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Ketten, D. R., Fischer, I., Cramer, S. R., Bartol, S. M., & Omalley, J. Water, fat, and acoustic impedance: soft tissue adaptations for underwater hearing in turtles, seabirds, and marine mammals. NOAA Technical Memorandum NMFS SEFSC . no. 536, p. 162. 
Added by: Admin (21 Nov 2009 11:53:15 UTC)
Resource type: Unpublished Work
BibTeX citation key: Ketten2006
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Categories: General
Keywords: akustische Kommunikation = acoustic communication, Morphologie = morphology, Physiologie = physiology, Schildkröten = turtles + tortoises
Creators: Bartol, Cramer, Fischer, Ketten, Omalley
Publisher: NOAA Technical Memorandum NMFS SEFSC . no. 536, p. 162
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Remarkably little is known about underwater hearing in sea turtles. In fact, one of the most fundamental issues, how sound is channeled to the inner ear, has not been fully investigated. Turtles share a common problem with dolphins. Both lack conventional external ear canals. Nevertheless, turtles, birds, seals, and whales are believed to hear underwater and, possibly, as has been demonstrated at least for dolphins, to have good sensitivity and sound localization abilities. In this study, computerized tomography (CT) and magnetic resonance imaging (MRI) were used to explore underwater sound reception mechanisms through density analysis and mapping of tissues associated with the outer and middle ears of multiple species of dolphins, seals, turtles, and sea birds. The scans revealed well-organized bundles of coherent fatty tissues emerging from the middle ear in all species examined. The densities of these fats are similar across all species examined and are consistent with sound speeds of sea water. Three-dimensional reconstructions of the scan data showed that in turtles, the fats formed a discrete column fused to the tympanum. Seals and sea birds have distinct columns of fat that parallel an air-filled canal. In dolphins, the fats form three distinct bundles: two directed anteriorly with a third projecting postero-laterally. These findings suggest that all four groups evolved parallel soft tissue specializations that act as low impedance channels for underwater sound conduction to the ear.
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