Hearing in Pinnipeds, the Amphibious Ear
Pinnipeds (seals, sea lions, and walruses), sea otter, and polar bear spend time on land as well as in the water. Consequently, their ears have some adaptations in common with the ears of land mammals.
In pinnipeds the pinnae (external ear flaps) are reduced or absent. Otariids (eared seals) have small ear flaps. Phocids (true seals) have no pinnae. Muscles and a cartilage valve along the external ear canal function to close the ear canal to water. In general, the middle and inner ears of pinnipeds, polar bears, and otters are similar to those of humans and other terrestrial mammals. The mechanisms for hearing are essentially the same (See Hearing in Land Mammals). These animals that spend time both on land and in the water have a mix of adaptations. Depending on their life styles, some species hear best in air, whereas others hear better underwater.
Additional Links on DOSITS
- Wartzok, D. and Ketten, D.R. 1999, "Marine Mammal Sensory Systems." Pages 117-175 in Reynolds, J.E. III and Rommel, S.A. (eds.). Biology of Marine Mammals. Smithsonian Institution Press, Washington D.C.
- Computerized Scanning and Imaging Facility at Woods Hole Oceanographic Institution, "2 dimensional and 3 dimensional CT scan images of cetaceans and other animals." (Link)