A crown group is a living
monophyletic group or
clade, consisting of the last common ancestor of all living examples, plus all of its descendants. The name was given by
Willi Hennig, the formulator of
phylogenetic systematics, as a way of classifying living organisms relative to extinct ones. Extinct members of crown groups are possible. Because the
Dodo, although extinct, is still descended from the last common ancestor of all living birds, for example, it is nevertheless included in the bird crown group.
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