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167-830: Hibbertopterus is a genus of eurypterid , a group of extinct aquatic arthropods . Fossils of Hibbertopterus have been discovered in deposits ranging from the Devonian period in Belgium , Scotland and the United States to the Carboniferous period in Scotland, Ireland , the Czech Republic and South Africa . The type species, H. scouleri , was first named as a species of the significantly different Eurypterus by Samuel Hibbert in 1836. The generic name Hibbertopterus , coined more than

334-516: A Hox -gene , could result in parallel gains of leg segments. In arthropods, each of the leg segments articulates with the next segment in a hinge joint and may only bend in one plane. This means that a greater number of segments is required to achieve the same kinds of movements that are possible in vertebrate animals, which have rotational ball-and-socket joints at the base of the fore and hind limbs. The appendages of arthropods may be either biramous or uniramous . A uniramous limb comprises

501-564: 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

668-509: 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,

835-404: A hexapodal (six-legged) gait. Although not enough fossil material is known of the other hibbertopterid eurypterids to discuss the differences between them with full confidence, Hibbertopterus is defined based on a collection of definite characteristics. The telson (the posteriormost division of the body) was hastate (e.g. shaped like a gladius , a Roman sword) and had a keel running down

1002-408: 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

1169-413: A 2023 study describing a new species H. lamsdelli argued that Dunsopterus and Vernonopterus should be synonymized with Hibbertopterus , while Cyrtoctenus is distinct from it. Hibbertopterids such as Hibbertopterus were sweep-feeders, having modified spines on their forward-facing prosomal appendages that allowed them to rake through the substrate of their living environments. Though sweep-feeding

1336-400: A central groove. The slow progression and dragging of the tail indicate that the animal responsible was moving out of water. The presence of terrestrial tracks indicate that Hibbertopterus was able to survive on land at least briefly, possible due to the probability that their gills could function in air as long as they remained wet. Additionally, some studies suggest that eurypterids possessed

1503-523: A century later, combines his name and the Greek word πτερόν ( pteron ) meaning "wing". Hibbertopterus was the largest eurypterid within the stylonurine suborder, with the largest fossil specimens suggesting that H. scouleri could reach lengths around 180–200 centimetres (5.9–6.6 ft). Though this is significantly smaller than the largest eurypterid overall, Jaekelopterus , which could reach lengths of around 250 centimetres (8.2 ft), Hibbertopterus

1670-566: A different feeding method altogether. As such, it is more than possible that later ontogenetic stages of Hibbertopterus developed the structures seen in Cyrtoctenus to be able to continue to feed at larger body sizes. Fossil specimens of Hibbertopterus frequently occur together with fragments referred to Cyrtoctenus , Dunsopterus and Vernonopterus . The three fragmentary genera were suggested to by synonyms of each other by American paleontologist James Lamsdell in 2010, which would have meant

1837-536: A distinct eurypterid genus, Vernonopterus . Størmer and Waterston concluded that the Glyptoscorpius species G. caledonicus was to be part of a new genus, which they named Cyrtoctenus (the name deriving from the Greek Cyrtoctenos , a curved comb) and they named a new species, C. peachi (named in honour of Ben Peach), as its type. Both of these species were based on fragmentary fossil remains. Furthermore,

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2004-580: A dual respiratory system , which would allow short periods of time in terrestrial environments. In the Midland Valley of Scotland, 27 kilometres (16.8 miles) to the west of Edinburgh , East Kirkton Quarry contains deposits that were once a freshwater lake near a volcano. The locality has preserved a diverse fauna of the Viséan age of the Carboniferous (about 335 million years ago). Other than H. scouleri ,

2171-726: 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

2338-424: A hastate telson similar to that of Hibbertopterus , 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 the prosoma. Historically, the morphology of Hibbertopterus and

2505-499: A large and open fresh to brackish water lake, with possibly occasional influences by storms and glacial processes, fossil remains recovered is most commonly that of various types of fish. Among these types are palaeoniscoids , sharks and acanthodians . Though shark material is too fragmentary to be identifiable, at least some fossils might represent the remains of protacrodontoids . Among the acanthodians, at least three genera have been identified from fossil scales and spines, including

2672-416: 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

2839-424: A median bristle or empodium , meaning the meeting place of the pulvilli. On the underside of the tarsal segments, there frequently are pulvillus-like organs or plantulae . The arolium, plantulae and pulvilli are adhesive organs enabling their possessors to climb smooth or steep surfaces. They all are outgrowths of the exoskeleton and their cavities contain blood. Their structures are covered with tubular tenent hairs,

