Morphology, phylogeny, and paleoecology of the Kekenodontidae (Mammalia: Cetacea) from the Late Oligocene of New Zealand

The increasingly dense fossil record of archaeocetes (stem cetaceans) is well represented in Eocene strata from the tropics to northern mid-temperate latitudes. Fossils provisionally identified as archaeocetes from Oligocene marine rocks, however, are usually poorly preserved and fragmentary. One of the first-recognized species is the enigmatic Kekenodon onamata, from New Zealand, representing the single-named taxon of the family Kekenodontidae. Despite having moderately-preserved tympanoperiotics, the otherwise fragmentary holotype has long been of uncertain relationships. New and more complete fossils from the upper Oligocene Kokoamu Greensand of the South Island, New Zealand elucidate the anatomy, feeding ecology, and phylogenetic affinities of the Kekenodontidae. Tooth form in Kekenodon onamata indicates a macrophagous diet perhaps including other cetaceans, suggesting an apex predator position similar to the ecological niche occupied by the more basal Basilosaurus isis. The well-preserved new genus and species Tupunatomuri kauaekopi, has an estimated body length of ca. 4 m, smaller than the coeval and sympatric Kekenodon onamata (ca. 8 m). Another new genus and species of small-bodied kekenodontid, Awawaihao nihoratarata, preserves a nearly complete dentition that is structurally similar to Tupunatomuri kauaekopi. The latter dentitions differ from those of Kekenodon onamata, suggesting different feeding strategies and prey selection, and thus niche partitioning, amongst coeval Kekenodontidae. The basilosaurid-like structure of the feeding apparatus combined with a low skull profile, gracile mandibles, and general absence of enamel wear suggests that kekenodontids were suction feeders rather than macrophagous raptors. One denticulate tooth of Awawaihao nihoratarata is nearly identical to the holotype tooth of ‘Squalodon’ gambierensis (Late Oligocene, South Australia), leading to the new combination Awawaihao gambierensis, and representing the first record of Kekenodontidae from Australia. A juvenile specimen of a small-bodied kekenodontid is similar to Tupunatomuri kauaekopi and Awawaihao nihoratarata, but lack of adult characters precludes identification. Teeth of the juvenile are structurally similar to deciduous teeth known from the basilosaurids Dorudon atrox and Zygorhiza kochii, possibly indicating diphyodonty in at least one species of Kekenodontidae. Phylogenetic analyses place the Kekenodontidae as the sister clade to the Neoceti, representing the latest-diverging family of archaeocetes. The small-bodied kekenodontids form an additional clade to the exclusion of Kekenodon onamata