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58-508: Holocephali ("complete heads"), sometimes given the name Euchondrocephali , is a subclass of cartilaginous fish in the class Chondrichthyes. The earliest fossils are of teeth and come from the Devonian period. Little is known about these primitive forms, and the only surviving group in the subclass is the order Chimaeriformes . Chimaeriformes, commonly known as chimaeras, rat fish, or ghost sharks, include three living families and

116-442: A taxonomic rank ; groups of a given rank can be aggregated to form a more inclusive group of higher rank, thus creating a taxonomic hierarchy. The principal ranks in modern use are domain , kingdom , phylum ( division is sometimes used in botany in place of phylum ), class , order , family , genus , and species . The Swedish botanist Carl Linnaeus is regarded as the founder of the current system of taxonomy, as he developed

174-469: A basis of morphological and physiological facts as possible, and one in which "place is found for all observational and experimental data relating, even if indirectly, to the constitution, subdivision, origin, and behaviour of species and other taxonomic groups". Ideals can, it may be said, never be completely realized. They have, however, a great value of acting as permanent stimulants, and if we have some, even vague, ideal of an "omega" taxonomy we may progress

232-557: A chaotic and disorganized taxonomic literature. He not only introduced the standard of class, order, genus, and species, but also made it possible to identify plants and animals from his book, by using the smaller parts of the flower (known as the Linnaean system ). Plant and animal taxonomists regard Linnaeus' work as the "starting point" for valid names (at 1753 and 1758 respectively). Names published before these dates are referred to as "pre-Linnaean", and not considered valid (with

290-443: A different sense, to mean the delimitation of species (not subspecies or taxa of other ranks), using whatever investigative techniques are available, and including sophisticated computational or laboratory techniques. Thus, Ernst Mayr in 1968 defined " beta taxonomy " as the classification of ranks higher than species. An understanding of the biological meaning of variation and of the evolutionary origin of groups of related species

348-551: 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 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

406-424: A distinct rank of biological classification having its own distinctive name – and not just called 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

464-650: A little over 50 species of surviving holocephalans. These fishes move by using sweeping movements of their large pectoral fins . They are deep sea fish with slender tails, living close to the seabed to feed on benthic invertebrates. They lack a stomach, their food moving directly into the intestine. Extinct holocephalans were much more diverse in lifestyles, including shark -like predatory forms and slow, durophagous fish. Members of this taxon preserve today some features of elasmobranch life in Paleozoic times, though in other respects they are aberrant. They live close to

522-455: A little way down the Greek alphabet. Some of us please ourselves by thinking we are now groping in a "beta" taxonomy. Turrill thus explicitly excludes from alpha taxonomy various areas of study that he includes within taxonomy as a whole, such as ecology, physiology, genetics, and cytology. He further excludes phylogenetic reconstruction from alpha taxonomy. Later authors have used the term in

580-681: A much more restricted definition. Based on genetic research, it is estimated the Holocephali split from the Elasmobranchii (the branch of chondrichthyans containing true sharks and rays) about 421 million years ago. Analysis of the 280 million-year-old holocephalian Dwykaselachus demonstrates that early members of the group were more shark-like. † Extinct * position uncertain [REDACTED] [REDACTED] [REDACTED] [REDACTED] [REDACTED] [REDACTED] [REDACTED] Subclass (biology) The class as

638-504: A notable renaissance, principally with respect to theoretical content. Part of the theoretical material has to do with evolutionary areas (topics e and f above), the rest relates especially to the problem of classification. Taxonomy is that part of Systematics concerned with topics (a) to (d) above. A whole set of terms including taxonomy, systematic biology, systematics , scientific classification, biological classification, and phylogenetics have at times had overlapping meanings – sometimes

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696-516: A ranked system known as Linnaean taxonomy for categorizing organisms and binomial nomenclature for naming organisms. With advances in the theory, data and analytical technology of biological systematics, the Linnaean system has transformed into a system of modern biological classification intended to reflect the evolutionary relationships among organisms, both living and extinct. The exact definition of taxonomy varies from source to source, but

