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137-663: Campylocephalus is a genus of eurypterid , a group of extinct aquatic arthropods . Fossils of Campylocephalus have been discovered in deposits ranging from the Carboniferous period in the Czech Republic (the species C. salmi ) to the Permian period of Russia (species C. oculatus and C. permianus ). The generic name is composed of the Greek words καμπύλος ( kampýlos ), meaning "curved", and κεφαλή ( kephalē ), meaning "head". It

274-564: 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

411-509: 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 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,

548-408: 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

685-431: A class of simple eyes. Many kinds of holometabolous larvae bear no other form of eyes until they enter their final stage of growth. Adults of several orders of hexapods also have stemmata, and never develop compound eyes at all. Examples include fleas , springtails , and Thysanura . Some other Arthropoda , such as some Myriapoda , rarely have any eyes other than stemmata at any stage of their lives (exceptions include

822-413: A clue to their ontogenetic role is their lateral position on the head; ocelli, that in other ways resemble stemmata, tend to be borne in sites median to the compound eyes, or nearly so. Among some researchers, this distinction has led to the use of the term "lateral ocelli" for stemmata. A number of genetic pathways are responsible for the occurrence and positioning of the ocelli. The gene orthodenticle

959-452: A distinct retina, lens, and cornea. Many snails and slugs also have ocelli, either at the tips or bases of their tentacles. Some other gastropods, such as the Strombidae , have much more sophisticated eyes. Giant clams have ocelli that allow light to penetrate their mantles . Spiders do not have compound eyes, but instead have several pairs of simple eyes with each pair adapted for

1096-409: A distinguishing feature in C. permianus , where they were placed more posteriorly than in the other species. Fossils today recognized as belonging to Campylocephalus were first described in 1838 as belonging to a species of the genus Limulus , the same genus as the modern atlantic horseshoe crab , by Russian paleontologist Stepan S. Kutorga. Citing similarities with members of the modern genus in

1233-409: A family of sawflies) are only "simple" in that they represent immature or embryonic forms of the compound eyes of the adult. They can possess a considerable degree of acuity and sensitivity, and can detect polarized light. They may be optimized for light sensitivity, as opposed to detailed image formation. In the pupal stage, such stemmata develop into fully fledged compound eyes. One feature offering

1370-726: 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

1507-463: A hastate (e.g. shaped like a gladius , a Roman sword) telson (which was the posteriormost division of the body) with paired keels on the ventral side, ornamentation consisting of scales or other similar structures on the exoskeleton, the fourth pair of appendages possessing spines, the more posterior tergites of the abdomen possessing tongue-shaped scales near their edges and there being lobes positioned posterolaterally (posteriorly on both sides) on

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1644-590: A lumbering, jerking and dragging movement and that the keeled belly and the telson left a central groove behind. Some studies suggest that eurypterids possessed a dual respiratory system, which would have allowed for this kind of occasional terrestrial movement. C. salmi is known from the Ostrava Formation of the Czech Republic and would have lived during the Arnsbergian age (326.4–318.1 million years ago) of

1781-416: 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

1918-492: A member of the hibbertopterid family of eurypterids , Campylocephalus was overall similar to the other members of the family. It was a large, broad and heavy creature quite unlike most earlier and more famous swimming eurypterids such as Pterygotus and Eurypterus . As a member of the stylonurine suborder , Campylocephalus completely lacked swimming paddles. Several distinguishing features separate Campylocephalus from other genera in its family, in particular from

2055-425: 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 ,

2192-404: A number of neighbouring retinulae. Some jellyfish , sea stars , flatworms , and ribbonworms have the simplest "eyes" – pigment spot ocelli – which have randomly distributed pigment, and which have no other structure (such as a cornea , or lens ). The apparent "eye color" in these animals is red or black. Certain groups such as box jellyfish have more complex eyes, including some with

2329-471: 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

2466-409: A specific task or tasks. The principal and secondary eyes in spiders are arranged in four, or occasionally fewer, pairs. Only the principal eyes have moveable retinas. The secondary eyes have a reflector at the back of the eyes. The light-sensitive part of the receptor cells is next to this, so they get direct and reflected light. In hunting or jumping spiders, for example, a forward-facing pair possesses

