''Bassipterus'' ("wing from

Bass Bass or Basses may refer to: Fish * Bass (fish), various saltwater and freshwater species Music * Bass (sound), describing low-frequency sound or one of several instruments in the bass range: ** Bass (instrument), including: ** Acoustic bass gui ...

") 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. ''Bassipterus'' 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 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 ...

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. 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 ...

, ''B. virgnicus'', have 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 ...

age in

West Virginia West Virginia is a state in the Appalachian, Mid-Atlantic and Southeastern regions of the United States.The Census Bureau and the Association of American Geographers classify West Virginia as part of the Southern United States while the Bur ...

and

Maryland Maryland ( ) is a state in the Mid-Atlantic region of the United States. It shares borders with Virginia, West Virginia, and the District of Columbia to its south and west; Pennsylvania to its north; and Delaware and the Atlantic Ocean to ...

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 ...

. The genus is named after Bass, where most of the fossils have been recovered. ''Bassipterus'' was a well-known basal ("primitive") genus that was distinguished from the more derived adelophthalmids by the specialization of its genital operculum (a plate-like segment which contains the genital aperture) and its long and narrow eyes, being '' Pittsfordipterus''s closest relative.

Description

''Bassipterus'' is almost completely known, with the first to fifth pair of limbs and type B genital appendage being the only unknown body parts. The body had a lanceolate (lance-shaped) and streamlined shape. 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") was long, rounded and tray-shaped. 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 ...

( dorsal plate of the head) was surrounded by a narrow marginal rim, with eyes placed frontally, placed intramarginally (within the margin) and unusually long. PE 6139, a 15.2 millimeter (0.6 inch) long carapace, had eyes 4.5 mm (2 in) long and 2.2 mm (0.1 in) wide. The ocelli are preserved, and were placed in the center of the carapace, immediately behind the eyes. The

metastoma The metastoma is a ventral single plate located in the opisthosoma of non-arachnid dekatriatan chelicerates such as eurypterids, chasmataspidids and the genus ''Houia''. The metastoma located between the base of 6th prosomal appendage pair and m ...

(a large plate part of the

abdomen The abdomen (colloquially called the belly, tummy, midriff, tucky or stomach) is the part of the body between the thorax (chest) and pelvis, in humans and in other vertebrates. The abdomen is the front part of the abdominal segment of the torso. ...

) was long, truncated (shortened as by cutting it) at the base and cordate (heart-shaped) in 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 ...

(frontal) part. One specimen preserves a metastoma of 8.3 mm (0.3 in) in length and 5 mm (0.2 in) in width. Of the appendages (limbs), the swimming legs (sixth pair of appendages) are the only known ones. These were 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 ...

''-type (with enlarged seventh and eighth leg segments and the ninth very small), but in this

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 ...

, it was serrated along the anterior edge of the sixth to seventh joints. The terminal joint was a sharped spur. The

mesosoma The mesosoma is the middle part of the body, or tagma, of arthropods whose body is composed of three parts, the other two being the prosoma and the metasoma. It bears the legs, and, in the case of winged insects, the wings. In hymenopterans of t ...

(comprising body segments 1 to 6) was tapered, with the first tergite (dorsal part of the segment) considerably narrower than the rest. The

metasoma The metasoma is the posterior part of the body, or tagma, of arthropods whose body is composed of three parts, the other two being the prosoma and the mesosoma. In insects, it contains most of the digestive tract, respiratory system, and circula ...

(comprising segments 7 to 12) followed the taperation of the mesosoma and ended in a long dirk-like

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 posteriormost division of the body). The telson was smooth in the ventral part, but carinated (with a keel) dorsally towards the end, which was a very sharped point. The specimen PE 6208 had a 32.5 mm (1.3 in) long telson. 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 ...

in ''Bassipterus'' is well known and developed. The carapace was covered by triangular scales. The tergites and abdominal plates had mucrones (sharped points) typical of

, but these were considerably larger and more prominent than in related genera. In some places, the mucrones touched each other and formed a rhombic ornamentation, while in others, they were so elongated that they resembled the linear striations present in the more

("advanced")

Adelophthalmus ''Adelophthalmus'' is a genus of eurypterid, an extinct group of aquatic arthropods. Fossils of ''Adelophthalmus'' have been discovered in deposits ranging in age from the Early Devonian to the Early Permian, which makes it the longest lived of ...

