cladistics

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cladistics

(klədĭs`tĭks) or

phylogenetic systematics

(fī'lōjənĕt`ĭk), an approach to the classificationclassification,
in biology, the systematic categorization of organisms into a coherent scheme. The original purpose of biological classification, or systematics, was to organize the vast number of known plants and animals into categories that could be named, remembered, and
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 of living things in which organisms are defined and grouped by the possession of one or more shared characteristics (called characters) that are derived from a common ancestor and that were not present in any ancestral group (as envisioned by Charles DarwinDarwin, Charles Robert,
1809–82, English naturalist, b. Shrewsbury; grandson of Erasmus Darwin and of Josiah Wedgwood. He firmly established the theory of organic evolution known as Darwinism.
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's idea of "descent with modification"). Developed by Willi Hennig, a German entomologist, in the 1950s, it is a method of reconstructing evolutionary relationships that emphasizes the importance of descent and common ancestry rather than chronology.

Cladistics places species in a group, or clade, based on a shared character. Within a clade, species that share other characters unique to them are grouped together, and so on, until a cladogram (a branching diagram that resembles a family tree) is assembled. For example, all vertebrates make up a clade; all tetrapods (vertebrates that have four limbs with wrists, ankles, toes, and fingers) form their own clade within the vertebrate clade. In this example the vertebrate clade would be considered "primitive" and the tetrapod clade "derived" or "advanced." In living creatures genetic characters or behaviors as well as more obvious anatomical features might be considered in assembling a cladogram. In paleontologypaleontology
[Gr.,= study of early beings], science of the life of past geologic periods based on fossil remains. Knowledge of the existence of fossils dates back at least to the ancient Greeks, who appear to have regarded them as the remains of various mythological creatures.
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 the characters are necessarily skeletal.

Cladistics is especially significant in paleontology, as it points out gaps in the fossil evidence. It is also felt to be more objective than fossil study, which of necessity extrapolates from a limited number of finds that may or may not be representative of the whole.

See also fossilfossil,
remains or imprints of plants or animals preserved from prehistoric times by the operation of natural conditions. Fossils are found in sedimentary rock, asphalt deposits, and coal and sometimes in amber and certain other materials.
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; datingdating,
the determination of the age of an object, of a natural phenomenon, or of a series of events. There are two basic types of dating methods, relative and absolute.
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.

cladistics

Biology a method of grouping animals that makes use of lines of descent rather than structural similarities
References in periodicals archive ?
Both Cupressus and Taxodium show a single shortest tree of 19 steps when analyzed with group 2 taxa [ILLUSTRATION FOR FIGURES 16 & 18 OMITTED], and both are linked as sister taxa with Cephalotaxus in their trees (((((Cupressus or Taxodium, Cephalotaxus)((Dolmitia, Pseudovoltzia) Araucaria) Majonica, Podocarpus) Pinus) outgroup).
In the strict consensus tree this genus branches from within the Pseudovoltzia subclade from a polytomy involving the latter genus, the sister taxa Cryptomeria and Cunninghamia, and a subclade consisting of Taxodium and Cupressus as sister taxa sharing a node with Sciadopitys, which in turn shares a node with Dolmitia ((Aethophyllum, Pseudovoltzia (Cryptomeria, Cunninghamia) (((Taxodium, Cupressus) Sciadopitys) Dommitia) outgroup).
Because both Araucaria and Cycadocarpidium appear as sister taxa with Cunninghamia when each is analyzed individually with group 1 taxa, the two were included together in an analysis.
In the strict consensus tree (((((Dolmitia, Pseudovoltzia) Araucaria) Pararaucaria, Cephalotaxus, Podocarpus) Pinus) outgroup) Dolmitia and Pseudovoltzia are sister taxa.
Schizolepis shares a node with the sister taxa Cupressus and Taxodium in six trees, and in four other trees the genus occurs at the base of a subclade consisting of all group 1 genera except Majonica.
Dolmitia and Pseudovoltzia are sister taxa, and the two paired with Araucaria.
In the remaining two trees Swedenborgia shares a node with Dolmitia and Pseudovoltzia, which occur as sister taxa.
In another Voltzia branches from an unresolved trichotomy with the latter genus and the sister taxa Dolmitia and Pseudovoltzia.
In all four equally parsimonious trees Dolmitia and Pseudovoltzia appear as sister taxa, and this pair shares a node with Majonica [ILLUSTRATION FOR FIGURE 3 OMITTED].
1995), and by the present analysis, for neither of these analyses resolves Bambusa and Guadua as sister taxa [ILLUSTRATION FOR FIGURE 3 OMITTED].
1995) indicated that the trichotomy within the BOP clade in the consensus tree reflects two alternative equally parsimonious structures; in one tree Pooideae and Bambuseae were resolved as sister taxa, with Ehrhartoideae as the sister group of that clade, and in the other Bambuseae and Ehrhartoideae were resolved as sister taxa, with Pooideae as the sister group of that clade.
Koch is included in Poeae; see below), and the four tribes are united within a single clade in which Agrostideae and Poeae are sister taxa and together constitute the sister of a clade that includes Bromeae and Hordeeae as sister taxa [ILLUSTRATION FOR FIGURE 3 OMITTED].