''Eysyslopterus'' is a

genus Genus ( plural genera ) is a taxonomic rank used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In the hierarchy of biological classification, genus com ...

of eurypterid, 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. ''Eysyslopterus'' is classified as part of the

family Family (from la, familia) is a Social group, group of people related either by consanguinity (by recognized birth) or Affinity (law), affinity (by marriage or other relationship). The purpose of the family is to maintain the well-being of its ...

Adelophthalmidae Adelophthalmidae (the name deriving from the type genus ''Adelophthalmus'', meaning "no obvious eyes") is a family of eurypterids, an extinct group of aquatic arthropods. Adelophthalmidae is the only family classified as part of the superfamily ...

, the only

clade A clade (), also known as a monophyletic group or natural group, is a group of organisms that are monophyletic – that is, composed of a common ancestor and all its lineal descendants – on a phylogenetic tree. Rather than the English term, ...

within the

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 ...

("advanced") Adelophthalmoidea

superfamily SUPERFAMILY is a database and search platform of structural and functional annotation for all proteins and genomes. It classifies amino acid sequences into known structural domains, especially into SCOP superfamilies. Domains are functional, str ...

of eurypterids. One fossil 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 ...

, ''E. patteni'', has been discovered in deposits of the Late

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 ...

period ( Ludlow

epoch 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 ...

) in Saaremaa,

Estonia Estonia, formally the Republic of Estonia, is a country by the Baltic Sea in Northern Europe. It is bordered to the north by the Gulf of Finland across from Finland, to the west by the sea across from Sweden, to the south by Latvia, a ...

. The genus is named after ''Eysysla'', the

Viking Vikings ; non, víkingr is the modern name given to seafaring people originally from Scandinavia (present-day Denmark, Norway and Sweden), who from the late 8th to the late 11th centuries raided, pirated, traded and se ...

name for Saaremaa, and ''opterus'', a traditional suffix for the eurypterid genera, meaning "wing". The

species In biology, a species is the basic unit of classification and a taxonomic rank of an organism, as well as a unit of biodiversity. A species is often defined as the largest group of organisms in which any two individuals of the appropriate s ...

name honors William Patten, an American

biologist A biologist is a scientist who conducts research in biology. Biologists are interested in studying life on Earth, whether it is an individual Cell (biology), cell, a multicellular organism, or a Community (ecology), community of Biological inter ...

and

zoologist Zoology ()The pronunciation of zoology as is usually regarded as nonstandard, though it is not uncommon. is the branch of biology that studies the Animal, animal kingdom, including the anatomy, structure, embryology, evolution, Biological clas ...

who discovered the only known fossil of ''Eysyslopterus''. ''Eysyslopterus'' is a little-known basal genus that was distinguished from the rest of adelophthalmids by the position near the head margin of the eyes, different from the rest of its relatives. Its

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 (approximately U-shaped) and with

transverse Transverse may refer to: *Transverse engine, an engine in which the crankshaft is oriented side-to-side relative to the wheels of the vehicle *Transverse flute, a flute that is held horizontally * Transverse force (or ''Euler force''), the tangen ...

deep furrows forming the

ornamentation An ornament is something used for decoration. Ornament may also refer to: Decoration *Ornament (art), any purely decorative element in architecture and the decorative arts *Biological ornament, a characteristic of animals that appear to serve on ...

. With an estimated length of 8 cm (3.1 in), ''Eysyslopterus'' was a small eurypterid. It lived in a nearshore lagoonal quiet community along other eurypterid species.

Description

Like the other

adelophthalmid Adelophthalmidae (the name deriving from the type genus ''Adelophthalmus'', meaning "no obvious eyes") is a family of eurypterids, an extinct group of aquatic arthropods. Adelophthalmidae is the only family classified as part of the superfamily ...

eurypterids, ''Eysyslopterus'' was a small eurypterid. The total size of the only known specimen is estimated at only 8 centimetres (3.1 inches), far from the largest adelophthalmids like '' Adelophthalmus khakassicus'' of 32 cm (12.6 in) in length. ''Eysyslopterus'' is a little known eurypterid, with only one specimen collected that only preserves 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") with no appendages (limbs). The prosoma was rather broad, with a parabolic (approximately U-shaped) outline. It was 19.5 millimetres (0.77 in) long and 22 mm (0.87 in) wide. Although the

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 ...

part of the prosoma is not preserved, the fossil mold indicates a pointed portion. The posterior border was slightly convex. A narrow rim surrounded the lateral margins of the

( dorsal shield of the prosoma). The prosoma surface was gently arched, with the central portion rather level. The eyes were reniform (bean-shaped) and with a thin and light-colored test (external "shield") on its surface. They measured 4.5 mm (0.18 in) in length. The ocelli (simple eyes) were located in the posterior half of the prosoma and consisted of two circular spots. The posterior part was smooth, but the previous part had a distinctive

. This ornamentation extended until the end of the eyes and was composed of

lines developed as deep furrows. ''Eysyslopterus'' was a basal ("primitive")

with respect to the rest of adelophthalmids, with the eyes closer to the margin than to the ocelli, suggesting that the eyes migrated towards a central position from the basal genera to ''Adelophthalmus''.