''. The

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, ...

of the genital operculum (a plate-like segment which contains the genital aperture) allows an easy differentiation between ''Bassipterus'' and the other adelophthtalmids. The type A genital appendage ( assumed to represent females) was long, reaching the second pair of abdominal plates, and was divided into three joints. The first had a short, triangular and hastate (with protruding lobes) portion followed by a tubular shaft that ended in two lateral triangular projections at the point of union with the following joint. The second joint was shorter and composed of three different areas. On both sides of the central shaft, two long narrow sclerites (hardened parts), possibly plates, lengthened themselves at their ends. The third joint was very short and finished in two long points reminiscent of ''

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 ...

'', a more basal genus. The appendage in its entirety was covered by triangular mucrones which pointed outwards. The genital operculum differentiates ''Bassipterus'' from other eurypterid genera and suggests a close relationship with '' Pittsfordipterus''.

History of research

''Bassipterus virginicus'' was described by the paleontologists Erik Norman Kjellesvig-Waering and Kenneth Edward Caster based on 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 ...

(PE 6201, an almost complete specimen), seven paratypes and dozens of fragments. Most of the fossils were found in the

Wills Creek Formation Wills Creek Formation is a mapped Silurian bedrock unit in Pennsylvania, Maryland, Virginia, and West Virginia. Description The Wills Creek is defined as a moderately well bedded greenish-gray shale containing local limestone and sandstone zon ...

, as well as an isolated carapace of the same

formation Formation may refer to: Linguistics * Back-formation, the process of creating a new lexeme by removing or affixes * Word formation, the creation of a new word by adding affixes Mathematics and science * Cave formation or speleothem, a secondar ...

Cumberland Cumberland ( ) is a historic county in the far North West England. It covers part of the Lake District as well as the north Pennines and Solway Firth coast. Cumberland had an administrative function from the 12th century until 1974. From 19 ...

(previously referred to ''Hughmilleria''). The name ''Bassipterus'' is translated as "wing from Bass", with the first word of the name referring to the West Virginian

unincorporated community An unincorporated area is a region that is not governed by a local municipal corporation. Widespread unincorporated communities and areas are a distinguishing feature of the United States and Canada. Most other countries of the world either have ...

of Bass and the last word composed of the Greek word πτερόν (''

pteron Pteron ( Gr. ''πτερον'' – ''pteron'' — ''wing'') is an architectural term used by Pliny the Elder for the peristyle of the tomb of Mausolus, which was raised on a lofty podium, and so differed from an ordinary peristyle raised only on a s ...

'', wing). Although Kjellesvig-Waering and Caster initially classified ''Bassipterus'' in the

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 ...

, Victor P. Tollerton, Jr. moved the genus along with others to the new family Adelophthalmidae. In 2004, the paleontologist Odd Erik Tetlie concluded that ''Bassipterus'' was a

synonym A synonym is a word, morpheme, or phrase that means exactly or nearly the same as another word, morpheme, or phrase in a given language. For example, in the English language, the words ''begin'', ''start'', ''commence'', and ''initiate'' are all ...

of ''Parahughmilleria bellistriata'' and the more basal '' Stoermeropterus nodosus''. Although subsequent authors have followed this study, the most accepted

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 ...

classification places ''Bassipterus'' together with ''Pittsfordipterus'', forming a basal clade.

Classification

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

("group") within the

. It was originally described as a hughmilleriid, but since then it has been considered closer to ''Adelophthalmus'' than to ''Hughmilleria''. ''Bassipterus'' and ''Pittsfordipterus'' form a basal ("primitive") group that differentiate them from the other adelophthalmids. This clade is backed by a pair of

synapomorphies In phylogenetics, an apomorphy (or derived trait) is a novel character or character state that has evolved from its ancestral form (or plesiomorphy). A synapomorphy is an apomorphy shared by two or more taxa and is therefore hypothesized to have ...

