62-643: Proetida is an order of trilobite that lived from the Ordovician to the Permian . It was the last surviving order of trilobite, dying out in the Permian-Triassic extinction event . These typically small trilobites resemble those of the order Ptychopariida , from which the new order Proetida was separated in 1975 by Fortey and Owens. Like the order Phacopida , the proetids have exoskeletons that sometime have pits or small tubercles, especially on
124-557: A clade called Arachnomorpha , while others consider them to be more closely related to Mandibulata (which contains insects , crustaceans and myriapods ) as part of a clade called Antennulata . The earliest trilobites known from the fossil record are redlichiids and ptychopariid bigotinids dated to around 520 million years ago. Contenders for the earliest trilobites include Profallotaspis jakutensis (Siberia), Fritzaspis spp. (western USA), Hupetina antiqua (Morocco) and Serrania gordaensis (Spain). Trilobites appeared at
186-526: A lattice of chitin , and is curled round the lower edge to produce a small fringe called the "doublure". Their appendages and soft underbelly were non-mineralized. Three distinctive tagmata (sections) are present: cephalon (head); thorax (body) and pygidium (tail). As might be expected for a group of animals comprising c. 5,000 genera, the morphology and description of trilobites can be complex. Despite morphological complexity and an unclear position within higher classifications, there are
248-519: A natant (unattached) hypostome . The most recently recognized of the nine trilobite orders, Harpetida, was erected in 2002. The progenitor of order Phacopida is unclear. When trilobites are found, only the exoskeleton is preserved (often in an incomplete state) in all but a handful of locations. A few locations ( Lagerstätten ) preserve identifiable soft body parts (legs, gills, musculature & digestive tract) and enigmatic traces of other structures (e.g. fine details of eye structure) as well as
310-427: A new order, Eodiscida. Over 20,000 species of trilobite have been described. Despite their rich fossil record with thousands of described genera found throughout the world, the taxonomy and phylogeny of trilobites have many uncertainties. Except possibly for the members of the orders Phacopida and Lichida (which first appear during the early Ordovician ), nine of the eleven trilobite orders appear prior to
372-430: A number of characteristics which distinguish the trilobites from other arthropods: a generally sub-elliptical, dorsal , chitinous exoskeleton divided longitudinally into three distinct lobes (from which the group gets its name); having a distinct, relatively large head shield (cephalon) articulating axially with a thorax comprising articulated transverse segments, the hindmost of which are almost invariably fused to form
434-640: A roughly equivalent time in Laurentia , Siberia and West Gondwana . All Olenellina lack facial sutures (see below ), and this is thought to represent the original state. The earliest sutured trilobite found so far ( Lemdadella ), occurs almost at the same time as the earliest Olenellina, suggesting the trilobites origin lies before the start of the Atdabanian, but without leaving fossils. Other groups show secondary lost facial sutures, such as all Agnostina and some Phacopina . Another common feature of
496-471: A tail shield ( pygidium ). When describing differences between trilobite taxa , the presence, size, and shape of the cephalic features are often mentioned. During moulting , the exoskeleton generally splits between the head and thorax, which is why so many trilobite fossils are missing one or the other. In most groups facial sutures on the cephalon helped facilitate moulting. Similar to lobsters and crabs , trilobites would have physically "grown" between
558-573: Is 72 cm (28 in) in length. It was found in 1998 by Canadian scientists in Ordovician rocks on the shores of Hudson Bay . However, a partial specimen of the Ordovician trilobite Hungioides bohemicus found in 2009 in Arouca , Portugal is estimated to have measured when complete 86.5 cm (34.1 in) in length. Only the upper (dorsal) part of their exoskeleton is mineralized, composed of calcite and calcium phosphate minerals in
620-465: Is a strong indication that novel morphologies were developing very rapidly. Changes within the trilobite fauna during the Ordovician foreshadowed the mass extinction at the end of the Ordovician, allowing many families to continue into the Silurian with little disturbance. Ordovician trilobites were successful at exploiting new environments, notably reefs . The Ordovician mass extinction did not leave
