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50-701: Osteichthyes ( / ˌ ɒ s t iː ˈ ɪ k θ iː z / ost-ee- IK -theez ), also known as osteichthyans or commonly referred to as the bony fish , is a diverse superclass of vertebrate animals that have endoskeletons primarily composed of bone tissue . They can be contrasted with the Chondrichthyes (cartilaginous fish) and the extinct placoderms and acanthodians , which have endoskeletons primarily composed of cartilage . The vast majority of extant fish are members of Osteichthyes, being an extremely diverse and abundant group consisting of 45 orders , over 435 families and 28,000 species . It

100-495: A top-level genus (genus summum) – was first introduced by French botanist Joseph Pitton de Tournefort in the classification of plants that appeared in his Eléments de botanique of 1694. Insofar as a general definition of a class is available, it has historically been conceived as embracing taxa that combine a distinct grade of organization—i.e. a 'level of complexity', measured in terms of how differentiated their organ systems are into distinct regions or sub-organs—with

150-407: A bony operculum , and a predominantly bony skeleton. Under this classification system, Osteichthyes was considered paraphyletic with regard to land vertebrates , as the common ancestor of all osteichthyans includes tetrapods amongst its descendants. While the largest subclass, Actinopterygii (ray-finned fish), is monophyletic, with the inclusion of the smaller sub-class Sarcopterygii, Osteichthyes

200-423: A crown group to be extant, only to have resulted from a "major cladogenesis event". The first definition forms the basis of this article. Often, the crown group is given the designation "crown-", to separate it from the group as commonly defined. Both birds and mammals are traditionally defined by their traits, and contain fossil members that lived before the last common ancestors of the living groups or, like

250-455: A crown group, which includes the most recent common ancestor of all modern birds, and all of its extant or extinct descendants. The concept was developed by Willi Hennig , the formulator of phylogenetic systematics , as a way of classifying living organisms relative to their extinct relatives in his "Die Stammesgeschichte der Insekten", and the "crown" and "stem" group terminology was coined by R. P. S. Jefferies in 1979. Though formulated in

300-498: A dead sunfish near the coast of Faial Island , Azores , with a weight of 2,744 kilograms (6,049 lb) and 3.6 metres (12 ft) tall and 3.5 metres (11 ft) long established the biggest giant sunfish ever captured. The longest is the king of herrings , a type of oarfish . Other very large bony fish include the Atlantic blue marlin , some specimens of which have been recorded as in excess of 820 kilograms (1,810 lb),

350-434: A distinct type of construction, which is to say a particular layout of organ systems. This said, the composition of each class is ultimately determined by the subjective judgment of taxonomists . In the first edition of his Systema Naturae (1735), Carl Linnaeus divided all three of his kingdoms of nature ( minerals , plants , and animals ) into classes. Only in the animal kingdom are Linnaeus's classes similar to

400-428: A host of prefixes have been defined to describe various branches of the phylogenetic tree relative to extant organisms. A pan-group or total group is the crown group and all organisms more closely related to it than to any other extant organisms. In a tree analogy, it is the crown group and all branches back to (but not including) the split with the closest branch to have living members. The Pan-Aves thus contain

450-432: A stem group allows the order of these acquisitions to be established, and thus the ecological and functional setting of the evolution of the major features of the group in question. Stem groups thus offer a route to integrate unique palaeontological data into questions of the evolution of living organisms. Furthermore, they show that fossils that were considered to lie in their own separate group because they did not show all

500-632: Is no consensus phylogeny. Stem arthropods constitute a group that has seen attention in connection with the Burgess Shale fauna. Several of the finds , including the enigmatic Opabinia and Anomalocaris have some, though not all, features associated with arthropods , and are thus considered stem arthropods. The sorting of the Burgess Shale fauna into various stem groups finally enabled phylogenetic sorting of this enigmatic assemblage and also allowed for identifying velvet worms as

