''Hughmilleria'' 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. Fossils of ''Hughmilleria'' have been discovered in deposits of 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 Paleozo ...

age in

China China, officially the People's Republic of China (PRC), is a country in East Asia. It is the world's most populous country, with a population exceeding 1.4 billion, slightly ahead of India. China spans the equivalent of five time zones and ...

and the

United States The United States of America (U.S.A. or USA), commonly known as the United States (U.S. or US) or America, is a country primarily located in North America. It consists of 50 states, a federal district, five major unincorporated territorie ...

. Classified as part of the basal 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 ...

, the genus contains three species, ''H. shawangunk'' from the eastern

, ''H. socialis'' from

Pittsford, New York Pittsford is a town in Monroe County, New York. A suburb of Rochester, its population was 30,617 at the time of the 2020 census. The Town of Pittsford (formerly part of the town of Northfield) was settled in 1789 and incorporated in 1796. The ...

, and ''H. wangi'' from

Hunan Hunan (, ; ) is a landlocked province of the People's Republic of China, part of the South Central China region. Located in the middle reaches of the Yangtze watershed, it borders the province-level divisions of Hubei to the north, Jiangxi to ...

. The genus is named in honor of the Scottish

geologist A geologist is a scientist who studies the solid, liquid, and gaseous matter that constitutes Earth and other terrestrial planets, as well as the processes that shape them. Geologists usually study geology, earth science, or geophysics, althou ...

Hugh Miller Hugh Miller (10 October 1802 – 23/24 December 1856) was a self-taught Scottish geologist and writer, folklorist and an evangelical Christian. Life and work Miller was born in Cromarty, the first of three children of Harriet Wright (''b ...

. ''H. socialis'' is the type species of

, a

family classified in the superfamily

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 ...

that is differentiated by their streamlined bodies, the enlargement of their 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

appendage An appendage (or outgrowth) is an external body part, or natural prolongation, that protrudes from an organism's body. In arthropods, an appendage refers to any of the homologous body parts that may extend from a body segment, including anten ...

s. With the biggest specimen measuring 20 centimetres (8 inches) in length, ''Hughmilleria'' is considered a eurypterid of small size.

Description

''Hughmilleria'' is the most basal (primitive) known member of the

. It was a small-sized eurypterid, with the largest specimen measuring 20 cm (8 in), being surpassed by other members of its superfamily, 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 ...

'', which measured 100 cm (39 in) in length, and '' Pterygotus grandidentatus'', which could reach 1.75 meters (5 ft 8 in). 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), which was lanceolate and styliform, is distinctly a ''

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 ...

''-like feature. The marginal

compound eyes A compound eye is a visual organ found in arthropods such as insects and crustaceans. It may consist of thousands of ommatidia, which are tiny independent photoreception units that consist of a cornea, lens, and photoreceptor cells which distin ...

, the relatively large

chelae A chela ()also called a claw, nipper, or pinceris a pincer (biology), pincer-like organ at the end of certain limbs of some arthropods. The name comes from Ancient Greek , through New Latin '. The plural form is chelae. Legs bearing a chela are ...

and the cordate (heart-shaped) metastoma (a large plate that is part of the abdomen) show a great resemblance to ''Pterygotus''. The

carapace A carapace is a Dorsum (biology), dorsal (upper) section of the exoskeleton or shell in a number of animal groups, including arthropods, such as crustaceans and arachnids, as well as vertebrates, such as turtles and tortoises. In turtles and tor ...

was parabolic or subquadrate with oval marginal eyes, the chelicerae were able to extend beyond the carapace margin and the appendages II–V were spiniferous. The genus is in various ways similar to the more

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 ...

eurypterids of its superfamily, the Pterygotioidea, however, it lacked the expanded and flattened telson that the

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 and ''Slimonia'' had. This suggests that ''Hughmilleria'' did not need to use the telson as a rudder to swim. ''Hughmilleria'' is distinguished from other members of

by its streamlined body, its subquadrate prosoma (head), its medium-sized chelicerae, its small overall size and the various characteristics it shares with ''Eurypterus''.

History of research

Hughmilleria shawangunk The Eurypterida of New York

The genus ''Hughmilleria'' was erected by the American

Clifton J. Sarle in 1903 to contain the species ''H. socialis'', which was recovered for the first time in the Pittsford Shale Member of the Vernon Formation,

New York New York most commonly refers to: * New York City, the most populous city in the United States, located in the state of New York * New York (state), a state in the northeastern United States New York may also refer to: Film and television * '' ...