682-564: Is based on differences in early larval stages. While the remaining Proetida taxa have globular larvae very unlike the adult form, the Aulacopleurids have adultlike larvae with paired spines. Others observe that globular non-adult larvae also occur in some taxa within the proposed order Aulacopleurida. More recently phylogenetic analysis of both larval and adult characters suggests the proetids as earlier understood probably are monophyletic . Two larval characters are unique to all Proetida;
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#1732771854524744-426: Is based on the use of trilobite marker fossils. Trilobites are the state fossils of Ohio ( Isotelus ), Wisconsin ( Calymene celebra ) and Pennsylvania ( Phacops rana ). The 10 most commonly recognized trilobite orders are Agnostida , Redlichiida , Corynexochida , Lichida , Odontopleurida , Phacopida , Proetida , Asaphida , Harpetida and Ptychopariida . In 2020, an 11th order, Trinucleida ,
806-575: Is best known from these samples preserved similarly to bodies in Pompeii. The French palaeontologist Joachim Barrande (1799–1883) carried out his landmark study of trilobites in the Cambrian, Ordovician and Silurian of Bohemia , publishing the first volume of Système silurien du centre de la Bohême in 1852. The study of Paleozoic trilobites in the Welsh-English borders by Niles Eldredge
868-494: Is foreshadowed. Some of the genera of Trilobites appearing in the Ordovician include: Most Early Silurian families constitute a subgroup of the Late Ordovician fauna. Few, if any, of the dominant Early Ordovician fauna survived to the end of the Ordovician, yet 74% of the dominant Late Ordovician trilobite fauna survived the Ordovician. Late Ordovician survivors account for all post-Ordovician trilobite groups except
930-1830: Is found in the Silurian Wenlock Group . This trilobite is featured on the town's coat of arms and was named the Dudley Bug or Dudley Locust by quarrymen who once worked the now abandoned limestone quarries. Llandrindod Wells , Powys , Wales , is another famous trilobite location. The well-known Elrathia kingi trilobite is found in abundance in the Cambrian Wheeler Shale of Utah . Spectacularly preserved trilobite fossils, often showing soft body parts (legs, gills, antennae, etc.) have been found in British Columbia , Canada (the Cambrian Burgess Shale and similar localities); New York , U.S.A. (Ordovician Walcott–Rust quarry , near Russia , and Beecher's Trilobite Bed , near Rome ); China (Lower Cambrian Maotianshan Shales near Chengjiang ); Germany (the Devonian Hunsrück Slates near Bundenbach ) and, much more rarely, in trilobite-bearing strata in Utah (Wheeler Shale and other formations), Ontario , and Manuels River, Newfoundland and Labrador . Sites in Morocco also yield very well-preserved trilobites, many buried in mudslides alive and so perfectly preserved. An industry has developed around their recovery, leading to controversies about practices in restoral. The variety of eye and upper body forms and fragile protuberances
992-529: Is no surprise that trilobite evolutionary history is marked by a number of extinction events where some groups perished, and surviving groups diversified to fill ecological niches with comparable or unique adaptations. Generally, trilobites maintained high diversity levels throughout the Cambrian and Ordovician periods before entering a drawn-out decline in the Devonian , culminating in the final extinction of
1054-428: Is recorded at the same time as the extinctions, suggesting major environmental upheaval. Notable trilobite genera appearing in the Cambrian include: The Early Ordovician is marked by vigorous radiations of articulate brachiopods, bryozoans, bivalves, echinoderms, and graptolites, with many groups appearing in the fossil record for the first time. Although intra-species trilobite diversity seems to have peaked during
1116-517: The Artiopoda , a group of extinct arthropods morphologically similar to trilobites, though only the trilobites had mineralised exoskeletons. Thus, other artiopodans are typically only found in exceptionally preserved deposits, mostly during the Cambrian period. The exact relationships of artiopods to other arthropods is uncertain. They have been considered closely related to chelicerates (which include horseshoe crabs and arachnids ) as part of
1178-548: The Harpetida . Silurian and Devonian trilobite assemblages are superficially similar to Ordovician assemblages, dominated by Lichida and Phacopida (including the well-known Calymenina ). A number of characteristic forms do not extend far into the Devonian and almost all the remainder were wiped out by a series of dramatic Middle and Late Devonian extinctions . Three orders and all but five families were exterminated by
1240-567: The Permian (when the vast majority of species on Earth were wiped out ). It is unknown why the order Proetida alone survived the Devonian. The Proetida maintained relatively diverse faunas in both deep and shallow water shelf environments throughout the Carboniferous. For many millions of years the Proetida existed untroubled in their ecological niche . An analogy would be today's crinoids , which mostly exist as deep-water species; in