550-481: Is the largest class of vertebrates in existence today, encompassing most aquatic vertebrates, as well as all semi-aquatic and terrestrial vertebrates. The group is divided into two main clades , the ray-finned fish ( Actinopterygii , which makes up the vast majority of extant fish) and the lobe-finned fish ( Sarcopterygii , which gave rise to all land vertebrates, i.e. tetrapods ). The oldest known fossils of bony fish are about 425 million years old from

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600-458: Is thought by some to make the Cambrian explosion easier to understand without invoking unusual evolutionary mechanisms; however, application of the stem group concept does nothing to ameliorate the difficulties that phylogenetic telescoping poses to evolutionary theorists attempting to understand both macroevolutionary change and the abrupt character of the Cambrian explosion . Overemphasis on

650-437: Is usually oviparous (egg-laying) but can be ovoviviparous , or viviparous . Although there is usually no parental care after birth, before birth parents may scatter, hide, guard or brood eggs, with sea horses being notable in that the males undergo a form of "pregnancy", brooding eggs deposited in a ventral pouch by a female. The giant sunfish is the heaviest bony fish in the world, in late 2021, Portuguese fishermen found

700-442: The black marlin , some sturgeon species, and the giant and goliath grouper , which both can exceed 300 kilograms (660 lb) in weight. In contrast, Paedocypris progenetica and the stout infantfish can measure less than 8 millimetres (0.31 in). The beluga sturgeon is the largest species of freshwater bony fish extant today, and Arapaima gigas is among the largest of the freshwater fish. The largest bony fish ever

750-1099: The cladogram below. Whole-genome duplication took place in the ancestral Osteichthyes. Coelacanthiformes [REDACTED] Ceratodontiformes [REDACTED] Tetrapoda [REDACTED] Polypteriformes [REDACTED] Acipenseriformes [REDACTED] Lepisosteiformes [REDACTED] Amiiformes [REDACTED] Elopiformes [REDACTED] Albuliformes [REDACTED] Notacanthiformes [REDACTED] Anguilliformes [REDACTED] Osteoglossiformes [REDACTED] Hiodontiformes [REDACTED] Clupeiformes [REDACTED] Alepocephaliformes [REDACTED] Gonorynchiformes [REDACTED] Cypriniformes [REDACTED] Characiformes [REDACTED] Gymnotiformes [REDACTED] Siluriformes [REDACTED] Lepidogalaxiiformes Argentiniformes [REDACTED] Galaxiiformes [REDACTED] Salmoniformes [REDACTED] Esociformes [REDACTED] Osmeriformes [REDACTED] Stomiatiformes [REDACTED] Neoteleostei [REDACTED] All bony fish possess gills . For

800-405: The dinosaurs and the pterosaurs . The last common ancestor of birds and crocodilians—the first crown group archosaur—was neither bird nor crocodilian and possessed none of the features unique to either. As the bird stem group evolved, distinctive bird features such as feathers and hollow bones appeared. Finally, at the base of the crown group, all traits common to extant birds were present. Under

850-429: The inner ear contains large otoliths . The braincase, or neurocranium, is frequently divided into anterior and posterior sections divided by a fissure . Early bony fish had simple respiratory diverticula (an outpouching on either side of the esophagus ) which helped them breathe air in low-oxygen water as a form of supplementary enteral respiration . In ray-finned fish these have evolved into swim bladders ,

900-466: The last common ancestor of the crown group and their closest living relatives. It follows from the definition that all members of a stem group are extinct. The "stem group" is the most used and most important of the concepts linked to crown groups, as it offers a means to reify and name paraphyletic assemblages of fossils that otherwise do not fit into systematics based on living organisms. While often attributed to Jefferies (1979), Willmann (2003) traced

950-426: The lungfish , our nearest relatives among the fishes. In addition to a series of lobe-finned fishes , they also include some of the early labyrinthodonts . Exactly what labyrinthodonts are in the stem group tetrapods rather than the corresponding crown group is uncertain, as the phylogeny of early tetrapods is not well understood. This example shows that crown and stem group definitions are of limited value when there

