23-402: Choanozoa is a clade of opisthokont eukaryotes consisting of the choanoflagellates (Choanoflagellatea) and the animals (Animalia, Metazoa). The sister-group relationship between the choanoflagellates and animals has important implications for the origin of the animals. The clade was identified in 2015 by Graham Budd and Sören Jensen, who used the name Apoikozoa . The 2018 revision of
46-525: 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
69-479: 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
92-623: 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
115-422: 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
138-429: 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 ,
161-577: A unique characteristic) of the clade. A synonym of this clade, Apoikozoa , was used in previous years; however, it was rejected as being neither formally defined nor appropriate, since it refers to the ability to form colonies , a characteristic not unique to this clade. Although the last common ancestor of the Choanozoa cannot be reconstructed with certainty, Budd and Jensen suggest that these organisms formed benthic colonies that competed for space amongst other mat-forming organisms known to have existed during
184-499: 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,
207-471: 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
230-515: 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
253-489: 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
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#1732852067864276-458: The Ediacaran Period some 635–540 million years ago. As such they would form an important link between the unicellular ancestors of the animals and the enigmatic "Ediacaran" organisms known from this interval, thus allowing some sort of reconstruction of the earliest animals and their ecology. In the following cladogram, an indication is given of approximately how many million years ago (Mya)
299-434: The multicellularity found in animals. A synonym for the Choanozoa, Apoikozoa, derives from the ancient Greek for "colony" and "animal", referring to the ability of both animals and (some) choanoflagellates to form multicellular units. While animals are permanently multicellular, the colony-building choanoflagellates are only sometimes so, which raises the question of whether or not the colony-building ability in both groups
322-611: The clades diverged into newer clades. (Note that the later Budd and Jensen paper gives significantly younger dates. See also Kimberella .) The Holomycota tree follows Tedersoo et al. Fonticulida Nucleariida [REDACTED] BCG2 True Fungi [REDACTED] Aphelida BCG1 Rozella [REDACTED] Namako-37 Microsporidia [REDACTED] Ichthyosporea [REDACTED] Syssomonas Corallochytrium [REDACTED] Filasterea [REDACTED] Choanoflagellatea [REDACTED] Animalia [REDACTED] Clade In biological phylogenetics ,
345-488: The classification first proposed by the International Society of Protistologists in 2012 recommends the use of the name Choanozoa. A close relationship between choanoflagellates and animals has long been recognised , dating back at least to the 1840s. A particularly striking and famous similarity between the single-celled choanoflagellates and multicellular animals is provided by the collar cells of sponges and
368-451: 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
391-448: The group paraphyletic . Its classification was the following: The International Society of Protistologists rejected the use of this name for the paraphyletic group. Instead, since 2017, the name Choanozoa is considered appropriate for the clade that unites choanoflagellates and animals, since the Greek choanē (χοάνη), meaning 'funnel', refers to the collar, which is a synapomorphy (i.e.
414-546: 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"
437-590: 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"
460-518: 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
483-436: The overall morphology of the choanoflagellate cell. The relationship has since been confirmed by multiple molecular analyses. This proposed homology was however thrown into some doubt in 2013 by the still controversial suggestion that ctenophores , and not sponges, are the sister group to all other animals. More recent genomic work has suggested that choanoflagellates possess some of the important genetic machinery necessary for
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#1732852067864506-501: 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. Aphelida Aphelida is a phylum of Fungi that appears to be the sister to true fungi . This fungus -related article is
529-425: Was present at the base of the entire clade , or whether it was independently derived within the animals and choanoflagellates. The name "Choanozoa" was first used by protozoologist Thomas Cavalier-Smith in 1991 to refer to a group of basal protists that later proved not to form a clade . This group had the rank of phylum and contained all opisthokont protists while excluding both fungi and animals , making
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