The first fossil of Eurypterus was found in 1818 by S. L. Mitchill, a fossil collector. It was recovered from the Bertie Formation of New York (near Westmoreland, Oneida County). Mitchill interpreted the swimming paddles characteristic of the genus as barbels arising from the mouth. He consequently identified the fossil as a catfish.
The American zoologist James Ellsworth De Kay correctly identified the fossil as an arthropod in 1825. He named it Eurypterus remipes and established the genus Eurypterus in the process. The name means "wide wing" or "broad paddle", refering to the swimming legs, from Greek εὐρύς (eurús, wide) and πτερόν (pteron, wing).
However, De Kay though Eurypterus was a branchiopod (a group of crustaceans which include fairy shrimps and water fleas). Soon after, Eurypterus lacustris was also discovered in New York in 1835 by the paleontologist Richard Harlan. Another species was discovered in Estonia in 1858 by Jan Nieszkowski. He considered it to be of the same species as the first discovery (E remipes), it is now known as Eurypterus tetragonophthalmus.
More fossils were recovered in great abundance in New York in the 19th century, and elsewhere in eastern Eurasia and North America. Today, Eurypterus remains one of the most commonly found and best known eurypterid genus, comprising more than 95% of all known eurypterid fossils.
The genus Eurypterus belongs to the family Eurypteridae. They are classified under the superfamily Eurypteroidea, suborder Eurypterina, order Eurypterida, and the subphylum Chelicerata. Until recently, eurypterids were thought to belong to the class Merostomata along with order Xiphosura. It is now believed that eurypterids are a sister group to Arachnida, closer to spiders and scorpions than to horseshoe crabs.
Eurypterus was the first recognized taxon of eurypterids and the most common. As a consequence, almost every remotely similar eurypterid in the 19th century were classified under the genus (except for the distinctive members of the family Pterygotidae and Stylonuridae). The genus was eventually split into several genera as the science of taxonomy developed.
In 1958, several species distinguishable by closer placed eyes and spines on their swimming legs were split of into the separate genus by Erik Kjellesvig-Waering. They are now known under the closely related genus Eiropterus. Another split was proposed by Lief Størmer in 1973 when he reclassified of some Eurypterus to Baltoeurypterus based on the size of the some of the last segments of their swimming legs. O. Erik Tetlie in 2006 deemed these differences too insignificant to justify a separate genus. He merged Baltoeurypterus back into Eurypterus. It is now believed that the minor variations described by Størmer are simply the differences found in adults and juveniles within a species.
The largest arthropods to have ever existed were eurypterids. The largest known species (Jaekelopterus rhenaniae) reached up to 2.5 m (8.2 ft) in length, about the size of a crocodile. Species of Eurypterus, however, were much smaller.
E. remipes are usually between 5 to 8 in (13 to 20 cm) in length. E. lacustris average at larger sizes at 6 to 9 in (15 to 23 cm) in length. The largest specimen of E. remipes ever found was 1.3 metres (4.3 ft) long, currently on display at the Paleontological Research Institution of New York.
Eurypterus fossils often occur in similar sizes in a given area. This may be a result of the fossils being 'sorted' into windrows as they were being deposited in shallow waters by storms and wave action.
The prosoma is the forward part of the body, it is actually composed of six segments fused together to form the head and the thorax. It contains the semicircular to subrectangular platelike carapace, on the dorsal side of which are two large crescent-shaped compound eyes. They also possessed two smaller light-sensitive simple eyes (the median ocelli) near the center of the carapace on a small elevation (known as the ocellar mound). Underneath the carapace is the mouth and six appendages, usually referred to in roman numerals I-VI. Each appendage in turn is composed of nine segments (known as podomeres) labeled in arabic numerals 1-9. The first segments which connect the appendages to the body are known as the coxa (plural coxae).
