| Summary: | The early evolution of toothless baleen whales (Chaeomysticeti) remains elusive despite a robust record of Eocene-Oligocene archaeocetes and toothed mysticetes. Eomysticetids, a group of archaic longirostrine toothless baleen whales fill in a crucial morphological gap between well-known toothed mysticetes and more modernized Neogene Mysticeti. Eomysticetids have been reported from South Carolina, USA, and Japan. Problematic fossils from New Zealand including "Mauicetus" lophocephalus Marples, 1956 and "Mauicetus" waitakiensis Marples, 1956, have been proposed as southern hemisphere eomysticetids. The fragmentary nature of this material has hampered interpretation of the relationships of these species. A large new collection of Eomysticetidae from the Oligocene Kokoamu Greensand and Otekaike Limestone of New Zealand permits reassessment of the skeletal anatomy, functional morphology, ontogeny, monophyly, and phylogenetic relationships of the family. This collection includes significant specimens including skulls, tympanoperiotics, mandibles, and postcrania of juveniles and adults. Discovery of new material similar to the "Mauicetus" of Marples permits referral of these species to the new genera Tohoraata and Tokarahia, recombined as Tohoraata waitakiensis and Tokarahia lophocephalus. More complete material of similar species Tohoraata raekohao and Tokarahia lophocephalus indicates that the two species of Tohoraata are stratigraphically separated whereas both species of Tokarahia were contemporaneous. The new genus and species Waharoa ruwhenua is represented by an ontogenetic series of skeletons that highlight the elongation of the palate during ontogeny; other morphofunctional aspects of the feeding apparatus suggest right whale-like skim feeding. The new genus and species Matapa waihao is the oldest and most archaic eomysticetid from New Zealand, indicating the presence of the family in the Southern Hemisphere by the earliest Chattian. Fragmentary specimens indicate the survival of eomysticetids to the Oligo-Miocene boundary or perhaps into the earliest Miocene, and the possible occurrence of the Japanese eomysticetid Yamatocetus in the Southern Hemisphere. Cladistic analysis confirms placement of the family Eomysticetidae as sister to crown Mysticeti. Eomysticetidae is for the first time recognized as being monophyletic; cladistic results indicate inclusion of Micromysticetus rothauseni. The Eomysticetidae were a specialized, worldwide, diverse, and short-lived Oligocene radiation of the earliest toothless mysticetes.
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