Structure , Function , and Adaptation of the Manatee Ear

The West Indian manatee, Trichechus manatus, is common throughout the Caribbean yet little is known about its sensory abilities. Hearing in particular is of interest since large numbers of one subspecies, the Florida manatee (~manatus latirostris), die annually from collisions with boats in shallow coastal waters and canals. There is no published audiogram for Trichechus manatus and the auditory system has not been fully described. Earlier studies of manatee hearing were based on isolated, dehydrated tympano-periotic bones (Robineau, 1969; Fleischer, 1978). This paper describes all major hard and soft tissues of the peripheral auditory system of ~ manatus, presents new information on specialized cranial features that may be important for sound conduction, and provides morphometrybased estimates of the frequency range and sensitivity of West Indian manatee ears.