''Eusarcana'' (meaning "true flesh") is a genus 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. Fossils of ''Eusarcana'' have been discovered in deposits ranging in age from the Early Silurian to the Early Devonian. Classified as part of the family

Carcinosomatidae Carcinosomatidae (the name deriving from the type genus ''Carcinosoma'', meaning "crab body")Meaning osomaat ''www.dictionary.com''. Retrieved 7 September 2018. is a family of eurypterids, an extinct group of aquatic arthropods. They were member ...

, the genus contains three species, ''E. acrocephalus'', ''E. obesus'' and ''E. scorpionis'', from 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 ...

Devonian The Devonian ( ) is a geologic period and system of the Paleozoic era, spanning 60.3 million years from the end of the Silurian, million years ago (Mya), to the beginning of the Carboniferous, Mya. It is named after Devon, England, whe ...

Scotland Scotland (, ) is a country that is part of the United Kingdom. Covering the northern third of the island of Great Britain, mainland Scotland has a border with England to the southeast and is otherwise surrounded by the Atlantic Ocean to the ...

, the

Czech Republic The Czech Republic, or simply Czechia, is a landlocked country in Central Europe. Historically known as Bohemia, it is bordered by Austria to the south, Germany to the west, Poland to the northeast, and Slovakia to the southeast. The ...

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 ...

respectively. ''Eusarcana'' is known for its odd proportions and features; the broad abdomen, thin and long tail, spined and forward-facing walking appendages and sharp and curved tail spike differentiate it from most other eurypterids, but are shared with other carcinosomatid eurypterids. The triangular carapace, oddly positioned forward-facing eyes differentiate the genus further from its closest relatives. At 80 centimetres (31.5 in) in length, ''E. scorpionis'' represents a moderately large species of eurypterid, and far exceeded other representatives of the genus in size, such as the 4 cm (1.5 in) long ''E. obesus''. Originally described under the name ''

Eusarcus ''Eusarcus'' is a genus of harvestmen The Opiliones (formerly Phalangida) are an order of arachnids colloquially known as harvestmen, harvesters, harvest spiders, or daddy longlegs. , over 6,650 species of harvestmen have been discovered wo ...

'', this name was preoccupied by a genus of living harvestmen in the family

Gonyleptidae Gonyleptidae is a neotropical family of harvestmen (Order Opiliones) with more than 800 species, the largest in the Suborder Laniatores and the second largest of the Opiliones as a whole. The largest known harvestmen are gonyleptids. Like most h ...

. Following the discovery of this

homonym In linguistics, homonyms are words which are homographs (words that share the same spelling, regardless of pronunciation), or homophones (equivocal words, that share the same pronunciation, regardless of spelling), or both. Using this definition, ...

, the genus was also wrongly recognized as synonymous with the related ''

Carcinosoma ''Carcinosoma'' (meaning "crab body") is a genus of eurypterid, an extinct group of aquatic arthropods. Fossils of ''Carcinosoma'' are restricted to deposits of late Silurian (Late Llandovery to Early Pridoli) age. Classified as part of the fam ...

'' and was only given replacement names for the older name decades after the error was discovered, first as ''Eusarcana'' in 1942 and later as ''Paracarcinosoma'' (assumed to have been named without knowledge of the earlier replacement name) in 1964.

Description

''Eusarcana'' can be differentiated from other

eurypterids Eurypterids, often informally called sea scorpions, are a group of extinct 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 group is l ...

