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(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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Biology a method of grouping animals that makes use of lines of descent rather than structural similarities
References in periodicals archive ?
The two subdivisions represented by Linnavuori's niokanus, pseudobrunnescens and hipponax and the other by nigriventris, brunnascens, basalis and minor appear to play sister group and out group relationship with each other and appear neatly held together by the synapomorphies such as lateral margins of pronotum at least slightly curved or convex.
He further diagnosed the sister group relationships of Hydrometrinae and Limnobatodinae based on the absence of ocelli, the body with spinous macrohairs, pronotal lobe with almost parallel sides; the forewing venation reduced to two longitudinal veins and 1-2 crossveins; the abdominal tergum without paired, longitudinal ridges; the absence of an abdominal scent gland, and the egg shell with an open air-filled inner layer and outer plastron.
21), two hypotheses are presented, as to whether Phallofractus or Gonzobandia constitute the sister group to the other genera in the clade; on geographical grounds, it would seem sensible to consider the former as the sister group to the rest of the assemblage, and it so appears in two of the three most parsimonious trees.
The extremists used the recent attacks as a vile opportunity to score points over the sister group.
Scotiabank T&T Ltd, together with its sister group Scotia DBG Investments Ltd, launched a new investment product called the Scotia DBG Caribbean Income Fund, reports The Trinidad Guardian (Jan.
Hundreds of militants from the separatist Kurdistan Workers' Party (PKK), which has waged a bloody campaign for self-rule in southeast Turkey, and its sister group in Iran, PJAK, are based in the mountains of northern Iraq.
Procolophonoids have also become the focus of broader interest because they been proposed to be the sister group of turtles (Laurin and Reisz, 1995; Reisz and Laurin, 1991) and it has also been estimated that up to 80% of procolophonoid lineages survived the Permian-Triassic (P/Tr) extinction event (Ketchum and Barrett, 2004; Modesto et al.
The group, backed by Cairde Na hEireann, a sister group of Sinn Fein, were protesting against Celtic joining the rest of the SPL clubs and wearing a woven poppy on their strip this weekend.
The academy is a new sister group of the CBSO Youth Orchestra.
In other instances Hemiptera is the sister group of Thysanoptera + Psocodea (e.
In a sister group in his wing, only one made its way back to England.
Portraying the sister group The Taffetas are Bianca Caruso of Hollywood, Noel Britton of Woodland Hills, Lauren Nasman of Woodland Hills and Kathi Funston of Studio City.