754-477: A single continuum, as per the scala naturae (the Natural Ladder). This, as well, was taken into consideration in the great chain of being. Advances were made by scholars such as Procopius , Timotheus of Gaza , Demetrios Pepagomenos , and Thomas Aquinas . Medieval thinkers used abstract philosophical and logical categorizations more suited to abstract philosophy than to pragmatic taxonomy. During

812-419: A taxonomy of the flowering plants up to 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

870-524: A truly scientific attempt to classify organisms did not occur until the 18th century, with the possible exception of Aristotle, whose works hint at a taxonomy. Earlier works were primarily descriptive and focused on plants that were useful in agriculture or medicine. There are a number of stages in this scientific thinking. Early taxonomy was based on arbitrary criteria, the so-called "artificial systems", including Linnaeus 's system of sexual classification for plants (Linnaeus's 1735 classification of animals

928-497: Is a critical component of the taxonomic process. As a result, it informs the user as to what the relatives of the taxon are hypothesized to be. Biological classification uses taxonomic ranks, including among others (in order from most inclusive to least inclusive): Domain , Kingdom , Phylum , Class , Order , Family , Genus , Species , and Strain . The "definition" of a taxon is encapsulated by its description or its diagnosis or by both combined. There are no set rules governing

986-400: Is a novel analysis of the variation patterns in a particular taxon . This analysis may be executed on the basis of any combination of the various available kinds of characters, such as morphological, anatomical , palynological , biochemical and genetic . A monograph or complete revision is a revision that is comprehensive for a taxon for the information given at a particular time, and for

1044-458: Is a resource for fossils. Biological taxonomy is a sub-discipline of biology , and is generally practiced by biologists known as "taxonomists", though enthusiastic naturalists are also frequently involved in the publication of new taxa. Because taxonomy aims to describe and organize life , the work conducted by taxonomists is essential for the study of biodiversity and the resulting field of conservation biology . Biological classification

1102-454: Is considered a part of taxonomy (definitions 1 and 2), or a part of systematics outside taxonomy. For example, definition 6 is paired with the following definition of systematics that places nomenclature outside taxonomy: In 1970, Michener et al. defined "systematic biology" and "taxonomy" (terms that are often confused and used interchangeably) in relation to one another as follows: Systematic biology (hereafter called simply systematics)

1160-419: Is even more important for the second stage of taxonomic activity, the sorting of species into groups of relatives ("taxa") and their arrangement in a hierarchy of higher categories. This activity is what the term classification denotes; it is also referred to as "beta taxonomy". How species should be defined in a particular group of organisms gives rise to practical and theoretical problems that are referred to as

1218-400: Is the field that (a) provides scientific names for organisms, (b) describes them, (c) preserves collections of them, (d) provides classifications for the organisms, keys for their identification, and data on their distributions, (e) investigates their evolutionary histories, and (f) considers their environmental adaptations. This is a field with a long history that in recent years has experienced

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1276-529: The Aristotelian system , with additions concerning the philosophical and existential order of creatures. This included concepts such as the great chain of being in the Western scholastic tradition, again deriving ultimately from Aristotle. The Aristotelian system did not classify plants or fungi , due to the lack of microscopes at the time, as his ideas were based on arranging the complete world in

1334-585: The Neomura , the clade that groups together the Archaea and Eucarya , would have evolved from Bacteria, more precisely from Actinomycetota . His 2004 classification treated the archaeobacteria as part of a subkingdom of the kingdom Bacteria, i.e., he rejected the three-domain system entirely. Stefan Luketa in 2012 proposed a five "dominion" system, adding Prionobiota ( acellular and without nucleic acid ) and Virusobiota (acellular but with nucleic acid) to

1392-512: The Renaissance and the Age of Enlightenment , categorizing organisms became more prevalent, and taxonomic works became ambitious enough to replace the ancient texts. This is sometimes credited to the development of sophisticated optical lenses, which allowed the morphology of organisms to be studied in much greater detail. One of the earliest authors to take advantage of this leap in technology

1450-439: The species problem . The scientific work of deciding how to define species has been called microtaxonomy. By extension, macrotaxonomy is the study of groups at the higher taxonomic ranks subgenus and above, or simply in clades that include more than one taxon considered a species, expressed in terms of phylogenetic nomenclature . While some descriptions of taxonomic history attempt to date taxonomy to ancient civilizations,

