Clade

[citation needed] Clades are the fundamental unit of cladistics, a modern approach to taxonomy adopted by most biological fields.

Over the last few decades, the cladistic approach has revolutionized biological classification and revealed surprising evolutionary relationships among organisms.

Rodents, for example, are a branch of mammals that split off after the end of the period when the clade Dinosauria stopped being the dominant terrestrial vertebrates 66 million years ago.

The idea of a clade did not exist in pre-Darwinian Linnaean taxonomy, which was based by necessity only on internal or external morphological similarities between organisms.

The phenomenon of convergent evolution is responsible for many cases of misleading similarities in the morphology of groups that evolved from different lineages.

German biologist Emil Hans Willi Hennig (1913–1976) is considered to be the founder of cladistics.

classification of Anas platyrhynchos (the mallard duck) with 40 clades from Eukaryota down by following this Wikispecies link and clicking on "Expand".

A unique exception is the reptile clade Dracohors, which was made by haplology from Latin "draco" and "cohors", i.e. "the dragon cohort"; its form with a suffix added should be e.g. "dracohortian".

The results of phylogenetic/cladistic analyses are tree-shaped diagrams called cladograms; they, and all their branches, are phylogenetic hypotheses.

Cladogram (a branching tree diagram) illustrating the relationships of organisms within groups of taxa known as clades. The vertical line stem at the base represents the last common ancestor . The blue and orange subgroups are clades, each defined by a common ancestor stem at the base of its respective subgroup branch . The green subgroup alone, however, is not a clade; it is a paraphyletic group relative to the blue subgroup because it excludes the blue branch, which shares the same common ancestor. Together, the green and blue subgroups form a clade.
Early phylogenetic tree by Haeckel , 1866. Groups once thought to be more advanced, such as birds ("Aves"), are placed at the top.
Gavialidae, Crocodylidae and Alligatoridae are clade names that are here applied to a phylogenetic tree of crocodylians.
Cladogram of modern primate groups; all tarsiers are haplorhines, but not all haplorhines are tarsiers; all apes are catarrhines, but not all catarrhines are apes; etc.
Phylogenetic tree of the SIV and HIV viruses showing clades (subtypes) of the virus.