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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.
Protostomia (/ ˌ p r oʊ t ə ˈ s t oʊ m i. ə /) is the clade of animals once thought to be characterized by the formation of the organism's mouth before its anus during embryonic development. This nature has since been discovered to be extremely variable among Protostomia's members, although the reverse is typically true of its sister ...
Archelosauria is a clade grouping turtles and archosaurs (birds and crocodilians) and their fossil relatives, to the exclusion of lepidosaurs (the clade containing lizards, snakes and the tuatara). The majority of phylogenetic analyses based on molecular data (e.g. DNA and proteins) have supported a sister-group relationship between turtles and ...
Gnathifera is a member of Spiralia. It is the sister taxon of a clade comprising all other spiralians. [1] [19] An alternative phylogeny place Gnathifera into a main spiralian clade Platyzoa s.l. as sister clade to Mesozoa and Platyhelminthes. [21]
The crown age of a clade refers to the age of the most recent common ancestor of all of the species in the clade. The stem age of a clade refers to the time that the ancestral lineage of the clade diverged from its sister clade. A clade's stem age is either the same as or older than its crown age. [15] Ages of clades cannot be directly observed.
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 ...
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The Zygnematophyceae are the sister clade of the Embryophyta (land plants). [ 4 ] [ 5 ] [ 6 ] Common members of the Zygnematophyceae include the filamentous algae Spirogyra and Mougeotia , as well as desmids , which are microscopic algae characterized by symmetrical and elaborately ornate cells.