1508-467: The vertebrates ), as well as groups like the sharks and cetaceans , are commonly used. His student Theophrastus (Greece, 370–285 BC) carried on this tradition, mentioning some 500 plants and their uses in his Historia Plantarum . Several plant genera can be traced back to Theophrastus, such as Cornus , Crocus , and Narcissus . Taxonomy in the Middle Ages was largely based on

1566-488: The 1960s. In 1958, Julian Huxley used the term clade . Later, in 1960, Cain and Harrison introduced the term cladistic . The salient feature is arranging taxa in a hierarchical evolutionary tree , with the desideratum that all named taxa are monophyletic. A taxon is called monophyletic if it includes all the descendants of an ancestral form. Groups that have descendant groups removed from them are termed paraphyletic , while groups representing more than one branch from

1624-491: The Origin of Species (1859) led to a new explanation for classifications, based on evolutionary relationships. This was the concept of phyletic systems, from 1883 onwards. This approach was typified by those of Eichler (1883) and Engler (1886–1892). The advent of cladistic methodology in the 1970s led to classifications based on the sole criterion of monophyly , supported by the presence of synapomorphies . Since then,

1682-522: The animal and plant kingdoms toward the end of the 18th century, well before Charles Darwin's On the Origin of Species was published. The pattern of the "Natural System" did not entail a generating process, such as evolution, but may have implied it, inspiring early transmutationist thinkers. Among early works exploring the idea of a transmutation of species were Zoonomia in 1796 by Erasmus Darwin (Charles Darwin's grandfather), and Jean-Baptiste Lamarck 's Philosophie zoologique of 1809. The idea

1740-460: The animal kingdom are Linnaeus's classes similar to 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

1798-446: The bottom and feed on molluscs and other invertebrates . The tail is long and thin and they move by sweeping movements of the large pectoral fins. The erectile spine in front of the dorsal fin is sometimes venomous. There is no stomach (that is, the gut is simplified and the 'stomach' is merged with the intestine), and the mouth is a small aperture surrounded by lips, giving the head a parrot-like appearance. The only surviving members of

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1856-426: The core of the discipline remains: the conception, naming, and classification of groups of organisms. As points of reference, recent definitions of taxonomy are presented below: The varied definitions either place taxonomy as a sub-area of systematics (definition 2), invert that relationship (definition 6), or appear to consider the two terms synonymous. There is some disagreement as to whether biological nomenclature

1914-550: The definition of taxa, but the naming and publication of new taxa is governed by sets of rules. In zoology , the nomenclature for the more commonly used ranks ( superfamily to subspecies ), is regulated by the International Code of Zoological Nomenclature ( ICZN Code ). In the fields of phycology , mycology , and botany , the naming of taxa is governed by the International Code of Nomenclature for algae, fungi, and plants ( ICN ). The initial description of

1972-399: The entire world. Other (partial) revisions may be restricted in the sense that they may only use some of the available character sets or have a limited spatial scope. A revision results in a conformation of or new insights in the relationships between the subtaxa within the taxon under study, which may lead to a change in the classification of these subtaxa, the identification of new subtaxa, or

2030-494: The evidentiary basis has been expanded with data from molecular genetics that for the most part complements traditional morphology . Naming and classifying human surroundings likely began with the onset of language. Distinguishing poisonous plants from edible plants is integral to the survival of human communities. Medicinal plant illustrations show up in Egyptian wall paintings from c.  1500 BC , indicating that

2088-524: The exception of spiders published in Svenska Spindlar ). Even taxonomic names published by Linnaeus himself before these dates are considered pre-Linnaean. Modern taxonomy is heavily influenced by technology such as DNA sequencing , bioinformatics , databases , and imaging . A pattern of groups nested within groups was specified by Linnaeus' classifications of plants and animals, and these patterns began to be represented as dendrograms of

2146-486: The first modern groups tied to fossil ancestors was birds. Using the then newly discovered fossils of Archaeopteryx and Hesperornis , Thomas Henry Huxley pronounced that they had evolved from dinosaurs, a group formally named by Richard Owen in 1842. The resulting description, that of dinosaurs "giving rise to" or being "the ancestors of" birds, is the essential hallmark of evolutionary taxonomic thinking. As more and more fossil groups were found and recognized in

