Stylonuroidea is an extinct superfamily of

eurypterid Eurypterids, often informally called sea scorpions, are a group of extinct arthropods that form the Order (biology), order Eurypterida. The earliest known eurypterids date to the Darriwilian stage of the Ordovician period 467.3 Myr, million yea ...

s, an extinct group of

chelicerate The subphylum Chelicerata (from New Latin, , ) constitutes one of the major subdivisions of the phylum Arthropoda. It contains the sea spiders, horseshoe crabs, and arachnids (including harvestmen, scorpions, spiders, solifuges, ticks, and mite ...

arthropod Arthropods (, (gen. ποδός)) are invertebrate animals with an exoskeleton, a Segmentation (biology), segmented body, and paired jointed appendages. Arthropods form the phylum Arthropoda. They are distinguished by their jointed limbs and Arth ...

s commonly known as "sea scorpions". It is one of four superfamilies classified as part of the suborder

Stylonurina 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 from ...

. Stylonuroidea, which lived from the Early Silurian to the

Late 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, wher ...

, were characterized by their last pair of prosomal (head) appendages, which were developed as walking legs, or less commonly developed as swimming legs with paddles formed by the expansion of the two or three penultimate joints. 1955. Merostomata. ''Treatise on Invertebrate Paleontology, Part P Arthropoda 2, Chelicerata'', P36. as Stylonuracea

Description

Stylonuroids are designated as stylonurines with flattened or truncated posterior metastomata margins. Of the four stylonurine superfamilies, the Stylonuroidea is the most poorly known. Whilst the topology of most stylonurine clades fit well with the stratigraphic record, Stylonuroidea is an exception in that the earliest record of the most derived genera (''

Ctenopterus ''Ctenopterus'' is a genus of prehistoric eurypterid of the family Stylonuridae. It contains only one species, ''Ctenopterus cestrotus'' from the Early Silurian of Otisville, New York.Dunlop, J. A., Penney, D. & Jekel, D. 2015. A summary list of ...

'' and '' Laurieipterus'') first appear at the same time as the earliest record of the most primitive genera (''

Parastylonurus ''Parastylonurus'' is a genus of prehistoric eurypterid. It is classified within the Parastylonuridae family and contains three species, ''P. hendersoni'' and ''P. ornatus'' from the Silurian of Scotland and ''P. sigmoidalis'' from the Silurian ...

'' and '' Stylonurella''). Sweep-feeding strategies evolved independently in two of the four stylonurine superfamilies, the Stylonuroidea and the Hibbertopteroidea. In both superfamilies, the adaptations to this lifestyle involves modifications to the spines on their anterior prosomal appendages for raking through the substrate of their habitats. Stylonuroids have fixed spines on appendages II-IV which could have been used as dragnets to rake through the sediments and thus entangling anything in their way.

Systematics and genera

Due to the majority of specimens being incomplete, the internal topology of the Stylonuroidea is among the least well-resolved and supported in the

and the

Eurypterid Eurypterids, often informally called sea scorpions, are a group of extinct arthropods that form the Order (biology), order Eurypterida. The earliest known eurypterids date to the Darriwilian stage of the Ordovician period 467.3 Myr, million yea ...

a at large. This is mostly due to the poor fossil record of many of the genera included within the superfamily, for instance the single known specimen of '' Stylonurus powriensis'' lacks the anterior prosomal appendages and virtually all ventral structures. Similar situations can be seen in many specimens, such as '' Stylonurella spinipes'' not preserving the metastoma or pretelson and telson and '' Pagea sturrocki'' lacking all dorsal structures. The lack of fossil remains compounds the problem of the internal systematics. For instance, the family

Parastylonuridae The Parastylonuridae are a family of eurypterids, an extinct group of chelicerate arthropods commonly known as "sea scorpions". The family is one of two families contained in the superfamily Stylonuroidea (along with Stylonuridae), which in tu ...

is likely

paraphyletic In taxonomy (general), taxonomy, a group is paraphyletic if it consists of the group's most recent common ancestor, last common ancestor and most of its descendants, excluding a few Monophyly, monophyletic subgroups. The group is said to be pa ...

but it is retained as it is due to the lack of complete specimens of the genera included within it, ''

'' and '' Stylonurella''. Superfamily Stylonuroidea Kjellesvig-Waering, 1959 * Family

Waterston, 1979 ** ''

'' Kjellesvig-Waering, 1966 ** '' Stylonurella'' Kjellesvig-Waering, 1966 * Family

Stylonuridae Stylonuridae is a family of eurypterids, an extinct group of chelicerate arthropods commonly known as "sea scorpions". The family is one of two families contained in the superfamily Stylonuroidea (along with Parastylonuridae), which in turn is o ...

Diener, 1924 **''

Pagea ''Pagea'' is a genus of prehistoric eurypterid classified as part of the family Stylonuridae. It contains three species, all from the Devonian (Lochkovian to Pragian); ''P. plotnicki'' from Nunavut, Canada and ''P. sturrocki'' and ''P. symond ...

'' Waterston, 1962 ** '' Soligorskopterus'' Plax ''et al.'', 2018 ** ''

Stylonurus ''Stylonurus'' is a genus of prehistoric eurypterid of the family Stylonuridae. The genus contains three species: ''Stylonurus powriensis'' from the Devonian of Scotland, ''Stylonurus shaffneri'' from the Devonian of Pennsylvania and ''Stylonurus ...

'' Page, 1856 ** Subfamily Laurieipterinae Kjellesvig-Waering, 1966 ***''

'' Clarke & Ruedermann, 1912 *** '' Laurieipterus'' Kjellesvig-Waering, 1966

References

{{Taxonbar, from=Q2359716 Cisuralian extinctions Arthropod superfamilies