The Marine Mammal Ear: Specializations for Aquatic Audition and Echolocation

Abstract

“Marine mammal” is a broad categorization for over 150 species that have one feature in common: the ability to function effectively in an aquatic environment. They have no single common aquatic ancestor and are distributed among four orders (see Appendix 1). Each group arose during the Eocene in either the temperate northern Pacific Ocean or in the Tethys Sea, a paleolithic body of water from which the Mediterranean and middle eastern limnetic basins were formed. Otariids (sea lions), odobenids (walrus), and marine fissipeds (sea otters) developed primarily in the Pacific, while the earliest cetacean (whale), sirenian (manatee and dugong), and phocid (true seal) fossils come from regions bordering Tethys Sea remnants (Kellogg 1936; Domning 1982; Barnes, Domning, and Ray 1985). The level of adaptation to the marine environment varies in marine mammals; many are amphibious and only the Cetacea and Sirenia are fully aquatic, unable to move, reproduce, or feed on land.