2603-547: 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

2740-495: 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

2877-445: Is absent. The sideways-facing ocelli can be called "lateral ocelli", referring to their direction and position in the triplet, however this is not to be confused with the stemmata of some insect larvae, which are also known as lateral ocelli. A dorsal ocellus consists of a lens element ( cornea ) and a layer of photoreceptors ( rod cells ). The ocellar lens may be strongly curved or flat. The photoreceptor layer may also be separated from

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3014-550: Is adapted from Lamsdell (2012), collapsed to only show the superfamily Mycteropoidea. Drepanopterus pentlandicus Drepanopterus abonensis Drepanopterus odontospathus Woodwardopterus scabrosus Mycterops mathieui Hastimima whitei Megarachne servinei Campylocephalus oculatus Hibbertopterus scouleri Hibbertopterus wittebergensis Hibbertopterids such as Campylocephalus were sweep-feeders, having modified spines on their forward-facing prosomal appendages that allowed them to rake through

3151-506: Is allelic to ocelliless, a mutation that stops ocelli from being produced. In Drosophila , the rhodopsin Rh2 is only expressed in simple eyes. While (in Drosophila at least) the genes eyeless and dachshund are both expressed in the compound eye but not the simple eye, no reported 'developmental' genes are uniquely expressed in the simple eye. Epidermal growth factor receptor ( Egfr ) promotes

3288-523: 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

3425-483: 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

3562-487: 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,

3699-517: 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

3836-537: 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

3973-688: Is one of the latest known surviving eurypterid species. The sole fossil representing the species was discovered in the Komi Autonomous Soviet Socialist Republic of the Soviet Union (the modern Komi Republic of Russia) in deposits of approximately the age of the Permian–Triassic extinction event 251.9 million years ago. In the Permian, Komi would have been a coastal region of the supercontinent Pangaea . Though no other fossils of

4110-625: 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

4247-439: 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

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4384-795: 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

4521-418: 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

4658-742: 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 the Ordovician, eurypterids became major components of marine faunas during the Silurian , from which

4795-554: The Early Permian , which left Campylocephalus as one of only two living genera of eurypterids for more than 20 million years until its own extinction in the Permian–Triassic extinction event. Woodwardopterus also went extinct around this time. Eurypterid Eurypterids , often informally called sea scorpions , are a group of extinct arthropods that form the order Eurypterida . The earliest known eurypterids date to

4932-526: The International Commission on Zoological Nomenclature ; If an author designates a certain species as genotype, it is to be assumed that his determination of the species is correct; if a case presents itself in which it appears that an author has based his genus on certain definite specimens , rather than upon a species , it would be well to submit the case, with full details, to the Commission. At

5069-420: The Permian of Russia and C. salmi from the Carboniferous of the Czech Republic . The classification of C. salmi is considered somewhat uncertain, with C. salmi being fragmentary (as all other species of the genus) and possessing some unique features (e.g. the differently sized protuberances around the carapace). The hibbertopterids are united as a group by being large mycteropoids with broad prosomas,

5206-521: 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

5343-530: 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, 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

5480-442: 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

5617-405: 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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5754-840: The substrate of their living environments. Though sweep-feeding was used as a strategy by many genera within the Stylonurina, it was most developed within the hibbertopterids, which possessed blades on the second, third and fourth pair of appendages. Some species of the closely related Hibbertopterus had specialized comb-like rachis (shafts) that were able to entrap small prey and other organic food particles. Though they would have been slow owing to their massive size and robust form, studies on Hibbertopterus footprints discovered in Scotland have demonstrated that hibbertopterids would have been able to walk on land for at least short periods of time. The tracks discovered indicate that they would have utilized

5891-656: The telson , the posteriormost division of the body, which in most species took the form of a blade-like shape. In some lineages, notably 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

6028-489: The 16 eurypterid families that had lived during the beginning of the Devonian period, three families survived and persisted into the Carboniferous period, all of which contained only non-marine species. By the Permian, only four genera were still alive; Adelophthalmus (a adelophthalmid ), Hastimima and Woodwardopterus ( mycteroptids ), and Campylocephalus itself. Both Adelophthalmus and Hastimima went extinct during

