Carcinosoma
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''Carcinosoma'' (meaning "crab body") is a genus of
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 ...
, an extinct group of aquatic
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. Fossils of ''Carcinosoma'' are restricted to deposits of
late Silurian The Silurian ( ) is a geologic period and system spanning 23.5 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 third and shortest period of t ...
(Late
Llandovery Llandovery (; ) is a market town and community (Wales), community in Carmarthenshire, Wales. It lies on the River Tywi and at the junction of the A40 road, A40 and A483 road, A483 roads, about north-east of Carmarthen, north of Swansea and w ...
to Early Pridoli) age. Classified as part of the family Carcinosomatidae, which the genus lends its name to, ''Carcinosoma'' contains seven species from
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 ...
and
Great Britain Great Britain is an island in the North Atlantic Ocean off the north-west coast of continental Europe, consisting of the countries England, Scotland, and Wales. With an area of , it is the largest of the British Isles, the List of European ...
. Carcinosomatid eurypterids had unusual proportions and features compared to other eurypterids, with a broad abdomen, thin and long tail and spined and forward-facing walking appendages. They were not as streamlined as other groups but had considerably more robust and well developed walking appendages. In ''Carcinosoma'', these spined walking appendages are thought to have been used to create a trap to capture prey in. The
telson The telson () is the hindmost division of the body of an arthropod. Depending on the definition, the telson is either considered to be the final segment (biology), segment of the arthropod body, or an additional division that is not a true segm ...
(the posteriormost division of the body) of ''Carcinosoma'' appears to have possessed distinct segmentation, ''Carcinosoma'' is the only known eurypterid to possess this feature. At in length, the species ''C. punctatum'' is the largest carcinosomatoid eurypterid by far and is among the largest eurypterids overall, rivalling the large
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 ...
eurypterids (such as ''
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 ...
'') in size. Other species of the genus were considerably smaller, with most ranging from to in length.


Description

''Carcinosoma'' was among the largest
eurypterids Eurypterids, often informally called sea scorpions, are a group of extinct marine arthropods that form the order Eurypterida. The earliest known eurypterids date to the Darriwilian stage of the Ordovician period, 467.3 million years ago. The ...
, with isolated fossil remains consisting of a long
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 ...
(a plate overlaying the coxae of the first six appendages) of the species ''C. punctatum'' indicating a full length of . Fossil prosomal appendages (appendages attached to the head) referred to the species could possibly increase this estimate to an overall length of around . This massive size makes ''C. punctatum'' the largest of all known carcinosomatoid eurypterids and it rivals the largest
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 ...
eurypterids, such as the long ''
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 ...
'', in size. Other species of ''Carcinosoma'' were smaller, most being in the range of to in length. Perhaps the most recognizable features of ''Carcinosoma'' are its spined appendages and its broad and flattened
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. Wasps, bees and a ...
(the first six segments of its abdomen). Carcinosomatid eurypterids such as ''Carcinosoma'' had less streamlined bodies than those of some other groups, notably the highly streamlined pterygotid eurypterids. In contrast, the walking legs of the carcinosomatids were in general more robust and better developed. Indeed, the walking legs (the second to fifth pair of appendages) were stout and strong and increased in size
anteriorly Standard anatomical terms of location are used to describe unambiguously the anatomy of humans and other animals. The terms, typically derived from Latin or Greek language, Greek roots, describe something in its standard anatomical position. Thi ...
, from the fifth to third pair of appendages, though the first pair of appendages were much shorter than the following pairs. As such, the second pair of walking legs were the longest. Each walking appendage possessed long and curved spines, often two such spines occurring per joint. These spines are one of the defining features of the carcinosomatid family, along with that the swimming legs have slightly elongated and expanded seventh and eighth
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, : ...
s (leg segments). The body of ''Carcinosoma'' was somewhat oddly proportioned in comparison to other eurypterids, though similar to that of related carcinosomatids (particularly '' Eusarcana''). The preabdomen (frontal part of the body) was broad and ovally shaped whilst the postabdomen (the posterior part of the body) was narrow and cylindrical. 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 subtriangular in shape with the small compound eyes placed at the front. The
metasoma The metasoma is the posterior part of the body, or tagma (biology), 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 sy ...
of ''Carcinosoma'' was covered in fine and elongated scales and was quite flat, a feature which separates the genus from ''Eusarcana'' where the metasoma was almost cylindrical.