1000-418: The opah , swordfish and tuna have independently evolved various levels of endothermy . Bony fish can be any type of heterotroph : numerous species of omnivore , carnivore , herbivore , filter-feeder , detritivore , or hematophage are documented. Some bony fish are hermaphrodites , and a number of species exhibit parthenogenesis . Fertilization is usually external, but can be internal. Development

1050-525: The swim bladders and lungs , respectively. Osteichthyes can be compared to Euteleostomi . In paleontology the terms are synonymous. In ichthyology the difference is that Euteleostomi presents a cladistic view which includes the terrestrial tetrapods that evolved from lobe-finned fish. Until recently, the view of most ichthyologists has been that Osteichthyes were paraphyletic and include only fishes. However, since 2013 widely cited ichthyology papers have been published with phylogenetic trees that treat

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1100-408: The 1970s, the term was not commonly used until its reintroduction in 2000 by Graham Budd and Sören Jensen . It is not necessary for a species to have living descendants in order for it to be included in the crown group. Extinct side branches on the family tree that are descended from the most recent common ancestor of living members will still be part of a crown group. For example, if we consider

1150-527: The Crocodilia branch. Basal branch names such as Avemetatarsalia are usually more obscure. However, not so advantageous are the facts that "Pan-Aves" and "Aves" are not the same group, the circumscription of the concept of "Pan-Aves" (synonymous with Avemetatarsalia) is only evident by examination of the above tree, and calling both groups "birds" is ambiguous. Stem mammals are those in the lineage leading to living mammals, together with side branches, from

1200-484: The Osteichthyes as a clade including tetrapods. Bony fish are characterized by a relatively stable pattern of cranial bones , rooted, medial insertion of mandibular muscle in the lower jaw. The head and pectoral girdles are covered with large dermal bones. The eyeball is supported by a sclerotic ring of four small bones, but this characteristic has been lost or modified in many modern species. The labyrinth in

1250-452: The changing sizes of which help to alter the body's specific density and buoyancy . In elpistostegalians , a crown group of lobe-finned fish that gave rise to the land-dwelling tetrapods , these respiratory diverticula became further specialized for obligated air breathing and evolved into the modern amphibian , reptilian , avian and mammalian lungs . Early bony fish did not have fin spines like most modern fish, but instead had

1300-450: The classes used today; his classes and orders of plants were never intended to represent natural groups, but rather to provide a convenient "artificial key" according to his Systema Sexuale , largely based on the arrangement of flowers. In botany, classes are now rarely discussed. Since the first publication of the APG system in 1998, which proposed a taxonomy of the flowering plants up to

1350-520: The closest living relatives of arthropods. Stem priapulids are other early Cambrian to middle Cambrian faunas, appearing in Chengjiang to Burgess Shale. The genus Ottoia has more or less the same build as modern priapulids , but phylogenetic analysis indicates that it falls outside the crown group, making it a stem priapulid. The name plesion has a long history in biological systematics, and plesion group has acquired several meanings over

1400-436: The crown-birds (i.e. all extant birds and the rest of the family tree back to their most recent common ancestor), extinct side branches like the dodo or great auk are still descended from the most recent common ancestor of all living birds , so fall within the bird crown group. One very simplified cladogram for birds is shown below: † Archaeopteryx other extinct groups Neornithes (modern birds, some extinct like

1450-488: The diagnostic features of a living clade, can nevertheless be related to it by lying in its stem group. Such fossils have been of particular importance in considering the origins of the tetrapods , mammals , and animals . The application of the stem group concept also influenced the interpretation of the organisms of the Burgess shale . Their classification in stem groups to extant phyla, rather than in phyla of their own,

1500-515: The divergence of the lineage from the Sauropsida to the last common ancestor of the living mammals. This group includes the synapsids as well as mammaliaforms like the morganucodonts and the docodonts ; the latter groups have traditionally and anatomically been considered mammals even though they fall outside the crown group mammals. Stem tetrapods are the animals belonging to the lineage leading to tetrapods from their divergence from

