Erettopterus

Erettopterus Temporal range: Rhuddanian–Lochkovian Llan. W L P Early Dev. Mid. Late Dev.
Fossil of E. bilobus at the Natural History Museum, Vienna.
Scientific classification
Kingdom:	Animalia
Phylum:	Arthropoda
Subphylum:	Chelicerata
Order:	†Eurypterida
Superfamily:	†Pterygotioidea
Family:	†Pterygotidae
Genus:	†Erettopterus Salter in Huxley & Salter, 1859
Type species
†Erettopterus bilobus Salter, 1856
Species
17 species †E. bilobus Salter, 1856 †E. brodiei Kjellesvig-Waering, 1961 †E. canadensis Dawson, 1879 †E. exophthalmus Kjellesvig-Waering & Leutze, 1966 †E. gigas Salter in Huxley & Salter, 1859 †E. globiceps Clarke & Ruedemann, 1912 †E. grandis Pohlman, 1881 †E. holmi Størmer, 1934 †E. laticauda Schmidt, 1883 †E. marstoni Kjellesvig-Waering, 1961 †E. megalodon Kjellesvig-Waering, 1961 †E. osiliensis Schmidt, 1883 †E. qujingensis Ma et al., 2022 †E. serricaudatus Kjellesvig-Waering, 1979 †E. spatulatus Kjellesvig-Waering, 1961 †E. vogti Størmer, 1934 †E. waylandsmithi Kjellesvig-Waering & Caster, 1955
Synonyms
Genus synonymy Himantopterus Salter, 1856, preoccupied ?Necrogammarus Woodward, 1870 Truncatiramus Kjellesvig-Waering, 1961 Synonyms of E. bilobus Himantopterus perornatus Salter, 1856 Pterygotus bilobus var. acidens Woodward, 1869 Pterygotus bilobus var. crassus Woodward, 1869 Pterygotus bilobus var. inornatus Woodward, 1869 Pterygotus bilobus var. perornatus Woodward, 1869 Pterygotus lanarkensis Kjellesvig-Waering, 1964 Pterygotus perornatus var. plicatissimus Salter, 1859 Synonyms of E. osiliensis Pterygotus impacatus Kjellesvig-Waering, 1964 Pterygotus monroensis Kjellesvig-Waering, 1964 Synonyms of E. serricaudatus Erettopterus carinatus Kjellesvig-Waering, 1979

Erettopterus is a genus of large predatory eurypterid, an extinct group of aquatic arthropods. Fossils of Erettopterus have been discovered in deposits ranging from Early Silurian (the Rhuddanian age) to the Early Devonian (the Lochkovian age), and have been referred to several different species. Fossils have been recovered from three continents; Asia, Europe and North America. The genus name is composed by the Ancient Greek words ἐρέττω (eréttō), which means "rower", and πτερόν (pterón), which means "wing", and therefore, "rower wing".

Erettopterus is classified as part of the eurypterid family Pterygotidae, a family differentiated from other eurypterids by their flattened telsons (the most posterior segment of the body) and their modified chelicerae (frontal appendages), ending in well-developed chelae (claws). Although some pterygotid eurypterids, such as Jaekelopterus or Acutiramus grew to gigantic proportions, it is estimated that the largest species of Erettopterus, E. osiliensis, reached 90 cm (35 in). Fragmentary remains suggest much larger sizes, perhaps approaching the largest eurypterids. Erettopterus had a bilobed (divided into two lobes) telson, which is its main characteristic. The forms of chelicerae are very diverse between species, but they are generally very long with small curved teeth without serrations.

Studies on the chelicerae and compound eyes of Erettopterus have revealed that it was a predator with high visual acuity, but it was not as highly specialized or active as Jaekelopterus and Pterygotus, it was more like Slimonia acuminata, and probably used its enlarged chelicerae for grasping rather than a more specialized feeding.