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96-470: Rhenopterus is an extinct prehistoric eurypterid . Fossils of Rhenopterus have been recovered from deposits of Lower Devonian age in Germany . Rhenopterids were small, characterized by scattered tubercules and knobs on the outer surface of the exoskeleton. Their first two (or possibly three) pairs of walking legs had spines; the last two pairs were long and powerful, without spines. The prosoma (head)

192-578: A cosmopolitan distribution . Though the eurypterids continued to be abundant and diversify during the Early Devonian (for instance leading to the evolution of the pterygotid Jaekelopterus , the largest of all arthropods), the group was one of many heavily affected by the Late Devonian extinction . The extinction event, only known to affect marine life (particularly trilobites, brachiopods and reef -building organisms) effectively crippled

288-408: A lung , plastron or a pseudotrachea . Plastrons are organs that some arthropods evolved secondarily to breathe air underwater. This is considered an unlikely explanation since eurypterids had evolved in water from the start and they would not have organs evolved from air-breathing organs present. In addition, plastrons are generally exposed on outer parts of the body while the eurypterid gill tract

384-459: A few genera, such as Adelophthalmus and Pterygotus , achieved a cosmopolitan distribution with fossils being found worldwide. Like all other arthropods , eurypterids possessed segmented bodies and jointed appendages (limbs) covered in a cuticle composed of proteins and chitin . As in other chelicerates , the body was divided into two tagmata (sections); the frontal prosoma (head) and posterior opisthosoma (abdomen). The prosoma

480-742: A gait like that of most modern insects. The weight of its long abdomen would have been balanced by two heavy and specialized frontal appendages, and the center of gravity might have been adjustable by raising and positioning the tail. Preserved fossilized eurypterid trackways tend to be large and heteropodous and often have an associated telson drag mark along the mid-line (as with the Scottish Hibbertopterus track). Such trackways have been discovered on every continent except for South America. In some places where eurypterid fossil remains are otherwise rare, such as in South Africa and

576-670: 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 likely to have appeared first either during the Early Ordovician or Late Cambrian period. With approximately 250 species, the Eurypterida is the most diverse Paleozoic chelicerate order. Following their appearance during

672-416: A manner similar to modern horseshoe crabs, by grabbing and shredding food with their appendages before pushing it into their mouth using their chelicerae. Fossils preserving digestive tracts have been reported from fossils of various eurypterids, among them Carcinosoma , Acutiramus and Eurypterus . Though a potential anal opening has been reported from the telson of a specimen of Buffalopterus , it

768-425: A meter (1.64 ft) even if the extended chelicerae are not included. Two other eurypterids have also been estimated to have reached lengths of 2.5 metres; Erettopterus grandis (closely related to Jaekelopterus ) and Hibbertopterus wittebergensis , but E. grandis is very fragmentary and the H. wittenbergensis size estimate is based on trackway evidence, not fossil remains. The family of Jaekelopterus ,

864-471: A rowing type of propulsion similar to that of crabs and water beetles . Larger individuals may have been capable of underwater flying (or subaqueous flight ) in which the motion and shape of the paddles are enough to generate lift , similar to the swimming of sea turtles and sea lions . This type of movement has a relatively slower acceleration rate than the rowing type, especially since adults have proportionally smaller paddles than juveniles. However, since

960-553: Is a genital appendage. This appendage, an elongated rod with an internal duct, is found in two distinct morphs, generally referred to as "type A" and "type B". These genital appendages are often preserved prominently in fossils and have been the subject of various interpretations of eurypterid reproduction and sexual dimorphism. Type A appendages are generally longer than those of type B. In some genera they are divided into different numbers of sections, such as in Eurypterus where

1056-495: Is a lightweight build. Factors such as locomotion, energy costs in molting and respiration, as well as the actual physical properties of the exoskeleton , limit the size that arthropods can reach. A lightweight construction significantly decreases the influence of these factors. Pterygotids were particularly lightweight, with most fossilized large body segments preserving as thin and unmineralized. Lightweight adaptations are present in other giant paleozoic arthropods as well, such as

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1152-529: Is also possible and the structure may represent the unfused tips of the appendages. Located between the dorsal and ventral surfaces of the Blattfüsse associated with the type A appendages is a set of organs traditionally described as either "tubular organs" or "horn organs". These organs are most often interpreted as spermathecae (organs for storing sperm ), though this function is yet to be proven conclusively. In arthropods, spermathecae are used to store

