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Abstract
A fragment of mandible of an indeterminate squalodontid dolphin (Upper Oligocene or lowermost Miocene, New Zealand) has 2 anomalous single-rooted teeth intercalated between typically squalodontid anterior cheek-teeth. The anomalous teeth are considered to be truly supernumerary, and not homologous with any erupted teeth in phylogenetically earlier Cetacea. This type of anomaly appears not to have been reported previously for any fossil cetacean. Polydonty, a characteristic of extant odontocetes, was probably attained initially in primitive odontocetes by intercalation of permanent and deciduous teeth, and later was elaborated by the addition of supernumerary teeth. The present specimen represents a morphological (but not phylogenetic) stage between odontocetes with limited and advanced polydonty. Some fossil mysticetes and embryonic extant mysticetes are also polydont, but mysticete polydonty and that of odontocetes have probably evolved convergently.
