Abstract
Eurhinodelphinids are a family of extremely long-snouted dolphins that once was widespread across the North Atlantic realm, but so far has not been recorded from the epicontinental Paratethys Sea. Here, we describe a new specimen of Xiphiacetus cristatus, including the cranium, left ear bones and a partial mandible, from the Middle Miocene (Badenian) of Austria. Our new fossil is the first record of this species outside the North Atlantic proper, and the first unequivocal record of eurhinodelphinids from the Paratethys. Its presence suggests a local invasion via the Mediterranean, and corroborates the persistence of an active marine gateway between the Mediterranean and the Central Paratethys throughout the Middle Miocene. Measurements of the bony labyrinth reveal that X. cristatus likely employed narrow-band high-frequency echolocation, making eurhinodelphinids only the second extinct odontocete family with this trait. Marked non-orthogonality of the semicircular canals suggests that X. cristatus was unsuited to rapid head movements, and thus more likely a benthic forager than a snap feeder.