by the considerably narrow border between the prosoma (head) and opisthosoma (abdomen), which is particularly thin considering the subsequent broad and large ellipse-shape of the abdomen. The postabdomen (or tail) also narrows rather quickly from the preceding segments. Further features distinctive of the genus include that the carapace (segment covering the head) is clearly triangular in shape, with eyes placed on the rim of it and positioned forwards, the fact that all walking legs possess spines and that they decrease in length the further back they were placed as well as the cylindrically shaped and sharp telson (the posteriormost division of the body).Clarke, J. K., Ruedemann R. (1912) " The Eurypterida of New York" In comparison with many other eurypterids, ''Eusarcana'' was a rather large animal, with the largest species (also the type species) ''E. scorpionis'' reaching lengths of 80 cm (31.5 in). In comparison, the species ''E. obesus'' was significantly smaller, with the largest specimen only being 4 cm (1.5 in) long. The appearance of ''Eusarcana'' is somewhat odd in comparison with other eurypterids, not only in its overall shape and proportions but also in that the surface of its exoskeleton is covered in small scale-like ornamentation that is circular in shape, crowded and small in size which differentiates it from other eurypterids in which such ornamentation is usually triangular. Overall, ''Eusarcana'' is mostly similar in appearance to other carcinosomatid eurypterids, particularly ''

'' which shares its forwardly positioned eyes, and is primarily defined by the small degree of spinosity on its second to fifth pair of appendages and its curved telson.

History of research

Original description and subsequent discoveries

''Eusarcana'' was first described as "''Eusarcus''" by the American geologists August R. Grote and William Henry Pitt based on fossils recovered from the Pridoli-age

Buffalo waterlime Buffalo most commonly refers to: * Bubalina, including most "Old World" buffalo, such as water buffalo * Bison, including the American buffalo * Buffalo, New York Buffalo or buffaloes may also refer to: Animals * Bubalina, a subtribe of the tr ...

New York State New York, officially the State of New York, is a state in the Northeastern United States. It is often called New York State to distinguish it from its largest city, New York City. With a total area of , New York is the 27th-largest U.S. stat ...

. This name derives from the

Ancient Greek Ancient Greek includes the forms of the Greek language used in ancient Greece and the ancient world from around 1500 BC to 300 BC. It is often roughly divided into the following periods: Mycenaean Greek (), Dark Ages (), the Archaic peri ...

εὖ, (''eu-'') meaning "true", and σάρξ (''sarx''), meaning "flesh", meaning "true flesh". The designated type species was ''E. scorpionis''. Though Grote and Pitt did not provide a generic diagnosis for the genus, the species was well diagnosed with a number of distinctive characters. Furthermore, the genus of Grote and Pitt was seemingly based solely on outlines and shape, which prompted some researchers, such as the prominent English geologist Henry Woodward, to regard the genus as lacking generic characters and as such being invalid, referring ''E. scorpionis'' to ''Eurypterus'' on the grounds that several British species of ''Eurypterus'', notably ''E. scorpiodes'' and ''E. punctatus'' (today recognized as species of ''Carcinosoma''), were similar in shape. Unbeknownst to Grote and Pitt, ''

'' had already been named as a genus of extant (currently living) laniatorid harvestmen of the family

, in 1833 and as such constituted a preoccupied name. The preoccupied nature of the name was not immediately recognized, and it continued to be used for eurypterid species described in the late 19th to early 20th centuries. 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 ...

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 ...

declared that the differences between ''Eusarcus'' and all related forms of eurypterids were so great that it was "entirely evident" that ''Eusarcus'' was distinct from other eurypterids. They referred the Scottish Wenlock-age ''Eurypterus'' species ''E. obesus'' (described by English geologist Henry Woodward in 1868) to the genus, alongside the Pridoli- Lochkovian-age Czech species ''E. acrocephalus'' (described by Austrian paleontologist Max Semper in 1898) on the grounds of both possessing triangular carapaces similar to ''E. scorpionis'' as well as an abruptly narrowing postabdomen. Furthermore, Clarke and Ruedemann concluded that ''Eusarcus'' was sufficiently similar to the related ''Carcinosoma'' to be designated as synonymous with it. As ''Eusarcus'' had been named earlier than ''Carcinosoma'', the taxonomical laws of priority dictated that ''Eusarcus'' would be the name of the taxon. ''E. acrocephalus'' (sometimes referred to erroneously as "''E. acrocephala''") can be distinguished from the other two species by the strongly recurved lateral sides of its carapace, the oval mesosoma and the first segment of the metasoma being unusually wide and short for the genus. The holotype of ''E. acrocephalus'', UW 1906/V/2 discovered in the Požáry Formation of the Czech Republic, is composed of the carapace and a partial abdomen, portions of which were broken off during bombing runs on

Prague Prague ( ; cs, Praha ; german: Prag, ; la, Praga) is the capital and largest city in the Czech Republic, and the historical capital of Bohemia. On the Vltava river, Prague is home to about 1.3 million people. The city has a temperate ...

during the

Second World War World War II or the Second World War, often abbreviated as WWII or WW2, was a world war that lasted from 1939 to 1945. It involved the vast majority of the world's countries—including all of the great powers—forming two opposin ...