6165-400: The Carboniferous period. The deposits were the eurypterid fossils were found are lacustrine , meaning that they formed on the bottom of an ancient lake. Spiders of the genus Eophrynus , part of the extinct arachnid order Trigonotarbida , are known from the same location and age, and numerous anthozoans (the group that contains animals such as corals and sea anemones ) are known from

6302-527: 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

6439-804: 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

6576-590: 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

6713-641: 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

6850-456: The Permian. Ocelli The structure of an animal's eye is determined by the environment in which it lives, and the behavioural tasks it must fulfill to survive. Arthropods differ widely in the habitats in which they live, as well as their visual requirements for finding food or conspecifics , and avoiding predators. Consequently, an enormous variety of eye types are found in arthropods to overcome visual problems or limitations. Use of

6987-549: 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

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7124-532: 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

7261-538: 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

7398-530: 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

7535-442: 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

7672-403: The appearance and anatomy of the somewhat incomplete fossil, Kutorga named it Limulus oculatus . Scottish naturalist John Scouler described the genus Eidothea in 1831 based on a single fossil prosoma from Scotland , but did not grant it any specific name . Creating a genus with no species goes against orthodox zoological nomenclature, specifically conflicting for instance with Opinion 65 of

7809-454: 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

7946-634: The best resolution (and even some telescopic ability) to help spot prey from a distance. Nocturnal spiders' eyes are very sensitive in low light levels and are large to capture more light, equivalent to f/0.58 in the rufous net-casting spider . The term "ocellus" (plural ocelli) is derived from the Latin oculus (eye), and literally means "little eye". In insects, two distinct ocellus types exist: dorsal (top-most) ocelli, and lateral ocelli (often referred to as ocelli and stemmata , respectively), most insects have dorsal ocelli while stemmata are found in

8083-414: 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

8220-465: The carapace and thoracic segments which had been described by Kutorga were quite distinct from Limulus , and thus a new genus was named to contain Limulus oculatus , dubbed by D'Eichwald as Campylocephalus . This generic name is composed of the Greek words καμπύλος ( kampýlos ), meaning "curved", and κεφαλή ( kephalē ), meaning "head". The second species of Campylocephalus to be described, C. salmi ,

8357-467: The carapace. Comparing the ornamentation of the carapace to other eurypterids, Størmer found it to be similar to the genus Tarsopterella (where the legs were also more or less unknown) which allowed Campylocephalus to be firmly placed within the family Stylonuridae (which would later be raised to become the suborder Stylonurina, not to be confused with the presently recognized eurypterid family Stylonuridae ). English paleontologist Charles D. Waterston

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8494-458: 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

8631-406: The closely related Hibbertopterus . Campylocephalus had a subelliptical (almost elliptical) prosoma (head), which was subsemicircular (almost shaped like a semicircle ) and strongly convex, being at its broadest in the midsection. The compound eyes of Campylocephalus were laterally placed (on the sides of the head) and were separated from each other by inflated lobes in the middle. Behind

8768-420: 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

8905-585: The compound eyes. Additionally, given the relatively simple neural arrangement of the eye (small number of synapses between detector and effector ), as well as the extremely large diameter of some ocellar interneurons (often the largest diameter neurons in the animal's nervous system), the ocelli are typically considered to be "faster" than the compound eyes. One common theory of ocellar function in flying insects holds that they are used to assist in maintaining flight stability. Given their underfocused nature, wide fields of view , and high light-collecting ability,

9042-405: The conclusion that, with some exceptions in predatory insects, the ocelli are incapable of perceiving proper images and are thus solely suitable for light-metering functions. Given the large aperture and low f -number of the lens, as well as high convergence ratios and synaptic gains (amplification of photoreceptor signals), the ocelli are generally considered to be far more sensitive to light than

