Revised phylogeny of whales suggested by mitochondrial ribosomal DNA sequences

Living cetaceans are subdivided into two highly distinct suborders, Odontoceti (the echolocating toothed whales) and Mysticeti (the filter-feeding baleen whales), which are believed to have had a long independent history. Here we report the determination of DNA sequences from two mitochondrial ribosomal gene segments (930 base pairs per species) for 16 species of cetaceans, a perissodactyl and a sloth, and construct the first phylogeny for whales and dolphins based on explicit cladistic methods. Our data (and earlier published myoglobin sequences) confirmed that cetaceans are closely related to artiodactyls and that all families and superfamilies of cetaceans are monophyletic. A surprising finding was that one group of toothed whales, the sperm whales, is more closely related to the baleen whales than to other odontocetes. The common ancestor of baleen whales and sperm whales might have lived only 10-15 million years ago. The suggested paraphyly of toothed whales has many implications for classification, phylogeny and our understanding of the evolutionary history of cetaceans.