1550-537: The dodo) In this diagram, the clade labelled "Neornithes" is the crown group of birds: it includes the most recent common ancestor of all living birds and its descendants, living or not. Although considered to be birds (i.e. members of the clade Aves), Archaeopteryx and other extinct groups are not included in the crown group, as they fall outside the Neornithes clade, being descended from an earlier ancestor. An alternative definition does not require any members of

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1600-479: The early nineteenth century. Crown group In phylogenetics , the crown group or crown assemblage is a collection of species composed of the living representatives of the collection, the most recent common ancestor of the collection, and all descendants of the most recent common ancestor. It is thus a way of defining a clade , a group consisting of a species and all its extant or extinct descendants. For example, Neornithes (birds) can be defined as

1650-463: The epidermis in the process. The three categories of scales for Osteichthyes which are cosmoid scales, ganoid scales, teleost scales. The teleost scales are also then divided into two subgroups which are the cycloid scales, and the ctenoid scales. All these scales have a base of bone that they all originate from, the only difference is that the teleost scales only have one layer of bone. Ganoid scales have lamellar bone, and vascular bone that lies on top of

1700-488: The epidermis of the fish. ...it is increasingly widely accepted that tetrapods, including ourselves, are simply modified bony fishes, and so we are comfortable with using the taxon Osteichthyes as a clade, which now includes all tetrapods... Fishes of the World (5th ed) Traditionally, Osteichthyes was considered a class , recognised on the presence of a swim bladder , only three pairs of gill arches hidden behind

1750-505: The extinct moa ) The crown group here is Neornithes , all modern bird lineages back to their last common ancestor. The closest living relatives of birds are crocodilians . If we follow the phylogenetic lineage leading to Neornithes to the left, the line itself and all side branches belong to the stem birds until the lineage merges with that of the crocodilians. In addition to non-crown group primitive birds like Archaeopteryx , Hesperornis and Confuciusornis , stem group birds include

1800-494: The fleshy paddle-like fins similar to other non-bony clades of fish, although the lobe-finned fish evolved articulated appendicular skeletons within their paired fins , which gave rise to tetrapods' limbs . They also evolved a pair of opercula (gill covers), which can actively draw water across the gills so they can breathe without having to swim. Bony fish do not have placoid scales like cartilaginous fish, instead they consist of three types of scales that do not penetrate

1850-432: The full bifurcating phylogeny. Stem birds perhaps constitute the most cited example of a stem group, as the phylogeny of this group is fairly well known. The following cladogram, based on Benton (2005), illustrates the concept: Crocodilia Pterosauria Hadrosauridae Stegosauria Sauropoda Tyrannosauridae Archaeopteryx Neognathae (including the extinct dodo ) Paleognathae (including

1900-423: The lamellar bone, then enamel lies on top of both layers of bone. Cosmoid scales have the same two layers of bone that ganoid scales have except they have dentin in-between the enamel and vascular bone and lamellar (vascular and lamellar two subcategories for bone found in scales). All these scales are found underneath the epidermis and do not break the epidermis of the fish. Unlike the placoid scales that poke through

1950-440: The late Silurian , which are also transitional fossils showing a tooth pattern that is in between the tooth rows of sharks and true bony fishes. Despite the name, these early basal bony fish had not yet evolved ossification and their skeletons were still mostly cartilaginous, and the main distinguishing feature that set them apart from other fish clades were the development of foregut pouches that eventually evolved into

2000-503: The level of orders, many sources have preferred to treat ranks higher than orders as informal clades . Where formal ranks have been assigned, the ranks have been reduced to a very much lower level, e.g. class Equisitopsida for the land plants, with the major divisions within the class assigned to subclasses and superorders. The class was considered the highest level of the taxonomic hierarchy until George Cuvier 's embranchements , first called Phyla by Ernst Haeckel , were introduced in