(shared characteristics different from that of their

latest common ancestor In biology and genetic genealogy, the most recent common ancestor (MRCA), also known as the last common ancestor (LCA) or concestor, of a set of organisms is the most recent individual from which all the organisms of the set are descended. The ...

); relatively long and narrow eyes and a complex termination of the genital appendage. Therefore, ''Pittsfordipterus'' is the

sister group 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 ''Bassipterus''. ''Bassipterus'' was also similar to ''Parahughmilleria'', a derived adelophthalmid whose metastoma, telson and body were slightly differentiated. This has led some authors to synonymize ''Bassipterus'' with ''Parahughmilleria'', though this is not currently supported. 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 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 ...

and the waeringopteroids), as inferred by Odd Erik Tetlie and Markus Poschmann in 2008, based on the results of a 2008 analysis specifically pertaining to the Adelophthalmoidea and a preceding 2004 analysis.

Paleoecology

''Bassipterus'' fossils have been recovered from

deposits of the Late Ludlow (

Ludfordian In the geologic timescale, the Ludfordian is the upper of two chronostratigraphic stages within the Ludlow Series. Its age is the late Silurian Period, and within both the Palaeozoic Era and Phanerozoic Eon. The rocks assigned to the Ludfordian ...

) and Early Pridoli

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 ...

of the Wills Creek Formation of West Virginia and Maryland,

. In the Marylander part of the formation, fossils of other eurypterids have been found, such as ''Eurypterus remipes'' or '' Waeringopterus cumberlandicus'' together with an indeterminate species of 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''. On the other hand, in the West Virginian section, remains of ''W. cumberlandicus'', '' Erettopterus exophthalmus'', ''Parahughmilleria bellistriata'' and ''Stoermeropterus nodosus'' have been associated, as well as unclassified brachiopods and

bivalve Bivalvia (), in previous centuries referred to as the Lamellibranchiata and Pelecypoda, is a class of marine and freshwater molluscs that have laterally compressed bodies enclosed by a shell consisting of two hinged parts. As a group, bival ...

s. ''Bassipterus'' lived in a

lagoon A lagoon is a shallow body of water separated from a larger body of water by a narrow landform, such as reefs, barrier islands, barrier peninsulas, or isthmuses. Lagoons are commonly divided into ''coastal lagoons'' (or ''barrier lagoons'') a ...

al or restricted shallow subtidal (the area where

sunlight Sunlight is a portion of the electromagnetic radiation given off by the Sun, in particular infrared, visible, and ultraviolet light. On Earth, sunlight is scattered and filtered through Earth's atmosphere, and is obvious as daylight when t ...

reaches the bottom of the

ocean The ocean (also the sea or the world ocean) is the body of salt water that covers approximately 70.8% of the surface of Earth and contains 97% of Earth's water. An ocean can also refer to any of the large bodies of water into which the wo ...

) environment. 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 ...

(description of the physical characteristics of the rocks) of the zone was composed of argillaceous (composed of clay-like materials)

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 ...

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 ...

(containing

calcium Calcium is a chemical element with the symbol Ca and atomic number 20. As an alkaline earth metal, calcium is a reactive metal that forms a dark oxide-nitride layer when exposed to air. Its physical and chemical properties are most similar to ...

)

shale Shale is a fine-grained, clastic sedimentary rock formed from mud that is a mix of flakes of clay minerals (hydrous aluminium phyllosilicates, e.g. kaolin, Al2 Si2 O5( OH)4) and tiny fragments (silt-sized particles) of other minerals, especial ...

References

{{Taxonbar, from=Q4868161 Adelophthalmoidea Silurian arthropods of North America Silurian eurypterids Eurypterids of North America Fossil taxa described in 1966