CYTOCHROME-B NUCLEOTIDE-SEQUENCES AND THE IDENTIFICATION OF 5 PRIMARYLINEAGES OF EXTANT CETACEANS

Relationships among and within baleen and toothed whales were examined using the complete sequence of the mitochondrial cytochrome b gene. B ased on parsimony analyses of conservative nucleotide substitutions, f ive primary evolutionary lineages of extant cetaceans were identified, one represented by baleen whales (Mysticeti) and four represented by odontocetes (toothed whales). Based on the most comprehensive represen tation of taxa, both cetaceans and artiodactyls, the most parsimonious relationship among the five lineages is (Mysticeti, Odontoceti (Plata nistoidea (Physeteroidea (Ziphioidea (Delphinida))))). This relationsh ip, however, is labile and sensitive to ingroup representation and the choice of outgroup. The short nodes among the five cetacean lineages suggest that the divergence among these lineages occurred over a narro w time period, a finding consistent with the limited fossil evidence t hat indicates a major cetacean radiation 30-34 Mya. The level of diver gence among the five cetacean lineages, and that seen between cetacean s and artiodactyls, suggests that cetaceans and artiodactyls had a com mon ancestor approximate to 60 Mya.