1302-543: The Precambrian this is no longer supported, and it is thought that trilobites originated shortly before they appeared in the fossil record. Very shortly after trilobite fossils appeared in the lower Cambrian, they rapidly diversified into the major orders that typified the Cambrian— Redlichiida , Ptychopariida , Agnostida , and Corynexochida . The first major crisis in the trilobite fossil record occurred in
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#17327718545241364-796: The Proetida died out. The last trilobites disappeared in the mass extinction at the end of the Permian about 251.9 million years ago. Trilobites were among the most successful of all early animals, existing in oceans for almost 270 million years, with over 22,000 species having been described. By the time trilobites first appeared in the fossil record, they were already highly diversified and geographically dispersed. Because trilobites had wide diversity and an easily fossilized mineralised exoskeleton , they left an extensive fossil record. The study of their fossils has facilitated important contributions to biostratigraphy , paleontology , evolutionary biology , and plate tectonics . Trilobites are placed within
1426-523: The class Trilobita . Trilobites form one of the earliest known groups of arthropods. The first appearance of trilobites in the fossil record defines the base of the Atdabanian stage of the Early Cambrian period ( 521 million years ago ) and they flourished throughout the lower Paleozoic before slipping into a long decline, when, during the Devonian , all trilobite orders except
1488-497: The glabella (middle portion of the head). Because of their resemblance to the Ptychopariida in some features, the proetids are included in the subclass Librostoma. Unlike the trilobites of the phacopid suborder Phacopina , whose eyes are schizochroal , the proetids have the more common holochroal eyes . These eyes are characterized by close packing of biconvex lenses beneath a single corneal layer that covers all of
1550-406: The labrum in well-preserved trilobite specimens from Cambrian Stage 4 of Morocco, providing new anatomical information regarding the external and internal morphology of trilobites, and the cause of such extraordinary preservation is probably due to their rapid death after an underwater pyroclastic flow. Trilobites saw great diversification over time. For such a long-lasting group of animals, it
1612-419: The taxonomy and phylogeny of trilobites. The dorsal surface of the trilobite cephalon (the frontmost tagma , or the 'head') can be divided into two regions—the cranidium and the librigena ("free cheeks"). The cranidium can be further divided into the glabella (the central lobe in the cephalon) and the fixigena ("fixed cheeks"). The facial sutures lie along the anterior edge, at the division between
1674-704: The 1970s by Dan Cooper. As a well-known rock collector, he incited scientific and public interest in the location. The fossils are dated to the Givetian (387.2 - 382.7 million years ago) when the Western New York Region was 30 degrees south of the equator and completely covered in water. The site was purchased from Vincent C. Bonerb by the Town of Hamburg with the cooperation of the Hamburg Natural History Society to protect
1736-402: The Cambrian, trilobites were still active participants in the Ordovician radiation event, with a new fauna taking over from the old Cambrian one. Phacopida and Trinucleioidea are characteristic forms, highly differentiated and diverse, most with uncertain ancestors. The Phacopida and other "new" clades almost certainly had Cambrian forebears, but the fact that they have avoided detection
1798-605: The Middle Cambrian ; surviving orders developed isopygius or macropygius bodies and developed thicker cuticles, allowing better defense against predators (see Thorax below). The end- Cambrian mass extinction event marked a major change in trilobite fauna; almost all Redlichiida (including the Olenelloidea) and most Late Cambrian stocks became extinct. A continuing decrease in Laurentian continental shelf area
1860-574: The Olenellina also suggests this suborder to be the ancestral trilobite stock: early protaspid stages have not been found, supposedly because these were not calcified, and this also is supposed to represent the original state. Earlier trilobites may be found and could shed more light on their origins. Three specimens of a trilobite from Morocco, Megistaspis hammondi , dated 478 million years old contain fossilized soft parts. In 2024, researchers discovered soft tissues and other structures including
