Type of Document	Thesis
Author	Chapla, Marie Elise
URN	etd-04102006-143144
Title	Florida Manatee (Trichechus Manatus Latirostris) Outer And Middle Ear Morphology: Potential Sound Conduction Pathways And Middle Ear Mechanism
Degree	Master of Science
Department	Oceanography, Department of
Advisory Committee	Advisor Name Title Douglas Nowacek Committee Chair Louis St. Laurent Committee Member Markus Huettel Committee Member Sentiel Rommel Committee Member
Keywords	Middle Ear Anatomy Three-Dimensional Reconstruction Manatee Hearing Inertial Bone Conduction
Date of Defense	2006-04-07
Availability	unrestricted
Abstract 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).
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