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A clade is a taxonomic group of organisms comprising a single common ancestor and all the descendants of that ancestor. Any such group is considered to be a monophyletic group of organisms, and can be represented by both a phylogenetic analysis, as in a tree diagram, and by a cladogram (see cladistics), or simply as a taxonomic reference.

If a clade proves robust in alternate cladistic analyses using different sets of data, it may be adopted into taxonomy and become a taxon. Not all taxa, however, are considered to be clades. Reptiles, for example, are a paraphyletic group because they do not include aves (birds), which are thought to also have evolved from the common ancestor of the reptiles.

In cladistics, a clade that is located within another more inclusive clade is said to be "nested" within that clade. Nested clade analysis is beneficial in many ways. For instance, it enables the detection of range expansions in isolated geographic areas.

Phylogenetic nomenclature

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Phylogenetic nomenclature is formulated in terms of evolution and common descent rather than the type specimens, categorical ranks, and morphological characters. The latter is used most commonly in cladistic analysis. Taxon names are strictly connected to phylogenetic tree topology and evolutionary history. In taxonomy, each name is attached to a clade taxonomic group containing a common ancestor and all its descendants. Phylogenetic nomenclature discards categorical ranks. The problem with ranks are evident when one considers biodiversity lineages and clades. Questions like "how many lineages are there?" or "how many clades are there?" become pointless, since there are no answers. These are relative concepts, illustrating the fractal nature of the tree of life and the need to let a phylogenetic hypothesis be the focus, rather than the categories, when biodiversity is quantified. Phylogenetic nomenclature helps to put focus on phylogenetic trees by offering an explicit link between names and parts of species history, that is, clades.

Traditional binomial nomenclature

In phylogenetics, binomial names are associated with the relationships of each described species. But this creates a problem because it makes assumptions about relationships about the description of the species identification. It suggests that species or genera are a unique category, and this contradicts the idea of recognizing only clades and lineages.

Phylogenetic alternatives

To avoid the pitfalls of traditional Linnaean taxonomy in phylogenetic nomenclature, three new methods of phylogenetic naming have been proposed: node-, stem-, and apomorphy-based. In node-based naming, taxon name A might refer to the least inclusive clade containing X and Y. In stem-based naming, A would refer to the most inclusive clade containing X and Y but not Z. In apomorphy (derived feature)-based naming, A would refer to the clade identified by a feature synapomorphic (sharing a derivation) with a feature in specimen (taxon) X. Differences between a traditional approach and these phylogenetic alternatives become obvious when the phylogenetic hypothesis changes. Comparison between the traditional Linnaean approach to nomenclature and a phylogenetic alternative (node-based naming). Suppose that all we want to do is to give a name ("A") to a clade containing X and Y. In the Linnaean system this means that we have to introduce names for sister taxa, assigning all taxa to the categories species, genus, and family, and designate type species. No explicit reference to phylogeny is made. The phylogenetic alternative provides an explicit reference to evolutionary history, and nothing but the clade containing X and Y needs to be named. When the hypothesis of relationship changes, the phylogenetic alternative is cleaner and more explicit about what it refers to.

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Topics in phylogenetics
Relevant fieldsphylogenetics
Basic conceptssynapomorphy
Phylogeny inference methodsmaximum parsimony
Current topicsPhyloCode
List of evolutionary biology topics
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Basic topics in

External links

For the science of classifying living things, see .


Taxonomy is the practice and science of classification. The word comes from the Greek τάξις, taxis, 'order' +
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Plantae
  • Chromalveolata
  • Heterokontophyta
  • Haptophyta
  • Cryptophyta
  • Alveolata

