''Herefordopterus'' is a genus 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 ...

, an extinct group of aquatic

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. ''Herefordopterus'' is classified as part of the family

Hughmilleriidae Hughmilleriidae (the name deriving from the type genus '' Hughmilleria'', which is named in honor of Scottish geologist Hugh Miller) is a family of eurypterids, an extinct group of aquatic arthropods. The hughmilleriids were the most basal memb ...

, a basal family in the highly derived

Pterygotioidea Pterygotioidea (the name deriving from the type genus ''Pterygotus'', meaning "winged one") is a superfamily of eurypterids, an extinct group of aquatic arthropods. Pterygotioids were the most derived members of the infraorder Diploperculata and ...

superfamily of eurypterids. Fossils of the single and

type species In zoological nomenclature, a type species (''species typica'') is the species name with which the name of a genus or subgenus is considered to be permanently taxonomically associated, i.e., the species that contains the biological type specimen ...

, ''H. banksii'', have been discovered in deposits of

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 Paleozo ...

age in

Herefordshire Herefordshire () is a county in the West Midlands of England, governed by Herefordshire Council. It is bordered by Shropshire to the north, Worcestershire to the east, Gloucestershire to the south-east, and the Welsh counties of Monmouthshire ...

and

Shropshire Shropshire (; alternatively Salop; abbreviated in print only as Shrops; demonym Salopian ) is a landlocked historic county in the West Midlands region of England. It is bordered by Wales to the west and the English counties of Cheshire to th ...

England England is a country that is part of the United Kingdom. It shares land borders with Wales to its west and Scotland to its north. The Irish Sea lies northwest and the Celtic Sea to the southwest. It is separated from continental Europe b ...

. The genus is named after

, where most of the ''Herefordopterus'' fossils have been found. The

specific epithet In taxonomy, binomial nomenclature ("two-term naming system"), also called nomenclature ("two-name naming system") or binary nomenclature, is a formal system of naming species of living things by giving each a name composed of two parts, bot ...

honors Richard Banks, who found several well-preserved specimens, including the first ''Herefordopterus'' fossils. ''Herefordopterus'' is classified in

, a pterygotioid family that is differentiated by their streamlined bodies, the enlargement of its medium-sized

chelicerae The chelicerae () are the mouthparts of the subphylum Chelicerata, an arthropod group that includes arachnids, horseshoe crabs, and sea spiders. Commonly referred to as "jaws", chelicerae may be shaped as either articulated fangs, or similarly ...

and the presence of paired spines on the walking appendages. It was distinguished for combining characteristics of ''

Hughmilleria ''Hughmilleria'' is a genus of eurypterid, an extinct group of aquatic arthropods. Fossils of ''Hughmilleria'' have been discovered in deposits of the Silurian age in China and the United States. Classified as part of the basal family Hughmille ...

'' with those of the derived pterygotioids, showing a more advanced

morphology Morphology, from the Greek and meaning "study of shape", may refer to: Disciplines * Morphology (archaeology), study of the shapes or forms of artifacts * Morphology (astronomy), study of the shape of astronomical objects such as nebulae, galaxies ...

than that of ''Hughmilleria''. With the biggest specimen measuring 12 centimetres (5 inches) in length, ''Herefordopterus'' is considered a eurypterid of small size.

Description

''Herefordopterus'' was a small-sized eurypterid with only 12 cm (5 in) in length, being surpassed in size by other pterygotioids such as ''

Slimonia acuminata ''Slimonia'' is a genus of eurypterid, an extinct group of aquatic arthropods. Fossils of ''Slimonia'' have been discovered in deposits of Silurian age in South America and Europe. Classified as part of the family Slimonidae alongside the relat ...

'' with 100 cm (39 in) or ''

Jaekelopterus rhenaniae ''Jaekelopterus'' is a genus of predatory eurypterid, a group of extinct aquatic arthropods. Fossils of ''Jaekelopterus'' have been discovered in deposits of Early Devonian age, from the Pragian and Emsian stages. There are two known species: the ...

