The Oligocene Epoch was a time of major radiation of the Odontoceti (echolocating toothed whales, dolphins). Fossils reveal many odontocete lineages and considerable structural diversity, but whether the clades include some crown taxa or only archaic groups is contentious. The New Zealand fossil dolphin “Prosqualodon” marplesi (latest Oligocene, ≥23.9 Ma) is here identified as a crown odontocete that represents a new genus, Otekaikea, and adds to the generic diversity of Oligocene odontocetes. Otekaikea marplesi is known only from the holotype, which comprises a partial skeleton from the marine Otekaike Limestone of the Waitaki Valley. Otekaikea marplesi was about 2.5 m long; it had procumbent anterior teeth, and a broad dished face for the nasofacial muscles implicated in production of echolocation sounds. The prominent condyles and unfused cervical vertebrae suggest a flexible neck. A phylogenetic analysis based on morphological features places Otekaikea marplesi in the extinct group Waipatiidae, within the clade Platanistoidea. The phylogeny implies an Oligocene origin for the lineage now represented by the endangered Ganges River dolphin (Platanista gangetica), supporting an Oligocene history for the crown Odontoceti.