Waipatia maerewhenua, from the Otekaike Limestone (late Oligocene). Waitaki Valley. New Zealand, is a new genus and species in a new family Waipatiidae (Odontoceti: Platanistoidea) near the base of the radiation of platanistoids. Its features include skull about 600 mm long; rostrum long and narrow; incisors long, procumbent, and gracile; cheek teeth heterodont and polydont: maxillae telescoped back over frontals toward supraoccipital; parietal narrowly exposed on vertex; pterygoid sinus fossa restricted to basicranium; and palatine broad and not invaded by pterygoid sinus fossa. Features of the tympano-periotic, periotic fossa, and foramen spinosum indicate platanistoid relationships. Waipatia maerewhenua is more closely related to the Squalodelphidae and Platanistidae than to the Squalodontidae. Of the similar small dolphins previously identified as Squalodontidae. Mierocetus ambiguus ( late Oligocene. Germany ) and Sachalinocetus cholmicus (early or middle Miocene. Sakhalin) are possible waipatiids. Mierocetus hectori (earliest Miocene. New Zealand! is a probable squalodelphid. Prosqualodon marplesi (early Miocene. New Zealand) is transferred to Notocetus (Squalodelphidae) as Notocetus marplesi (new combination). Sulakocetus dagestanicus (late Oligocene, Caucasus) is probably a waipatiid close to W. maerewhenua. These taxa reveal an early radiation of the Platanistoidea by the late Oligocene.
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R. Ewan Fordyce (1994) studied this question.