Abstract

Stem cetaceans (archaeocetes) have a substantial Eocene fossil record but are largely absent since the Eocene–Oligocene boundary. Putative Oligocene archaeocetes are mostly represented by fragmentary denticulate teeth, making systematic classification difficult. The New Zealand species Kekenodon onamata (Wharekuri Greensand, Duntroonian local Stage, Chattian) is one of the most widely mentioned Oligocene archaeocetes and is the single-named species of the family Kekenodontidae. The holotype includes heterodont teeth in addition to cranial and post-cranial elements, and partial tympanoperiotics, with potential for a strong phylogenetic signal. Hitherto, the strikingly disparate Kekenodon onamata has been excluded from published phylogenetic analyses, with its affinities largely remaining speculative. Here, a detailed anatomical account allows a redescription of Kekenodon onamata, and a comprehensive phylogenetic analysis. The phylogenetic analysis shows Kekenodon onamata as the latest-surviving archaeocete, sister-taxon to the Neoceti. The large heterodont teeth with patterns of extensive enamel macrowear suggest Kekenodon onamata utilized a raptorial feeding strategy and hunted hard-boned prey, such as other marine mammals and penguins. Combined with an estimated body size of c. 8 m, Kekenodon onamata probably occupied an apex predator ecological niche similar to the modern killer whale.