1922-468: The Paleozoic era, vast 'forests' of crinoids lived in shallow near-shore environments. Some of the genera of trilobites during the Carboniferous and Permian periods include: Exactly why the trilobites became extinct is not clear; with repeated extinction events (often followed by apparent recovery) throughout the trilobite fossil record, a combination of causes is likely. After the extinction event at
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1984-570: The Redlichiida or Corynexochida in the Middle Cambrian. Order Ptychopariida is the most problematic order for trilobite classification. In the 1959 Treatise on Invertebrate Paleontology , what are now members of orders Ptychopariida, Asaphida , Proetida and Harpetida were grouped together as order Ptychopariida; subclass Librostoma was erected in 1990 to encompass all of these orders, based on their shared ancestral character of
2046-521: The age of the rocks in which they are found. They were among the first fossils to attract widespread attention, and new species are being discovered every year. In the United States, the best open-to-the-public collection of trilobites is located in Hamburg, New York . The shale quarry, informally known as Penn Dixie, stopped mining in the 1960s. The large amounts of trilobites were discovered in
2108-473: The clade Artiopoda , which includes many organisms that are morphologically similar to trilobites, but are largely unmineralised. The relationship of Artiopoda to other arthropods is uncertain. Trilobites evolved into many ecological niches; some moved over the seabed as predators , scavengers , or filter feeders , and some swam, feeding on plankton . Some even crawled onto land. Most lifestyles expected of modern marine arthropods are seen in trilobites, with
2170-518: The combination of sea level changes and a break in the redox equilibrium (a meteorite impact has also been suggested as a cause). Only a single order, the Proetida , survived into the Carboniferous. Genera of trilobites during the Silurian and Devonian periods include: The Proetida survived for millions of years, continued through the Carboniferous period and lasted until the end of
2232-418: The end of nearly 300 million successful years for the trilobites would not have been unexpected at the time. Trilobites appear to have been primarily marine organisms, since the fossilized remains of trilobites are always found in rocks containing fossils of other salt-water animals such as brachiopods, crinoids, and corals. Some trackways suggest trilobites made at least temporary excursions onto land. Within
2294-610: The end of the Cambrian . Most scientists believe that order Redlichiida , more specifically its suborder Redlichiina , contains a common ancestor of all other orders, with the possible exception of the Agnostina. While many potential phylogenies are found in the literature, most have suborder Redlichiina giving rise to orders Corynexochida and Ptychopariida during the Lower Cambrian, and the Lichida descending from either
2356-467: The end of the Devonian period, what trilobite diversity remained was bottlenecked into the order Proetida. Decreasing diversity of genera limited to shallow-water shelf habitats coupled with a drastic lowering of sea level ( regression ) meant that the final decline of trilobites happened shortly before the end Permian mass extinction event . With so many marine species involved in the Permian extinction,
2418-477: The exoskeleton. Of the 20,000 known species only 38 have fossils with preserved appendages. Trilobites range in length from minute (less than 1 millimetre (0.039 in)) to very large (over 70 centimetres (28 in)), with an average size range of 3–10 cm (1.2–3.9 in). Supposedly the smallest species is Acanthopleurella stipulae with a maximum of 1.5 millimetres (0.059 in). The world's largest-known trilobite specimen, assigned to Isotelus rex
2480-467: The families Dimeropygidae and Toernquistiidae. At the third node, the superfamily Aulacopleuroidea (consisting of Aulacopleuridae and Brachymetopidae) split off. The fourth branch is the family Scharyiidae. The fifth branch consists of the families Roringtoniidae and Tropidocoryphidae. The sixth node combines a restricted Bathyuridae split off from Bathyurella with the family Proetidae (including Phillipsiidae, which, according to Lamsdell, has been demoted to
2542-565: The families should be combined in a new proposed order, Aulacopleurida (Adrian, 2011), that would consist of the families Aulacopleuridae , Brachymetopidae , Dimeropygidae , Rorringtoniidae , Scharyiidae , Bathyuridae , Telephinidae , Holotrachelidae and Hystricuridae (considered Proetida before), combined with the Ptychopariid families Alokistocaridae , Crepicephalidae , Ehmaniellidae , Marjumiidae , Solenopleuridae and Tricrepicephalidae . The reasoning for this proposed split