1248-489: Is located behind the Blattfüssen . Instead, among arthropod respiratory organs, the eurypterid gill tracts most closely resemble the pseudotracheae found in modern isopods . These organs, called pseudotracheae, because of some resemblance to the tracheae (windpipes) of air-breathing organisms, are lung-like and present within the pleopods (back legs) of isopods. The structure of the pseudotracheae has been compared to

1344-487: Is made up of the first six exoskeleton segments fused together into a larger structure. The seventh segment (thus the first opisthosomal segment) is referred to as the metastoma and the eighth segment (distinctly plate-like) is called the operculum and contains the genital aperature. The underside of this segment is occupied by the genital operculum, a structure originally evolved from ancestral seventh and eighth pair of appendages. In its center, as in modern horseshoe crabs,

1440-521: Is more likely that the anus was opened through the thin cuticle between the last segment before the telson and the telson itself, as in modern horseshoe crabs. Eurypterid coprolites discovered in deposits of Ordovician age in Ohio containing fragments of a trilobite and eurypterid Megalograptus ohioensis in association with full specimens of the same eurypterid species have been suggested to represent evidence of cannibalism . Similar coprolites referred to

1536-544: Is much more of a marine influence in many of the sections yielding Adelophthalmus than has previously been acknowledged." Similarly, a study of the eurypterid Hibbertopterus from the Carboniferous of New Mexico concluded that the habitat of some eurypterids "may need to be re-evaluated". The sole surviving eurypterine family, Adelophthalmidae, was represented by only a single genus, Adelophthalmus . The hibbertopterids, mycteroptids and Adelophthalmus survived into

1632-414: Is not true for all of the traits all of the time: many lack segmentation in the body wall, coelom and musculature. Although perhaps not as well understood as Drosophila , the embryological process of segmentation has been studied in many vertebrate groups, such as fish ( Zebrafish , Medaka ), reptiles ( Corn Snake ), birds ( Chicken ), and mammals ( Mouse ). Segmentation in chordates is characterized as

1728-638: Is possible that many eurypterid species thought to be distinct actually represent juvenile specimens of other species, with paleontologists rarely considering the influence of ontogeny when describing new species. Studies on a well-preserved fossil assemblage of eurypterids from the Pragian -aged Beartooth Butte Formation in Cottonwood Canyon , Wyoming , composed of multiple specimens of various developmental stages of eurypterids Jaekelopterus and Strobilopterus , revealed that eurypterid ontogeny

1824-470: Is referred to as the metastoma, originally derived from a complete exoskeleton segment. The opisthosoma itself can be divided either into a " mesosoma " (comprising segments 1 to 6) and " metasoma " (comprising segments 7 to 12) or into a "preabdomen" (generally comprising segments 1 to 7) and "postabdomen" (generally comprising segments 8 to 12). The underside of the opisthosoma was covered in structures evolved from modified opisthosomal appendages. Throughout

1920-439: Is the first record of land locomotion by a eurypterid. The trackway provides evidence that some eurypterids could survive in terrestrial environments, at least for short periods of time, and reveals information about the stylonurine gait. In Hibbertopterus , as in most eurypterids, the pairs of appendages are different in size (referred to as a heteropodous limb condition). These differently sized pairs would have moved in phase, and

2016-816: Is the metastoma becoming proportionally less wide. This ontogenetic change has been observed in members of several superfamilies, such as the Eurypteroidea, the Pterygotioidea and the Moselopteroidea . No fossil gut contents from eurypterids are known, so direct evidence of their diet is lacking. The eurypterid biology is particularly suggestive of a carnivorous lifestyle. Not only were many large (in general, most predators tend to be larger than their prey), but they had stereoscopic vision (the ability to perceive depth). The legs of many eurypterids were covered in thin spines, used both for locomotion and

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2112-461: Is the most highly studied. Early screens to identify genes involved in cuticle development led to the discovery of a class of genes that was necessary for proper segmentation of the Drosophila embryo. To properly segment the Drosophila embryo, the anterior - posterior axis is defined by maternally supplied transcripts giving rise to gradients of these proteins. This gradient then defines

2208-418: Is unlikely the "gill tract" contained functional gills when comparing the organ to gills in other invertebrates and even fish. Previous interpretations often identified the eurypterid "gills" as homologous with those of other groups (hence the terminology), with gas exchange occurring within the spongy tract and a pattern of branchio-cardiac and dendritic veins (as in related groups) carrying oxygenated blood into

2304-533: The Ancient Greek words εὐρύς ( eurús ), meaning 'broad' or 'wide', and πτερόν ( pterón ), meaning 'wing', referring to the pair of wide swimming appendages present in many members of the group. The eurypterid order includes the largest known arthropods ever to have lived. The largest, Jaekelopterus , reached 2.5 meters (8.2 ft) in length. Eurypterids were not uniformly large and most species were less than 20 centimeters (8 in) long;