9179-695: 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

9316-412: The dorsal ocelli vary markedly throughout insect orders. They tend to be larger and more strongly expressed in flying insects (particularly bees, wasps, dragonflies and locusts) where they are typically found as a triplet. Two ocelli are directed to either side of the head, while a central (median) ocellus is directed forwards. In some terrestrial insects (e.g. some ants and cockroaches), the median ocellus

9453-504: 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 the Ancient Greek words εὐρύς ( eurús ), meaning 'broad' or 'wide', and πτερόν ( pterón ), meaning 'wing', referring to

9590-409: 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

9727-411: 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

9864-508: 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

10001-462: The exact same age have been reported, other Permian-age life known from the region include bryozoans and bivalves . By the beginning of the Permian, the eurypterids were already in decline relative to what their numbers and diversity had once been. The group was one of many heavily affected by the Late Devonian extinction , which rendered all but a single genus of eurypterine (those with swimming paddles) eurypterids extinct ( Adelophthalmus ). Of

10138-402: The exceptional acrobatic abilities of these animals. Research on the ocelli is of high interest to designers of small unmanned aerial vehicles . Designers of these craft face many of the same challenges that insects face in maintaining stability in a three-dimensional world. Engineers are increasingly taking inspiration from insects to overcome these challenges. Stemmata (singular stemma) are

10275-516: The eyes on the carapace (the exoskeleton segment covering the head) there were some further lobe-like structures referred to as palpebral lobes. As with the prosoma, the tergites (segments on the upper side of the body) of the abdomen were convex in shape, and possessed articular processes (projecting structures that helped the segments to fit together). The appendages (limbs) of Campylocephalus are only very rarely preserved and are as such almost completely unknown. Due to just how incomplete

10412-447: The eyes were semilunar in shape (almost moon-shaped) and placed near the middle of the carapace, with small ocelli (light-sensitive simple eyes) between them. Its carapace had small irregular prominences, a rounded anterior edge and an indented posterior edge. The thoracic segments (segments of the thorax ) of the species were straight and narrow. The eyes of C. salmi were similar, being placed very close together. The eyes were also

10549-454: 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

10686-403: The fossil remains referred to Campylocephalus are, determining its size is difficult and as of yet, no formal published size estimates exist for either the type species C. oculatus or the species C. salmi . The sole known fossil remains of C. permianus , a massive incomplete carapace, suggests a very large eurypterid, potentially reaching lengths of 1.4 metres (4.6 feet). In C. oculatus ,

10823-476: 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

10960-568: 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

11097-651: 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

11234-425: The genus Campylocephalus and thus reclassified it as its current combination. Though Ponomarenko had mentioned several features that also distinguished C. permianus from the then currently recognized species of Campylocephalus , including a different carapace shape and some thickening of the exoskeleton around the eyes, Lamsdell determined that these distinctions were not valid. In the view of Lamsdell, specimens of

11371-513: 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

11508-429: 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,

11645-412: 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

11782-432: 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 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

11919-580: 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

12056-420: The large and well-developed compound eyes of the house centipedes, Scutigera ). Behind each lens of a typical functional stemma lies a single cluster of photoreceptor cells, termed a retinula. The lens is biconvex , and the body of the stemma has a vitreous or crystalline core. Although stemmata are simple eyes, some kinds (such as those of the larvae of Lepidoptera and especially those of Tenthredinidae ,

12193-491: 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

12330-495: 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

12467-768: The larvae of some insect orders. Despite the shared name, they are structurally and functionally very different. Simple eyes of other animals may also be referred to as ocelli, but again the structure and anatomy of these eyes is quite distinct from those of insect dorsal ocelli. Dorsal ocelli are light-sensitive organs found on the dorsal surface or frontal surface of the head of many insects, including Hymenoptera ( bees , ants , wasps , sawflies ), Diptera (flies), Odonata ( dragonflies , damselflies ), Orthoptera ( grasshoppers , locusts ) and Mantodea (mantises). These ocelli coexist with compound eyes; thus, most insects possess two anatomically separate and functionally different visual pathways. The number, forms, and functions of

