94 - Detailing the Basicranial Region and Hearing Apparatus Anatomy of the Hawaiian Monk Seal (Neomonachus Schauinslandi)

Poster Board Number: 94
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Abstract Body : The anatomy of phocid hearing apparatuses is relatively unknown due to extremely limited studies. Although diverse skull morphologies are well-documented in pinnipeds (seals, sea lions, fur seals, and walruses), it remains unclear how they hear efficiently in both aquatic and terrestrial environments. In phylogenetic morphological studies, portions of the basicrania are used as diagnostic characters. This is common since the mammalian basicrania can be thought of as more evolutionarily conservative and therefore less variable in comparison to other parts of the skull. This study focuses on the morphology of the basicranial region and auditory osteology of the Hawaiian Monk seal (Neomonachus schauinslandi), an endangered species of Phocidae (true seals) that is endemic to the Hawaiian Islands. This species is thought to be less aquatically derived compared to other phocids and can be directly compared to otariids (sea lions and fur seals) and odobenids (walruses), who often are grouped together due to similar morphology. Multiple specimens from the Smithsonian National Museum of Natural History (NMNH) were examined. Osteological measurements, morphological descriptions, and modern imaging software were used to analyze specimens and detail specific morphology. Results demonstrate that the Hawaiian monk seal has a distinct morphology of the tympanic bullar region, unique structure surrounding the opening of the round window, and different orientations of the semicircular canals from typical terrestrial carnivorans. After establishing accurate auditory morphology of phocids and other pinnipeds, future functional studies can determine how exactly these carnivorans hear in the water and can specify the evolutionary timeline of semiaquatic hearing. To date, there is no functional anatomical research on pinnipeds due to the lack of information on specific auditory morphology, demonstrating the need for evaluation and comparison of the auditory morphologies of modern carnivorans in relation to hearing.