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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.
The idea of a tree of life arose from ancient notions of a ladder-like progression from lower into higher forms of life (such as in the Great Chain of Being).Early representations of "branching" phylogenetic trees include a "paleontological chart" showing the geological relationships among plants and animals in the book Elementary Geology, by Edward Hitchcock (first edition: 1840).
Analyses of recent taxa suggested the harvestmen to be the sister group of the three others, collectively called Novogenuata. [2] An analysis also considering fossil taxa [ 1 ] concluded that the harvestmen are sister to Haplocnemata (Pseudoscorpions and Solifugae), with Scorpions being the sister group of those three combined. [ 3 ]
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 ...
[1] Level 2 — The inference of a character that leaves a signature on the skeleton of only one of the extant sister groups. [1] For example, saying that Tyrannosaurus rex had air sacs running through its skeleton is a level 2 inference as birds are the only extant sister group to Tyrannosaurus rex to show such air sacs.
Phylogenetic tree of early lophophorates. Fossil discoveries lead to the hypothesis that Annelida and the lophophorates are more closely related to each other than any other phyla. Because of the body plan of lophotrochozoan fossils, a phylogenetic analysis found the lophophorates as the sister group of annelids.
The diagram shows three common ways of doing this. For previously defined clades A, B, and C, the clade X can be defined as: The three most common ways to define the name of a clade: node-based, branch-based and apomorphy-based definition. The tree represents a phylogenetic hypothesis of the relations of A, B and C.
Lineages are typically visualized as subsets of a phylogenetic tree. A lineage is a single line of descent or linear chain within the tree, while a clade is a (usually branched) monophyletic group, containing a single ancestor and all its descendants. [3] Phylogenetic trees are typically created from DNA, RNA or protein sequence data. Apart ...