The first pair (Appendage I) are the chelicerae, small pincer-like arms used for tearing food apart (mastication) during feeding. After the chelicerae are three pairs of short legs (Appendages II, III, and IV). They are spiniferous (covered in spines) and are used both for walking and for food capture. The next pair (Appendage V) is the most leg-like of all appendages, longer than the first three pairs and are mostly spineless except at the tipmost segment. The last pair (Appendage VI) are two broad paddle-like legs used for swimming.
The ophisthosoma (the abdomen) is composed of 12 segments, composed of fused upper plates (tergites) and bottom plates (sternites). It is further subdivided into two groups: the first seven segments are known as the preabdomen (or the mesosoma), while segments eight to twelve are known as the postabdomen (the metasoma).
On the bottom side of the preabdomen are central clasping appendages used for reproduction. In the female they are very short with lateral lobes. In males, they are longer, with diverging distal spines that fit into genital appendages of the females.
The main respiratory organs or Eurypterus were book gills, located in branchial chambers within the preabdomen and used for underwater respiration. They are composed of several layers of stacked thin tissue resembling the pages of a book, hence the name. In addition, they also possessed five pairs of oval-shaped areas covered with microscopic projections on the underside of the preabdomen. These areas are known as Kiemenplatten (or gill-tracts, though the former term is preferred). They are unique to eurypterids.
The postabdomen are the last five segments of the Eurypterus body. Each of the segments contain lateral flattened protrusions known as the epimera with the exception of the last needle-like (styliform) segment known as the telson (the 'tail'). The segment immediately preceding the telson (which also has the largest epimera of the postabdomen) is known as the pretelson.
The exoskeleton of Eurypterus is often covered with small outgrowths known as ornamentation. They include pustules (small protrusions), scales, and striations. They vary by species and are used for identification. For more detailed diagnostic descriptions of each species under Eurypterus, see sections below.
Eurypterus (and other members of Eurypteroidea) were unable to cross vast expanses of oceans during the Silurian. Thus they were limited to the ancient supercontinent of Laurussia (modern North America and western Eurasia).
The ancestors of Eurypterus were believed to have originated from Baltica (eastern Laurussia, modern western Eurasia) based on the earliest recorded fossils. During the Silurian, they spread to Laurentia (western Laurussia, modern North America). They rapidly colonized the continent as an invasive species, becoming the most dominant eurypterid in the region. This accounts for why they are the most commonly found genus of eurypterids.
Today they are known from fossils from North America, Europe, and northwestern Asia, the former components of Laurussia. Three species of Eurypterus were purportedly discovered in China in 1957, in a location not part of Laorussia. But the evidence of them belonging to the genus (or if they were even eurypterids at all), is nonexistent.
Eurypterus are very common fossils in their regions of occurrence, millions of specimens are possible in a given area, though access to the rock formations may be difficult. Most fossil eurypterids are the disjointed shed exoskeleton of individuals after molting (ecdysis), but complete remains of eurypterids are still relatively common (though they may also be molts as well). Fossil eurypterids are often deposited in characteristic windrows, probably a result of wave and wind action.
Paleobiology and paleoecology
Juvenile Eurypterus differed from adults in several ways. Their carapaces were narrower and longer (parabolic) in contrast to the trapezoidal carapaces of adults. The eyes are aligned almost laterally but move to a more anterior location during growth. The preabdomen also lengthened, increasing the overall length of the ophisthosoma. The swimming legs also became narrower and the telsons shorter and broader (though in E. tetragonophthalmus and E. henningsmoeni the telsons changed from being angular in juveniles to larger and more rounded in adults). All these changes are believed to be a result of the respiratory and reproductive requirements of adults.
- Eurypterus De Kay, 1825
- ?Eurypterus cephalaspis Salter, 1856 — Silurian, England
- No raised scales on the posterior margin of the carapace or of the three front-most tergites. The rest of the tergites each have four raised scales. Four to six spines on each podomere of Appendages III and IV. Pretelson has large, rounded epimera without ornamentation on the margins. The species is very similar to E. laculatus. The species is named after James Ellsworth De Kay. Specimens recovered from New York and Ontario.
