Crown group

C1 and C2 are crown groups of extant species within the clade T – the total group or pan-group – which also contains the stem group S1 of extinct species. The crown group C1 and the stem group S1 form the total group T1. T1 and C2 are sisters.

In phylogenetics, the crown group or crown assemblage is a collection of species composed of the living representatives of the collection, the most recent common ancestor of the collection, and all descendants of the most recent common ancestor. It is thus a way of defining a clade, a group consisting of a species and all its extant or extinct descendants. For example, Neornithes (birds) can be defined as a crown group, which includes the most recent common ancestor of all modern birds, and all of its extant or extinct descendants.

The concept was developed by Willi Hennig, the formulator of phylogenetic systematics, as a way of classifying living organisms relative to their extinct relatives in his "Die Stammesgeschichte der Insekten",[1] and the "crown" and "stem" group terminology was coined by R. P. S. Jefferies in 1979.[2] Though formulated in the 1970s, the term was not commonly used until its reintroduction in 2000 by Graham Budd and Sören Jensen.[3]

  1. ^ Hennig, W. (1969). Die Stammesgeschichte der Insekten (in German). Frankfurt am Main: Waldemar Kramer. ASIN B0000EGSML. OCLC 1612960.
  2. ^ Jefferies, R.P.S. (1979). "The Origin of Chordates — A Methodological Essay". In House, M.R. (ed.). The Origin of Major Invertebrate Groups. London ; New York: Academic Press for The Systematics Association. pp. 443–447. ISBN 0123574501. OCLC 767789225.
  3. ^ Budd, G.E.; Jensen, S. (2000). "A critical reappraisal of the fossil record of the bilaterian phyla". Biological Reviews. 75 (2): 253–295. doi:10.1111/j.1469-185X.1999.tb00046.x. PMID 10881389. S2CID 39772232.

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