3006-425: 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 ,

3173-552: A ring-like shape of hardened integument (absent in Campylocephalus ). The eyes of Hibbertopterus are also located near the center of the head whereas those of Campylocephalus are located further back. The generic name Hibbertopterus was selected to honor the original descriptor of H. scouleri , Samuel Hibbert. The fact that Glyptoscorpius was questionable at best and that its type species, G. perornatus , (and other species, such as G. kidstoni ) had recently been referred to

3340-471: 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

3507-401: A shared, derived character , so uniramous arthropods were grouped into a taxon called Uniramia . It is now believed that several groups of arthropods evolved uniramous limbs independently from ancestors with biramous limbs, so this taxon is no longer used. Arachnid legs differ from those of insects by the addition of two segments on either side of the tibia, the patella between the femur and

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3674-508: A single series of segments attached end-to-end. A biramous limb, however, branches into two, and each branch consists of a series of segments attached end-to-end. The external branch (ramus) of the appendages of crustaceans is known as the exopod or exopodite , while the internal branch is known as the endopod or endopodite . Other structures aside from the latter two are termed exites (outer structures) and endites (inner structures). Exopodites can be easily distinguished from exites by

3841-483: A stretch of land, dragging its telson (the posteriormost division of its body) across the ground after it. How Hibbertopterus could survive on land, however briefly, is unknown but it might have been possible through either its gills being able to function in air as long as they were wet or by the animal possessing a dual respiratory system , theorised to have been present in at least some eurypterids. Though sometimes, and often historically, treated as distinct genera,

4008-422: A tarsal claw. Myriapod legs show a variety of modifications in different groups. In all centipedes, the first pair of legs is modified into a pair of venomous fangs called forcipules. In most millipedes, one or two pairs of walking legs in adult males are modified into sperm-transferring structures called gonopods . In some millipedes, the first leg pair in males may be reduced to tiny hooks or stubs, while in others

4175-547: 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

4342-495: 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

4509-407: Is adapted for running ( cursorial ), rather than for digging, leaping, swimming, predation, or other similar activities. The legs of most cockroaches are good examples. However, there are many specialized adaptations, including: The embryonic body segments ( somites ) of different arthropods taxa have diverged from a simple body plan with many similar appendages which are serially homologous, into

4676-523: 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

4843-472: Is also supported by the complete lack of adaptations towards any organs used for trapping prey in younger specimens (though they are present on adult specimens once referred to Cyrtoctenus ) and a lack of swimming adaptations. Through sweep-feeding, Hibbertopterus could sweep up small animals from the soft sediments of shallow bodies of water, presumably small crustaceans and other arthropods, and could then sweep them into its mouth when it detected them. Through

5010-400: Is highly problematic; some of the diagnostic characteristics used when describing it are either questionable or outright meaningless. For instance, the original description had been based on G. caledonicus and G. perornatus but since the parts of the body preserved in the fossils described don't completely overlap it is impossible to say if Peach's diagnostic characteristics actually apply to

5177-485: Is likely to have been the heaviest due to its broad and compact body. Furthermore, trackway evidence indicates that the South African species H. wittebergensis might have reached lengths similar to Jaekelopterus . Like many other stylonurine eurypterids, Hibbertopterus fed through a method called sweep-feeding. It used its specialised forward-facing appendages (limbs), equipped with several spines, to rake through

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5344-483: 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

5511-487: 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,

5678-517: 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

5845-481: 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

6012-625: 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

6179-619: Is quite similar to filter feeding . This has led some researchers to suggest that Hibbertopterus would have been a pelagic animal, as modern filter feeding crustaceans, but the robust and massive nature of the genus (in contrast to modern filter feeding crustaceans which are typically very small) makes such a conclusion unlikely. The chelicerae (pincers) of Hibbertopterus were weak and they would not have been able to grasp any potential prey which means Hibbertopterus would probably have been incapable of preying on larger animals. The conclusion that Hibbertopterus wasn't preying on large animals

6346-439: 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

6513-486: Is the fourth section of the typical insect leg. As a rule, the tibia of an insect is slender in comparison to the femur, but it generally is at least as long and often longer. Near the distal end, there is generally a tibial spur, often two or more. In the Apocrita , the tibia of the foreleg bears a large apical spur that fits over a semicircular gap in the first segment of the tarsus. The gap is lined with comb-like bristles, and