  • ..... Click the link for more information.
    • A group of organisms is said to have common descent if they have a common ancestor. In modern biology, it is generally accepted that all living organisms on Earth are descended from a common ancestor or ancestral gene pool.
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    In phylogenetics, a group is monophyletic (Greek: "of one race") if it consists of an inferred common ancestor and all its descendants. A taxonomic group that contains organisms but not their common ancestor is called polyphyletic, and a group that contains some but not all
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    phylogenetics (Greek: phyle = tribe, race and genetikos = relative to birth, from genesis = birth) is the study of evolutionary relatedness among various groups of organisms (e.g., species, populations).
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    Cladistics is a philosophy of classification that arranges organisms only by their order of branching in an evolutionary tree and not by their morphological similarity, in the words of Luria et al. (1981).
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    Cladistics is a philosophy of classification that arranges organisms only by their order of branching in an evolutionary tree and not by their morphological similarity, in the words of Luria et al. (1981).
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    For the journal, see .
    A taxon (plural taxa), or taxonomic unit, is a name designating an organism or group of organisms. A taxon is assigned a rank and can be placed at a particular level in a systematic hierarchy reflecting evolutionary
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    For the journal, see .
    A taxon (plural taxa), or taxonomic unit, is a name designating an organism or group of organisms. A taxon is assigned a rank and can be placed at a particular level in a systematic hierarchy reflecting evolutionary
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    Sauropsida*
    Goodrich, 1916

    Subclasses
    • Anapsida
    • Diapsida
    Synonyms
    • Reptilia Laurenti, 1768
    Reptiles are tetrapods and amniotes, animals whose embryos are surrounded by an amniotic membrane, and members of the class
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    In phylogenetics, a group of organisms is said to be paraphyletic (Greek para = near and phyle = race) if the group contains its most recent common ancestor, but does not contain all the descendants of that ancestor.
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    Aves
    Linnaeus, 1758

    Orders

    About two dozen - see section below

    Birds (class Aves) are bipedal, warm-blooded, egg-laying vertebrate animals.
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    Aves
    Linnaeus, 1758

    Orders

    About two dozen - see section below

    Birds (class Aves) are bipedal, warm-blooded, egg-laying vertebrate animals.
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    Cladistics is a philosophy of classification that arranges organisms only by their order of branching in an evolutionary tree and not by their morphological similarity, in the words of Luria et al. (1981).
    ..... Click the link for more information.
    Phylogenetic nomenclature is an alternative to rank-based nomenclature. Its two defining features are the use of phylogenetic definitions of biological taxon names, and the lack of obligatory ranks.
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    In biology, a type is that which fixes a name to a taxon. Depending on the nomenclature code which is applied to the organism in question, a type may be a specimen, culture, illustration, description or taxon.
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    The term morphology in biology refers to the outward appearance (shape, structure, color, pattern) of an organism or taxon and its component parts. This is in contrast to physiology, which deals primarily with function.
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    character is an attribute of an organism that allows it to be compared with another. In genetics this refers to heritable features which can exist in more than one state.[1] A trait
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    A phylogenetic tree, also called an evolutionary tree, is a tree showing the evolutionary relationships among various biological species or other entities that are believed to have a common ancestor.
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    binomial nomenclature is the formal system of naming species. The system is also called binominal nomenclature (particularly in zoological circles), binary nomenclature (particularly in botanical circles), or the binomial classification system.
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    Linnaean taxonomy is a method of classifying living things originally devised by, and named for, Carl Linnaeus although it has changed considerably since his time. The greatest innovation of Linnaeus, and still the most important aspect of this system, is the general use of
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    phylogenetics (Greek: phyle = tribe, race and genetikos = relative to birth, from genesis = birth) is the study of evolutionary relatedness among various groups of organisms (e.g., species, populations).
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    In evolutionary biology, a synapomorphy is a derived character state shared by two or more terminal groups (taxa included in a cladistic analysis as further indivisible units) and inherited from their most recent common ancestor.
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    Maximum parsimony, often simply referred to as "parsimony," is a non-parametric statistical method commonly used in computational phylogenetics for estimating phylogenies. Under maximum parsimony, the preferred phylogenetic tree is the tree that requires the least number of
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    The International Code of Phylogenetic Nomenclature, known for short as the PhyloCode, is a developing draft for a formal set of rules governing phylogenetic nomenclature.
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    This is a list of topics in evolutionary biology and evolution.

    See also: List of biology topics, List of biochemistry topics, WikiProject Evolutionary biology

    A


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    evidence of the theory of evolution provides a wealth of information on the natural processes by which the variety of life on Earth developed.

    Fossils are important for estimating when various lineages developed.
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    An adaptation is a positive characteristic of an organism that has been favored by natural selection.[1] The concept is central to biology, particularly in evolutionary biology.
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    Macroevolution refers to evolution that occurs at or above the level of species, in contrast with microevolution,[1] which refers to smaller evolutionary changes (typically described as changes in allele frequencies) within a species or population.
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