2400-520: The Permian–Triassic extinction event (or sometime shortly before) 251.9   million years ago. Although popularly called "sea scorpions", only the earliest eurypterids were marine ; many later forms lived in brackish or fresh water , and they were not true scorpions . Some studies suggest that a dual respiratory system was present, which would have allowed for short periods of time in terrestrial environments. The name Eurypterida comes from

2496-597: The Pterygotioidea , the Hibbertopteridae and the Mycteroptidae , the telson was flattened and may have been used as a rudder while swimming. Some genera within the superfamily Carcinosomatoidea , notably Eusarcana , had a telson similar to that of modern scorpions and may have been capable of using it to inject venom . The coxae of the sixth pair of appendages were overlaid by a plate that

2592-532: The Stylonuroidea , Kokomopteroidea and Mycteropoidea as well as eurypterine groups such as the Pterygotioidea, Eurypteroidea and Waeringopteroidea . The most successful eurypterid by far was the Middle to Late Silurian Eurypterus , a generalist , equally likely to have engaged in predation or scavenging . Thought to have hunted mainly small and soft-bodied invertebrates, such as worms , species of

2688-429: The fruit fly form segments from a field of equivalent cells based on transcription factor gradients. Vertebrates like the zebrafish use oscillating gene expression to define segments known as somites . Annelids such as the leech use smaller blast cells budded off from large teloblast cells to define segments. Although Drosophila segmentation is not representative of the arthropod phylum in general, it

2784-401: The leech has been described as “budding” segmentation. Early divisions within the leech embryo result in teloblast cells, which are stem cells that divide asymmetrically to create bandlets of blast cells. Furthermore, there are five different teloblast lineages (N, M, O, P, and Q), with one set for each side of the midline. The N and Q lineages contribute two blast cells for each segment, while

2880-442: The rhizodonts , were the new apex predators in marine environments. However, various recent findings raise doubts about this, and suggest that these eurypterids were euryhaline forms that lived in marginal marine environments, such as estuaries, deltas, lagoons, and coastal ponds. One argument is paleobiogeographical; pterygotoid distribution seems to require oceanic dispersal. A recent review of Adelophthalmoidea admitted that "There

2976-405: The spermatophore received from males. This would imply that the type A appendage is the female morph and the type B appendage is the male. Further evidence for the type A appendages representing the female morph of genital appendages comes in their more complex construction (a general trend for female arthropod genitalia). It is possible that the greater length of the type A appendage means that it

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3072-539: The Devonian, large two meter (6.5+ ft) pterygotids such as Acutiramus were already present during the Late Silurian. Their ecology ranged from generalized predatory behavior to ambush predation and some, such as Pterygotus itself, were active apex predators in Late Silurian marine ecosystems. The pterygotids were also evidently capable of crossing oceans, becoming one of only two eurypterid groups to achieve

3168-469: The M, O, and P lineages only contribute one cell per segment. Finally, the number of segments within the embryo is defined by the number of divisions and blast cells. Segmentation appears to be regulated by the gene Hedgehog , suggesting its common evolutionary origin in the ancestor of arthropods and annelids. Within the annelids, as with the arthropods, the body wall, nervous system, kidneys, muscles and body cavity are generally segmented. However, this

3264-825: The Middle Ordovician suggests that eurypterids either originated during the Early Ordovician and experienced a rapid and explosive radiation and diversification soon after the first forms evolved, or that the group originated much earlier, perhaps during the Cambrian period. As such, the exact eurypterid time of origin remains unknown. Though fossils referred to as "primitive eurypterids" have occasionally been described from deposits of Cambrian or even Precambrian age, they are not recognized as eurypterids, and sometimes not even as related forms, today. Some animals previously seen as primitive eurypterids, such as

3360-602: The Middle Ordovician, 467.3 million years ago . There are also reports of even earlier fossil eurypterids in the Fezouata Biota of Late Tremadocian (Early Ordovician) age in Morocco , but these have yet to be thoroughly studied, and are likely to be peytoiid appendages. Pentecopterus was a relatively derived eurypterid, part of the megalograptid family within the carcinosomatoid superfamily. Its derived position suggests that most eurypterid clades, at least within

3456-658: The Middle Silurian and the Early Devonian, with an absolute peak in diversity during the Pridoli epoch , 423 to 419.2 million years ago, of the very latest Silurian. This peak in diversity has been recognized since the early twentieth century; of the approximately 150 species of eurypterids known in 1916, more than half were from the Silurian and a third were from the Late Silurian alone. Though stylonurine eurypterids generally remained rare and low in number, as had been