6680-795: 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

6847-413: Is the presence of grooves on its podomeres, which studies on Drepanopterus suggest might have been a feature which appeared late in an animal's life cycle. Differences in the positions of the eyes in specimens of Hibbertopterus and Cyrtoctenus is not surprising as movements of the eyes through ontogeny has been described in other eurypterid genera. Lamsdell considered it almost certain that Dunsopterus

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7014-418: 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

7181-399: Is yet to be published. In 1831, Scottish naturalist John Scouler described the remains, consisting of a massive and unusual prosoma (head) and several tergites (segments from the back of the animal), of a large and strange arthropod discovered in deposits in Scotland of Lower Carboniferous age, but did not assign a name to the fossils. Through Scouler's examination, the fossils represent

7348-459: The Apterygota , the legs of immature specimens are in effect smaller versions of the adult legs. A representative insect leg, such as that of a housefly or cockroach , has the following parts, in sequence from most proximal to most distal : Associated with the leg itself there are various sclerites around its base. Their functions are articular and have to do with how the leg attaches to

7515-507: The Cerylonidae have four tarsomeres on each tarsus. The distal segment of the typical insect leg is the pretarsus. In the Collembola , Protura and many insect larvae, the pretarsus is a single claw. On the pretarsus most insects have a pair of claws ( ungues , singular unguis ). Between the ungues, a median unguitractor plate supports the pretarsus. The plate is attached to the apodeme of

7682-742: 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

7849-523: The Opiliones . The site also preserves abundant plant life, including the genera Lepidodendron , Lepidophloios , Stigmaria and Sphenopteris . Locally, the strange fossil carapaces of H. scouleri have been given the common name "Scouler's heids" ("heid" being Scots for "head"). The Waaipoort Formation, where H. wittebergensis has been discovered, also preserves a diverse Carboniferous fauna and some species of plants. Interpreted as having been

8016-605: The Scarabaeidae and Dytiscidae have thoracic legs, but no prolegs. Some insects that exhibit hypermetamorphosis begin their metamorphosis as planidia , specialised, active, legged larvae, but they end their larval stage as legless maggots, for example the Acroceridae . Among the Exopterygota , the legs of larvae tend to resemble those of the adults in general, except in adaptations to their respective modes of life. For example,

8183-521: 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

8350-530: 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

8517-442: 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

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8684-405: 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

8851-442: The substrate of the environments in which it lived in search for small invertebrates to eat, which it could then push towards its mouth. Though long hypothesised, the fact that eurypterids were capable of terrestrial locomotion was definitely proven through the discovery of a fossil trackway made by Hibbertopterus in Scotland. The trackway showed that an animal measuring around 160 centimetres (5.2 ft) had slowly lumbered across

9018-473: The tarsal organ . The situation is identical in scorpions , but with the addition of a pre-tarsus beyond the tarsus. The claws of the scorpion are not truly legs, but are pedipalps , a different kind of appendage that is also found in spiders and is specialised for predation and mating. In Limulus , there are no metatarsi or pretarsi, leaving six segments per leg. The legs of crustaceans are divided primitively into seven segments, which do not follow

9185-656: 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

9352-442: The "cyrtoctenids" were definitely Hibbertopterus -type eurypterids, not representatives of a new order of arthropods. Hibbertopterus is classified as part of the family Hibbertopteridae, which it also lends its name to, a family of eurypterids within the superfamily Mycteropoidea , alongside the genera Campylocephalus and Vernonopterus . The hibbertopterids are united as a group by being large mycteropoids with broad prosomas,

9519-627: The 10 species listed below follow a 2018 survey by German paleontologists Jason A. Dunlop and Denise Jekel and British paleontologist David Penney and size- and temporal ranges follow a 2009 study by American paleontologists James Lamsdell and Simon J. Braddy unless otherwise noted. The distinguishing features of H. caledonicus , H. dewalquei , H. ostraviensis and H. peachi follow the 1968 description of these species. The descriptors, Norwegian paleontologist Leif Størmer and British paleontologist Charles D. Waterston, did not consider these species to represent eurypterids, though any emended diagnosis of them

9686-527: 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

9853-804: 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

10020-590: 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

10187-641: 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

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10354-465: The Odonata. In parasitic Hymenoptera, the base of the femur has the appearance of a second trochanter. In most insects, the femur is the largest region of the leg; it is especially conspicuous in many insects with saltatorial legs because the typical leaping mechanism is to straighten the joint between the femur and the tibia, and the femur contains the necessary massive bipennate musculature. The tibia

