''Stylonuroides'' is a genus of prehistoric

eurypterid 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 ...

. The genus is classified as a

stylonurine Stylonurina is one of two suborders of eurypterids, a group of extinct arthropods commonly known as "sea scorpions". Members of the suborder are collectively and informally known as "stylonurine eurypterids" or "stylonurines". They are known fro ...

but more precise classification has proven difficult, with the genus remaining classified as ''

incertae sedis ' () or ''problematica'' is a term used for a taxonomic group where its broader relationships are unknown or undefined. Alternatively, such groups are frequently referred to as "enigmatic taxa". In the system of open nomenclature, uncertain ...

'' within the suborder. The genus contains two species, ''S. dolichopteroides'' from the

Silurian The Silurian ( ) is a geologic period and system spanning 24.6 million years from the end of the Ordovician Period, at million years ago (Mya), to the beginning of the Devonian Period, Mya. The Silurian is the shortest period of the Paleozoi ...

of Ringerike,

Norway Norway, officially the Kingdom of Norway, is a Nordic country in Northern Europe, the mainland territory of which comprises the western and northernmost portion of the Scandinavian Peninsula. The remote Arctic island of Jan Mayen and t ...

and ''S. orientalis'' from the

Devonian The Devonian ( ) is a geologic period and system of the Paleozoic era, spanning 60.3 million years from the end of the Silurian, million years ago (Mya), to the beginning of the Carboniferous, Mya. It is named after Devon, England, w ...

Lake Shunet Lake Shunet is a meromictic lake near the ''village#Russia, selo'' of Shira, Russia, Shira in the Republic of Khakassia, Russia. It belongs to the Shirin group of lakes. It is located 7 km south of the Lake Shira, in a deep basin, at around 390 m a ...

Southern Siberia South Central Siberia is a geographical region north of the point where Russia, China, Kazakhstan and Mongolia come together. Regions of Asia North Asia The Four Corners At approximately , the borders of Russia, China, Mongolia and Kaza ...

.Dunlop, J. A., Penney, D. & Jekel, D. 2015. A summary list of fossil spiders and their relatives. In World Spider Catalog. Natural History Museum Bern, online at http://wsc.nmbe.ch, version 16.0 http://www.wsc.nmbe.ch/resources/fossils/Fossils16.0.pdf (PDF).

Description

The compound eyes of ''Stylonuroides'' are comparatively large, though their exact shape is unclear due to poor preservation. The posterior margin of the eyes lie in the middle of the

prosoma The cephalothorax, also called prosoma in some groups, is a tagma of various arthropods, comprising the head and the thorax fused together, as distinct from the abdomen behind. (The terms ''prosoma'' and ''opisthosoma'' are equivalent to ''ce ...

. ''Stylonuroides orientalis'' is smaller in size than ''S. dolichopteroides'', with a prosoma measuring about 12 mm. ''S. orientalis'' differs from ''S. dolichopteroides'' in a number of features, including that it preserves processes on the genal angles, a slightly convex posterior margin of the prosoma and slightly more widely set compound eyes. ''S. orientalis'' is based on a single specimen, PIN 1220/1 (consisting of parts of a prosoma and five anterior segments of the opisthosoma), which can be placed in the genus based on a combination of features, including its strongly elongated parabolic prosoma, large compound eyes and the broad marginal rim of the prosoma.

Species

''Stylonuroides'' contains two valid species, with other named species now seen as invalid. * ''Stylonuroides orientalis'' Shpinev, 2012 - Siberia, Russia (

) * ''Stylonuroides dolichopteroides'' Størmer, 1934 - Ringerike, Norway (

) Invalid or reassigned species are listed below: * ''Stylonuroides limbatus'' Clarke & Rudemann, 1912 - New York, United States (

Ordovician The Ordovician ( ) is a geologic period and system, the second of six periods of the Paleozoic Era. The Ordovician spans 41.6 million years from the end of the Cambrian Period million years ago (Mya) to the start of the Silurian Period Mya. ...

), a

pseudofossil Pseudofossils are inorganic objects, markings, or impressions that might be mistaken for fossils. Pseudofossils may be misleading, as some types of mineral deposits can mimic lifeforms by forming what appear to be highly detailed or organized str ...

References

{{Taxonbar, from=Q7629704 Stylonurina Silurian eurypterids Fossils of Norway Eurypterids of Europe Devonian eurypterids Eurypterids of Asia