Ankle morphology of the earliest cetaceans and its implications for the phylogenetic relations among ungulates

Recent molecular studies are inconsistent with ungulate phylogenetic- trees that are based on morphological traits. These inconsistencies especially r elate to the position of cetaceans and perissodactyls. Evaluation of the cl ose phylogenetic ties between artiodactyls and cetaceans has been hampered by the absence of tarsal bones of primitive cetaceans, as artiodactyls are often diagnosed on the basis of their tarsus. We here describe newly discov ered tarsal bones that are the oldest cetacean tarsals known. We present a character analysis for primitive ungulate tarsals and evaluate their impact on the ungulate phylogenetic tree. Tarsal data are consistent with some mo lecular studies in suggesting that the extant sister group of Cetacea is Ar tiodactyla or that Cetacea should be included within the latter order. Tars al data do not support Cete (Mesonychia plus Cetacea) and are consistent wi th the exclusion of perissodactyls from paenungulates as suggested by some molecular studies.