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Related to Sister taxa: Artificial classification, Sister taxon


(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 ?
Paleontology also provides information on the approximate age of origination of clades which may be useful in testing the reliability of conflicting hypotheses of sister taxa relationships derived from the separate analyses of data sets.
However, the hypothesis that Ilyphagus octobranchus and Diplocirrus glaucas are not sister taxa to each other is not significantly worse than the best tree.
For this reason, only the bootstrap support values for each of the six pairs of sister taxa were considered.
However, Keen and McLean (1971) note the presence of at least 3 other putative Ostrea species in the Gulf of California, for which molecular data are unavailable, but who might serve as sister taxa to either focal species in this study.
In the present study we examine the extent to which differences in calling song observed between two sister taxa of ground crickets, Allonemobius fasciatus and A.
Phylogenetica is the name used to recognize the least inclusive [largest] clade including all of Cladograma and its potential sister taxa.
2000) that the Harrimaniid worms are sister taxa to the colonial class Pterobranchia; the evidence also suggests that these taxa evolved from a worm-like ancestor with indirect development.
It will be important to more accurately assess the benzaldehyde secretion of iridescent species and their cryptic sister taxa within a phylogenetic context, because the observation of moderate benzaldehyde secretion in the iridescent C.
florinii as sister taxa on another branch, and a remaining branch including Ortesia, Moyliostrobus, Ernestiodendron, and Walchiostrobus gothanii.
For example comparing evolutionary rates in two terminal sister taxa, A and B, is easy (e.
We would be a lot more upset if you had fish and humans coming out as sister taxa than if you had changes within mammals.