2204-687: The formal naming of clades. Linnaean ranks are optional and have no formal standing under the PhyloCode , which is intended to coexist with the current, rank-based codes. While popularity of phylogenetic nomenclature has grown steadily in the last few decades, it remains to be seen whether a majority of systematists will eventually adopt the PhyloCode or continue using the current systems of nomenclature that have been employed (and modified, but arguably not as much as some systematists wish) for over 250 years. Well before Linnaeus, plants and animals were considered separate Kingdoms. Linnaeus used this as

2262-414: The group are the rabbit fish ( Chimaera ), and the elephant fishes ( Callorhinchus ). The fossil record of the Holocephali starts during the Devonian period. The record is extensive, but most fossils are of teeth, and the body forms of numerous species are not known, or at best poorly understood. Some experts further group the orders Petalodontiformes , Iniopterygiformes , and Eugeneodontida into

2320-466: The late 19th and early 20th centuries, palaeontologists worked to understand the history of animals through the ages by linking together known groups. With the modern evolutionary synthesis of the early 1940s, an essentially modern understanding of the evolution of the major groups was in place. As evolutionary taxonomy is based on Linnaean taxonomic ranks, the two terms are largely interchangeable in modern use. The cladistic method has emerged since

2378-401: The merger of previous subtaxa. Taxonomic characters are the taxonomic attributes that can be used to provide the evidence from which relationships (the phylogeny ) between taxa are inferred. Kinds of taxonomic characters include: The term " alpha taxonomy " is primarily used to refer to the discipline of finding, describing, and naming taxa , particularly species. In earlier literature,

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2436-434: The possibilities of closer co-operation with their cytological, ecological and genetics colleagues and to acknowledge that some revision or expansion, perhaps of a drastic nature, of their aims and methods, may be desirable ... Turrill (1935) has suggested that while accepting the older invaluable taxonomy, based on structure, and conveniently designated "alpha", it is possible to glimpse a far-distant taxonomy built upon as wide

2494-818: The rank of Order, although both exclude fossil representatives. A separate compilation (Ruggiero, 2014) covers extant taxa to the rank of Family. Other, database-driven treatments include the Encyclopedia of Life , the Global Biodiversity Information Facility , the NCBI taxonomy database , the Interim Register of Marine and Nonmarine Genera , the Open Tree of Life , and the Catalogue of Life . The Paleobiology Database

2552-407: The same, sometimes slightly different, but always related and intersecting. The broadest meaning of "taxonomy" is used here. The term itself was introduced in 1813 by de Candolle , in his Théorie élémentaire de la botanique . John Lindley provided an early definition of systematics in 1830, although he wrote of "systematic botany" rather than using the term "systematics". Europeans tend to use

2610-532: The taxon " Paraselachimorpha ", and treat it as a sister group to Chimaeriformes. However, as almost all members of Paraselachimorpha are poorly understood, most experts suspect this taxon to be either paraphyletic or a wastebasket taxon . Lund & Grogan (1997) coined the subclass Euchondrocephali to refer to the total group of holocephalians, i.e. all fish more closely related to living holocephalians than to living elasmobranchs such as sharks and rays. Under this classification scheme, "Holocephali" would have

2668-562: The taxonomic hierarchy until George Cuvier 's embranchements , first called Phyla by Ernst Haeckel , were introduced in the early nineteenth century. Taxonomist In biology , taxonomy (from Ancient Greek τάξις ( taxis )  'arrangement' and -νομία ( -nomia )  ' method ') is the scientific study of naming, defining ( circumscribing ) and classifying groups of biological organisms based on shared characteristics. Organisms are grouped into taxa (singular: taxon) and these groups are given

2726-472: The term had a different meaning, referring to morphological taxonomy, and the products of research through the end of the 19th century. William Bertram Turrill introduced the term "alpha taxonomy" in a series of papers published in 1935 and 1937 in which he discussed the philosophy and possible future directions of the discipline of taxonomy. ... there is an increasing desire amongst taxonomists to consider their problems from wider viewpoints, to investigate