10521-483: The Permian. Arthropod leg Homologies of leg segments between groups are difficult to prove and are the source of much argument. Some authors posit up to eleven segments per leg for the most recent common ancestor of extant arthropods but modern arthropods have eight or fewer. It has been argued that the ancestral leg need not have been so complex, and that other events, such as successive loss of function of

10688-549: 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

10855-586: 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

11022-538: 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

11189-411: The actual mortalities, susceptible to scavengers . In a 2019 graduate thesis , American geologist Emily Hughes suggested the synonymization of Hibbertopterus and Dunsopterus due to the "strong morphological similarities" between them, and as Dunsopterus was found to be paraphyletic in regards to Cyrtoctenus , all three were subsumed into just Hibbertopterus . In particular, she noted that though

11356-530: 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

11523-442: 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

11690-445: The apices of which are moistened by a glandular secretion. The organs are adapted to apply the hairs closely to a smooth surface so that adhesion occurs through surface molecular forces. Insects control the ungues through muscle tension on a long tendon, the "retractor unguis" or "long tendon". In insect models of locomotion and motor control, such as Drosophila ( Diptera ), locusts ( Acrididae ), or stick insects ( Phasmatodea ),

11857-454: 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

12024-414: 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

12191-458: 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

12358-420: 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

12525-507: The coxa has two lobes where it articulates with the pleuron. The posterior lobe is the meron which is usually the larger part of the coxa. A meron is well developed in Periplaneta, the Isoptera, Neuroptera and Lepidoptera. The trochanter articulates with the coxa but usually is attached rigidly to the femur. In some insects, its appearance may be confusing; for example it has two subsegments in

12692-695: 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

12859-493: The derived climatiiform Gyracanthides . Among the palaeoniscoids, eight distinct genera have been identified. Several of these palaeoniscoid genera also occur in deposits of similar age in Scotland. Other than H. wittebergensis , the only known invertebrates are two rare species of bivalves , possibly representing unionids . Plant fossils in the Waaiport Formation are notably less diverse than those of preceding ages in

13026-448: The different adaptations of juveniles and adults (" Cyrtoctenus "), individuals of different ages would possibly have preferred different types of prey, which would have reduced competition between members of the same genus. A fossil trackway discovered near St Andrews in Fife , Scotland, reveals that Hibbertopterus was capable of at least limited terrestrial locomotion . The trackway found

13193-504: 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

13360-518: The end of each limb was covered with sensory organs. These adaptations suggest that Hibbertopterus , like other hibbertopterids, would have fed by a method referred to as sweep-feeding, using its limbs to sweep through the substrate of its environment in search for food. The fourth pair of appendages, though used in feeding like the second and third pairs, was also used for locomotion and the two final pairs of legs (pairs five and six overall) were solely locomotory. As such, Hibbertopterus would have used

13527-409: 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

13694-411: 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

13861-508: 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

14028-454: 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

14195-406: The fauna includes several terrestrial animals, such as anthracosaurs , aistopods , baphetids and temnospondyls , representing some of the oldest known terrestrial tetrapods . Several terrestrial invertebrates are also known from the location, including several species of millipedes , Gigantoscorpio (one of the earliest scorpions proven to have been terrestrial) and early representatives of

14362-532: The feeding appendages were different, the ornamentation and form of the raking tools seen in Hibbertopterus were probably the precursors of the more moveable finger-like organs present in Cyrtoctenus . Hughes suggested that Vernonopterus , due to its distinct ornamentation, represented a genus distinct from Hibbertopterus . The same conclusions and suggestions were also published in a later 2020 conference abstract, co-authored by Hughes and James Lamsdell. However,

14529-511: The first pair may be enlarged. Insects and their relatives are hexapods, having six legs, connected to the thorax , each with five components. In order from the body they are the coxa, trochanter, femur, tibia, and tarsus. Each is a single segment, except the tarsus which can be from three to seven segments, each referred to as a tarsomere . Except in species in which legs have been lost or become vestigial through evolutionary adaptation, adult insects have six legs, one pair attached to each of

14696-470: The flexor muscle of the ungues. In the Neoptera , the parempodia are a symmetrical pair of structures arising from the outside (distal) surface of the unguitractor plate between the claws. It is present in many Hemiptera and almost all Heteroptera . Usually, the parempodia are bristly (setiform), but in a few species they are fleshy. Sometimes the parempodia are reduced in size so as to almost disappear. Above

