Hearing from the ocean and into the river: The evolution of the inner ear of Platanistoidea (Cetacea, Odontoceti)

The inner ear of the two higher clades of modern cetaceans (Neoceti) is highly adapted for hearing infrasonic (mysticetes) or ultrasonic (odontocetes) frequencies. Within odontocetes, Platanistoidea comprises a single extant riverine representative, Platanista gangetica, and a diversity of mainly extinct marine species from the late Oligocene onward. Recent studies, drawing on features including the disparate tympanoperiotic, have not yet provided a consensus phylogenetic hypothesis for platanistoids. Further, cochlear morphology and evolutionary patterns have never been reported. Here, we describe for the first time the inner ear morphology of late Oligocene–early Miocene extinct marine platanistoids and their evolutionary patterns. We initially hypothesized that extinct marine platanistoids lacked a specialised inner ear like Platanista gangetica and thus, their morphology and inferred hearing abilities were more similar to pelagic odontocetes. Our results reveal there is no “typical”...