A biological taxonomy that pertains to a certain group of organisms does include some but not all of the descendants from the common ancestors.
Paraphyletic occurs when all descendants of the last common ancestor of the group members separate to form another groups. Like for example in class Reptilia as conventionally delineate, are paraphyletic since it excludes the two groups of its descendants, the class Aves and class Mammalia wherein birds are descended from dinosaurs of which classified as reptiles and mammals from mammal-like reptiles. Other usually known paraphyletic groups include fish and lizards.
A Paraphyletic group is frequently raised on the basis of ancestral similarities rather than derived similarities. The presence of paraphyletic in cladistics school of taxonomy is an adequate sacrifice if it makes taxonomy more reasonable and is needed to encompass a comprehensive classification together with that of extinct group since every species originates from part of another.
Paraphyletic is used when studying significant traits that led a subclade in an evolutionary divergent from more inclusive clade since it is always useful to consider the paraphyletic group without taking into consideration the larger clade.
• paraphyly (noun)
• paraphyletically (adverb)