Tuesday, April 28, 2015

Word of the Day -- Paraphyly

In taxonomy, a group is said to be paraphyletic if it consists of all the descendants of the last common ancestor of the group's members minus a small number of monophyletic groups of descendants, typically just one or two such groups. Such a group is said to be paraphyletic with respect to the excluded groups. The term is commonly used in phylogenetics (a subfield of biology) and in linguistics.

For example, the group of reptiles, as traditionally defined, is paraphyletic with respect to the mammals and birds: it contains the last common ancestor of the reptiles—including the extant reptiles as well as the extinct mammal-like reptiles—along with all descendants of that ancestor except for mammals and birds. Other commonly recognized paraphyletic groups include fish and lizards.


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