MORPHOLOGY, MOLECULES, AND THE PHYLOGENETICS OF CETACEANS

Recent phylogenetic analyses of cetacean relationships based on DNA se quence data have challenged the traditional view that baleen whales (M ysticeti) and toothed whales (Odontoceti) are each monophyletic, argui ng instead that baleen whales are the sister group of the odontocete f amily Physeteridae (sperm whales). We reexamined this issue in light o f a morphological data set composed of 207 characters and molecular da ta sets of published 12S, 165, and cytochrome b mitochondrial DNA sequ ences. We reach four primary conclusions: (1) Our morphological data s et strongly supports the traditional view of odontocete monophyly; (2) the unrooted molecular and morphological trees are very similar, and most of the conflict results from alternative rooting positions; (3) t he rooting position of the molecular tree is sensitive to choice of ar tiodactyl outgroup taxa and the treatment of two small but ambiguously aligned regions of the 12S and 16S sequences, whereas the morphologic al root is strongly supported; and (4) combined analyses of the morpho logical and molecular data provide a well-supported phylogenetic estim ate consistent with that based on the morphological data alone (and th e traditional view of toothed-whale monophyly) but with increased boot strap support at nearly every node of the tree.