'' and (potentially) '' Erettopterus grandis'' with 2.5 m (8.2 ft). This size makes it the smallest genus and one of the smallest species of the entire Pterygotioidea superfamily, the related ''Hughmilleria wangi'' at 6 cm (3 in) being the smallest one. It had a parabolic (approximately U-shaped) to campanulate (bell-shaped) carapace (head plate) with an angular

anterior Standard anatomical terms of location are used to unambiguously describe the anatomy of animals, including humans. The terms, typically derived from Latin or Greek roots, describe something in its standard anatomical position. This position prov ...

margin that narrows toward the eyes, the second to fifth pair of prosomal appendages with a single pair of short spines on each

podomere The arthropod leg is a form of jointed appendage of arthropods, usually used for walking. Many of the terms used for arthropod leg segments (called podomeres) are of Latin origin, and may be confused with terms for bones: ''coxa'' (meaning hip, pl ...

(leg segments) and large oval and marginal eyes. The ocelli (light-sensitive simple eyes) were relatively large and placed between the posterior part of the eyes. The postabdominal segments (segments 8 to 12) were longer than the preabdominal segments (segments 1 to 7) and lacking of ornamentation. It had 12-13 gnathobasic (of the gnathobase, a lower appendage used in feeding) teeth in the sixth appendage, as in

pterygotid Pterygotidae (the name deriving from the type genus ''Pterygotus'', meaning "winged one") is a family of eurypterids, an extinct group of aquatic arthropods. They were members of the superfamily Pterygotioidea. Pterygotids were the largest known ...

s. The genital operculum (a plate-like segment which contains the genital aperture) of ''Herefordopterus'' was composed by two fused opercular segments posterior to the deltoid plates (two small plates above the genital appendage), which are more clearly expressed in the type B specimens ( assumed to be males). It was ornamented with prominent scales. The

telson The telson () is the posterior-most division of the body of an arthropod. Depending on the definition, the telson is either considered to be the final segment of the arthropod body, or an additional division that is not a true segment on accou ...

(the most posterior segment of the body) was wide anteriorly posteriorly tapering to a lanceolate shape with a keel. It presents a marginal ornamentation of crenulated (slightly notched) margins composed of dark scales. ''Herefordopterus'' stands out for its great resemblance to ''Hughmilleria'' with

derived Derive may refer to: * Derive (computer algebra system), a commercial system made by Texas Instruments * ''Dérive'' (magazine), an Austrian science magazine on urbanism *Dérive, a psychogeographical concept See also * *Derivation (disambiguatio ...

(more "advanced") elements reminiscent of

Slimonidae Slimonidae (the name deriving from the type genus '' Slimonia'', which is named in honor of Welsh fossil collector and surgeon Robert Slimon) is a family of eurypterids, an extinct group of aquatic arthropods. Slimonids were members of the super ...

and

Pterygotidae Pterygotidae (the name deriving from the type genus ''Pterygotus'', meaning "winged one") is a family of eurypterids, an extinct group of aquatic arthropods. They were members of the superfamily Pterygotioidea. Pterygotids were the largest kno ...

, such as its number of gnathobasic teeth or the ornamentation of the telson.

History of research

''Herefordopterus banksii'' was first considered a species of ''Himantopterus'' (a genus now considered synonymous with '' Slimonia''), ''H. banksii'', by

John William Salter John William Salter (15 December 1820 – 2 December 1869) was an England, English natural history, naturalist, geologist, and palaeontologist. Salter was apprenticed in 1835 to James De Carle Sowerby, and was engaged in drawing and engraving ...

in 1856, making it one of the oldest eurypterid species. The first fossils, discovered in Kington, include 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 ''cepha ...