Color

A well-preserved specimen of ''C. newlini'', specimen number 502 in the collections of the
American Museum of Natural History The American Museum of Natural History (AMNH) is a natural history museum on the Upper West Side of Manhattan in New York City. Located in Theodore Roosevelt Park, across the street from Central Park, the museum complex comprises 21 interconn ...
(collected in the Kokomo Formation of
Indiana Indiana ( ) is a U.S. state, state in the Midwestern United States, Midwestern region of the United States. It borders Lake Michigan to the northwest, Michigan to the north and northeast, Ohio to the east, the Ohio River and Kentucky to the s ...
), preserves the integument in enough detail to determine the coloration ''C. newlini'' would have possessed in life. By surveying the distribution of fossilized pigment cells and comparing them with those of modern
scorpion Scorpions are predatory arachnids of the Order (biology), order Scorpiones. They have eight legs and are easily recognized by a pair of Chela (organ), grasping pincers and a narrow, segmented tail, often carried in a characteristic forward cur ...
s, scientists were able to see the pattern and specific colors ''C. newlini'' would have possessed in life. Overall, the color was similar to that of modern scorpions and to that of another eurypterid which had been similarly studied, '' Megalograptus ohioensis''. The dorsal side of the prosoma, mesosoma and the tergites (segments) of the metasoma were light brown while elongated scales alongside the exoskeleton were darker brown grading into black at the apex of the scales. Smaller scales alongside the edges of the metasomal tergites were also brown but contrasted against the lighter brown of the other integument. The operculum (the first and second abdominal segments) and the plates of the abdomen were brown but lighter than the tergites and their scales were, as with the other scales, darker than the surrounding integument. Black-tipped scales also occurred on the legs, where the general integument was dark brown. The spines of the walking legs were dark brown but black at their tips. The flattened scales on the swimming paddles also graded into black, though the paddle was otherwise brown. The coxae were light brown, with darker scales. The gnathobases ("tooth-plates" on the coxae used when feeding) were completely black, as were the
telson The telson () is the hindmost division of the body of an arthropod. Depending on the definition, the telson is either considered to be the final segment (biology), segment of the arthropod body, or an additional division that is not a true segm ...
(the posteriormost division of the body) whose color contrasted with the preceding and adjacent brown segment.


Size

''Carcinosoma'' ranged in size from to in length, with the largest species by far being ''C. punctatum'', known from the
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, Engl ...
of
England England is a Countries of the United Kingdom, country that is part of the United Kingdom. It is located on the island of Great Britain, of which it covers about 62%, and List of islands of England, more than 100 smaller adjacent islands. It ...
, and the smallest being ''C. libertyi'', known from the Late Llandovery epoch of
Canada Canada is a country in North America. Its Provinces and territories of Canada, ten provinces and three territories extend from the Atlantic Ocean to the Pacific Ocean and northward into the Arctic Ocean, making it the world's List of coun ...
. Though no other species came close to the size of ''C. punctatum'', many species were moderately large, including ''C. harleyi'' from the Late Ludlow epoch of England at , ''C. newlini'' from the Early
Pridoli epoch In the geologic timescale, the Přídolí Epoch () is the uppermost subdivision of the Silurian Period, dated at between 423 ± 2.3 and 419.2 ± 3.2 mya (million years ago). The Přídolí Epoch succeeds the Ludfordian Stage and precedes the Lochk ...
of the United States at , ''C. scoticus'' from the Llandovery epoch of
Scotland Scotland is a Countries of the United Kingdom, country that is part of the United Kingdom. It contains nearly one-third of the United Kingdom's land area, consisting of the northern part of the island of Great Britain and more than 790 adjac ...
at and ''C. spiniferum'' from the Late Ludlow epoch of the United States at . The second smallest known species was ''C. scorpioides'' from the
Wenlock epoch The Wenlock Epoch (sometimes referred to as the Wenlockian) is the second epoch of the Silurian. It is preceded by the Llandovery Epoch and followed by the Ludlow Epoch. Radiometric dates constrain the Wenlockian between and million years ago. ...
of Scotland at in length.