- Eurypterus flintstonensis Swartz, 1923 — Silurian, USA
- Small Eurypterus species, averaging at 10 to 15 centimetres (3.9 to 5.9 in) long. The largest specimen found is about 20 to 25 centimetres (7.9 to 9.8 in) in length. They can be distinguished by pustules and six scales at the rear margin of their carapaces. Appendages I to IV has two spines on each podomere. The postabdomen have small epimera. The pretelson has long pointed epimera. Telson has striations near its attachment to the pretelson. The species is named after Norwegian paleontologist Nils-Martin Hanken, of the University of Tromsø. Found in the Steinsfjorden Formation of Ringerike, Norway.
- Eurypterus henningsmoeni (Tetlie, 2002) — Silurian, Norway
- Eurypterus with broad paddles and metastoma. Postabdomen has small epimera. Pretelson has large rounded epimera with imbricate scales (overlapping, similar to fish scales). It is very similar and closely related to E. tetragonophthalmus. The species was named after the Norwegian paleontologist Gunnar Henningsmoen. Found in Bærum, Norway.
- Eurypterus laculatus Kjellesvig-Waering, 1958 — Silurian, USA & Canada
- The visual area of the compound eyes of this species are surrounded by depressions. The ocelli and the ocellar mound are small. No pustules or raised scales on the carapace or the first tergite. It is probably closely related to E. dekayi. Its specific name means "four-cornered", from Latin laculatus (four-cornered or checkered). Found in New York and Ontario.
- Eurypterus lacustris Harlan, 1834 — Silurian, USA & Canada
- = Eurypterus pachycheirus Hall, 1859 — Silurian, USA & Canada
- = Eurypterus robustus Hall, 1859 — Silurian, USA & Canada
- One of the two most common Eurypterus fossils found. It is very similar to E. remipes and often found in the same localities, but the eyes are placed at a more posterior position on the carapace of E. lacustris. It is also slightly larger with a slightly narrower metastoma. Its status as a distinct species was once disputed before diagnostic analysis by Tollerton in 1993. Its specific name means "from a lake", from Latin lacus (lake). Found in New York and Ontario.
- Eurypterus leopoldi Tetlie, 2006 — Silurian, Canada
- Frontmost tergite is reduced. Metasoma is rhombiovate in shape with tooth-like projections at the anterior part. The pretelson has serrated edges. the epimera are large, semi-angular with angular striations. The telson is styliform with large angular striations interspersed among smaller more numerous striations. The species is named after Port Leopold and the Leopold Formation were they were collected. Found in the Leopold Formation of Somerset Island, Canada.
- Eurypterus megalops Clarke & Ruedemann, 1912 — Silurian, USA
- ?Eurypterus minor Laurie, 1899 — Silurian, Scotland
- Small Eurypterus with large pustules on the carapace and abdomen. Does not possess the scale ornamentation found in other species of Eurypterus. It is the earliest known species of Eurypterus. They have large palpebral lobes (part of "cheeks" of the carapace adjacent to the compound eyes), making it easy to mistake their eyes for being oval. This enlargement is more typical of the genus Dolichopterus and it may actually belong to Dolichopteridae. The specific name means "smaller", from Latin minor. Found in the Reservoir Formation of Pentland Hills, Scotland.
- Eurypterus ornatus Leutze, 1958 — Silurian, USA
- Eurypterus pittsfordensis Sarle, 1903 — Silurian, USA
- The posterior margin of the carapace has three raised scales. Apendages II to IV has two spines per podomere. The metastoma is rhomboid in shape with a deep notch at the front part. The postabdomen has serrated fringes at the middle with small angular epimera at the sides. The pretelson has large, semiangular epimera with angular striations at the margins. The telson is styliform with sparse angular striations at the margins. The name of the species comes from its place of discovery - Pittsford, New York.
- Eurypterus quebecensis Kjellesvig-Waering, 1958 — Silurian, Canada
- Has six raised scales on the posterior margin of the carapace but does not possess pustule ornamentation. It is named after the location it was recovered from - Quebec, Canada.