(head) and fragmentary remains of the nine first segments. Salter noted a scale-like sculpturing on its forward margin and related the species to ''H. lanceolatus'' (now tentatively placed in the genus '' Nanahughmilleria''). He decided to dedicate the specific name ''banksii'' to Richard Banks of Kington, who found several well-preserved specimens of ''Himantopterus'' and sent them to Salter. Three years later, Salter erroneously assigned ''H. banksii'' to ''

Pterygotus ''Pterygotus'' is a genus of giant predatory eurypterid, a group of extinct aquatic arthropods. Fossils of ''Pterygotus'' have been discovered in deposits ranging in age from Middle Silurian to Late Devonian, and have been referred to several di ...

'' (''Erettopterus'') based on bilobed telsons of ''Erettopterus spatulatus'' that he misidentified as belonging to ''H. banksii''. In turn, the telsons of ''H. banksii'' were referred to '' Stylonurus megalops'' (now in the genus '' Hardieopterus''). It would not be until 1934 when Størmer classified ''P. (E.) banksii'' in ''Hughmilleria''. ''H. banksii'' was described in more detail in 1951 by Kjellesvig-Waering, who agreed that specimens assigned to ''S. megalops'' should be assigned to ''H. banksii''. However, he was also wrong in assigning a walking leg of '' Salteropterus abbreviatus'' to the hughmilleriid species. Currently, all descriptions prior to 2006 of ''H. banksii'' are considered inadequate or of little use. The separation of ''H. banksii'' as an independent genus was predicted by Størmer in 1973, when he noticed that the morphology of the type B genital appendage was more similar to that of '' Parahughmilleria''. In 2006, O. Erik Tetlie redescribed the species based on the majority of available material. The new study helped to redistribute erroneously assigned material, to reinterpret the morphology of ''H. banksii'' and to question the basality and phylogenetic position of ''Hughmilleria'' with respect to Slimonidae and Pterygotidae. Tetlie erected a new genus due to the obvious similarity with ''Hughmilleria'' with several derived characteristics shared with the slimonids and pterygotids. The name ''Herefordopterus'' derives from

, where the vast majority of its fossils have been found. In addition, the poorly known species ''Hughmilleria acuminata'', previously known only by two telsons, was synonymized with ''Herefordopterus'' due to being anteriorly wide. However, these telsons had a wider portion than usual than in the rest of the telsons of ''H. banksii'', in addition to being completely flattened, although this may be due to the different degree of compression and preservation.

Classification

''Herefordopterus'' is classified within the family

in the superfamily

.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 18.5 http://www.wsc.nmbe.ch/resources/fossils/Fossils18.5.pdf (PDF). Originally, ''Herefordopterus'' was considered a species of ''Himantopterus'', later it would be classified under ''Hughmilleria'' until it was reclassified in its own genus in 2006 by O. Erik Tetlie. ''Herefordopterus'' and ''Hughmilleria'' shared a subtriangular carapace outline with the

s and the wide telson and genital appendages of all three taxa were similar, although the genital appendages of ''Herefordopterus'' and ''Hughmilleria'' were more similar to those of ''Slimonia'' by the division of these into three segments, in contrast to the undivided morphology in the pterygotids. Still, ''Herefordopterus'' and ''Hughmilleria'' differ from pterygotids and

slimonid Slimonidae (the name deriving from the type genus '' Slimonia'', which is named in honor of Welsh fossil collector and surgeon Robert Slimon) is a family of eurypterids, an extinct group of aquatic arthropods. Slimonids were members of the super ...

s by the presence of paired spines on the walking appendages, that along with the characteristics that ''Slimonia'' and ''

Ciurcopterus ''Ciurcopterus'' is a genus of eurypterid, an extinct group of aquatic arthropods. Fossils of ''Ciurcopterus'' have been discovered in deposits of Late Silurian age in North America. Classified as part of the family Pterygotidae, the genus conta ...

