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27-461: ParaHoxozoa (or Parahoxozoa ) is a clade of animals that consists of Bilateria , Placozoa , and Cnidaria . The relationship of Parahoxozoa relative to the two other animal lineages Ctenophora and Porifera is debated. Some phylogenomic studies have presented evidence supporting Ctenophora as the sister to Parahoxozoa and Porifera as the sister group to the rest of animals (e.g. ). Other studies have presented evidence supporting Porifera as

54-534: A clade (from Ancient Greek κλάδος (kládos)  'branch'), also known as a monophyletic group or natural group , is a grouping of organisms that are monophyletic – that is, composed of a common ancestor and all its lineal descendants – on a phylogenetic tree . In the taxonomical literature, sometimes the Latin form cladus (plural cladi ) is used rather than the English form. Clades are

81-493: A polytomy .   Choanoflagellata [REDACTED]   Ctenophora [REDACTED]   Porifera [REDACTED]   Placozoa [REDACTED]   Cnidaria [REDACTED]   Bilateria [REDACTED] "ParaHox" genes are usually referred to in CamelCase and the original paper that named the clade used "ParaHoxozoa"; the single initial capital format "Parahoxozoa" has also come to be used in

108-479: A "ladder", with supposedly more "advanced" organisms at the top. Taxonomists have increasingly worked to make the taxonomic system reflect evolution. When it comes to naming , this principle is not always compatible with the traditional rank-based nomenclature (in which only taxa associated with a rank can be named) because not enough ranks exist to name a long series of nested clades. For these and other reasons, phylogenetic nomenclature has been developed; it

135-476: A ParaHox gene is ever definitively identified, Parahoxozoa, as originally defined, is monophyletic and therefore continues to be used as such. The original Bilaterian is hypothesized to be a bottom dwelling worm with a single body opening. A through-gut may already have developed with the Ctenophora. The through-gut may have developed from the corners of a single opening with lips fusing. E.g. Acoela resemble

162-623: A clade can be described based on two different reference points, crown age and stem age. The crown age of a clade refers to the age of the most recent common ancestor of all of the species in the clade. The stem age of a clade refers to the time that the ancestral lineage of the clade diverged from its sister clade. A clade's stem age is either the same as or older than its crown age. Ages of clades cannot be directly observed. They are inferred, either from stratigraphy of fossils , or from molecular clock estimates. Viruses , and particularly RNA viruses form clades. These are useful in tracking

189-454: A greater emphasis on experiments. There are more frequent discontinuities present in paleontology than in neontology, because paleontology involves extinct taxa. Neontology has organisms actually present and available to sample and perform research on. Neontology's research method uses cladistics to examine morphologies and genetics . Neontology data has more emphasis on genetic data and the population structure than paleontology does. When

216-491: A name to contrast ourselves with all you folks who study modern organisms in human or ecological time . You therefore become neontologists. We do recognize the unbalanced and parochial nature of this dichotomous division. Neontological evolutionary biology has a temporal perspective between 100 and 1000 years. Neontology's fundamental basis relies on models of natural selection as well as speciation . Neontology's methods, when compared to evolutionary paleontology , have

243-422: A revised taxonomy based on a concept strongly resembling clades, although the term clade itself would not be coined until 1957 by his grandson, Julian Huxley . German biologist Emil Hans Willi Hennig (1913–1976) is considered to be the founder of cladistics . He proposed a classification system that represented repeated branchings of the family tree, as opposed to the previous systems, which put organisms on

270-429: A suffix added should be e.g. "dracohortian". A clade is by definition monophyletic , meaning that it contains one ancestor which can be an organism, a population, or a species and all its descendants. The ancestor can be known or unknown; any and all members of a clade can be extant or extinct. The science that tries to reconstruct phylogenetic trees and thus discover clades is called phylogenetics or cladistics ,

297-499: Is also used with a similar meaning in other fields besides biology, such as historical linguistics ; see Cladistics § In disciplines other than biology . The term "clade" was coined in 1957 by the biologist Julian Huxley to refer to the result of cladogenesis , the evolutionary splitting of a parent species into two distinct species, a concept Huxley borrowed from Bernhard Rensch . Many commonly named groups – rodents and insects , for example – are clades because, in each case,

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324-476: Is in turn included in the mammal, vertebrate and animal clades. The idea of a clade did not exist in pre- Darwinian Linnaean taxonomy , which was based by necessity only on internal or external morphological similarities between organisms. Many of the better known animal groups in Linnaeus's original Systema Naturae (mostly vertebrate groups) do represent clades. The phenomenon of convergent evolution

351-515: Is responsible for many cases of misleading similarities in the morphology of groups that evolved from different lineages. With the increasing realization in the first half of the 19th century that species had changed and split through the ages, classification increasingly came to be seen as branches on the evolutionary tree of life . The publication of Darwin's theory of evolution in 1859 gave this view increasing weight. In 1876 Thomas Henry Huxley , an early advocate of evolutionary theory, proposed

378-489: Is still controversial. As an example, see the full current classification of Anas platyrhynchos (the mallard duck) with 40 clades from Eukaryota down by following this Wikispecies link and clicking on "Expand". The name of a clade is conventionally a plural, where the singular refers to each member individually. A unique exception is the reptile clade Dracohors , which was made by haplology from Latin "draco" and "cohors", i.e. "the dragon cohort "; its form with

