page_title: Sister group
section_title: Example
hierarchical_section_title: Sister group / Example
caption_attribution_description: Phylogeny of Dinosauria within Archosauriformes
context_page_description: A sister group or sister taxon is a phylogenetic term denoting the closest relative of another given unit in an evolutionary tree.
context_section_description: The term "sister group" is used in phylogenetic analysis, and only groups identified in the analysis are labeled as sister groups. An example is in birds, whose sister group is commonly cited as the crocodiles, but that is true only when dealing with extant taxa.  The bird family tree is rooted in the dinosaurs, and there were a number of extinct groups branching off of dinosaurs before coming to the last common ancestor of birds and crocodiles. Thus, the term sister group must be seen as a relative term, with the caveat that the sister group is the closest relative only among the groups/species/specimens that are included in the analysis.
caption: A Dinosauria phylogeny including two extant taxa: birds (Theropoda) and crocodiles (Suchia).
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