, during which the National Museum of Prague was damaged. The obesity of 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 to a ...

l (abdominal) segments in ''E. obesus'' is its most remarkable feature (and is also what lends the species its name), the fourth segment is as wide as the first eight segments combined are long. The surface of the exoskeleton of the carapace and the segments is thin and seemingly lacks ornamentation. In 2014, American paleontologist James Lamsdell suggested that ''E. obesus'' may represent a juvenile of the related and contemporary ''Carcinosoma scorpioides''. Unlike other species of ''Eusarcana'', ''E. obesus'' does not appear to possess spines on its appendages.

Recognition as preoccupied name

It was first in 1934, 59 years after its original description, that ''Eusarcus'' was recognized as a name

preoccupied The Botanical and Zoological Codes of nomenclature treat the concept of synonymy differently. * In botanical nomenclature, a synonym is a scientific name that applies to a taxon that (now) goes by a different scientific name. For example, Linn ...

by a harvestman. The Norwegian geologist Leif Størmer 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, 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 contemporary researchers critiquing 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. The naming of ''Eusarcana'' was one of many contributions to nomenclature by Strand seen as unhelpful today. His journal '' Folia Zoologica et Hydrobiologica'' would later re-emerge within the field to create all kinds of systematic problems that could have been avoided. Strand was also notorious for applying new species names to incomplete or poorly preserved fossils. In 1964, American paleontologists Kenneth Edward Caster and Erik N. Kjellesvig-Waering 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. 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. With ''Eusarcana'' all but forgotten, all subsequent researchers used ''Paracarcinosoma'' for the genus. In 2012, American paleontologists Jason A. Dunlop and James Lamsdell noted that whilst the name ''Eusarcana'' had been completely unnecessary (and of questionable validity, as Strand did not designate a type species) at the time of its creation, it is the oldest available valid name for the taxon and as such should constitute its name under the rules of priority, despite ''Paracarcinosoma'' being more widely used. As such, ''Paracarcinosoma'' was designated as a junior synonym, with all three species assigned to it being transferred to ''Eusarcana''.

Classification

''Eusarcana'' is classified as part of the family

, a family within the superfamily

Carcinosomatoidea Carcinosomatoidea is an extinct superfamily of eurypterids, an extinct group of chelicerate arthropods commonly known as "sea scorpions". It is one of the superfamilies classified as part of the suborder Eurypterina. Some carcinosomatoid genera ...

, alongside the genera ''Carcinosoma'', ''

Eocarcinosoma ''Eocarcinosoma'' is a genus of eurypterid, an extinct group of aquatic arthropods. The type and only species of ''Eocarcinosoma'', ''E. batrachophthalmus'', is known from deposits of Late Ordovician age in the United States. The generic name i ...

'', ''

Rhinocarcinosoma ''Rhinocarcinosoma'' is a genus of eurypterid, an extinct group of aquatic arthropods. Fossils of ''Rhinocarcinosoma'' have been discovered in deposits ranging of Late Silurian age in the United States, Canada and Vietnam. The genus contains thr ...

'' and possibly ''

Holmipterus ''Holmipterus'' is a problematic genus of eurypterid, an extinct group of aquatic arthropods. The type and only species of ''Holmipterus'', ''H. suecicus'', is known from deposits of Middle Silurian age in the Sweden. The generic name honours , ...