12604-497: 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

12741-470: The lens by a clear vitreous humour . The number of photoreceptors also varies widely, but may number in the hundreds or thousands for well-developed ocelli. In bees, locusts, and dragonflies, the lens is strongly curved; while in cockroaches it is flat. Locusts possess vitreous humour while blowflies and dragonflies do not. Two somewhat unusual features of ocelli are particularly notable and generally common between insect orders. These two factors have led to

12878-531: 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 the Permian–Triassic extinction event (or sometime shortly before) 251.9   million years ago. Although popularly called "sea scorpions", only

13015-488: The ocelli are superbly adapted for measuring changes in the perceived brightness of the external world as an insect rolls or pitches around its body axis during flight. Locusts and dragonflies in tethered flight have been observed to try and "correct" their flight posture based on changes in light. Other theories of ocellar function have ranged from roles as light adaptors or global excitatory organs to polarization sensors and circadian entrainers . Recent studies have shown

13152-442: The ocelli of some insects (most notably the dragonfly, but also some wasps) are capable of "form vision" similar to camera eyes, as the ocellar lens forms an image within, or close to, the photoreceptor layer. In dragonflies it has been demonstrated that the receptive fields of both the photoreceptors and the second-order neurons can be quite restricted. Further research has demonstrated these eyes not only resolve spatial details of

13289-403: The ommatidia of most insects and the central eyes of camel spiders . Jumping spiders and some other predatory spiders with seemingly simple eyes also emulate retinal vision in various ways. Many insects have unambiguously compound eyes consisting of multiple lenses (up to tens of thousands), but achieve an effect similar to that of a camera eye, in that each ommatidium lens focuses light onto

13426-501: 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 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

13563-808: The opisthosoma was covered in structures evolved from modified opisthosomal appendages. Throughout 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

13700-424: 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

13837-623: 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; 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

13974-548: 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

14111-433: 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

14248-434: 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,

14385-535: The present moment, it is difficult to lay down a general rule. Any taxonomical difficulties implied with Scouler's designation were easily avoided, however, by the discovery that the genus name was preoccupied by a genus of molluscs described in 1826. Nevertheless, the name Eidothea would be associated with the Scottish eurypterid species Eurypterus scouleri , with a near identical prosoma, described in 1836. In 1860 French paleontologist Edouard D'Eichwald recognized that

14522-567: The prosoma. The features of Campylocephalus and Vernonopterus makes it clear that both genera represent hibbertopterid eurypterids, but the incomplete nature of all fossil specimens referred to them make any further study of the precise phylogenetic relationships within the Hibbertopteridae difficult. Both genera could even represent synonyms of Hibbertopterus itself, though the highly incomplete nature of their remains again makes that hypothesis impossible to confirm. The cladogram below

14659-452: 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

14796-455: The related Hibbertopterus scouleri . In the second carapace specimen, the carapace began to stretch forward above the eyes. Both of these fossils also possessed protuberances of different sizes across the exoskeleton, showing vague forms and shapes not seen in other specimens of the genus. Fossils of Eurypterus scouleri were compared to the carapace described by Kutorga in 1838 by Norwegian paleontologist Leif Størmer in 1951, who concluded that

14933-445: 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

15070-458: 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

15207-435: 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

15344-602: The same age within the Ostrava Formation. It is difficult to make any statements on the paleoecology of the type species, C. oculatus , as the precise location and dating of the fossil specimen remains somewhat unclear. Most accounts place the fossil as having been found at a location named Dourasovo in Russia and being from the Guadalupian epoch (272.3–259.8 million years ago) of the Permian period. The species of C. permianus

15481-405: 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

15618-413: 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

15755-429: The sixth pair of appendages were overlaid by a plate that 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

15892-441: 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

16029-427: 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

16166-492: 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

16303-517: The stylonurine suborder , sweep-feeders. Sweep-feeding food strategies involve specialized appendages with blades that could be used by the animals to rake through the substrate of their living environments in search for small prey items. The species C. permianus , known from deposits of Late Permian age in Russia, is the only species of Campylocephalus preserved well enough to allow for size estimates, published estimates putting its size at potentially 1.4 metres (4.6 feet) in length. This species