3552-597: The Ordovician, eurypterids became major components of marine faunas during the Silurian , from which the majority of eurypterid species have been described. The Silurian genus Eurypterus accounts for more than 90% of all known eurypterid specimens. Though the group continued to diversify during the subsequent Devonian period, the eurypterids were heavily affected by the Late Devonian extinction event . They declined in numbers and diversity until becoming extinct during

3648-665: The Permian. Segmentation (biology) Segmentation is a difficult process to satisfactorily define. Many taxa (for example the molluscs) have some form of serial repetition in their units but are not conventionally thought of as segmented. Segmented animals are those considered to have organs that were repeated, or to have a body composed of self-similar units, but usually it is the parts of an organism that are referred to as being segmented. Segmentation in animals typically falls into three types, characteristic of different arthropods , vertebrates , and annelids . Arthropods such as

3744-555: The Pterygotidae, is noted for several unusually large species. Both Acutiramus , whose largest member A. bohemicus measured 2.1 meters (6.9 ft), and Pterygotus , whose largest species P. grandidentatus measured 1.75 meters (5.7 ft), were gigantic. Several different contributing factors to the large size of the pterygotids have been suggested, including courtship behaviour, predation and competition over environmental resources. Giant eurypterids were not limited to

3840-598: The Stylonurina, this appendage takes the form of a long and slender walking leg, while in the Eurypterina, the leg is modified and broadened into a swimming paddle. Other than the swimming paddle, the legs of many eurypterines were far too small to do much more than allow them to crawl across the sea floor . In contrast, a number of stylonurines had elongated and powerful legs that might have allowed them to walk on land (similar to modern crabs ). A fossil trackway

3936-550: The abundance and diversity previously seen within the eurypterids. A major decline in diversity had already begun during the Early Devonian and eurypterids were rare in marine environments by the Late Devonian. During the Frasnian stage four families went extinct, and the later Famennian saw an additional five families going extinct. As marine groups were the most affected, the eurypterids were primarily impacted within

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4032-537: The ancient continent of Laurentia , and demersal (living on the seafloor ) and basal animals from the continents Avalonia and Gondwana. The Laurentian predators, classified in the family Megalograptidae (comprising the genera Echinognathus , Megalograptus and Pentecopterus ), are likely to represent the first truly successful eurypterid group, experiencing a small radiation during the Late Ordovician. Eurypterids were most diverse and abundant between

4128-442: The animal in question could possibly have measured just short of 2 meters (6.6 ft) in length. More robust than the pterygotids, this giant Hibbertopterus would possibly have rivalled the largest pterygotids in weight, if not surpassed them, and as such be among the heaviest arthropods. The two eurypterid suborders, Eurypterina and Stylonurina , are distinguished primarily by the morphology of their final pair of appendages. In

4224-454: The appendage via tracts, but these supposed tracts remain unpreserved in available fossil material. Type B appendages, assumed male, would have produced, stored and perhaps shaped spermatophore in a heart-shaped structure on the dorsal surface of the appendage. A broad genital opening would have allowed large amounts of spermatophore to be released at once. The long furca associated with type B appendages, perhaps capable of being lowered like

4320-414: The body. The primary analogy used in previous studies has been horseshoe crabs, though their gill structure and that of eurypterids are remarkably different. In horseshoe crabs, the gills are more complex and composed of many lamellae (plates) which give a larger surface area used for gas exchange. In addition, the gill tract of eurypterids is proportionally much too small to support them if it is analogous to

4416-458: The case during the preceding Ordovician, eurypterine eurypterids experienced a rapid rise in diversity and number. In most Silurian fossil beds, eurypterine eurypterids account for 90% of all eurypterids present. Though some were likely already present by the Late Ordovician (simply missing from the fossil record so far), a vast majority of eurypterid groups are first recorded in strata of Silurian age. These include both stylonurine groups such as

4512-420: The coastlines and shallow inland seas of Euramerica. During the Late Silurian the pterygotid eurypterids, large and specialized forms with several new adaptations, such as large and flattened telsons capable of being used as rudders, and large and specialized chelicerae with enlarged pincers for handling (and potentially in some cases killing) prey appeared. Though the largest members of the family appeared in