History of research

''Carcinosoma'' was first described under the name ''Eurysoma'' (meaning "wide body", deriving from
Greek Greek may refer to: Anything of, from, or related to Greece, a country in Southern Europe: *Greeks, an ethnic group *Greek language, a branch of the Indo-European language family **Proto-Greek language, the assumed last common ancestor of all kno ...
εὐρύς, "wide", and
Latin Latin ( or ) is a classical language belonging to the Italic languages, Italic branch of the Indo-European languages. Latin was originally spoken by the Latins (Italic tribe), Latins in Latium (now known as Lazio), the lower Tiber area aroun ...
''soma'', "body"Meaning o
soma
at ''www.dictionary.com''. Retrieved 7 September 2018.
) by British American geologist and paleobotanist Edward Waller Claypole in 1890, who named the type species of the new genus ''E. newlini'' in honor of a C. E. Newlin who had collected the fossils. The ''Eurysoma'' specimens had been discovered in deposits of Early Pridoli age in the Kokomo Formation of Indiana alongside several other eurypterid specimens, all of which at the time were referred to ''Eurypterus lacustris'' (though Claypole noted in the same paper that this may have been done hastily). Later in the same year, Claypole discovered that the name ''Eurysoma'' was
preoccupied In biology, a homonym is a name for a taxon that is identical in spelling to another such name, that belongs to a different taxon. The rule in the International Code of Zoological Nomenclature is that the first such name to be published is the s ...
and thus not available to be used for his genus of eurypterids. ''Eurysoma'' had been named in 1831 for a genus of modern
beetles Beetles are insects that form the Taxonomic rank, order Coleoptera (), in the superorder Holometabola. Their front pair of wings are hardened into wing-cases, elytra, distinguishing them from most other insects. The Coleoptera, with about 40 ...
and is today considered synonymous with the genus ''
Brachygnathus ''Brachygnathus'' is a genus of ground beetles in the family Carabidae, the sole genus of the tribe Brachygnathini. Species These seven species belong to the genus ''Brachygnathus'': * ''Brachygnathus angusticollis'' (Burmeister, 1885) (Argenti ...
''. Claypole replaced the name ''Eurysoma'' with the new name ''Carcinosoma''. ''Carcinosoma'' means "crab body" deriving from Latin ''cancer'', "crab", and ''soma'', "body". In 1868, English geologist and paleontologist Henry Woodward named a new species of ''Eurypterus'', ''E. scorpioides'', based on fossils from
Lanarkshire Lanarkshire, also called the County of Lanark (; ), is a Counties of Scotland, historic county, Lieutenancy areas of Scotland, lieutenancy area and registration county in the Central Lowlands and Southern Uplands of Scotland. The county is no l ...
, Scotland. Woodward could easily distinguish the species from other genera present at the locality, such as '' Slimonia'' and ''
Pterygotus ''Pterygotus'' is an extinct 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 s ...
''. Another species of ''Eurypterus'', ''E. scoticus'' was named in 1899 by Scottish zoologist and paleontologist
Malcolm Laurie Malcolm Laurie FRSE FLS (27 February 1866 – 16 July 1932) was a Scottish zoologist and palaeontologist. Biography He was born in Brunstane House south of Portobello, Edinburgh on 27 February 1866, the son of Catherine Ann Hibburd and h ...
based on fragmentary remains recovered in deposits of Llandovery age in Scotland. In 1912, American paleontologists
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 State ...
noted that ''Carcinosoma'' was sufficiently similar to the related eurypterid ''Eusarcus'' to be designated as
synonymous A synonym is a word, morpheme, or phrase that means precisely 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 a ...
with it. As ''Eusarcus'' had been named in 1875, fifteen years earlier than ''Carcinosoma'', its name had priority and replaced ''Carcinosoma''. At this time, the combined genus of ''Eusarcus'' contained several species that are today seen as ''Carcinosoma'', including ''C. newlini'', ''C. scoticus'' and ''C. scorpioides'', which Clarke and Ruedemann had referred to the genus on account of their similarities with ''C. newlini'' and species previously referred to ''Eusarcus''. In 1934, 59 years after it had been described, ''Eusarcus'' was recognized as a name preoccupied by a
harvestman The Opiliones (formerly Phalangida) are an order of arachnids, colloquially known as harvestmen, harvesters, harvest spiders, or daddy longlegs (see below). , over 6,650 species of harvestmen have been discovered worldwide, although the total n ...
. The Norwegian geologist
Leif Størmer Leif Størmer (1 July 1905 – 15 May 1979) was a Norway, 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 ...
proposed that the name of the taxon should be next oldest available and valid name for the genus, ''Carcinosoma''. During the preparation for his paper on the issue, Størmer also discussed the situation with fellow Norwegian researcher
Embrik Strand Embrik Strand (2 June 1876 – 3 November 1947) was an entomologist and arachnologist who classified many insect and spider species, including the greenbottle blue tarantula. Life and career Strand was born in Ål, Norway. He studied at t ...
