Stylonurina is one of two

suborders Order () is one of the eight major hierarchical taxonomic ranks in Linnaean taxonomy. It is classified between family and class. In biological classification, the order is a taxonomic rank used in the classification of organisms and recognized ...

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

s, a group of extinct

arthropod Arthropods ( ) are invertebrates in the phylum Arthropoda. They possess an arthropod exoskeleton, exoskeleton with a cuticle made of chitin, often Mineralization (biology), mineralised with calcium carbonate, a body with differentiated (Metam ...

s commonly known as "sea scorpions". Members of the suborder are collectively and informally known as "stylonurine eurypterids" or "stylonurines". They are known from deposits primarily in

Europe Europe is a continent located entirely in the Northern Hemisphere and mostly in the Eastern Hemisphere. It is bordered by the Arctic Ocean to the north, the Atlantic Ocean to the west, the Mediterranean Sea to the south, and Asia to the east ...

and

North America North America is a continent in the Northern Hemisphere, Northern and Western Hemisphere, Western hemispheres. North America is bordered to the north by the Arctic Ocean, to the east by the Atlantic Ocean, to the southeast by South Ameri ...

, but also in

Siberia Siberia ( ; , ) is an extensive geographical region comprising all of North Asia, from the Ural Mountains in the west to the Pacific Ocean in the east. It has formed a part of the sovereign territory of Russia and its predecessor states ...

. Compared to the other suborder,

Eurypterina Eurypterina is one of two suborders of eurypterids, an extinct group of chelicerate arthropods commonly known as "sea scorpions". Eurypterine eurypterids are sometimes informally known as "swimming eurypterids". They are known from fossil depos ...

, the stylonurines were comparatively rare and retained their posterior prosomal appendages for walking. Despite their rarity, the stylonurines have the longest temporal range of the two suborders. The suborder contains some of the oldest known eurypterids, such as ''

Brachyopterus ''Brachyopterus'' is a genus of prehistoric eurypterid of the family Rhenopteridae. It is one of the earliest known eurypterids, having been recovered from Middle Ordovician deposits in Montgomeryshire, Wales.Dunlop, J. A., Penney, D. & Jekel, D. ...

'', from the

Middle Ordovician The Ordovician ( ) is a geologic period and system, the second of six periods of the Paleozoic Era, and the second of twelve periods of the Phanerozoic Eon. The Ordovician spans 41.6 million years from the end of the Cambrian Period Ma (milli ...

as well as the youngest known eurypterids, from the

Late Permian Late or LATE may refer to: Everyday usage * Tardy, or late, not being on time * Late (or the late) may refer to a person who is dead Music * ''Late'' (The 77s album), 2000 * Late (Alvin Batiste album), 1993 * Late!, a pseudonym used by Dave Groh ...

. They remained rare throughout the Ordovician and Silurian, though the radiation of the mycteropoids (a group of large sweep-feeding forms) in the

Late Devonian The Devonian ( ) is a geologic period and system of the Paleozoic era during the Phanerozoic eon, spanning 60.3 million years from the end of the preceding Silurian period at million years ago ( Ma), to the beginning of the succeeding ...

and

Carboniferous The Carboniferous ( ) is a Geologic time scale, geologic period and System (stratigraphy), system of the Paleozoic era (geology), era that spans 60 million years, from the end of the Devonian Period Ma (million years ago) to the beginning of the ...

is the last major radiation of the eurypterids before their extinction in the

Permian The Permian ( ) is a geologic period and System (stratigraphy), stratigraphic system which spans 47 million years, from the end of the Carboniferous Period million years ago (Mya), to the beginning of the Triassic Period 251.902 Mya. It is the s ...

. Though the Eurypterina contains several famous giant eurypterids such as '' Pterygotus'' and ''

Jaekelopterus ''Jaekelopterus'' is a genus of predatory eurypterid Eurypterids, often informally called sea scorpions, are a group of extinct marine arthropods that form the Order (biology), order Eurypterida. The earliest known eurypterids date to the ...

'', the Stylonurina gave rise to large forms as well, several larger than a metre in length. The largest known stylonurine was ''

Hibbertopterus scouleri ''Hibbertopterus'' is a genus of eurypterid, a group of extinct marine arthropods. Fossils of ''Hibbertopterus'' have been discovered in deposits ranging from the Devonian period in Belgium, Scotland and the United States to the Carboniferous pe ...

'', with a potential length of almost .

Description

Stylonurina contains a wide variety of different genera and species. They are all unified by possessing transverse sutures on the ventral plates and lacking a modified podomere 7a on appendage VI. The suborder is divided into four major superfamilies; the

Rhenopteroidea The Rhenopteridae are a family of eurypterids, an extinct group of chelicerate arthropods commonly known as "sea scorpions". The family is the only family currently contained in the superfamily Rhenopteroidea, one of four superfamilies classifie ...