4608-695: The cuticle) after which they underwent rapid and immediate growth. Some arthropods, such as insects and many crustaceans, undergo extreme changes over the course of maturing. Chelicerates, including eurypterids, are in general considered to be direct developers, undergoing no extreme changes after hatching (though extra body segments and extra limbs may be gained over the course of ontogeny in some lineages, such as xiphosurans and sea spiders ). Whether eurypterids were true direct developers (with hatchlings more or less being identical to adults) or hemianamorphic direct developers (with extra segments and limbs potentially being added during ontogeny) has been controversial in

4704-412: The development of other structures, such as muscles, across the basic segments. Lower vertebrates such as zebrafish do not require retinoic acid repression of caudal Fgf8 for somitogenesis due to differences in gastrulation and neuromesodermal progenitor function compared to higher vertebrates. In other taxa, there is some evidence of segmentation in some organs, but this segmentation is not pervasive to

4800-405: The embryo and moves towards the anterior , creating travelling waves of gene expression. The "wavefront" is where clock oscillations arrest, initiating gene expression that leads to the patterning of somite boundaries. The position of the wavefront is defined by a decreasing posterior-to-anterior gradient of FGF signalling. In higher vertebrates including Mouse and Chick , (but not Zebrafish ),

4896-409: The eurypterine suborder, had already been established at this point during the Middle Ordovician. The earliest known stylonurine eurypterid, Brachyopterus , is also Middle Ordovician in age. The presence of members of both suborders indicates that primitive stem-eurypterids would have preceded them, though these are so far unknown in the fossil record. The presence of several eurypterid clades during

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4992-411: The eurypterine suborder. Only one group of stylonurines (the family Parastylonuridae ) went extinct in the Early Devonian. Only two families of eurypterines survived into the Late Devonian at all ( Adelophthalmidae and Waeringopteridae). The eurypterines experienced their most major declines in the Early Devonian, during which over 50% of their diversity was lost in just 10 million years. Stylonurines, on

5088-515: The eurypterine swimming paddles varied from group to group. In the Eurypteroidea , the paddles were similar in shape to oars. The condition of the joints in their appendages ensured their paddles could only be moved in near-horizontal planes, not upwards or downwards. Some other groups, such as the Pterygotioidea, would not have possessed this condition and were probably able to swim faster. Most eurypterines are generally agreed to have utilized

5184-427: The expression pattern for gap genes , which set up the boundaries between the different segments. The gradients produced from gap gene expression then define the expression pattern for the pair-rule genes . The pair-rule genes are mostly transcription factors , expressed in regular stripes down the length of the embryo. These transcription factors then regulate the expression of segment polarity genes , which define

5280-454: The family Pterygotidae. An isolated 12.7 centimeters (5.0 in) long fossil metastoma of the carcinosomatoid eurypterid Carcinosoma punctatum indicates the animal would have reached a length of 2.2 meters (7.2 ft) in life, rivalling the pterygotids in size. Another giant was Pentecopterus decorahensis , a primitive carcinosomatoid, which is estimated to have reached lengths of 1.7 meters (5.6 ft). Typical of large eurypterids

5376-467: The formation of a pair of somites on either side of the midline. This is often referred to as somitogenesis . In vertebrates, segmentation is most often explained in terms of the clock and wavefront model . The "clock" refers to the periodic oscillation in abundance of specific gene products, such as members of the Hairy and Enhancer of Split (Hes) gene family. Expression starts at the posterior end of

5472-476: The found tracks each being about 7.6 centimeters (3.0 in) in diameter. Other eurypterid ichnogenera include Merostomichnites (though it is likely that many specimens actually represent trackways of crustaceans) and Arcuites (which preserves grooves made by the swimming appendages). In eurypterids, the respiratory organs were located on the ventral body wall (the underside of the opisthosoma). Blattfüsse , evolved from opisthosomal appendages, covered

5568-453: The full list of organs mentioned above for arthropods and annelids. One might think of the serially repeated units in many Cycloneuralia , or the segmented body armature of the chitons (which is not accompanied by a segmented coelom). Segmentation can be seen as originating in two ways. To caricature, the 'amplification' pathway would involve a single-segment ancestral organism becoming segmented by repeating itself. This seems implausible, and

5664-582: The gathering of food. In some groups, these spiny appendages became heavily specialized. In some eurypterids in the Carcinosomatoidea, forward-facing appendages were large and possessed enormously elongated spines (as in Mixopterus and Megalograptus ). In derived members of the Pterygotioidea, the appendages were completely without spines, but had specialized claws instead. Other eurypterids, lacking these specialized appendages, likely fed in

