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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.
Pancrustacea is the clade that comprises all crustaceans and all hexapods (insects and relatives). [2] This grouping is contrary to the Atelocerata hypothesis, in which Hexapoda and Myriapoda are sister taxa, and Crustacea are only more distantly related.
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.
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.
Amborella trichopoda, the most basal extant angiosperm. The flowering plant family Amborellaceae, restricted to New Caledonia in the southwestern Pacific, [n 9] is a basal clade of extant angiosperms, [13] consisting of the most species, genus, family and order within the group that are sister to all other angiosperms (out of a total of about 250,000 angiosperm species).
Whether the Xenacoelomorpha clade is the sister group to the Ambulacraria remains a contentious issue, with some authors arguing that the former should be placed more basally among metazoans, [5] [6] [1] and other authors asserting that the best choices of phylogenetic methods support the position of Xenacoelomorpha as the sister group to ...
Deuterostomia's sister clade is Protostomia, animals that develop mouth first and whose digestive tract development is more varied. Protostomia includes the ecdysozoans and spiralians , as well as the extinct Kimberella .