''. 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 features of ''Eusarcana'' indicate that its lifestyle was completely different from many other swimming eurypterids, such as ''Eurypterus''. When walking, ''Eusarcana'' would likely have lifted the eye-bearing frontal part of its head above the ground, as indicated by the larger size of the forward walking legs and the placement of the eyes. In contrast, ''Eurypterus'' would have kept its head, shovel-shaped and broad, down to the ground while walking. Furthermore, the walking legs of ''Eusarcana'' are more powerful than those of ''Eurypterus'' in general. The legs decrease in strength the further back they are, indicating that there was an emphasis on lifting the front of the carapace. In ''Eurypterus'' the legs are the longest the further back they are, which indicates that it would have had an emphasis on keeping the head down. The swimming legs of ''Eusarcana'' were powerfully developed, with paddles both longer and broader than those of ''Eurypterus'', which corresponds to the fact that ''Eusarcana'' was a broader and heavier genus of eurypterids.

Tail spike

In the Pridoli-age Buffalo waterlime fauna where ''E. scorpionis'' lived, it represented one of the larger members of the ecosystem, being at least half as long as the larger predatory eurypterids of the genus ''

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 ...

''. With ''Eusarcana'' not having large and powerful pincers like the larger

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, which not only represented potential competitors but also dangerous predators, the only obvious organ it could use for defense was the pointed and sharp tail spike. The narrowed tail is so long and extended that it exceeds the principal parts of the body, the head and abdomen, in length. The fact that the tail has been preserved as curved in several fossil specimens proves that it would have been flexible in life, with the apparent curvature of the spike on its end making it a dangerous weapon. If curved forwards over the rest of the body, the spike would be positioned with its point turned upwards, effectively acting similar to a

scimitar A scimitar ( or ) is a single-edged sword with a convex curved blade associated with Middle Eastern, South Asian, or North African cultures. A European term, ''scimitar'' does not refer to one specific sword type, but an assortment of different ...

. The similarity between the spike of ''Eusarcana'' and that of scorpions opens up the possibility that the tail spike might possibly have possessed poison glands. Though the state in which the specimens have been preserved does not allow determination of either the absence or presence of a poison canal or pores for transferring the venom to potential victims, the shape of ''Eusarcana'' suggests that it was a rather slow and inactive animal that was not very agile, possibly adapted for burrowing or ambush predation. In such a lifestyle, a venomous and agile tail spike would greatly aid in securing prey and defense in absence of other prehensile and powerful organs with long reach.

Ecology

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. All species of ''Eusarcana'' described so far occur together with other eurypterid species. ''E. acrocephalus'' is known from both the Silurian and the Devonian of the Czech Republic, with a somewhat apparent difference in other fauna depending on the time period. Devonian ''E. acrocephalus'' occur together with other eurypterids ''

Slimonia ''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 ...

'', ''Pterygotus'' and ''

Acutiramus ''Acutiramus'' is a genus of giant predatory eurypterid, an extinct group of aquatic arthropods. Fossils of ''Acutiramus'' have been discovered in deposits of Late Silurian to Early Devonian age. Seven species have been described, five from Nor ...

'' as well as with various

trilobite Trilobites (; meaning "three lobes") are extinct marine arthropods that form the class Trilobita. Trilobites form one of the earliest-known groups of arthropods. The first appearance of trilobites in the fossil record defines the base of the At ...

s (including ''

Crotalocephalina ''Crotalocephalina'' is an extinct genus of trilobite in the order Phacopida found in Morocco. External links''Photo of a Crotocephalina'Crotalocephalina''at the Paleobiology Database The Paleobiology Database is an online resource for info ...

'', '' Otarion'', '' Warburgella'', '' Proetus'', '' Tropidocare'', ''

Leonaspis ''Leonaspis'' is a widespread genus of odontopleurid trilobite that lived from the Late Ordovician to the late Middle Devonian. Fossils of various species have been found on all continents except Antarctica. Sources * ''Fossils'' (Smithsonian ...

