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Related to Apomorphic: apomorphine, Synapomorphic


(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
Collins Discovery Encyclopedia, 1st edition © HarperCollins Publishers 2005
References in periodicals archive ?
Moreover, even if the character states themselves have remained unchanged, an apomorphic character might (because of a varying selective environment) have a higher current fitness than its plesiomorphic counterpart even if it did not initially spread through natural selection for current function.
This is because there are often apomorphic character changes that occur once within a given taxon that also occur once in another taxon.
Owing to the vital, water-conserving roles of the AQP2, -5, and -6 gene clusters in extant amphibians, sauropsids, and mammals, it is suggested that lineage-specific evolution of these apomorphic gene clusters was permissive for vertebrate terrestrial adaptation.
In particular, we presume that spiny proventriculi--derived from an omnivorous ancestor and modified for herbivory--are ubiquitous or at least plesiomorphic in Phasmatodea, and "gastric caeca" plus an oesophageal valve are apomorphic for Euphasmatodea.
(vi) Information on structures obtained across the analyzed dataset indicated that the group of corixids displayed 13 autapomorphies (more than in other nepomorphan taxa) indicating their strong apomorphic forms and their advanced position in the system of classification.
In contrast, recent investigations have identified several larval features (listed in a later section) that may lend apomorphic support for the monophyly of Nothochrysinae [7-10].
Scholtz and Kamenz (2006) argue that several other arachnid characters such as trichobothria, slit-sense organs, endodermal malphigian tubules, and extra-intestinal digestion can be interpreted as apomorphic arachnid adaptations to land (Scholtz & Kamenz 2006).
Given the above discussion, on the costs and benefits of amphidromy versus ALD, one might ask the question: which is ancestral (plesiomorphic) and which is derived (apomorphic)?
Based on the shared apomorphic condition of the anterior part of the thorax, Buck (2010) transferred Odontoloxozus peruanus Hennig, 1937 to Cerantichir, but this character is also shared with Longina Wiedemann.
Sphenisciformes is applied in a more exclusive sense to the clade including all Pansphenisciformes that share the apomorphic loss of aerial flight.