, an extinct group of aquatic arthropods. Bassipterus is classified as part of the family Adelophthalmidae, the only clade within the derived ("advanced") Adelophthalmoidea superfamily of eurypterids. Fossils of the single and type species, B. virgnicus, have been discovered in deposits of the Late Silurian age in West Virginia and Maryland, United States. The genus is named after Bass, where most of the fossils have been recovered.
Drepanopterus is an extinct genus of eurypterid and the only member of the family Drepanopteridae within the Mycteropoidea superfamily. There are currently three species assigned to the genus. The genus has historically included more species, with nine species having been associated with the genus Drepanopterus. Five of these have since been proven to be synonyms of pre-existing species, assigned to their own genera, or found to be based on insubstantial fossil data. The holotype of one species proved to be a lithic clast.
Nanahughmilleria is a genus of eurypterid, an extinct group of aquatic arthropods. Fossils of Nanahughmilleria have been discovered in deposits of Devonian and Silurian age in the United States, Norway, Russia, England and Scotland, and have been referred to several different species.
Onychopterella is a genus of predatory eurypterid, an extinct group of aquatic arthropods. Fossils of Onychopterella have been discovered in deposits from the Late Ordovician to the Late Silurian. The genus contains three species: O. kokomoensis, the type species, from the Early Pridoli epoch of Indiana; O. pumilus, from the Early Llandovery epoch of Illinois, both from the United States; and O. augusti, from the Late Hirnantian to Early Rhuddanian stages of South Africa.
Pittsfordipterus is a genus of eurypterid, an extinct group of aquatic arthropods. Pittsfordipterus is classified as part of the family Adelophthalmidae, the only clade in the derived ("advanced") Adelophthalmoidea superfamily of eurypterids. Fossils of the single and type species, P. phelpsae, have been discovered in deposits of Silurian age in Pittsford, New York state. The genus is named after Pittsford, where the two only known specimens have been found.
Kiaeropterus is a genus of prehistoric eurypterid classified as part of the Rhenopteridae family. Two species, both from the Silurian period, are known; K. cyclophthalmus from Scotland and K. ruedemanni from Norway.
Tylopterella is a genus of eurypterid, a group of extinct aquatic arthropods. Only one fossil of the single and type species, T. boylei, has been discovered in deposits of the Late Silurian period in Elora, Canada. The name of the genus is composed by the Ancient Greek words τύλη, meaning "knot", and πτερόν, meaning "wing". The species name boylei honors David Boyle, who discovered the specimen of Tylopterella.
Parahughmilleria is a genus of eurypterid, an extinct group of aquatic arthropods. Fossils of Parahughmilleria have been discovered in deposits of the Devonian and Silurian age in the United States, Canada, Russia, Germany, Luxembourg and Great Britain, and have been referred to several different species. The first fossils of Parahughmilleria, discovered in the Shawangunk Mountains in 1907, were initially assigned to Eurypterus. It would not be until 54 years later when Parahughmilleria would be described.
Adelophthalmus is a genus of eurypterid, an extinct group of aquatic arthropods. Fossils of Adelophthalmus have been discovered in deposits ranging in age from the Early Devonian to the Early Permian, which makes it the longest lived of all known eurypterid genera, with a total temporal range of over 120 million years. Adelopththalmus was the final genus of the Eurypterina suborder of eurypterids and consisted the only known genus of swimming eurypterids from the Middle Devonian until its extinction during the Permian, after which the few surviving eurypterids were all walking forms of the suborder Stylonurina.
Unionopterus is a genus of eurypterid, an extinct group of aquatic arthropods commonly known as "sea scorpions". Fossils have been registered from the Early Carboniferous period. The genus contains only one species, U. anastasiae, recovered from deposits of Tournaisian to Viséan stages in Kazakhstan. Known from one single specimen which was described in a publication of Russian language with poor illustrations, Unionopterus' affinities are extremely poorly known.
Bunodes is a genus of synziphosurine, a paraphyletic group of fossil chelicerate arthropods. Bunodes was regarded as part of the clade Planaterga. Fossils of the single and type species, B. lunula, have been discovered in deposits of the Silurian period in Ludlow, England. Bunodes is the type genus of the family Bunodidae, the other genera of the same family being Limuloides. There are 64 direct children of Bunodes.
Pterygotioidea is a superfamily of eurypterids, an extinct group of aquatic arthropods. Pterygotioids were the most derived members of the infraorder Diploperculata and the sister group of the adelophthalmoid eurypterids. The group includes the basal and small hughmilleriids, the larger and specialized slimonids and the famous pterygotids which were equipped with robust and powerful cheliceral claws.
Adelophthalmidae is a family of eurypterids, an extinct group of aquatic arthropods. Adelophthalmidae is the only family classified as part of the superfamily Adelophthalmoidea, which in turn is classified within the infraorder Diploperculata in the suborder Eurypterina.
Strobilopteridae is an extinct family of eurypterids that lived in the Silurian and Devonian periods. The family is one of three families contained in the superfamily Eurypteroidea, which in turn is one of the superfamilies classified as part of the suborder Eurypterina. The family contains two genera, Buffalopterus and Strobilopterus.
Dvulikiaspis is a genus of chasmataspidid, a group of extinct aquatic arthropods. Fossils of the single and type species, D. menneri, have been discovered in deposits of the Early Devonian period in the Krasnoyarsk Krai, Siberia, Russia. The name of the genus is composed by the Russian word двуликий (dvulikij), meaning "two-faced", and the Ancient Greek word ἀσπίς (aspis), meaning "shield". The species name honors the discoverer of the holotype of Dvulikiaspis, Vladimir Vasilyevich Menner.
Forfarella is a genus of chasmataspidid, a group of extinct aquatic arthropods. Fossils have been discovered in deposits of the Early Devonian period. The single and type species, F. mitchelli, is known from one only specimen found in Scotland, in the United Kingdom. Known as BMNH In 60023, it is poorly preserved and its type locality is uncertain, although it might be the Kelly Den stream section near the village of Arbirlot.
Pruemopterus is a genus of eurypterid, an extinct group of aquatic arthropods. The type and only species of Pruemopterus, P. salgadoi, is known only from a single fossil specimen discovered in geological deposits of Early Devonian age in Germany. The name of the genus is derived from the Prüm river and the surrounding Prüm valley, which contains the finding place of the fossil, and the Ancient Greek πτερόν, referring to the eurypterid swimming paddles, and the species name honors the Brazilian photographer and photojournalist Sebastião Salgado.