, who helped confirm that ''Carcinosoma'' was not preoccupied. Strand would subsequently propose the replacement name ''Eusarcana'' in 1942, despite the problem having been dealt with by Størmer, who he had been in contact with, eight years earlier. The reasons for proposing the name during the circumstances of the time remains unknown, but critique from contemporary researchers of Strand for his studies in systematics and an apparent desire to name as many taxa as possible may explain the situation somewhat. As it was seen as completely unnecessary at the time, Strand's ''Eusarcana'' was overlooked and not even mentioned in subsequent eurypterid studies. In 1961, American paleontologist Erik N. Kjellesvig-Waering classified ''Eurypterus punctatus'' (originally described as ''Pterygotus punctatus'' by English paleontologist and prominent eurypterid researcher
John William Salter John William Salter (15 December 1820 – 2 December 1869) was an English naturalist, geologist, and palaeontologist. Salter was apprenticed in 1835 to James De Carle Sowerby, and was engaged in drawing and engraving the plates for Sowerby' ...
in 1859) as ''Carcinosoma punctatum'' and named a new species ''C. harleyi'' based on fossils from the Ludlow epoch of the Welsh Borderland. Kjellesvig-Waering could differentiate ''C. harleyi'' from ''C. punctatum'' based on ''C. harleyi'' lacking serrations on the eighth podomere of the swimming leg and the serrations of the ninth podomere being less developed. ''C. punctatum'' was diagnosed by Kjellesvig-Waering in 1961 based on the considerably pronounced serrations of the
distal Standard anatomical terms of location are used to describe unambiguously the anatomy of humans and other animals. The terms, typically derived from Latin or Greek roots, describe something in its standard anatomical position. This position provi ...
parts of its swimming leg, but the diagnosis is only valid for the
lectotype In biology, a type is a particular specimen (or in some cases a group of specimens) of an organism to which the scientific name of that organism is formally associated. In other words, a type is an example that serves to anchor or centralizes ...
specimen of the species, BGS GSM89435 (compromising the distal parts of a swimming leg discovered in deposits of Middle Ludlow age in the Mocktree Shale of Leintwardine in Herefordshire, England), and four other specimens from the same locality (BMNH 39389, BMNH In. 43804, BGS GSM89561 and GSM89568). Due to a close resemblance of the swimming legs, ''C. punctatum'' is assumed to have been similar in appearance to ''C. newlini''. ''C. punctatum'' can be distinguished from ''C. newlini'' by the serration along the margin of the distal podomeres of ''C. punctatum'' being more pronounced. ''C. harleyi'', from the Late Ludlow epoch, was described mainly based on specimens previously known (some having been reported by Salter as early as 1859) but previously referred to ''Eurypterus punctatus''. Recognized by Kjellesvig-Waering as distinct, the species is named in honor of John Harley, one of the earliest collectors of eurypterid fossils in the region. Noted as moderately large in size by Kjellesvig-Waering, the
holotype specimen A holotype (Latin: ''holotypus'') is a single physical example (or illustration) of an organism used when the species (or lower-ranked taxon) was Species description, formally described. It is either the single such physical example (or illus ...
of ''C. harleyi'' (No. 89434 in the collection of the Geological Survey and Museum in London) is a fragment of a swimming leg measuring in length. The nearly complete lack of serrations in the joints of ''C. harleyi'' makes the species very distinct from ''C. punctatum'' and other species of ''Carcinosoma''. In 1964, both ''C. punctatum'' and ''C. harleyi'' were still recognized as part of ''Carcinosoma'' following an emended diagnosis of the genus by Kjellesvig-Waering and American paleontologist Kenneth Edward Caster, though ''C. harleyi'' was only tentatively recognized. Further species recognized at the time were ''C. libertyi'' and ''C. logani'' (both from Ontario, Canada; ''C. logani'' was later found to be a
crustacean Crustaceans (from Latin meaning: "those with shells" or "crusted ones") are invertebrate animals that constitute one group of arthropods that are traditionally a part of the subphylum Crustacea (), a large, diverse group of mainly aquatic arthrop ...
and not a eurypterid at all), ''C. spiniferum'' (from New York, United States), ''C. newlini'' (from Indiana, United States), ''C. scorpioides'' and ''C. scoticus'' (both from Scotland). Out of these species, only ''C. newlini'' and ''C. scorpioides'' preserve the swimming legs, where the diagnostic characters of the genus are, which makes the assignment of the other species to ''Carcinosoma'' less secure. Kjellesvig-Waering and Caster also recognized ''Eusarcus'' and ''Carcinosoma'' to be distinct genera when revising the superfamily Carcinosomatoidea, and coined the replacement name ''Paracarcinosoma'' to designate the species previously assigned to ''Eusarcus''. ''E. scorpionis'' was designated the
type species In International_Code_of_Zoological_Nomenclature, 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 spe ...
. Caster and Kjellesvig-Waering made no mention of Embrik Strand or ''Eusarcana'', and they were likely not aware of the existence of the previous name. In 2012, American paleontologists Jason A. Dunlop and James Lamsdell designated ''Paracarcinosoma'' as a
junior synonym In taxonomy, the scientific classification of living organisms, a synonym is an alternative scientific name for the accepted scientific name of a taxon. The botanical and zoological codes of nomenclature treat the concept of synonymy differently. ...
of ''Eusarcana'' per the taxonomic laws of priority.