14863-400: The fossil remains of a eurypterid by American paleontologist James Hall in 1884, three years later. Though Hall assigned the species to Stylonurus , that same year British paleontologists Henry Woodward and Thomas Rupert Jones assigned the fossil to the genus Echinocaris , believing the fossils represented a phyllocarid crustacean . The assignment to Echinocaris was probably based on

15030-633: The fossils were given due to their fragmentary nature. Though no specification was given as to why, Pterygotus hibernicus (a species described from Ireland by British paleontologist William Hellier Baily in 1872) was reassigned to Hibbertopterus by American paleontologist Erik N. Kjellesvig-Waering in 1964 as part of a greater re-examination of the various species assigned to the family Pterygotidae. Kjellesvig-Waering retained P. dicki as part of Pterygotus . Scottish paleontologists Lyall I. Anderson and Nigel H. Trewin and German paleontologist Jason A. Dunlop noted in 2000 that Kjellesvig-Waerings acception of

15197-476: 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

15364-568: 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

15531-407: The genus Adelophthalmus prompted Norwegian paleontologist Leif Størmer and British paleontologist Charles D. Waterston to in 1968 re-examine the various species that had been referred to it. Because G. perornatus was the type species of Glyptoscorpius , the genus itself became synonymous with Adelophthalmus . That same year, the species G. minutisculptus had been designated the type species of

15698-651: 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

15865-838: The genus Cyrtoctenus (where H. peachi is the type species). The idea that Dunsopterus and Cyrtoctenus were congeneric (e.g. synonymous) was first suggested by British geologist Charles D. Waterston in 1985. Dunsopterus is known from very fragmentary material, mainly sclerites (various hardened body parts) which have little diagnostic potential and are poorly known in fossils attributed to Cyrtoctenus . The morphology of fossils attributed to Dunsopterus and Cyrtoctenus does suggest that they were more specialised than H. scouleri , particularly in their adaptations to sweep-feeding. If valid, Cyrtoctenus would have had further adaptations towards sweep-feeding than any other hibbertopterid, with its blades modified into comb-like rachis that could entrap smaller prey or other organic food particles. It

16032-513: 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

16199-429: 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,

16366-412: 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

16533-432: 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

16700-463: The hibbertopterid eurypterids Cyrtoctenus and Dunsopterus have been suggested to represent adult ontogenetic stages of Hibbertopterus . The features of fossils associated with these genera suggest that the sweep-feeding strategy of Hibbertopterus changed significantly over the course of its life, from simpler raking organs present in younger specimens to specialised comb-like organs capable of trapping prey (rather than simply pushing it towards

16867-538: The highly incomplete nature of their remains again makes that hypothesis impossible to confirm. The cladogram below 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 Cyrtoctenus wittebergensis Many analyses and overviews treat

17034-560: The insect cleans its antennae by drawing them through. The ancestral tarsus was a single segment and in the extant Protura , Diplura and certain insect larvae the tarsus also is single-segmented. Most modern insects have tarsi divided into subsegments (tarsomeres), usually about five. The actual number varies with the taxon , which may be useful for diagnostic purposes. For example, the Pterogeniidae characteristically have 5-segmented fore- and mid-tarsi, but 4-segmented hind tarsi, whereas

17201-580: 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

17368-461: The larger size of the specimens referred to Cyrtoctenus . The method of Hibbertopterus , which involves raking, would have become significantly less effective the larger the animal grew since a larger and larger portion of its prey would be small enough to pass between its sweep-feeding spines. Any specimen over the size of a metre (3.2 ft) which continued to feed on small invertebrates would need modified sweep-feeding appendages or would need to employ

17535-491: 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

17702-495: 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

17869-497: 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

18036-464: The legs of larval insects, particularly in the Endopterygota , vary more than in the adults. As mentioned, some have prolegs as well as "true" thoracic legs. Some have no externally visible legs at all (though they have internal rudiments that emerge as adult legs at the final ecdysis ). Examples include the maggots of flies or grubs of weevils . In contrast, the larvae of other Coleoptera , such as

18203-465: The legs of most immature Ephemeroptera are adapted to scuttling beneath underwater stones and the like, whereas the adults have more gracile legs that are less of a burden during flight. Again, the young of the Coccoidea are called "crawlers" and they crawl around looking for a good place to feed, where they settle down and stay for life. Their later instars have no functional legs in most species. Among

