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The term sister group is used in phylogenetic analysis, however, only groups identified in the analysis are labeled as "sister groups".. An example is birds, whose commonly cited living sister group is the crocodiles, but that is true only when discussing extant organisms; [3] [4] when other, extinct groups are considered, the relationship between birds and crocodiles appears distant.
A clade located within a clade is said to be nested within that clade. In the diagram, the hominoid clade, i.e. the apes and humans, is nested within the primate clade. Two clades are sisters if they have an immediate common ancestor. In the diagram, lemurs and lorises are sister clades, while humans and tarsiers are not.
Branches down to the divergence to the next significant (e.g. extant) sister are considered stem-groupings of the clade, but in principle each level stands on its own, to be assigned a unique name. For a fully bifurcated tree, adding a group to a tree also adds an additional (named) clade, and a new level on that branch.
In this diagram, the clade labelled "Neornithes" is the crown group of birds: it includes the most recent common ancestor of all living birds and its descendants, living or not. Although considered to be birds (i.e. members of the clade Aves), Archaeopteryx and other extinct groups are not included in the crown group, as they fall outside the ...
One study based on DNA analysis suggests that Scandentia and Primates are sister clades, but does not discuss the position of Dermoptera. [9] Although it is known that Scandentia is one of the most basal Euarchontoglires clades, the exact phylogenetic position is not yet considered resolved, and it may be a sister of Glires, Primatomorpha or Dermoptera or to all other Euarchontoglires.
Whippomorpha is a suborder located within the Order Artiodactyla, and the clade Cetancodontamorpha. It contains the clades Hippopotamoidea (ancestors of hippopotamuses) and Cetaceamorpha (ancestors of whales and dolphins). Whippomorpha is considered a sister clade to Ruminantia (which contains cattle, sheep and deer), as well as the extinct ...
Overall, studies using mitochondrial DNA have tended to group them as a sister clade to Ferungulata (carnivorans+ungulates+pholidotans), while studies using nuclear DNA have identified them as 1) a sister clade to Afrotheria, 2) a sister clade to all placentals except Afrotheria, or 3) a trichotomy (three-way split): Afrotheria, Xenarthra, and ...
The clade Scrotifera is a sister group to the order Eulipotyphla (true insectivores) based on evidence from molecular phylogenetics, [1] and together they make superorder Laurasiatheria. The last common ancestor of Scrotifera is supposed to have diversified ca. 73.1 [ 3 ] to 85.5 [ 4 ] million years ago.