405-534: The planula larvae of some Cnidaria, which exhibit some bilaterian symmetry. They are vermiform, just as the cnidarian Buddenbrockia is. Placozoans have been noted to resemble planula. Usually, " Planulozoa " is a Cnidaria–Bilateria clade that excludes Placozoa. Otherwise, when including all three lineages, it is synonymous with Parahoxozoa. Triploblasty may have developed before the Cnidaria–Bilateria radiation. Clade In biological phylogenetics ,

432-451: The fundamental unit of cladistics , a modern approach to taxonomy adopted by most biological fields. The common ancestor may be an individual, a population , or a species ( extinct or extant ). Clades are nested, one in another, as each branch in turn splits into smaller branches. These splits reflect evolutionary history as populations diverged and evolved independently. Clades are termed monophyletic (Greek: "one clan") groups. Over

459-546: The group consists of a common ancestor with all its descendant branches. Rodents, for example, are a branch of mammals that split off after the end of the period when the clade Dinosauria stopped being the dominant terrestrial vertebrates 66 million years ago. The original population and all its descendants are a clade. The rodent clade corresponds to the order Rodentia, and insects to the class Insecta. These clades include smaller clades, such as chipmunk or ant , each of which consists of even smaller clades. The clade "rodent"

486-590: The last few decades, the cladistic approach has revolutionized biological classification and revealed surprising evolutionary relationships among organisms. Increasingly, taxonomists try to avoid naming taxa that are not clades; that is, taxa that are not monophyletic . Some of the relationships between organisms that the molecular biology arm of cladistics has revealed include that fungi are closer relatives to animals than they are to plants, archaea are now considered different from bacteria , and multicellular organisms may have evolved from archaea. The term "clade"

513-518: The latter term coined by Ernst Mayr (1965), derived from "clade". The results of phylogenetic/cladistic analyses are tree-shaped diagrams called cladograms ; they, and all their branches, are phylogenetic hypotheses. Three methods of defining clades are featured in phylogenetic nomenclature : node-, stem-, and apomorphy-based (see Phylogenetic nomenclature§Phylogenetic definitions of clade names for detailed definitions). The relationship between clades can be described in several ways: The age of

540-626: The literature. Parahoxozoa was defined by the presence of several gene (sub)classes (HNF, CUT, PROS, ZF, CERS, K50, S50-PRD), as well as Hox / ParaHox -ANTP from which the name of this clade originated. It was later proposed and contested that a gene of the same class (ANTP) as the Hox/ParaHox, the NK gene and the Cdx Parahox gene, is also present in Porifera , the sponges. Regardless of whether

567-545: The other great apes . If the concept of an ape-man were based on neontology, then our phenotype would resemble Bigfoot . Since the concept was based on paleontology, the idea of an ape-man could possibly be represented by the fossil hominids. Neontology studies extant (living) taxa and recently extinct taxa, but declaring a taxon to be definitively extinct is difficult. Taxa that have previously been declared extinct may reappear over time. Species that were once considered extinct and then reappear unscathed are characterized by

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594-524: The scientific community accepted the synthetic theory of evolution , taxonomies became phylogenetic . As a result, information gaps arose within the fossil record of species, especially in Homo sapiens . The anthropologists who accepted the synthetic theory reject the idea of an "ape-man" because the concept had mistaken paleontology with neontology. An ape-man, in actuality, would be a primate with traits that would represent anything in between humans and

621-453: The sister to Parahoxozoa and Ctenophora as the sister group to the rest of animals (e.g. ), finding that nervous systems either evolved independently in ctenophores and parahoxozoans, or were secondarily lost in poriferans. If ctenophores are taken to have diverged first, Eumetazoa is sometimes used as a synonym for ParaHoxozoa. The cladogram, which is congruent with the vast majority of these phylogenomic studies, conveys this uncertainty with

648-706: The spread of viral infections . HIV , for example, has clades called subtypes, which vary in geographical prevalence. HIV subtype (clade) B, for example is predominant in Europe, the Americas and Japan, whereas subtype A is more common in east Africa. Extant taxon A taxon can be classified as extinct if it is broadly agreed or certified that no members of the group are still alive. Conversely, an extinct taxon can be reclassified as extant if there are new discoveries of living species (" Lazarus species "), or if previously known extant species are reclassified as members of

675-404: The taxon. Most biologists, zoologists , and botanists are in practice neontologists, and the term neontologist is used largely by paleontologists referring to non- paleontologists . Stephen Jay Gould said of neontology: All professions maintain their parochialisms , and I trust that nonpaleontological readers will forgive our major manifestation . We are paleontologists, so we need

702-571: The term "the Lazarus effect", or are also called a Lazarus species . For example, a study determined that 36% of supposed mammalian extinction had been proven, while the other 64% had insufficient evidence to be declared extinct or had been rediscovered. Currently, the International Union for Conservation of Nature considers a taxon to be recently extinct if the extinction occurred after 1500 C.E. A recently considered extinct mammal

729-566: Was the Bouvier's red colobus monkey, who was considered extinct up until 2015 when it was rediscovered after 40 years with no recorded sightings. Neontology's fundamental theories rely on biological models of natural selection and speciation that connect genes, the unit of heredity with the mechanism of evolution by natural selection. For example, researchers utilized neontological and paleontological datasets to study nonhuman primate dentition compared with human dentition. In order to understand

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