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A polyphyletic taxon (in red, the group Haemothermia containing warm-blooded tetrapods) does not contain the most recent common ancestor of all its members. A polyphyletic group is an assemblage that includes organisms with mixed evolutionary origin but does not include their most recent common ancestor. [1]
In taxonomy, a group is polyphyletic if it consists of clades from multiple separate branches of the tree of life, not forming a complete clade. This classification is often due to phenotypes that have converged or reverted so as to appear to be the same but which have not been inherited from common ancestors.
A cladogram of the primates, showing a monophyletic taxon: the simians (in yellow); a paraphyletic taxon: the prosimians (in cyan, including the red patch); and a polyphyletic group: the night-active primates, i.e., the lorises and the tarsiers (in red). A cladogram of the vertebrates showing phylogenetic groups.
A clade, a monophyletic taxon, is a taxon that consists of the last common ancestor and all its descendants. [31] A clade is characterized by one or more apomorphies: derived character states present in the first member of the taxon, inherited by its descendants (unless secondarily lost), and not inherited by any other taxa. Paraphyly
More broadly, any taxon that is not paraphyletic or monophyletic can be called polyphyletic. Empirically, the distinction between polyphyletic groups and paraphyletic groups is rather arbitrary, since the character states of common ancestors are inferences, not observations. [citation needed]
There are no rules for how many species should make a genus, a family, or any other higher taxon (that is, a taxon in a category above the species level). [52] [53] It should be a natural group (that is, non-artificial, non-polyphyletic), as judged by a biologist, using all the information available to them. Equally ranked higher taxa in ...
Phylogenetic nomenclature is a method of nomenclature for taxa in biology that uses phylogenetic definitions for taxon names as explained below. This contrasts with the traditional method, by which taxon names are defined by a type, which can be a specimen or a taxon of lower rank, and a description in words. [1]
Bacterial taxonomy is the classification of strains within the domain Bacteria into hierarchies of similarity. This classification is similar to that of plants , mammals , and other taxonomies. However, biologists specializing in different areas have developed differing taxonomic conventions over time.