18370-408: The long tendon courses through the tarsus and tibia before reaching the femur. Tension on the long tendon is controlled by two muscles, one in the femur and one in the tibia, which can operate differently depending on how the leg is bent. Tension on the long tendon controls the claw, but also bends the tarsus and likely affects its stiffness during walking. The typical thoracic leg of an adult insect

18537-476: The main exoskeleton of the insect. Such sclerites differ considerably between unrelated insects. The coxa is the proximal segment and functional base of the leg. It articulates with the pleuron and associated sclerites of its thoracic segment, and in some species it articulates with the edge of the sternite as well. The homologies of the various basal sclerites are open to debate. Some authorities suggest that they derive from an ancestral subcoxa. In many species,

18704-589: 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

18871-424: The middle, with in turn had a small indentation in its own centre. The walking legs of Hibbertopterus had extensions at their base and lacked longitudinal posterior grooves in all of its podomeres (leg segments). Some of these characteristics, in particular the shape of the telson, are thought to have been shared by other hibbertopterids, which are much less well preserved than Hibbertopterus itself. The status of

19038-465: The mouth) in adults. Like other known hibbertopterid eurypterids , Hibbertopterus was a large, broad-bodied and heavy animal. It was the largest known eurypterid of the suborder Stylonurina , composed of those eurypterids that lacked swimming paddles. A carapace (the part of the exoskeleton which covered the head) referred to the species H. scouleri , from Carboniferous Scotland , measures 65 centimetres (26 in) wide. Since Hibbertopterus

19205-572: The naming system used in the other groups. They are: coxa, basis, ischium, merus, carpus, propodus, and dactylus. In some groups, some of the limb segments may be fused together. The claw ( chela ) of a lobster or crab is formed by the articulation of the dactylus against an outgrowth of the propodus. Crustacean limbs also differ in being biramous, whereas all other extant arthropods have uniramous limbs. Myriapods ( millipedes , centipedes and their relatives) have seven-segmented walking legs, comprising coxa, trochanter, prefemur, femur, tibia, tarsus, and

19372-452: The oldest name, Dunsopterus , taking priority and subsuming both Cyrtoctenus and Vernonopterus as junior synonyms . Following studies on the ontogeny of Drepanopterus , a more primitid mycteropoid eurypterid, large-scale changes in the developments of the appendages over the course of the life of a single animal have been proven to have happened in some eurypterids. One of the key features distinguishing Cyrtoctenus from Hibbertopterus

19539-501: 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

19706-808: 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

19873-419: The original designation for Pterygotus dicki was "burdensome" as it is based on highly fragmentary material. They noted that like many other pterygotid species, P. dicki represented yet another name applied to some scattered segments, a practice they deemed "taxonomically unsound". Though they suggested that further research was required to determine whether or not the taxon was valid at all, they did note that

20040-424: 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

20207-560: The other hibbertopterids has been seen as so unusual that they have been thought to be an order separate from Eurypterida . 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

20374-623: 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

20541-548: 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

20708-433: 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

20875-434: 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,

21042-417: The possession of internal musculature. The exopodites can sometimes be missing in some crustacean groups ( amphipods and isopods ), and they are completely absent in insects. The legs of insects and myriapods are uniramous. In crustaceans, the first antennae are uniramous, but the second antennae are biramous, as are the legs in most species. For a time, possession of uniramous limbs was believed to be

21209-402: The presence of a fringe to the segments formed by their ornamentation was absent in all other species of Pterygotus , but "strikingly similar" to what was present in Cyrtoctenus . Subsequent research treated P. dicki as a species of Cyrtoctenus . When Kjellesvig-Waering designated the genus Hibbertopterus in 1959, Eurypterus scouleri had already been referred to (considered a species of)

21376-516: The presence of eurypterid-type tergites, Størmer and Waterston thought that the Cyrtoctenus fossils represented remains of a new order of aquatic arthropods which they dubbed "Cyrtoctenida". The species C. dewalquei had originally been described as the fragmentary remains of a eurypterid in 1889 was assigned to Cyrtoctenus on the basis of the perceived filaments present on its appendages, similar to those of C. peachi . Størmer and Waterston disregarded specimens referred to C. caledonicus other than