5760-656: The genus Strabops from the Cambrian of Missouri , are now classified as aglaspidids or strabopids . The aglaspidids, once seen as primitive chelicerates, are now seen as a group more closely related to trilobites. The fossil record of Ordovician eurypterids is quite poor. The majority of eurypterids once reportedly known from the Ordovician have since proven to be misidentifications or pseudofossils . Today only 11 species can be confidently identified as representing Ordovician eurypterids. These taxa fall into two distinct ecological categories; large and active predators from

5856-525: The genus (of which the most common is the type species, E. remipes ) account for more than 90% (perhaps as many as 95%) of all known fossil eurypterid specimens. Despite their vast number, Eurypterus are only known from a relatively short temporal range, first appearing during the Late Llandovery epoch (around 432 million years ago) and being extinct by the end of the Pridoli epoch. Eurypterus

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5952-429: The giant millipede Arthropleura , and are possibly vital for the evolution of giant size in arthropods. In addition to the lightweight giant eurypterids, some deep-bodied forms in the family Hibbertopteridae were also very large. A carapace from the Carboniferous of Scotland referred to the species Hibbertoperus scouleri measures 65 cm (26 in) wide. As Hibbertopterus was very wide compared to its length,

6048-412: The gills of other groups. To be functional gills, they would have to have been highly efficient and would have required a highly efficient circulatory system. It is considered unlikely, however, that these factors would be enough to explain the large discrepancy between gill tract size and body size. It has been suggested instead that the "gill tract" was an organ for breathing air, perhaps actually being

6144-580: The invaginations leading to asphyxiation . Furthermore, most eurypterids would have been aquatic their entire lives. No matter how much time was spent on land, organs for respiration in underwater environments must have been present. True gills, expected to have been located within the branchial chamber within the Blattfüssen , remain unknown in eurypterids. Like all arthropods, eurypterids matured and grew through static developmental stages referred to as instars . These instars were punctuated by periods during which eurypterids went through ecdysis (molting of

6240-491: The larger sizes of adults mean a higher drag coefficient , using this type of propulsion is more energy-efficient. Some eurypterines, such as Mixopterus (as inferred from attributed fossil trackways), were not necessarily good swimmers. It likely kept mostly to the bottom, using its swimming paddles for occasional bursts of movements vertically, with the fourth and fifth pairs of appendages positioned backwards to produce minor movement forwards. While walking, it probably used

6336-505: The largest known arthropod ever to have lived, is Jaekelopterus rhenaniae . A chelicera from the Emsian Klerf Formation of Willwerath, Germany measured 36.4 centimeters (14.3 in) in length, but is missing a quarter of its length, suggesting that the full chelicera would have been 45.5 centimeters (17.9 in) long. If the proportions between body length and chelicerae match those of its closest relatives, where

6432-497: The last ever radiation within the eurypterids, which gave rise to several new forms capable of "sweep-feeding" (raking through the substrate in search of prey). Only three eurypterid families—Adelophthalmidae, Hibbertopteridae and Mycteroptidae—survived the extinction event in its entirety. It was assumed that these were all freshwater animals, which would have rendered the eurypterids extinct in marine environments, and with marine eurypterid predators gone, sarcopterygians , such as

6528-492: The limbs tended to get larger the farther back they were. In the Eurypterina suborder , the larger of the two eurypterid suborders, the sixth pair of appendages was also modified into a swimming paddle to aid in traversing aquatic environments. The opisthosoma comprised 12 segments and the telson , the posteriormost division of the body, which in most species took the form of a blade-like shape. In some lineages, notably

6624-494: The mouth. In one lineage, the Pterygotidae , the chelicerae were large and long, with strong, well-developed teeth on specialised chelae (claws). The subsequent pairs of appendages, numbers II to VI, possessed gnathobases (or "tooth-plates") on the coxae (limb segments) used for feeding. These appendages were generally walking legs that were cylindrical in shape and were covered in spines in some species. In most lineages,

6720-712: The opisthosoma, these structures formed plate-like structures termed Blattfüsse ( lit.   ' leaf-feet ' in German). These created a branchial chamber (gill tract) between preceding Blattfüsse and the ventral surface of the opisthosoma itself, which contained the respiratory organs. The second to sixth opisthosomal segments also contained oval or triangular organs that have been interpreted as organs that aid in respiration. These organs, termed Kiemenplatten or "gill tracts", would potentially have aided eurypterids to breathe air above water, while Blattfüssen , similar to organs in modern horseshoe crabs , would cover

6816-424: The other hand, persisted through the period with more or less consistent diversity and abundance but were affected during the Late Devonian, when many of the older groups were replaced by new forms in the families Mycteroptidae and Hibbertopteridae. It is possible that the catastrophic extinction patterns seen in the eurypterine suborder were related to the emergence of more derived fish. Eurypterine decline began at

