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A taxon (plural taxa), or taxonomic unit, is a grouping of , whether named or unnamed. Once named, a taxon will usually have a rank and can be placed at a particular hierarchical level.
In the case of , the hierarchical ranks areas follows:
- (animals) or (plants, fFungi, and microorganisms)
Prefixes are used to indicate further ranks; for example super- indicates a rank immediately above, and sub- a rank immediately below. infra- indicates a rank below sub-. For instance:
Ranking is often subjective or relative. For example, have been variously considered a family, order, or a class. Or a higher rank may be goiven to a familiar group of organisms - e.g. orders of , then to those that are less familiar but may be equally distinct - e.g. families or superfamilies of . There is also the tendency to , whereby a rank of lower staus is accorded progressively higher value - e.g. an order may become a class or even a subphylum.
The use of taxonomic ranks in this manner has been challenged by and has recently led to the development of a , on which ranking is determined purely , as nested , without use of Linnaean, , or characteristics.
A terminal taxon is "terminal taxon - one of the units of a phylogenetic tree whose collective phylogeny is reconstructed, i.e., the undivided tips of a tree (usually contemporary taxa). Terminals may be higher taxa, species, populations, individuals, fossils or even genes."
The above seems to mean that a terminal taxon consists of animals that are alive today or that died out without evolving into different species.
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MaAK061016 incorporating material from )