Crown group

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Two distinct crown groups (in red) are illustrated, connected by an ancestor (black circle). The two groups form a larger crown group (lilac).

A crown group is a group of living species and their ancestors back to the most recent common ancestor. It is a term in cladistics and phylogenetics.

The name was used by Willi Hennig, the founder of phylogenetic systematics. Though invented in the 1970s, the term was not often used until it was reintroduced in the 2000s.[1]

One very simplified cladogram for birds is shown below:[2]

Archaeopteryx and some other extinct groups are not included in the crown group. They fall outside the Neoaves clade, as they diverged earlier. They are not part of the clade which resulted in modern birds.

An alternative definition stresses the need for members of the crown group to have the clade's characteristic synapomorphy.[3]

Stem group[change | change source]

The stem group of birds would be all the earlier Aves minus the crown group.

References[change | change source]

  1. Budd, G.E.; Jensen, S. (2000), "A critical reappraisal of the fossil record of the bilaterian phyla", Biological Reviews 75 (2): 253–295, doi:10.1017/S000632310000548X, PMID 10881389, http://journals.cambridge.org/production/action/cjoGetFulltext?fulltextid=624
  2. Chiappe, Luis M. (2007), Glorified dinosaurs: the origin and early evolution of birds, Sydney: University of New South Wales Press, ISBN 978-0-86840-413-4
  3. UCMP Glossary: Phylogenetics, University of California Museum of Paleontology, http://www.ucmp.berkeley.edu/glossary/glossary_1.html, retrieved 2010-12-04