'' share, suggest that the hughmilleriids are more distant from the pterygotids than ''Slimonia'' is. Within Hughmilleriidae, both genera possessed a marginal rim much broader anteriorly than posteriorly and spiniferous appendages, but ''Hughmilleria'' had 18-20 gnathobasic teeth on appendage VI, unlike ''Herefordopterus'' and the pterygotids, which had 12-13. Therefore, ''Herefordopterus'' is placed as the

sister taxon In phylogenetics, a sister group or sister taxon, also called an adelphotaxon, comprises the closest relative(s) of another given unit in an evolutionary tree. Definition The expression is most easily illustrated by a cladogram: Taxon A and t ...

(closest relative) of the clade of Slimonidae and Pterygotidae and a more derived form than ''Hughmilleria''. The cladogram presented below, derived from a 2007 study by researcher O. Erik Tetlie, showcases the interrelationships between the pterygotioid eurypterids.

Paleoecology

The Late Silurian of Herefordshire was home to a wide array of different eurypterids, including species of ''

Erettopterus ''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 Lochkov ...

'', ''

Eurypterus ''Eurypterus'' ( ) is an extinct genus of eurypterid, a group of organisms commonly called "sea scorpions". The genus lived during the Silurian period, from around 432 to 418 million years ago. ''Eurypterus'' is by far the most well-studied and ...

'', '' Nanahughmilleria'', ''

Marsupipterus ''Marsupipterus'' is a genus of prehistoric eurypterid with an uncertain classification. The genus contains one species, ''M. sculpturatus'', from the Silurian of England.Dunlop, J. A., Penney, D. & Jekel, D. 2015. A summary list of fossil spider ...

'', ''

Salteropterus ''Salteropterus'' is a genus of eurypterid, an extinct group of aquatic arthropods. Fossils of ''Salteropterus'' have been discovered in deposits of Late Silurian age in Great Britain, Britain. Classified as part of the family Slimonidae, the ge ...

'' and potentially '' Slimonia'' (depending on the identity of ''S. stylops''). This eurypterid fauna coexisted with lingulids,

ostracod Ostracods, or ostracodes, are a class of the Crustacea (class Ostracoda), sometimes known as seed shrimp. Some 70,000 species (only 13,000 of which are extant) have been identified, grouped into several orders. They are small crustaceans, typic ...

s and cephalaspidimorph fish, such as ''

Hemicyclaspis ''Hemicyclaspis'' ( or 'semicircle plate') is an extinct genus of primitive jawless fish, closely related to ''Cephalaspis'', that lived in the Late Silurian ( Pridoli) to Devonian period in what is now Europe and North America. A typical cephal ...

'' and '' Thelodus''. ''Herefordopterus'' lived in a

benthic The benthic zone is the ecological region at the lowest level of a body of water such as an ocean, lake, or stream, including the sediment surface and some sub-surface layers. The name comes from ancient Greek, βένθος (bénthos), meaning "t ...

(at the lowest level of water) environment near an intertidal sandy shore and intertidal sandy mudflat environments. The

lithology The lithology of a rock unit is a description of its physical characteristics visible at outcrop, in hand or core samples, or with low magnification microscopy. Physical characteristics include colour, texture, grain size, and composition. Lit ...

of the site was of green

mudstone Mudstone, a type of mudrock, is a fine-grained sedimentary rock whose original constituents were clays or muds. Mudstone is distinguished from '' shale'' by its lack of fissility (parallel layering).Blatt, H., and R.J. Tracy, 1996, ''Petrology. ...

and

sandstone Sandstone is a clastic sedimentary rock composed mainly of sand-sized (0.0625 to 2 mm) silicate grains. Sandstones comprise about 20–25% of all sedimentary rocks. Most sandstone is composed of quartz or feldspar (both silicates) ...

, with mud cracks and pedogenic carbonate (

calcrete Caliche () is a sedimentary rock, a hardened natural cement of calcium carbonate that binds other materials—such as gravel, sand, clay, and silt. It occurs worldwide, in aridisol and mollisol soil orders—generally in arid or semiarid regions, ...

References

{{Taxonbar, from=Q48813166 Silurian eurypterids Fossil taxa described in 2006 Fossils of England Eurypterids of Europe Pterygotioidea