'' and '' Ceratocephala''),

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 ...

s (including '' Ceratiocaris'' and '' Aristozoe''),

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 ...

conodont Conodonts (Greek ''kōnos'', "cone", + ''odont'', "tooth") are an extinct group of agnathan (jawless) vertebrates resembling eels, classified in the class Conodonta. For many years, they were known only from their tooth-like oral elements, which ...

s, gastropods and crinoids. The Silurian-aged fauna of the same general area, also preserving ''E. acrocephalus'', were home to other eurypterids ''

Erettopterus ''Erettopterus'' is a genus of large predatory eurypterid, an extinct group of aquatic arthropods. Fossils of ''Erettopterus'' have been discovered in deposits ranging from Early Silurian (the Rhuddanian age) to the Early Devonian (the Lochkov ...

'', ''Pterygotus'' and ''Acutiramus'', a less diverse assemblage of trilobites (''Otarion'', '' Scharyia'' and '' Prionopeltis''), crustacean ''Ceratiocaris'',

cephalopod A cephalopod is any member of the molluscan class Cephalopoda (Greek plural , ; "head-feet") such as a squid, octopus, cuttlefish, or nautilus. These exclusively marine animals are characterized by bilateral body symmetry, a prominent head ...

s (including ''

Cycloceras ''Cycloceras'' is an extinct nautiloid cephalopod genus from the Carboniferous of Western Europe, (Ireland and Scotland) of unknown affinity with the Orthocerida. Taxonomy ''Cycloceras'' was named by McCoy (1844 and assigned to the Michelinocer ...

'' and '' Corbuloceras''), ostracods, gastropods, crinoids, conodonts and

bivalves 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 ...

. Silurian ''E. obesus'' from the United Kingdom lived in a marine environment also home to other eurypterids ''

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, ...

'', ''Pterygotus'', ''Slimonia'', ''Carcinosoma'', ''

Parastylonurus ''Parastylonurus'' is a genus of prehistoric eurypterid. It is classified within the Parastylonuridae family and contains three species, ''P. hendersoni'' and ''P. ornatus'' from the Silurian of Scotland and ''P. sigmoidalis'' from the Silurian ...

'' and ''Erettopterus'' as well as phyllocarid crustaceans, xiphosurans, gastropods and

anaspid Anaspida ("without shield") is an extinct group of primitive jawless vertebrates that lived primarily during the Silurian period, and became extinct soon after the start of the Devonian. They were classically regarded as the ancestors of lampre ...

fish ''

Birkenia ''Birkenia'' is a genus of extinct anaspid fish from Middle Silurian strata of Northern Europe, and Middle Silurian to possibly Earliest Devonian strata of Arctic Canada Canada is a country in North America. Its ten provinces and thre ...

''. In Silurian deposits of New York, ''E. scorpionis'' occurs together with a diverse fauna of eurypterids composed of ''

Buffalopterus ''Buffalopterus'' is a prehistoric eurypterid from the Silurian-aged Bertie Formation of New York and Ontario. The genus contains one species, ''B. pustulosus''. It is closely related to ''Strobilopterus'', but differs primarily by having a biza ...

'', ''

Dolichopterus ''Dolichopterus'' is a genus of prehistoric sea scorpions, arthropods in the order Eurypterida. Fossils of ''Dolichopterus'' have been discovered in deposits ranging from Silurian to Devonian, and have been referred to several different species, ...

'', ''Erettopterus'', ''

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 ...

'', ''Pterygotus'' and ''Acutiramus''. Also present were xiphosurans, crustaceans ('' Gonatocaris''), ostracods, bivalves, gastropods and cephalopods. Carcinosomatid eurypterids such as ''Eusarcana'' were among the most marine eurypterids, known from deposits that were once reefs, some in

lagoonal 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'') ...

settings, and deeper waters.

References

{{Taxonbar, from=Q48811753 Silurian eurypterids Devonian eurypterids Devonian arthropods of Europe Silurian arthropods of Europe Devonian arthropods of North America Silurian arthropods of North America Fossil taxa described in 1942 Fossils of Scotland Fossils of the Czech Republic Fossils of the United States Bertie Formation Eurypterids of Europe Eurypterids of North America Carcinosomatoidea