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2604-682: The feeding trace, are furrows through the sediment, which are believed to represent the movement of trilobites while deposit feeding. Many of the Diplichnites fossils are believed to be traces made by trilobites walking on the sediment surface. Care must be taken as similar trace fossils are recorded in freshwater and post-Paleozoic deposits, representing non-trilobite origins. Trilobite fossils are found worldwide, with thousands of known species. Because they appeared quickly in geological time, and moulted like other arthropods, trilobites serve as excellent index fossils , enabling geologists to date
2666-480: The first is that the eye develops on the side of the headshield, not at the front, and the second is a forwardly tapering glabella that is distanced from the rim of the headshield. The analysis identifies the taxa Asaphida , Olenina and Phacopida (including the Holotrachelidae) as sister groups . The earliest branch in Proetida is the family Hystricuridae. This is followed by a branch that consists of
2728-404: The glabella (impendent). Many variations in shape and placement of the hypostome have been described. The size of the glabella and the lateral fringe of the cephalon, together with hypostome variation, have been linked to different lifestyles, diets and specific ecological niches . The anterior and lateral fringe of the cephalon is greatly enlarged in the Harpetida , in other species a bulge in
2790-448: The headshield into so-called genal spines. These two features can aid in distinguishing proetids from some phacopid trilobites in the suborder Phacopina , to which they can be very similar. Opinions about the composition of and the affinities within the proetids, and to other trilobites, have been very divergent over time. In 2011 it was suggested to retain in Proetida only the families Proetidae and Tropidocoryphidae . The remainder of
2852-546: The land from development. In 1994, the quarry became Penn Dixie Fossil Park & Nature Reserve when they received 501(c)3 status and was opened for visitation and collection of trilobite samples. The two most common found samples are Eldredgeops rana and Greenops . A famous location for trilobite fossils in the United Kingdom is Wren's Nest , Dudley , in the West Midlands , where Calymene blumenbachii
2914-400: The last few survivors at the end of the Permian period. Principal evolutionary trends from primitive morphologies, such as exemplified by Eoredlichia , include the origin of new types of eyes, improvement of enrollment and articulation mechanisms, increased size of pygidium (micropygy to isopygy), and development of extreme spinosity in certain groups. Changes also included narrowing of
2976-407: The lenses. Each lens is generally hexagonal in outline and in direct contact with the others. They range in number from one to more than 15,000 per eye. Eyes are usually large, and because the individual lenses are hard to make out, they look smooth and sometimes bead-like. The thorax of proetids was made up of anywhere between 8–22 segments, but most commonly 10. Many also extend the backcorners of
3038-439: The marine paleoenvironment, trilobites were found in a broad range from extremely shallow water to very deep water. Trilobites, like brachiopods, crinoids, and corals, are found on all modern continents, and occupied every ancient ocean from which Paleozoic fossils have been collected. The remnants of trilobites can range from the preserved body to pieces of the exoskeleton, which it shed in the process known as ecdysis. In addition,
3100-426: The moult stage and the hardening of the new exoskeleton. A trilobite's cephalon, or head section, is highly variable with a lot of morphological complexity. The glabella forms a dome underneath which sat the "crop" or "stomach". Generally, the exoskeleton has few distinguishing ventral features, but the cephalon often preserves muscle attachment scars and occasionally the hypostome , a small rigid plate comparable to
3162-404: The possible exception of parasitism (where scientific debate continues). Some trilobites (particularly the family Olenidae ) are even thought to have evolved a symbiotic relationship with sulfur-eating bacteria from which they derived food. The largest trilobites were more than 70 centimetres (28 in) long and may have weighed as much as 4.5 kilograms (9.9 lb). Trilobites belong to
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#17327718545243224-417: The pre-glabellar area is preserved that suggests a brood pouch. Highly complex compound eyes are another obvious feature of the cephalon. Facial or cephalic sutures are the natural fracture lines in the cephalon of trilobites. Their function was to assist the trilobite in shedding its old exoskeleton during ecdysis (or molting). All species assigned to the suborder Olenellina , that became extinct at