2050-628: The living birds and all (fossil) organisms more closely related to birds than to crocodilians (their closest living relatives). The phylogenetic lineage leading back from Neornithes to the point where it merges with the crocodilian lineage, along with all side branches, constitutes pan-birds. In addition to non-crown group primitive birds like Archaeopteryx , Hesperornis and Confuciusornis , therefore, pan-group birds would include all dinosaurs and pterosaurs as well as an assortment of non-crocodilian animals like Marasuchus . Pan-Mammalia consists of all mammals and their fossil ancestors back to

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2100-434: The majority this is their sole or main means of respiration. Lungfish and other osteichthyan species are capable of respiration through lungs or vascularized swim bladders. Other species can respire through their skin, intestines, and/or stomach. Osteichthyes are primitively ectothermic (cold blooded), meaning that their body temperature is dependent on that of the water. But some of the larger marine osteichthyids, such as

2150-466: The mammal Haldanodon , were not descended from that ancestor although they lived later. Crown-Aves and Crown-Mammalia therefore differ slightly in content from the common definition of Aves and Mammalia. This has caused some confusion in the literature. The cladistic idea of strictly using the topology of the phylogenetic tree to define groups necessitates other definitions than crown groups to adequately define commonly discussed fossil groups. Thus,

2200-464: The narrower one. Often, an (extinct) grouping is identified as belonging together. Later, it may be realized other (extant) groupings actually emerged within such grouping, rendering them a stem grouping. Cladistically , the new groups should then be added to the group, as paraphyletic groupings are not natural. In any case, stem groupings with living descendants should not be viewed as a cohesive group, but their tree should be further resolved to reveal

2250-479: The origin of the stem group concept to Austrian systematist Othenio Abel (1914), and it was discussed and diagrammed in English as early as 1933 by A. S. Romer . Alternatively, the term "stem group" is sometimes used in a wider sense to cover any members of the traditional taxon falling outside the crown group. Permian synapsids like Dimetrodon or Anteosaurus are stem mammals in the wider sense but not in

2300-499: The phylogenetic split from the remaining amniotes (the Sauropsida ). Pan-Mammalia is thus an alternative name for Synapsida . A stem group is a paraphyletic assemblage composed of the members of a pan-group or total group, above, minus the crown group itself (and therefore minus all living members of the pan-group). This leaves primitive relatives of the crown groups , back along the phylogenetic line to (but not including)

2350-617: The widely used total-group perspective, the Crocodylomorpha would become synonymous with the Crocodilia, and the Avemetatarsalia would become synonymous with the birds, and the above tree could be summarized as Crocodilia Birds An advantage of this approach is that declaring Theropoda to be birds (or Pan-aves ) is more specific than declaring it to be a member of the Archosauria, which would not exclude it from

2400-491: The years. One use is as "nearby group" (plesion means close to in Greek ), i.e. sister group to a given taxon , whether that group is a crown group or not. The term may also mean a group, possibly paraphyletic , defined by primitive traits (i.e. symplesiomorphies ). It is generally taken to mean a side branch splitting off earlier on the phylogenetic tree than the group in question. Placing fossils in their right order in

2450-418: Was Leedsichthys , which dwarfed the beluga sturgeon as well as the ocean sunfish , giant grouper and all the other giant bony fishes alive today. [REDACTED] [REDACTED] [REDACTED] [REDACTED] [REDACTED] [REDACTED] [REDACTED] Superclass (biology) The class as a distinct rank of biological classification having its own distinctive name – and not just called

2500-403: Was regarded as paraphyletic. This has led to the current cladistic classification which splits the Osteichthyes into two full classes. Under this scheme Osteichthyes is monophyletic, as it includes the tetrapods making it a synonym of the clade Euteleostomi . Most bony fish belong to the ray-finned fish (Actinopterygii). A phylogeny of living Osteichthyes, including the tetrapods, is shown in

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