Eurypterina
| Eurypterina Temporal range: Middle Ordovician - Middle Permian, 467.3–270 Ma |
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| Reconstruction of the pterygotid Pterygotus anglicus. | |
| Scientific classification | |
| Kingdom: | Animalia |
| Phylum: | Arthropoda |
| Subphylum: | Chelicerata |
| Class: | Merostomata |
| Order: | † Eurypterida |
| Suborder: |
† Eurypterina Burmeister, 1843 |
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Eurypterina is one of two suborders of eurypterids, an extinct group of merostomatan arthropods commonly known as "sea scorpions". Members of the suborder are collectively and informally known as "eurypterine eurypterids" or "eurypterines". 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 pterygotids, 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, first appearing around the same time as the Stylonurina in the Middle Ordovician, but going extinct in the Middle Permian, millions of years before the Permian-Triassic extinction event that ended the stylonurines.
The Stylonurina and Eurypterina are most easily distinguished by the morphology of the posteriormost prosomal appendage. In the Stylonurina, this appendage takes the form of a long and slender walking leg, lacking a modified spine (termed podomere 7a). In the Eurypterina, the leg is most usually modified and broadened into a swimming paddle and always inlcudes a podomere 7a.
Swimming eurypterines represent the abosulte majority of both known eurypterid species and known specimens, though the morphology of the walking stylonurines 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.
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