FIGURE 1. A comparison of the strict consensus tree of Thewissen et al.(2001b)(A) and the strict consensus tree for the present study (B). Note that in the consensus of Thewissen et al.(2001b) the Cetacea are not inside the clade of extant artiodactyls, and the hippopotamus is not closely related to whales. In contrast, the morphological data analyzed in this study support the inclusion of Cetacea within Artiodactyla as the sister-group to Hippopotamidae, as suggested by numerous molecular studies (eg, Gatesy et al., 1999). To facilitate comparison and to highlight key features, some taxa have been collapsed into higher-level groups. In cases where a higher-level taxon includes three or more taxa, parentheses are used to describe the phylogeny in the strict consensus of the present study:(all taxa with"*" are in the current study only): Cameloidea=(Eotylops*(Poebrotherium (Llama*, Camelus*))); Entelodontidae (Archaeotherium); Hapalodectes=(H. hetangensis*, H. leptognathus*); Mesonychidae=(Dissacus praenuntius*, Dissacus navajovius*, Mongolian Dissacus*(Ankalagon (Sinonyx (Pachyaena gigantea*, Pachyaena ossifraga*,(Mesonyx, Harpagolestes, Synoplotherium))))); Mysticeti=(Balaenoptera); Odontoceti=(Physeter (Tursiops, Delphinapterus); Oreodontoidea=(Agriochoerus, Merycoidodon*); Perissodactyla=((Equus*, Mesohippus*)(Heptodon*, Hyracotherium*)); Phenacodontidae=(Meniscotherium, Phenacodus); Protoceratidae=(Leptoreodon*(Heteromeryx*, Protoceras*)); Ruminantia=(Hypertragulus*(Leptomeryx*(Tragulus (Bos*(Odocoileus*, Ovis*))))); Suina=(Perchoerus*(Sus, Tayassu*)); and Xiphodontoidea=(Xiphodon*, Amphimeryx*). In the