The Florida manatee (Trichechus manatus latirostris) is an obligate aquatic mammal that inhabits shallow coastal waterways. Previous research has demonstrated that manatees vocalize using frequencies that range from < 0.5 kHz to 12 kHz (Frisch and Frisch, 2003; Nowacek et al., 2003) and hear frequencies between 0.4 kHz and 45 kHz (Bullock et al., 1982; Gerstein et al., 1999). Although the auditory anatomy has been described previously (Fischer, 1988; Ketten et al., 1992; Chapla and Rommel, 2003), potential sound pathways and middle ear mechanisms have not been analyzed. In the current study, Computerized Tomography (CT) is utilized to generate three-dimensional reconstructions of manatee heads and isolated earbone (tympanoperiotic) complexes in order to visualize the in situ arrangement of soft tissue and bone. Density data attached to the CT data are used to make calculations regarding the transmission and reflection of sound waves, with varying angles of incidence, as they encounter the boundaries of different tissue layers. Sound waves with 90° angles of incidence (relative to the tissue/water interface) will transmit 94% to 99% of their total energy intensity to the skull. Sound waves approaching at oblique angles to the surface of the head will transmit less of their energy intensity. The fraction of energy intensity in the transmitted wave will decrease with a decrease in the angle of incidence. Additional calculations of critical angles and an isospeed channel suggest that the inner fatty tissue layer (bounded by muscle and bone) does not provide an efficient channel for sound waves. Other potential sound pathways are discussed. A model of inertial bone conduction predicts that the peak displacement amplitude of the stapes, relative to that of the head, will be 8.4 dB at 200 Hz, and that inertial bone conduction may be possible between 125 Hz and 1000 Hz. Comparisons are made with data from humans and golden moles (Mason, 2003). / A Thesis submitted to the Department of Oceanography in partial fulfillment of the requirements for the degree of Master of Science. / Spring Semester, 2006. / April 7, 2006. / Middle Ear Anatomy, Three-Dimensional Reconstruction, Manatee Hearing, Inertial Bone Conduction / Includes bibliographical references. / Douglas P. Nowacek, Professor Directing Thesis; Sentiel A. Rommel, Outside Committee Member; Markus Huettel, Committee Member; Louis St. Laurent, Committee Member.
| Identifer | oai:union.ndltd.org:fsu.edu/oai:fsu.digital.flvc.org:fsu_254626 |
| Contributors | Chapla, Marie E. (authoraut), Nowacek, Douglas P. (professor directing thesis), Rommel, Sentiel A. (outside committee member), Huettel, Markus (committee member), Laurent, Louis St. (committee member), Department of Earth, Ocean and Atmospheric Sciences (degree granting department), Florida State University (degree granting institution) |
| Publisher | Florida State University, Florida State University |
| Source Sets | Florida State University |
| Language | English, English |
| Detected Language | English |
| Type | Text, text |
| Format | 1 online resource, computer, application/pdf |
| Rights | This Item is protected by copyright and/or related rights. You are free to use this Item in any way that is permitted by the copyright and related rights legislation that applies to your use. For other uses you need to obtain permission from the rights-holder(s). The copyright in theses and dissertations completed at Florida State University is held by the students who author them. |
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