2784-482: The terms "systematics" and "biosystematics" for the study of biodiversity as a whole, whereas North Americans tend to use "taxonomy" more frequently. However, taxonomy, and in particular alpha taxonomy , is more specifically the identification, description, and naming (i.e., nomenclature) of organisms, while "classification" focuses on placing organisms within hierarchical groups that show their relationships to other organisms. A taxonomic revision or taxonomic review

2842-510: The three-domain method is the separation of Archaea and Bacteria , previously grouped into the single kingdom Bacteria (a kingdom also sometimes called Monera ), with the Eukaryota for all organisms whose cells contain a nucleus . A small number of scientists include a sixth kingdom, Archaea, but do not accept the domain method. Thomas Cavalier-Smith , who published extensively on the classification of protists , in 2002 proposed that

2900-427: The top rank, dividing the physical world into the vegetable, animal and mineral kingdoms. As advances in microscopy made the classification of microorganisms possible, the number of kingdoms increased, five- and six-kingdom systems being the most common. Domains are a relatively new grouping. First proposed in 1977, Carl Woese 's three-domain system was not generally accepted until later. One main characteristic of

2958-436: The traditional three domains. Partial classifications exist for many individual groups of organisms and are revised and replaced as new information becomes available; however, comprehensive, published treatments of most or all life are rarer; recent examples are that of Adl et al., 2012 and 2019, which covers eukaryotes only with an emphasis on protists, and Ruggiero et al., 2015, covering both eukaryotes and prokaryotes to

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3016-518: The tree of life are called polyphyletic . Monophyletic groups are recognized and diagnosed on the basis of synapomorphies , shared derived character states. Cladistic classifications are compatible with traditional Linnean taxonomy and the Codes of Zoological and Botanical nomenclature , to a certain extent. An alternative system of nomenclature, the International Code of Phylogenetic Nomenclature or PhyloCode has been proposed, which regulates

3074-642: The uses of different species were understood and that a basic taxonomy was in place. Organisms were first classified by Aristotle ( Greece , 384–322 BC) during his stay on the Island of Lesbos . He classified beings by their parts, or in modern terms attributes , such as having live birth, having four legs, laying eggs, having blood, or being warm-bodied. He divided all living things into two groups: plants and animals . Some of his groups of animals, such as Anhaima (animals without blood, translated as invertebrates ) and Enhaima (animals with blood, roughly

3132-486: Was Methodus Plantarum Nova (1682), in which he published details of over 18,000 plant species. At the time, his classifications were perhaps the most complex yet produced by any taxonomist, as he based his taxa on many combined characters. The next major taxonomic works were produced by Joseph Pitton de Tournefort (France, 1656–1708). His work from 1700, Institutiones Rei Herbariae , included more than 9000 species in 698 genera, which directly influenced Linnaeus, as it

3190-555: Was entitled " Systema Naturae " ("the System of Nature"), implying that he, at least, believed that it was more than an "artificial system"). Later came systems based on a more complete consideration of the characteristics of taxa, referred to as "natural systems", such as those of de Jussieu (1789), de Candolle (1813) and Bentham and Hooker (1862–1863). These classifications described empirical patterns and were pre- evolutionary in thinking. The publication of Charles Darwin 's On

3248-615: Was popularized in the Anglophone world by the speculative but widely read Vestiges of the Natural History of Creation , published anonymously by Robert Chambers in 1844. With Darwin's theory, a general acceptance quickly appeared that a classification should reflect the Darwinian principle of common descent . Tree of life representations became popular in scientific works, with known fossil groups incorporated. One of

3306-543: Was the Italian physician Andrea Cesalpino (1519–1603), who has been called "the first taxonomist". His magnum opus De Plantis came out in 1583, and described more than 1500 plant species. Two large plant families that he first recognized are in use: the Asteraceae and Brassicaceae . In the 17th century John Ray ( England , 1627–1705) wrote many important taxonomic works. Arguably his greatest accomplishment

3364-429: Was the text he used as a young student. The Swedish botanist Carl Linnaeus (1707–1778) ushered in a new era of taxonomy. With his major works Systema Naturae 1st Edition in 1735, Species Plantarum in 1753, and Systema Naturae 10th Edition , he revolutionized modern taxonomy. His works implemented a standardized binomial naming system for animal and plant species, which proved to be an elegant solution to

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