3D-Visualization of the Ear Morphology of Penguins (Spheniscidae): Implications for Hearing Abilities in Air and Underwater

The ear morphology of three penguin species (Aptenodytes forsteri, Pygoscelis papua and Spheniscus demersus) was analyzed using diffusible iodine-based contrast-enhanced computed tomography (diceCT). Main aural structures were visualized and the results were animated in 3D videos as open educational resources to facilitate UNESCOs mandate for a free use of these digital models for scholars and teachers. Based on the annotated segmentations, the morphology of main structures of the penguin ear is described. In general, the penguin ear can be regarded as an organ for the reception of air sound with adaptations to the semiaquatic lifestyle of the animals. No alternative pathways for the reception of sound in water, as are known in aquatic vertebrates, were detected by the used methods so far. The significance of missing contralateral connections between the air-filled spaces of the middle ear needs further evaluation in that respect. The low relation of the area of the tympanic membrane to the columella footplate and a potential venous corpus cavernosum in the middle ear are discussed as important factors for pressure regulation and for the protection of the sensitive tympanic membrane. Our results indicate that penguins have at least basic abilities to hear underwater even under high ambient pressures.