- Eurypterus remipes DeKay, 1825 — Silurian, USA, Canada
- = Carcinosoma trigona (Ruedemann, 1916) — Silurian, USA
- The most common Eurypterus species. Has four raised scales at the posterior margin of the carapace. Appendages I to IV has two spines on each podomere. Postabdomen has small epimera. Pretelson has small, semiangular epimera with imbricate scale ornamentation at the margins. The telson has serrated margins along most of its length. It is very similar to E. lacustris and can often only be distinguished by the position of the eyes. The specific name means "oar-foot", from Latin rēmus (oar) and pes (foot). Found in New York and Ontario.
- Eurypterus serratus (Jones & Woodward, 1888) — Silurian, Sweden
- = Eurypterus fischeri Eichwald, 1854 — Silurian, Ukraine
- = Eurypterus fischeri var. rectangularis Schmidt, 1883 — Silurian, Estonia
- Four raised scales on the posterior margin of the carapce. Appendages II to IV each have two spines on each podomere. Postabdomen has small epimera. The pretelson has large, rounded epimera with imbricate scale ornamentation at the margins. Telson has imbricate scale ornamentations at the margins of the base which become serrations towards the tip. Male individuals of E. tetragonophthalmus possess a distinctive scimitar-shaped lobe on its second appendage. This is not present in any other species of Eurypterus making them easy to recognize. The specific name means "four-edged eye", from Greek τέσσαρες (tessares, four), γωνία (gōnia, angle), and ὀφθαλμός (ophthalmos, eye). Found in the Rootsiküla Formation of Saaremaa (Ösel), Estonia with additional discoveries in Ukraine, and possibly Moldova and Romania.
The list does not include the large number of fossils previously classified under Eurypterus. Most of them are now reclassified to other genera, identified as other animals (like crustaceans) or pseudofossils, or remains of doubtful placement. Classification is based on Dunlop et al.(2011).
The genus Eurypterus derives from E. minor, the oldest known species from the Llandovery of Scotland. E. minor is believed to have diverged from Dolichopterus macrocheirus sometime in the Llandovery. The following is the phylogenetic tree of Eurypterus based on phylogenetic studies by O. Erik Tetlie in 2006. Some species are not represented.
In popular culture
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- ^ "Eurypterus remipes NPL4415". Texas Natural Science Center: Non-vertebrate Paleontology, The Univeristy of Texas. http://www.utexas.edu/tmm/npl/exhibits/eurypterus.html. Retrieved May 22, 2011.
- ^ a b c Conrad Burkert. Environment preference of eurypterids – indications for freshwater adaptation?. Technische Universität Bergakademie Freiberg. http://www.geo.tu-freiberg.de/oberseminar/os06_07/Conrad_Burkert.pdf. Retrieved May 21, 2011.
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- ^ a b c James Lamsdell. "Eurypterid Basics". Eurypterids.co.uk. http://www.eurypterids.co.uk/eurypterids.htm. Retrieved May 20, 2011.
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- ^ Lief Størmer (1955). "Merostomata". In C. Raymond. Treatise on Invertebrate Paleontology, Part P: Arthropoda 2: Chelicerata, Pycnogonida & Palaeoisopus. Geological Society of America and University of Kansas Press. pp. 31-34. ISBN 0813730163.
- ^ Phillip L. Manning & Jason A. Dunlop (1995). "The respiratory organs of Eurypterids". Palaeontology (The Palaeontological Association) 38 (2): 287-297. ISSN 0031-0239. http://palaeontology.palass-pubs.org/pdf/Vol%2038/Pages%20287-297.pdf. Retrieved May 21, 2011.
- ^ P. A. Selden (1985). "Eurypterid respiration". Philosophical Transactions of the Royal Society of London (Royal Society) B 309: 219-226. ISSN 0080-4622. http://homepage.mac.com/paulselden/Sites/Website/EuryResp.pdf. Retrieved May 22, 2011.
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- ^ "New York State Fossil - Eurypterus remipes". New York State Library. April 27, 2009. http://www.nysl.nysed.gov/emblems/fossil.htm. Retrieved May 20, 2011.