16440-631: The term simple eye is flexible, and must be interpreted in proper context; for example, the eyes of most large animals are camera eyes and are sometimes considered "simple" because a single lens collects and focuses an entire image onto the retina (analogous to a camera ). By other criteria, the presence of a complex retina distinguishes the vertebrate camera eye from the simple stemma or ommatidia which make up compound eyes. Additionally, not all invertebrate ocelli and ommatidium have simple photoreceptors . Many have various forms of retinula (a retina-like cluster of photoreceptor cells), including

16577-435: The two had been placed in the same genus, whilst the ventral anatomy and appendages of C. oculatus remained unknown. A year later, in 1959, American paleontologist Erik Norman Kjellesvig-Waering created the new genus Hibbertopterus to contain C. scouleri (now Hibbertopterus scouleri ) and placed both genera within the family Hibbertopteridae. Described by Russian paleontologist Alexey G. Ponomarenko in 1985, C. permianus

16714-429: The two were clearly congeneric. At this point, D'Eichwald had already recognized the fossils designated as " Eidothea " by Scouler as representatives of Campylocephalus . As such, E. scouleri was classified as Campylocephalus scouleri . Though the legs of Campylocephalus were still unknown at the time, even with the addition of the Scottish species, any grouping with other genera would have to be made using features of

16851-464: 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

16988-414: 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

17125-509: The type species C. oculatus are not well preserved enough to determine the precise structure of the eyes and because fossils of its carapace are either flattened or incomplete, its shape can not be ascertained with complete accuracy. Campylocephalus is classified as part of the family Hibbertopteridae, a family of eurypterids within the superfamily Mycteropoidea , alongside the genera Hibbertopterus and Vernonopterus . The genus contains three species; C. oculatus and C. permianus from

17262-400: 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

17399-429: 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

17536-443: The world, but also perceive motion. Second-order neurons in the dragonfly median ocellus respond more strongly to upwards-moving bars and gratings than to downwards-moving bars and gratings, but this effect is only present when ultraviolet light is used in the stimulus; when ultraviolet light is absent, no directional response is observed. Dragonfly ocelli are especially highly developed and specialised visual organs, which may support

17673-538: Was a member of the hibbertopterid family of eurypterids and probably looked much the same as the other members of the family, Hibbertopterus and Vernonopterus , in that it was a large, broad and heavy animal quite different from the famous swimming eurypterids (such as Pterygotus and Eurypterus ) which had been common during earlier periods. Like all other stylonurine eurypterids, Campylocephalus completely lacked swimming paddles. Hibbertopterids such as Campylocephalus were, as many other families within

17810-400: 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

17947-422: Was among the last known surviving eurypterid, living just before or during the Permian–Triassic extinction event 251.9 million years ago. Before the extinction event, eurypterids had been declining in numbers and diversity for millions of years; Campylocephalus had been the only known genus of living eurypterids for more than 20 million years since the extinction of the related genus Hastimima . Classified as

18084-497: 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

18221-452: 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)

18358-513: Was named as a species of the quite distantly related Eurypterus by the Slovak geologist and paleontologist Dionýs Štúr in 1877. Štúr's description was based on two incomplete fossil carapaces. The first fragmentary carapace only preserved the lower part of the head, ending in two pointed and concave arches. The eyes of this carapace were close together, in the middle of the carapace, and on a triangularly shaped elevated portion similar to some specimens of

18495-516: Was originally named as a species of Hibbertopterus . The only known specimen of this species is the holotype, PIN N1209/2, an incomplete carapace, but Ponomarenko could list several features that distinguished it from other species referred to Hibbertopterus . Among these were most prominently the posterior position of the lateral eyes and said eyes not being circular in shape. In 2012, American paleontologist James C. Lamsdell could demonstrate that these unique features were actually diagnostic features of

18632-426: Was the first to suggest that C. scouleri perhaps shouldn't be considered as congeneric with Campylocephalus , raising the issue in a 1958 paper. He posited that though the dorsal anatomy of the prosoma was quite similar between C. scouleri and C. oculatus , the designated type species, multiple well-preserved fossils had allowed for detailed research into the ventral anatomy and appendages of C. scouleri since

18769-518: 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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