| Summary: | Pinnipeds (e.g., seal, sea lion, walrus) are marine mammals that spend time both in and out of the water. All are able to vocalize in air using the pneumatically driven vocal fold vibrations, a mechanism common to terrestrial mammals. This is no surprise, as their ancestors were once terrestrial mammals. Pinnipeds, however, are also able to vocalize underwater. It is not known how they generate or transmit these sounds. This study explores pinniped laryngeal anatomy in: harbor seal ( Phoca vitulina ), gray seal ( Halichoerus grypus ), elephant seal ( Mirounga angustirostris ), California sea lion ( Zalophus californianus ), and walrus ( Odobenus rosmarus ). Comparisons were made with the laryngeal anatomy of several closely related terrestrial species including: dog ( Canis familiaris ) and black bear ( Ursus americanus ), and several semiaquatic species including: polar bear ( Ursus maritimus ), sea otter ( Enhydra lutris ), river otter ( Lontra canadensi s), beaver ( Castor canadensi s), muskrat ( Ondatra zibethicus ), and hippo ( Hippopotamus amphibius ). Comparisons were also made to fully aquatic mammals that can vocalize underwater including: manatee ( Trichechus manatus ), baleen whales ( Caperea marginata, Balaena glacialis, Megaptera novaeangliae, Balaenoptera musculus, B. physalus, B. borealis, B. acutorostrata ), and over 20 species of toothed whales (including sperm whales, beaked whales, dolphins, and porpoises). Results indicate that the harbor and gray seals have an unremarkable larynx that appears grossly similar to that of most other mammals. Elephant seal, sea lion, and walrus larynges, however, were unusual in having arytenoid cartilages that are extremely large and rounded on their rostral surface. The arytenoids form a valve across approximately half of the laryngeal lumen. Interestingly, this feature also occurs in sea otters. The corniculate and cuneiform cartilages are difficult to detect in the elephant seal, sea lion, and walrus. The epiglottic cartilage is very short in the sea lion ...
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