Classification

''Carcinosoma'' is classified as part of the family Carcinosomatidae, a family within the superfamily Carcinosomatoidea, alongside the genera ''Eusarcana'', '' Eocarcinosoma'', ''
Rhinocarcinosoma ''Rhinocarcinosoma'' is a genus of eurypterid, an extinct group of aquatic Arthropod, arthropods. Fossils of ''Rhinocarcinosoma'' have been discovered in deposits ranging of Late Silurian age in the United States, Canada and Vietnam. The genus c ...
'' and possibly '' Holmipterus''. The cladogram below is adapted from a larger cladogram (simplified to only display the Carcinosomatoidea) in a 2007 study by eurypterid researcher O. Erik Tetlie, in turn based on results from various phylogenetic analyses on eurypterids conducted between 2004 and 2007. The second cladogram below is simplified from a study by Lamsdell ''et al.'' (2015). Tetlie (2007) Lamsdell ''et al.'' (2015)


Paleobiology

The walking legs of ''Carcinosoma'' were turned forward, which also directed the large spines on the appendages forward. In ''C. newlini'', these flat and forward-facing legs are thought to have been used to create a trap to capture prey in. The strong structures seen in ''C. newlini'' are not reflected in other carcinosomatids. For instance, the appendages of ''Eusarcana'' were much more weakly developed and would not have served as an effective weapon. ''Eusarcana'' is more likely to have relied on its telson, taking the shape of a sharp and curved stinger similar to that of scorpions and potentially capable of injecting venom. Instead of taking the shape of a scorpion-like stinger, the telson of ''Carcinosoma'' was slightly flattened and expanded anteriorly. The telsons of most eurypterids ends in a spike but the telson of ''Carcinosoma'' ended in a small and expanded structure with distinct segmentation, fossils preserving ten segments (though a small portion of the structure is not preserved, making more segments possible), otherwise not definitely reported from a eurypterid. The only other eurypterid from which a segmented structure occurring as part of the telson has been reported in is the slimonid '' Salteropterus abbreviatus''. With such segmentation reported from two separate eurypterid genera, it is possible that the eurypterid telson is actually developed from a formerly normal abdominal segment and is thus not homologous to the telson of other arthropod groups. Further studies of ''Salteropterus'' has since revealed that the perceived "segmentation" of its "post-telson" was misinterpreted ornamentation of an elongated and unusually shaped telson and not actual segmentation, making the segmentation of ''Carcinosoma'' unique.