History of research

Hughmilleria patteni carapace restoration 1934 (outdated)

''Eysyslopterus'' is only known from one single specimen (and is therefore the

holotype A holotype is a single physical example (or illustration) of an organism, known to have been used when the species (or lower-ranked taxon) was formally described. It is either the single such physical example (or illustration) or one of several ...

, AMNH 32720, housed at the

American Museum of Natural History The American Museum of Natural History (abbreviated as AMNH) is a natural history museum on the Upper West Side of Manhattan in New York City. In Theodore Roosevelt Park, across the street from Central Park, the museum complex comprises 26 inter ...

) which preserves the carapace. This

fossil A fossil (from Classical Latin , ) is any preserved remains, impression, or trace of any once-living thing from a past geological age. Examples include bones, shells, exoskeletons, stone imprints of animals or microbes, objects preserved ...

was collected by the American

and

William Patten during his extensive explorations at the Rootsikula Formation in Saaremaa, Estonia (then part of the

Soviet Union The Soviet Union,. officially the Union of Soviet Socialist Republics. (USSR),. was a transcontinental country that spanned much of Eurasia from 1922 to 1991. A flagship communist state, it was nominally a federal union of fifteen national ...

). During a meeting between Patten and the Norwegian paleontologist and geologist

Leif Størmer Leif Størmer (1 July 1905 – 15 May 1979) was a Norwegian paleontologist and geologist. He was professor of historical geology at the University of Oslo from 1946 to 1975. His father was the mathematician Carl Størmer, and his son the mathemat ...

in 1932, Størmer observed Patten's

private collection A private collection is a privately owned collection of works (usually artworks) or valuable items. In a museum or art gallery context, the term signifies that a certain work is not owned by that institution, but is on loan from an individual ...

of eurypterids, among which he recognized a carapace of a new unknown

. He described it in 1934 as belonging to the genus ''

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 ...

patteni'', named after Patten, who died months after the meeting. Størmer noticed several differences between his new species and other ''Hughmilleria'' species, essentially the shape of the prosoma and the form or position of the eyes. He also suggested a close relationship between ''H. patteni'' and other species, especially the Scottish species ''H. lanceolata''. However, in 1961, the American paleontologist Erik Norman Kjellesvig-Waering split ''Hughmilleria'' in 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 ...

, ''H.'' (''Hughmilleria'') for species with large ovoid marginal eyes and ''H.'' (''

Nanahughmilleria ''Nanahughmilleria'' ("dwarf ''Hughmilleria''") is a genus of eurypterid, an extinct group of aquatic arthropods. Fossils of ''Nanahughmilleria'' have been discovered in deposits of Devonian and Silurian age in the United States, Norway, Russia, ...

'') for small reniform intramarginal (within the margin) eyes. Since ''H. patteni'' fulfilled this condition, it was referred to ''H.'' (''Nanahughmilleria''). It was not until 2008 when during a

phylogenetic In biology, phylogenetics (; from Greek φυλή/ φῦλον [] "tribe, clan, race", and wikt:γενετικός, γενετικός [] "origin, source, birth") is the study of the evolutionary history and relationships among or within groups o ...

review of the entire Adelophthalmidae

by the Norwegian Odd Erik Tetlie and German Markus Poschmann paleontologists, ''N. patteni'' was recognized as sufficiently different to represent its own genus due to the anterior position of its eyes, much more exaggerated than in the other adelophthalmid genera. The first part of the generic name is composed of the word ''Eysysla'', the

name for Saaremaa, and the second part by ''opterus'', a suffix commonly used in eurypterids which means "wing" (and therefore, translated as "wing of ''Eysysla''").