. This species is the most abundant species of pterygotioid in the area with around 450 specimens found. The generic name derives from

, a Scottish geologist and writer who found fossils of eurypterids of the Silurian, among them ''Hughmilleria''. A variety of ''H. socialis'' was also described, ''Hughmilleria socialis'' var. ''robusta'', but currently it is considered a synonym of the species mentioned.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). Four years later, a second species was discovered among the fauna of the Shawangunk grit at Otisville. It was described as ''Hughmilleria shawangunk'' and was smaller than ''H. socialis''. The temporal range of ''H. shawangunk'' has been placed between the

Llandovery Llandovery (; cy, Llanymddyfri ) is a market town and community in Carmarthenshire, Wales. It lies on the River Tywi and at the junction of the A40 and A483 roads, about north-east of Carmarthen, north of Swansea and west of Brecon. Histo ...

and

Ludlow epoch In the geological timescale, the Ludlow Epoch (from 427.4 ± 0.5 million years ago to 423.0 ± 2.3 million years ago) occurred during the Silurian Period, after the end of the Homerian Age. It is named for the town of Ludlow in Shropshire, England ...

. The largest specimens measured 12 cm (5 in) in length, and differ from the type species by the carapace, which was broader, and the compound eyes which were larger and more prominent than the eyes of ''H. socialis'', among other aspects. The family

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 ...

was erected in 1912 by

John Mason Clarke John Mason Clarke (April 15, 1857 – May 29, 1925) was an American teacher, geologist and paleontologist. __TOC__ Early career Born in Canandaigua, New York, the fifth of six children of Noah Turner Clarke and Laura Mason Merrill, he attended ...

and

Rudolf Ruedemann Rudolf Ruedemann (October 16, 1864–June 18, 1956) was a German American paleontologist, widely known as an expert in graptolites, enigmatic fossil animals. He worked at the New York State Museum for over 40 years, including a decade as Stat ...

to constitute a group for the genera ''

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 ...

'', '' Slimonia'', '' Hastimima'' and ''Hughmilleria''. However, Erik N. Kjellesvig-Waering emended the family in 1951, when the genera ''Hastimima'', ''Hughmilleria'', ''Grossopterus'' and ''Slimonia'' were referred to their own family, the

, which left ''Pterygotus'' as the only genus within the Pterygotidae. In 1961, Erik N. Kjellesvig-Waering split ''Hughmilleria'' into two

subgenera In biology, a subgenus (plural: subgenera) is a taxonomic rank directly below genus. In the International Code of Zoological Nomenclature, a subgeneric name can be used independently or included in a species name, in parentheses, placed between t ...

, ''Hughmilleria'' (''Hughmilleria'') and ''Hughmilleria'' (''Nanahughmilleria''), although '' Nanahughmilleria'' would be later raised to the genus level. In 2007, a new species of ''Hughmilleria'' from Hunan, China, was described as ''H. wangi'' based on an almost complete specimen (CNU-E-HLT2006001). The specific name is in honor of Junqing Wang, who found the fossil of the species in 1992. This species was recovered from the Xiaoxiyu Formation of Hunan, in deposits that suggest that it lived in the

Telychian In the geologic timescale, the Telychian is the geologic age, age of the Llandovery Epoch of the Silurian geologic period, Period of the Paleozoic geologic era, Era of the Phanerozoic geologic eon, Eon. The Telychian Age was between 438.5 ± 1.2 ...

age of the Silurian, which makes it the oldest eurypterid discovered in China. ''H. wangi'' differs from the North American species by the presence of epimera (lateral "extensions" of the segment) on the entire postabdomen and a slightly wider carapace than in the other species. Measuring 6 cm (2 in) in length, ''H. wangi'' is the smallest known species of ''Hughmilleria'' and of the Pterygotioidea superfamily. In addition, if the problematic ''H. lanceolata'', which has been suggested by some researchers to belong to this genus, really did so, it would extend the range of ''Hughmilleria'' to the Silurian of Scotland. It was originally described as a new species of the new genus ''Himantopterus'' by the English geologist and paleontologist

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 ...

. The body of this species was elongate and attenuated behind. Its telson was lanceolated and its swimming legs were narrow. This species has also been related to ''Nanahughmilleria'', but recent studies suggest that ''H. lanceolata'' was probably closer to Eurypteroidea. However, the lack of eyes on every specimen of ''H. lanceolata'' hinders the resolution of its phylogenetic position.

