  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 reptilesâincluding the extant reptiles as well as the extinct mammal-like reptilesâalong with all descendants of that ancestor except for mammals and birds. other commonly recognized paraphyletic groups include fish and lizards. ==phylogenetics==  ===relation to monophyletic groups=== groups that include all the descendants of a common ancestor are said to be monophyletic. a paraphyletic group is a monophyletic group from which one or more subsidiary clades (monophyletic groups) is excluded to form a separate group. ereshefsky has argued that paraphyletic taxa are the result of anagenesis in the excluded group or groups.http://books.google.ca/books?id=ucilijrex5cc&pg=pa9&lpg=pa9&dq=paraphyletic+anagenesis&oi=book_result&ct=result&resnum=1&#v=onepage&q=paraphyletic%20anagenesis&f=false for example, dinosaurs are paraphyletic with respect to birds because birds possess many features that dinosaurs lack and occupy a distinctive niche. a group whose identifying features evolved  convergently in two or more lineages is polyphyletic (greek ÏÎ¿Î»ÏÏ [polys], "many"). more broadly, any taxon that is not paraphyletic or monophyletic can be called polyphyletic. these terms were developed during the debates of the 1960s and 70s accompanying the rise of cladistics. ===examples of paraphyletic groups=== many of the older classifications contain paraphyletic groups, including the traditional 2â6 kingdom systems and the classic division of the vertebrates. examples of well-known paraphyletic groups include: * in the flowering plants, dicotyledons, in the traditional
Phylogenetics