6912-552: The parts that serve for underwater respiration . The appendages of opisthosomal segments 1 and 2 (the seventh and eighth segments overall) were fused into a structure termed the genital operculum, occupying most of the underside of the opisthosomal segment 2. Near the anterior margin of this structure, the genital appendage (also called the Zipfel or the median abdominal appendage) protruded. This appendage, often preserved very prominently, has consistently been interpreted as part of

7008-433: The past. Hemianamorphic direct development has been observed in many arthropod groups, such as trilobites , megacheirans , basal crustaceans and basal myriapods . True direct development has on occasion been referred to as a trait unique to arachnids . There have been few studies on eurypterid ontogeny as there is a general lack of specimens in the fossil record that can confidently be stated to represent juveniles. It

7104-434: The point when jawless fish first became more developed and coincides with the emergence of placoderms (armored fish) in both North America and Europe. Stylonurines of the surviving hibbertopterid and mycteroptid families completely avoided competition with fish by evolving towards a new and distinct ecological niche. These families experienced a radiation and diversification through the Late Devonian and Early Carboniferous,

7200-484: The polarity of each segment. Boundaries and identities of each segment are later defined. Within the arthropods, the body wall, nervous system, kidneys, muscles and body cavity are segmented, as are the appendages (when they are present). Some of these elements (e.g. musculature) are not segmented in their sister taxon, the onychophora . While not as well studied as in Drosophila and zebrafish , segmentation in

7296-452: The ratio between claw size and body length is relatively consistent, the specimen of Jaekelopterus that possessed the chelicera in question would have measured between 233 and 259 centimeters (7.64 and 8.50 ft), an average 2.5 meters (8.2 ft), in length. With the chelicerae extended, another meter (3.28 ft) would be added to this length. This estimate exceeds the maximum body size of all other known giant arthropods by almost half

7392-445: The reproduction and sexual dimorphism of eurypterids is difficult, as they are only known from fossilized shells and carapaces. In some cases, there might not be enough apparent differences to separate the sexes based on morphology alone. Sometimes two sexes of the same species have been interpreted as two different species, as was the case with two species of Drepanopterus ( D. bembycoides and D. lobatus ). The eurypterid prosoma

7488-458: The reproductive system and occurs in two recognized types, assumed to correspond to male and female. Eurypterids were highly variable in size, depending on factors such as lifestyle, living environment and taxonomic affinity . Sizes around 100 centimeters (3.3 ft) are common in most eurypterid groups. The smallest eurypterid, Alkenopterus burglahrensis , measured just 2.03 centimeters (0.80 in) in length. The largest eurypterid, and

7584-435: The rest of the former supercontinent Gondwana , the discoveries of trackways both predate and outnumber eurypterid body fossils. Eurypterid trackways have been referred to several ichnogenera, most notably Palmichnium (defined as a series of four tracks often with an associated drag mark in the mid-line), wherein the holotype of the ichnospecies P. kosinkiorum preserves the largest eurypterid footprints known to date with

7680-405: The same genera. The primary function of the long, assumed female, type A appendages was likely to take up spermatophore from the substrate into the reproductive tract rather than to serve as an ovipositor, as arthropod ovipositors are generally longer than eurypterid type A appendages. By rotating the sides of the operculum, it would have been possible to lower the appendage from the body. Due to

7776-413: The short stride length indicates that Hibbertopterus crawled with an exceptionally slow speed, at least on land. The large telson was dragged along the ground and left a large central groove behind the animal. Slopes in the tracks at random intervals suggest that the motion was jerky. The gait of smaller stylonurines, such as Parastylonurus , was probably faster and more precise. The functionality of

7872-479: The smallest eurypterid, Alkenopterus , was only 2.03 centimeters (0.80 in) long. Eurypterid fossils have been recovered from every continent. A majority of fossils are from fossil sites in North America and Europe because the group lived primarily in the waters around and within the ancient supercontinent of Euramerica . Only a handful of eurypterid groups spread beyond the confines of Euramerica and

7968-441: The species Lanarkopterus dolichoschelus from the Ordovician of Ohio contain fragments of jawless fish and fragments of smaller specimens of Lanarkopterus itself. Though apex predatory roles would have been limited to the very largest eurypterids, smaller eurypterids were likely formidable predators in their own right just like their larger relatives. As in many other entirely extinct groups, understanding and researching

8064-427: The spongy structure of the eurypterid gill tracts. It is possible the two organs functioned in the same way. Some researchers have suggested that eurypterids may have been adapted to an amphibious lifestyle, using the full gill tract structure as gills and the invaginations within it as pseudotrachea. This mode of life may not have been physiologically possible, however, since water pressure would have forced water into