Stylonuroidea Stylonuroidea is an extinct superfamily of eurypterids, an extinct group of chelicerate arthropods commonly known as "sea scorpions". It is one of four superfamilies classified as part of the suborder Stylonurina. Stylonuroidea, which lived from ...

, Kokomopteroidea and Mycteropoidea. The most primitive of these, the Rhenopteroidea, includes several previously enigmatic genera, such as ''

'', '' Kiaeropterus'' and '' Rhenopterus'', all united by a rounded posterior margin to the metastoma and the prosomal appendage III bearing single fixed spines. ''Brachyopterus'' is also one of the oldest known genera of

, being from the

. The least well-supported group is the

, containing the problematic genera '' Stylonurus'' and '' Stylonurella'', partly due to the incomplete nature of the only known specimen of '' Stylonurus powriei'' which does not preserve the anterior prosomal appendages or any details of the ventral structures. Specimens of other members of the group are similarly incomplete, with '' Stylonurella spinipes'' not preserving the metastoma or pretelson and telson and '' Pagea sturrocki'' not preserving any dorsal structures. The superfamilies Mycteropoidea and Kokomopteroidea are sister groups, united by a median ridge on the carapace between the lateral eyes and a distal thickening to the podomeres of the prosomal appendages. Though sometimes classified as an order separate from

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

a itself, the hibbertopterids are clearly recovered as stylonurine eurypterids in the latest analyses of the group.

Convergent evolution of sweep-feeding

Strategies for sweep-feeding (raking through the substrate in search of prey) evolved independently in two of the four stylonurine superfamilies, the

and the Mycteropoidea. 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. Rhenopteroids, kokomopterids and parastylonurids retained primitive prosomal appendages II-IV that were unsuited for sweep-feeding and likely adopted scavenging, whilst the hardieopterids may have been benthic bottomdwellers living partially buried in the substrate. 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, whilst the mycteropoids, which have some of the most extreme adaptations, likely were more selective and specialized. Mycteropoids possess modified blades on their anterior prosomal appendages that feature sensory setae. The tactile function of these might have allowed mycteropoids to select prey from the sediments in a way that stylonuroids could not.

Systematics

Historically, the phylogeny and systematics of the Stylonurina have been far less well understood and less resolved than that of the

. Many historical analyses were limited in scope or resolution and the unique hibbertopterids have even on occasion been suggested to be a separate, but closely related, order to Eurypterida, but have lacked an analysis either proving or disproving such an idea. Lamsdell ''et al''. (2011) performed the first major and comprehensive analysis of the suborder, which permitted a substantial systematic revision and comparisons to other eurypterid clades. Brachyopterus

The phylogenetic analysis established that Stylonurina indeed was a monophyletic group composed of four clades: the

, Kokomopteroidea and Mycteropoidea. These superfamilies in turn contain the following

families Family (from ) is a group of people related either by consanguinity (by recognized birth) or affinity (by marriage or other relationship). It forms the basis for social order. Ideally, families offer predictability, structure, and safety as ...

(and one

genus Genus (; : genera ) is a taxonomic rank above species and below family (taxonomy), family as used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In bino ...

incertae sedis or is a term used for a taxonomy (biology), 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, uncertainty ...

''): Suborder Stylonurina Diener, 1924 * '' Stylonuroides'' (''

'') Kjellesvig-Waering, 1966 * Superfamily

Størmer, 1951 ** Family

Rhenopteridae The Rhenopteridae are a family of eurypterids, an extinct group of chelicerate arthropods commonly known as "sea scorpions". The family is the only family currently contained in the superfamily Rhenopteroidea, one of four superfamilies classifie ...

Størmer, 1951 * Superfamily

Kjellesvig-Waering, 1959 ** 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 turn ...

Waterston, 1979 ** Family Stylonuridae Diener, 1924 * Superfamily Kokomopteroidea Kjellesvig-Waering, 1966 ** Family Kokomopteridae Kjellesvig-Waering, 1966 ** Family Hardieopteridae Tollerton, 1989 * Superfamily Mycteropoidea Cope, 1886 ** Family Drepanopteridae Kjellesvig-Waering, 1966 ** Family Hibbertopteridae Kjellesvig-Waering, 1959 ** Family Mycteroptidae Cope, 1886 The Eurypterida of New York plate 54

The cladogram presented below showcases the phylogeny of the Stylonurina as presented by Lamsdell et al. (2010). '' Alkenopterus'' (here shown as a rhenopterid) has since been reclassified as a basal eurypterine.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).

References

{{Taxonbar, from=Q2359714 Ordovician first appearances Permian extinctions Arthropod suborders

Description

Convergent evolution of sweep-feeding

Systematics

See also

References