3286-405: The rate of speciation during the period known as the Cambrian explosion because they are the most diverse group of metazoans known from the fossil record of the early Cambrian. Trilobites are excellent stratigraphic markers of the Cambrian period: researchers who find trilobites with alimentary prosopon, and a micropygium, have found Early Cambrian strata. Most of the Cambrian stratigraphy
3348-699: The subfamily Phillipsiinae). The following superfamilies, families and genera are recognized: Family Aulacopleuridae Family Brachymetopidae Family Rorringtoniidae Family Bathyuridae Family Dimeropygidae (including Celmidae) Family Holotrachelidae Family Hystricuridae Family Raymondinidae ? (including Glaphuridae) order placement considered uncertain by Adrain, 2011 Family Telephinidae Family Toernquistiidae Family Phillipsiidae Family Proetidae Family Tropidocoryphidae Trilobite Trilobites ( / ˈ t r aɪ l ə ˌ b aɪ t s , ˈ t r ɪ l ə -/ ; meaning "three lobes") are extinct marine arthropods that form
3410-594: The thoracic furrows, is also a common evolutionary trend. Notable examples of this were the orders Agnostida and Asaphida , and the suborder Illaenina of the Corynexochida . Effacement is believed to be an indication of either a burrowing lifestyle or a pelagic one. Effacement poses a problem for taxonomists since the loss of details (particularly of the glabella ) can make the determination of phylogenetic relationships difficult. Although it has historically been suggested that trilobites originated during
3472-406: The thorax and increasing or decreasing numbers of thoracic segments. Specific changes to the cephalon are also noted; variable glabella size and shape, position of eyes and facial sutures, and hypostome specialization. Several morphologies appeared independently within different major taxa (e.g. eye reduction or miniaturization). Effacement, the loss of surface detail in the cephalon, pygidium, or
3534-505: The tracks left behind by trilobites living on the sea floor are often preserved as trace fossils . There are three main forms of trace fossils associated with trilobites: Rusophycus , Cruziana and Diplichnites —such trace fossils represent the preserved life activity of trilobites active upon the sea floor. Rusophycus , the resting trace, are trilobite excavations involving little or no forward movement and ethological interpretations suggest resting, protection and hunting. Cruziana ,
3596-538: The trilobites unscathed; some distinctive and previously successful forms such as the Telephinidae and Agnostida became extinct. The Ordovician marks the last great diversification period amongst the trilobites: very few entirely new patterns of organisation arose post-Ordovician. Later evolution in trilobites was largely a matter of variations upon the Ordovician themes. By the Ordovician mass extinction , vigorous trilobite radiation has stopped, and gradual decline
3658-448: The ventral plate in other arthropods. A toothless mouth and stomach sat upon the hypostome with the mouth facing backward at the rear edge of the hypostome. Hypostome morphology is highly variable; sometimes supported by an un-mineralised membrane (natant), sometimes fused onto the anterior doublure with an outline very similar to the glabella above (conterminant) or fused to the anterior doublure with an outline significantly different from
3720-554: The very end of the Early Cambrian (like Fallotaspis , Nevadia , Judomia , and Olenellus ) lacked facial sutures. They are believed to have never developed facial sutures, having pre-dated their evolution. Because of this (along with other primitive characteristics), they are thought to be the earliest ancestors of later trilobites. Some other later trilobites also lost facial sutures secondarily. The type of sutures found in different species are used extensively in
3782-583: Was fundamental in formulating and testing punctuated equilibrium as a mechanism of evolution. Identification of the 'Atlantic' and 'Pacific' trilobite faunas in North America and Europe implied the closure of the Iapetus Ocean (producing the Iapetus suture), thus providing important supporting evidence for the theory of continental drift . Trilobites have been important in estimating
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#17327718545243844-469: Was proposed to be elevated out of the asaphid superfamily Trinucleioidea . Sometimes the Nektaspida are considered trilobites, but these lack a calcified exoskeleton and eyes. Some scholars have proposed that the order Agnostida is polyphyletic, with the suborder Agnostina representing non-trilobite arthropods unrelated to the suborder Eodiscina . Under this hypothesis, Eodiscina would be elevated to
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