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Paraphyletic
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phylogenetics
   
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Groups that include all the descendants of the most recent common ancestor are commonly termed Monophyletic or holophyletic. The former is more common, but sometimes paraphyletic groups are also considered monophyletic, in which case the latter is used. A paraphyletic group can be fixed by expanding it, and including other Clade s. A class which does not contain the most recent common ancestor of its members is called '' Polyphyletic ''.

Many of the older classifications contain paraphyletic groups, especially the traditional 2-6 Kingdom systems and the classic division of the Vertebrate s. For example, the class Reptilia as traditionally defined is paraphyletic because that class does not include birds (class Aves ), which are descended from reptiles. Paraphyletic groups are often erected on the basis of (sym)-plesiomorphies (ancestral similarities) instead of upon (syn)apomorphies (derived similarities).

  • . The term "evolutionary grade" is sometimes used for such groups.



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