Paleoecology

As the
opisthosoma The opisthosoma is the posterior part of the body in some arthropods, behind the prosoma ( cephalothorax). It is a distinctive feature of the subphylum Chelicerata (arachnids, horseshoe crabs and others). Although it is similar in most respects ...
of ''Carcinosoma'' wasn't as streamlined as that of more active eurypterids and on account of its unique telson morphology, it is believed that ''Carcinosoma'' was not a very active swimmer. It is unlikely to have been well adapted to a completely
nekton Nekton or necton (from the ) is any aquatic organism that can actively and persistently propel itself through a water column (i.e. swimming) without touching the bottom. Nektons generally have powerful tails and appendages (e.g. fins, pleopods, ...
ic (actively swimming) lifestyle and is more likely to have been nektobenthic (swimming near the bottom). The flat metasoma of ''Carcinosoma'' was probably used as at least partially as aid when swimming, suggested by the pretelson being slightly expanded in comparison to other eurypterids. As a considerable majority of described eurypterid species are known from the Silurian, particularly the late Silurian, researchers have concluded that the group peaked in diversity and number during this time. Complex eurypterid faunas, compromising several different species in different ecological roles, are typical of the period. These faunas were typically dominated by one or more particular eurypterid families, the dominant groups depending on the environment and location. Three such types of eurypterid faunas have been documented from the late Silurian, out of which a Carcinosomatidae-Pterygotidae fauna is the most marine type. All known examples of ''Carcinosoma'' are known from marine beds, typically occurring with
trilobites Trilobites (; meaning "three-lobed entities") are extinct marine arthropods that form the class Trilobita. One of the earliest groups of arthropods to appear in the fossil record, trilobites were among the most successful of all early animals, ...
,
starfish Starfish or sea stars are Star polygon, star-shaped echinoderms belonging to the class (biology), class Asteroidea (). Common usage frequently finds these names being also applied to brittle star, ophiuroids, which are correctly referred to ...
,
bryozoa Bryozoa (also known as the Polyzoa, Ectoprocta or commonly as moss animals) are a phylum of simple, aquatic animal, aquatic invertebrate animals, nearly all living in sedentary Colony (biology), colonies. Typically about long, they have a spe ...
ns,
brachiopods Brachiopods (), phylum Brachiopoda, are a phylum of animals that have hard "valves" (shells) on the upper and lower surfaces, unlike the left and right arrangement in bivalve molluscs. Brachiopod valves are hinged at the rear end, while the fron ...
, linguloids and other marine animals. ''Carcinosoma'' also prominently occurs together with pterygotid eurypterids. In the fossil deposits of the Welsh Borderland, examples of ''Carcinosoma'' occur together with representatives of the pterygotid genera ''Erettopterus'' and ''Pterygotus'' over a period of millions of years (though other eurypterids, such as ''Salteropterus'', '' Dolichopterus'', ''
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 ...
'', ''Eurypterus'', ''
Marsupipterus ''Marsupipterus'' is a genus of prehistoric eurypterid with an uncertain classification. The genus contains one species, ''Marsupipterus sculpturatus'', from the Silurian of England England is a Countries of the United Kingdom, country t ...
'', ''
Mixopterus ''Mixopterus'' is a genus of eurypterid, an extinct group of aquatic arthropods. Fossils of ''Mixopterus'' have been discovered in deposits from Late Silurian age, and have been referred to several different species. Fossils have been recovered f ...
'', '' Parahughmilleria'', '' Slimonia'', '' Tarsopterella'' and '' Stylonurus'' are also present in lesser numbers). Other types of late Silurian eurypterid faunas include one dominated by the Eurypteridae. When genera such as '' Erieopterus'' or ''Eurypterus'' occur in great numbers other genera and families are more rare, though groups such as dolichopterids, carcinosomatids and pterygotids tend to occur in small numbers. The environments with such faunas appear to be quieter waters such as
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'') an ...
s,
estuaries An estuary is a partially enclosed coastal body of brackish water with one or more rivers or streams flowing into it, and with a free connection to the open sea. Estuaries form a transition zone between river environments and maritime environm ...
and
bays A bay is a recessed, coastal body of water that directly connects to a larger main body of water, such as an ocean, a lake, or another bay. A large bay is usually called a ''gulf'', ''sea'', ''sound'', or ''bight''. A ''cove'' is a small, ci ...
. The third and final recognized type of fauna is one dominated by hughmilleriids and stylonurids, generally alongside sandy bottoms and with few other associated fossils. The environments inhabited by this third fauna was likely less marine than the others, possibly representing the more
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 ...
parts of bays and estuaries.


See also

  • List of eurypterid genera This list of eurypterid genera is a comprehensive listing of all genera that have ever been included in the order Eurypterida, excluding purely vernacular terms. The list includes all commonly accepted genera, but also genera that are now consider ...
  • Timeline of eurypterid research This timeline of eurypterid research is a chronologically ordered list of important fossil discoveries, controversies of interpretation, and Biological taxonomy, taxonomic revisions of eurypterids, a group of extinct aquatic arthropods closely re ...


References

{{Taxonbar, from=Q4348619 Carcinosomatoidea Silurian eurypterids Silurian arthropods of North America Silurian arthropods of Europe Paleozoic life of Ontario Paleozoic life of Nunavut Eurypterids of Europe Eurypterids of North America