Classification

''Eysyslopterus'' is classified as part of the family Adelophthalmidae, the only

("group") within the

Adelophthalmoidea. ''E. patteni'' was originally described as a species of the genus ''Hughmilleria'', but it was considered different enough to represent a new separate genus in 2008. ''Eysyslopterus'' is considered to be the most basal adelophthalmid genus due to the position of its eyes. These are placed closer to the margin than to the ocelli, in contrast to any other adelopthalmid. In fact, the carapace of ''Eysyslopterus'' and other basal genera belonging to superfamilies, ''

Orcanopterus ''Orcanopterus'' is a genus of a eurypterid classified as part of the family Waeringopteridae. The genus contains one species, ''O. manitoulinensis'', from the Ordovician of Manitoulin, Canada. Morphology Limbs ''Orcanopterus'' is estimat ...

'' and ''

Herefordopterus ''Herefordopterus'' is a genus of eurypterid, an extinct group of aquatic arthropods. ''Herefordopterus'' is classified as part of the family Hughmilleriidae, a basal family in the highly derived Pterygotioidea superfamily of eurypterids. Fossi ...

'', were almost identical. In the waeringopteroid ''Orcanopterus'', the eyes were separated from the margin by the marginal rim, whereas in ''Herefordopterus'' they were completely marginal, a feature present in all pterygotioid genera. In addition, the triangular anterior carapace margin present in ''Eysyslopterus'' was shared with ''Hughmilleria'', indicating that it might be a

plesiomorphic In phylogenetics, a plesiomorphy ("near form") and symplesiomorphy are synonyms for an ancestral character shared by all members of a clade, which does not distinguish the clade from other clades. Plesiomorphy, symplesiomorphy, apomorphy, and ...

trait (a trait present in a common ancestor). These characteristics have led some authors to question whether ''Eysyslopterus'' really represents an adelophthalmid or 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 ...

of a group formed by Pterygotioidea and Adelophthalmoidea, but until more fossil material is found this can not be proven. Adelophthalmus irinae

The cladogram below presents the inferred phylogenetic positions of most of the genera included in the three most derived superfamilies of the

Diploperculata Diploperculata is an infraorder of eurypterids, an extinct group of aquatic arthropods commonly known as "sea scorpions". The name, derived from Greek διπλόω ("double") and ''operculum'', refers to the distinguishing feature that unites the ...

infraorder of eurypterids (Adelophthalmoidea, Pterygotioidea and the waeringopteroids), as inferred by Tetlie and Poschmann in 2008, based on the results of a 2008 analysis specifically pertaining to the Adelophthalmoidea and a preceding 2004 analysis.

Paleoecology

The single known specimen of ''Eysyslopterus'' has been recovered from

deposits of the Ludlow

of the Rootsikula Formation of Saaremaa, Estonia. This formation was the

habitat In ecology, the term habitat summarises the array of resources, physical and biotic factors that are present in an area, such as to support the survival and reproduction of a particular species. A species habitat can be seen as the physical ...

of a

fauna Fauna is all of the animal life present in a particular region or time. The corresponding term for plants is ''flora'', and for fungi, it is '' funga''. Flora, fauna, funga and other forms of life are collectively referred to as '' biota''. Zoo ...

of eurypterids, among them ''Erettopterus laticauda'', ''E. osiliensis'', '' Eurypterus tetragonophthalmus'', '' Mixopterus simonsi'' and '' Strobilopterus laticeps''. Fossil remains of indeterminate osteostracid and thelodontid

fish Fish are aquatic, craniate, gill-bearing animals that lack limbs with digits. Included in this definition are the living hagfish, lampreys, and cartilaginous and bony fish as well as various extinct related groups. Approximately 95% of li ...

es have also been found. The habitat in which ''Eysyslopterus'' lived is considered to be a nearshore lagoonal quiet community. 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 ...

(the physical characteristics of the rocks) of the zone was composed of

mudcrack Mudcracks (also known as mud cracks, desiccation cracks or cracked mud) are sedimentary structures formed as muddy sediment Desiccation, dries and contracts.Jackson, J.A., 1997, ''Glossary of Geology'' (4th ed.), American Geological Institute, Ale ...

and

burrow An Eastern chipmunk at the entrance of its burrow A burrow is a hole or tunnel excavated into the ground by an animal to construct a space suitable for habitation or temporary refuge, or as a byproduct of locomotion. Burrows provide a form of sh ...

s of

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

limestone Limestone ( calcium carbonate ) is a type of carbonate sedimentary rock which is the main source of the material lime. It is composed mostly of the minerals calcite and aragonite, which are different crystal forms of . Limestone forms whe ...

."Eurypterid-Associated Biota of the Rootsikula Horizon, Saaremaa, Estonia: Rootsikula, Estonia"
''The Paleobiology Database''.

References

{{Taxonbar, from=Q48850505 Adelophthalmoidea Fossils of Estonia Silurian animals of Europe Silurian eurypterids Eurypterids of Europe Fossil taxa described in 2008