Classification

''Hughmilleria'' is classified within the family

in the superfamily

. Historically ''Hughmilleria'' was first considered a member of the

until it was assigned to its own family alongside other genera that would later be reclassified. ''Hughmilleria'' and ''Herefordopterus'' shared a subtriangular carapace outline with the pterygotids and the wide telson and genital appendages of all three taxa were similar, although the genital appendages of ''Hughmilleria'' and ''Herefordopterus'' 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, ''Hughmilleria'' and ''Herefordopterus'' differed from pterygotids and slimonids by the presence of paired spines on the walking appendages, that along with the characteristics that ''Slimonia'' and '' Ciurcopterus'' share, suggest that the hughmilleriids were more distant from the pterygotids than ''Slimonia'' was. Within Hughmilleriidae, both genera possessed a marginal rim much broader anteriorly than posteriorly and appendages spiniferous of ''Hughmilleria''-type, but ''Hughmilleria'' had 18-20 gnathobasic (of the gnathobase, a lower appendage used in the alimentation) teeth on appendage VI, unlike ''Herefordopterus'' and the pterygotids, who had 12-13. Therefore, ''Hughmilleria'' represents the most basal form of Pterygotioidea. According to Clifton J. Sarle, ''Hughmilleria'' was very similar to ''Eurypterus'', and could be confused with a species of this genus if it was not for the presence of the marginal position of the eyes and the relatively large

. However, by its cordate metastoma, the intramarginal to marginal position of the

, the slightly longer preoral appendages, less developed swimming legs and the opercular appendage, ''Hughmilleria'' was more like ''Pterygotus''.Clarke, J. K., Ruedemann R. (1912) " The Eurypterida of New York" The cladogram presented below, derived from a 2007 study by researcher O. Erik Tetlie, showcases the interrelationships between the pterygotioid eurypterids.

Paleoecology

Fossils of ''Hughmilleria'' have been found in

deposits from the

and

Ludlow Ludlow () is a market town in Shropshire, England. The town is significant in the history of the Welsh Marches and in relation to Wales. It is located south of Shrewsbury and north of Hereford, on the A49 road which bypasses the town. The t ...

epochs In chronology and periodization, an epoch or reference epoch is an instant in time chosen as the origin of a particular calendar era. The "epoch" serves as a reference point from which time is measured. The moment of epoch is usually decided by ...

. Together with its close relatives, ''Hughmilleria'' dominated the communities in

brackish Brackish water, sometimes termed brack water, is water occurring in a natural environment that has more salinity than freshwater, but not as much as seawater. It may result from mixing seawater (salt water) and fresh water together, as in estuari ...

and

fresh water Fresh water or freshwater is any naturally occurring liquid or frozen water containing low concentrations of dissolved salts and other total dissolved solids. Although the term specifically excludes seawater and brackish water, it does include ...

, while ''

'' and ''

'' dominated marine environments. The Silurian deposits of the Pittsford Shale Member in which fossils of ''H. socialis'' have been found shelter various faunas of eurypterids, including '' Mixopterus multispinosus'', '' Erettoperus osiliensis'', '' Eurypterus pittsfordensis'' and '' Carcinosoma spiniferus'', among others. Fossils from other organisms were also found, such as the

crustacean Crustaceans (Crustacea, ) form a large, diverse arthropod taxon which includes such animals as decapods, seed shrimp, branchiopods, fish lice, krill, remipedes, isopods, barnacles, copepods, amphipods and mantis shrimp. The crustacean group ...

Ceratiocaris ''Ceratiocaris'' is a genus of paleozoic phyllocarid crustaceans whose fossils are found in marine strata from the Upper Ordovician until the genus' extinction during the Silurian. They are typified by eight short thoracic segments, seven longe ...

'' and the

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 ...

'' Leperditia''. Geological features of the formation, such as the friable and

calcareous Calcareous () is an adjective meaning "mostly or partly composed of calcium carbonate", in other words, containing lime or being chalky. The term is used in a wide variety of scientific disciplines. In zoology ''Calcareous'' is used as an adje ...

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. ...

, the

argillaceous Clay minerals are hydrous aluminium phyllosilicates (e.g. kaolin, Al2 Si2 O5( OH)4), sometimes with variable amounts of iron, magnesium, alkali metals, alkaline earths, and other cations found on or near some planetary surfaces. Clay minerals ...

dolomite Dolomite may refer to: *Dolomite (mineral), a carbonate mineral *Dolomite (rock), also known as dolostone, a sedimentary carbonate rock *Dolomite, Alabama, United States, an unincorporated community *Dolomite, California, United States, an unincor ...

and 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 ...

and associated biota suggests that the environment was marginal marine, very shallow and probably brackish.

References

{{Taxonbar, from=Q1910855 Pterygotioidea Silurian eurypterids Fossils of the United States Fossil taxa described in 1903 Eurypterids of North America Eurypterids of Asia Bertie Formation