21543-572: The prosoma, the telson and several tergites, but also coxae and even part of the digestive system. The discovery was also important for eurypterid research in general, since it represents one of the few eurypterids known from the southern hemisphere , where eurypterid finds are rare and usually fragmentary. The presence of the gut in the fossil proves that the specimen represents a dead individual, and not only exuviae , and scientists examining it could conclude that it had been preserved as lying on its back. The description of H. wittebergensis affirmed that

21710-452: 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

21877-467: The related Campylocephalus for some time. Kjellesvig-Waering recognised Campylocephalus scouleri as distinct from the type species of that genus, C. oculatus , in that the prosoma of Campylocephalus was more narrow, had a subelliptical (almost elliptical) shape and had its widest point in the middle rather than at the base. Further differences were noted in the position and shape of the animal's compound eyes, which in Hibbertopterus are surrounded by

22044-445: 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

22211-458: 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

22378-435: 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

22545-405: 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

22712-402: The same location, possibly because of climate reasons. Among the genera present are the common Praeramunculus (possibly representing a progymnosperm ) and Archaeosigillaria (a small type of lycopod ). Eurypterid Eurypterids , often informally called sea scorpions , are a group of extinct arthropods that form the order Eurypterida . The earliest known eurypterids date to

22879-501: The same structure as modern adult insect legs, and there has been a great deal of debate as to whether they are homologous with them. Current evidence suggests that they are indeed homologous up to a very primitive stage in their embryological development, but that their emergence in modern insects was not homologous between the Lepidoptera and Symphyta . Such concepts are pervasive in current interpretations of phylogeny. In general,

23046-403: The second eurypterid to be scientifically studied, just six years after the 1825 description of Eurypterus itself. Five years later, in 1836, British geologist Samuel Hibbert redescribed the same fossil specimens, giving them the name Eurypterus scouleri . The eurypterid genus Glyptoscorpius was named by British geologist Ben Peach , who also named the species G. perornatus (treated as

23213-413: 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

23380-429: 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

23547-537: The slightly spinose surface of the fossils, but in 1888 Hall and American paleontologist John Mason Clarke pointed out that no described Echinocaris actually had spines similar to what Woodward and Jones suggested and as such, reassigned the species back to Stylonurus , interpreting the fossils as fragments of the long walking legs. An assignment to Stylonurus was affirmed by Clarke and American paleontologist Rudolf Ruedemann in their influential The Eurypterida of New York in 1912, though no distinguishing features of

23714-441: 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

23881-724: The species G. stevensoni , named in 1936, was referred to the new genus Dunsopterus . The key diagnostic feature of Cyrtoctenus was its comb-like first appendages. Waterston remarked in another 1968 paper that the "controversial" Stylonurus wrightianus was similar to the unusual and massive prosomal appendage of Dunsopterus and as such reassigned S. wrightianus to Dunsopterus , creating Dunsopterus wrightianus . Other than C. peachi and C. caledonicus , further species were added to Cyrtoctenus by Størmer and Waterston; Eurypterus dewalquei , described in 1889, and Ctenopterus ostraviensis , described in 1951, became Cyrtoctenus dewalquei and C. ostraviensis , respectively. Despite noting

24048-544: The species H. wittebergensis from South Africa indicates an animal around 250 centimetres (8.2 ft) in length (the same size attributed to the largest known eurypterid, Jaekelopterus ), though the largest known fossil specimens of the species only appear to have reached lengths of 135 centimetres (4.43 ft). The forward-facing appendages (limbs) of Hibbertopterus (pairs 2, 3 and 4) were specialised for gathering food. The distal podomeres (leg segments) of these three pairs of limbs were covered with long spines, and

24215-427: 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

24382-492: 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

24549-458: The ten species assigned to Hibbertopterus as composing three separate, but closely related, hibbertopterid genera. In these arrangements, Hibbertopterus is typically restricted to the species H. scouleri and H. hibernicus , with the species H. stevensoni being the type and only species of the genus Dunsopterus and the species H. caledonicus , H. dewalquei , H. dicki , H. ostraviensis , H. peachi and H. wittebergensis being referred to

24716-438: The three segments of the thorax. They have paired appendages on some other segments, in particular, mouthparts , antennae and cerci , all of which are derived from paired legs on each segment of some common ancestor . Some larval insects do however have extra walking legs on their abdominal segments; these extra legs are called prolegs . They are found most frequently on the larvae of moths and sawflies. Prolegs do not have

