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The term monophyly, or monophyletic, derives from the two Ancient Greek words μόνος (mónos), meaning "alone, only, unique", and φῦλον (phûlon), meaning "genus, species", [4] [5] and refers to the fact that a monophyletic group includes organisms (e.g., genera, species) consisting of all the descendants of a unique common ancestor.
In biological phylogenetics, a clade (from Ancient Greek κλάδος (kládos) 'branch'), also known as a monophyletic group or natural group, [1] is a grouping of organisms that are monophyletic – that is, composed of a common ancestor and all its lineal descendants – on a phylogenetic tree. [2]
Linnaean classification relies on an organism's phenotype or physical characteristics to group and organize species. [12] With the emergence of biochemistry, organism classifications are now usually based on phylogenetic data, and many systematists contend that only monophyletic taxa should be recognized as
This grouping method is often referred to as the "monophyletic species concept" or the "phylospecies" concept and was popularized by D.E. Rosen in 1979. Within this definition, a species is seen as "the least inclusive monophyletic group definable by at least one autapomorphy". [7]
A stem group is a paraphyletic assemblage composed of the members of a pan-group or total group, above, minus the crown group itself (and therefore minus all living members of the pan-group). This leaves primitive relatives of the crown groups , back along the phylogenetic line to (but not including) the last common ancestor of the crown group ...
The hypothesis that these form a monophyletic group has been long debated based on morphological evidence. Two morphological studies, published in 2001 [ 1 ] and 2003, [ 2 ] strongly support the monophyly of Glires.
[61] [62] Groups that have descendant groups removed from them are termed paraphyletic, [61] while groups representing more than one branch from the tree of life are called polyphyletic. [ 61 ] [ 62 ] Monophyletic groups are recognized and diagnosed on the basis of synapomorphies , shared derived character states.
Rhizaria is a monophyletic group composed of two sister phyla: Cercozoa and Retaria. Subsequently, Cercozoa and Retaria are also monophyletic. [18] [19] The following cladogram depicts the evolutionary relationships between all rhizarian classes, and is made after the works of Cavalier-Smith et al. (2018), [1] and Irwin et al. (2019). [20]