Animal Sonar pp 281-287 | Cite as

The Jaw-Hearing Dolphin: Preliminary Behavioral and Acoustical Evidence

  • Randall L. Brill
Part of the NATO ASI Science book series (NSSA, volume 156)


Two decades ago, Norris (1964, 1968) proposed that the lower jaw of the dolphin was the primary pathway to the tympanoperiotic bone for returning acoustic signals during echolocation. Unlike that of terrestrial mammals, the lower jaw in odontocetes is hollow and filled with a fatty material that extends beyond the pan bones to attach to the tympanic bulla. This material has been found to contain lipids which contribute to its ability to transmit sound (Varanasi and Malins, 1971; 1972). Electrophysiological studies have indicated that acoustical stimuli presented to the lower jaw evoke significant responses in the auditory system of the dolphin (Bullock et al., 1968; McCormick et al., 1970; 1980). Bullock et al. (1968) further reported that foam rubber or paper placed over the lower jaw to block acoustical stimuli significantly attenuated responses. Several investigators have considered the jaw-hearing hypothesis and its possible role, at least in part, in the findings of their acoustical experiments with dolphins as well (Renaud and Popper, 1975; Au, Floyd, and Haun, 1978; Au and Moore, 1984). Other than a limited attempt to hinder a dolphin’s use of its lower jaw which remained inconclusive (Norris, 1974), what has lacked in the evaluation of this theory is behavioral and acoustical evidence gained from a living animal actively echolocating under controlled conditions.


Acoustical Stimulus Echolocation Signal Acoustical Experiment Tympanic Bulla Cassette Tape Recorder 


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Copyright information

© Plenum Press, New York 1988

Authors and Affiliations

  • Randall L. Brill
    • 1
    • 2
  1. 1.Chicago Zoological SocietyBrookfieldUSA
  2. 2.Parmly Hearing InstituteLoyola University of ChicagoChicagoUSA

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