24883-418: The tibia, and the metatarsus (sometimes called basitarsus) between the tibia and the tarsus (sometimes called telotarsus), making a total of seven segments. The tarsus of spiders have claws at the end as well as a hook that helps with web-spinning. Spider legs can also serve sensory functions, with hairs that serve as touch receptors, as well as an organ on the tarsus that serves as a humidity receptor, known as

25050-462: The two original species. Though only represented by two small, jointed and vaguely cylindrical fossil fragments (both discovered in the Portage sandstones of Italy, New York ), the species today recognised as H. wrightianus has had a complicated taxonomic history. Originally described in 1881 as a species of plant, the fragmentary fossil referred to as " Equisetides wrightiana " was noted to represent

25217-464: 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

25384-414: 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

25551-724: The type species of Glyptoscorpius by later researchers although it had not originally been designated as such) in 1882. The genus was based on G. perornatus and the fragmentary species G. caledonicus , previously described as the plant Cycadites caledonicus by English paleontologist John William Salter in 1863. This designation was reinforced with more fossil fragments discovered in the Coomsdon Burn , which Peach referred to Glyptoscorpius caledonicus . In 1887 Peach described G. minutisculptus from Mount Vernon , Glasgow , and G. kidstoni from Radstock in Somerset . Peach's Glyptoscorpius

25718-400: 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

25885-492: The unguitractor plate, the pretarsus expands forward into a median lobe, the arolium . Webspinners ( Embioptera ) have an enlarged basal tarsomere on each of the front legs, containing the silk -producing glands. Under their pretarsi, members of the Diptera generally have paired lobes or pulvilli, meaning "little cushions". There is a single pulvillus below each unguis. The pulvilli often have an arolium between them or otherwise

26052-409: The unique fragmentary type specimen, which at this point had been plastically preserved in sandstone. Like C. caledonicus , C. ostraviensis was also known only from a single specimen, a fragment of an appendage described in 1951. No distinguishing features were given for the species, and the authors noted that it was possibly synonymous with C. peachi , but they chose to maintain it as distinct due to

26219-472: The very limited fossil material. Known from a single specimen described in 1985, H. wittebergensis (described as Cyrtoctenus wittebergensis ) is the only species of Hibbertopterus known from reasonably complete remains other than the type species itself. The fossil, discovered in the Waaipoort Formation near Klaarstroom , Cape Province , South Africa , is remarkably complete, preserving not only

26386-429: 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

26553-513: Was a junior synonym of Hibbertopterus and that Cyrtoctenus and Vernonopterus in turn represented junior synonyms of Dunsopterus , which would subsume all three into Hibbertopterus . Synonymizing Hibbertopterus with Cyrtoctenus and Dunsopterus would also explain why smaller Hibbertopterus specimens are more complete than the known fossil remains of Cyrtoctenus , often fragmentary. The majority of Hibbertopterus specimens would then represent exuviae whilst Cyrtoctenus specimens represent

26720-400: 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

26887-497: 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

27054-452: 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)

27221-408: Was roughly 6 metres (20 ft) long and 1 metre (3.3 ft) wide, and suggests that the eurypterid responsible was 160 centimetres (5.2 ft) long, consistent with other giant sizes attributed to Hibbertopterus . The tracks indicate a lumbering, jerky and dragging movement. Scarps with crescent-shapes were left by the outer limbs, inner markings were made by the keeled belly and the telson carved

27388-452: Was suggested as early as 1993 by American paleontologist Paul Selden and British paleontologist Andrew J. Jeram that these adaptations might not have been due to Dunsopterus and Cyrtoctenus representing more derived genera of hibbertopterids, but rather due to both genera perhaps representing adult forms of Hibbertopterus . In this case, the development of the more specialized sweep-feeding method of Cyrtoctenus can directly be explained by

27555-586: Was unusually wide relative to its length for a eurypterid, the animal in question would probably have measured around 180–200 centimetres (5.9–6.6 ft) in length. Even though there were eurypterids of greater length (such as Jaekelopterus and Carcinosoma ), Hibbertopterus was very deep-bodied and compact in comparison to other eurypterids and the mass of the specimen in question would likely have rivalled that of other giant eurypterids (and other giant arthropods), if not surpassed them. In addition to fossil finds of large specimens, fossil trackways attributed to

27722-426: 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. Inhabiting freshwater swamps and rivers, the diet of Hibbertopterus and other sweep-feeders was probably composed of what they could find raking through its living environment, likely primarily small invertebrates. This method of feeding

27889-518: 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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