8160-498: The structure. Though the Kiemenplatte is referred to as a "gill tract", it may not necessarily have functioned as actual gills. In other animals, gills are used for oxygen uptake from water and are outgrowths of the body wall. Despite eurypterids clearly being primarily aquatic animals that almost certainly evolved underwater (some eurypterids, such as the pterygotids, would even have been physically unable to walk on land), it

8256-468: The type A appendage is divided into three but the type B appendage into only two. Such division of the genital appendage is common in eurypterids, but the number is not universal; for instance, the appendages of both types in the family Pterygotidae are undivided. The type A appendage is also armed with two curved spines called furca (lit. 'fork' in Latin). The presence of furca in the type B appendage

8352-414: The type A appendage, could have been used to detect whether a substrate was suitable for spermatophore deposition. Until 1882 no eurypterids were known from before the Silurian. Contemporary discoveries since the 1880s have expanded the knowledge of early eurypterids from the Ordovician period. The earliest eurypterids known today, the megalograptid Pentecopterus , date from the Darriwilian stage of

8448-400: The underside and created a gill chamber where the "gill tracts" were located. Depending on the species, the eurypterid gill tract was either triangular or oval in shape and was possibly raised into a cushion-like state. The surface of this gill tract bore several spinules (small spines), which resulted in an enlarged surface area. It was composed of spongy tissue due to many invaginations in

8544-509: The wavefront also depends upon an opposing anterior-to-posterior decreasing gradient of retinoic acid which limits the anterior spreading of FGF8 ; retinoic acid repression of Fgf8 gene expression defines the wavefront as the point at which the concentrations of both retinoic acid and diffusible FGF8 protein are at their lowest. Cells at this point will mature and form a pair of somites. The interaction of other signaling molecules, such as myogenic regulatory factors , with this gradient promotes

8640-429: The way different plates overlay at its location, the appendage would have been impossible to move without muscular contractions moving around the operculum. It would have been kept in place when not it use. The furca on the type A appendages may have aided in breaking open the spermatophore to release the free sperm inside for uptake. The "horn organs," possibly spermathecae, are thought to have been connected directly to

8736-400: Was also restricted to the continent Euramerica (composed of the equatorial continents Avalonia, Baltica and Laurentia), which had been completely colonized by the genus during its merging and was unable to cross the vast expanses of ocean separating this continent from other parts of the world, such as the southern supercontinent Gondwana. As such, Eurypterus was limited geographically to

8832-496: Was covered by a carapace (sometimes called the "prosomal shield") on which both compound eyes and the ocelli (simple eye-like sensory organs) were located. The prosoma also bore six pairs of appendages which are usually referred to as appendage pairs I to VI. The first pair of appendages, the only pair placed before the mouth, is called the chelicerae ( homologous to the fangs of spiders). They were equipped with small pincers used to manipulate food fragments and push them into

8928-505: Was discovered in Carboniferous-aged fossil deposits of Scotland in 2005. It was attributed to the stylonurine eurypterid Hibbertopterus due to a matching size (the trackmaker was estimated to have been about 1.6 meters (5.2 ft) long) and inferred leg anatomy. It is the largest terrestrial trackway—measuring 6 meters (20 ft) long and averaging 95 centimeters (3.12 ft) in width—made by an arthropod found thus far. It

9024-452: Was more or less parallel and similar to that of extinct and extant xiphosurans, with the largest exception being that eurypterids hatched with a full set of appendages and opisthosomal segments. Eurypterids were thus not hemianamorphic direct developers, but true direct developers like modern arachnids. The most frequently observed change occurring through ontogeny (except for some genera, such as Eurypterus , which appear to have been static)

9120-473: Was subtrapezoidal, with arcuate compound eyes on parallel axes. The male genital appendages were short with two distal spines. Rhenopterus contains three valid species, with other named species now seen as invalid or part of other genera. Invalid or reassigned species are listed below: This eurypterid -related article is a stub . You can help Misplaced Pages by expanding it . Eurypterid Eurypterids , often informally called sea scorpions , are

9216-518: Was used as an ovipositor (used to deposit eggs). The different types of genital appendages are not necessarily the only feature that distinguishes between the sexes of eurypterids. Depending on the genus and species in question, other features such as size, the amount of ornamentation and the proportional width of the body can be the result of sexual dimorphism. In general, eurypterids with type B appendages (males) appear to have been proportionally wider than eurypterids with type A appendages (females) of

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