Abstract

A beautifully preserved cetacean ear bone has been recovered from the lower Miocene Iwamura Group, Gifu Prefecture, Japan. The specimen consists of the periotic, tympanic bulla and malleus. It represents the following combination of morphological characters, and here, we describe the specimen as Squalodlephinidae gen. et. sp. indet.:a distinct articular rim is present on the lateral surface of the posterior process of the periotic; aperture for the cochlear aqueduct is large and thin-edged, facing dorsally; aperture for the vestibular duct is smaller than aperture for the cochlear aqueduct; pars cochlearis is square-shaped in ventral view; the anterointernal sulcus is developed on the medial surface of the anterior process of periotic. The present specimen is the first described squalodelphinid from the Pacific realm in the northern hemisphere and thereby extends our knowledge of their distribution.