Role of the mental foramens in dolphin hearing

Vyacheslav Ryabov
DOI: 10.4236/ns.2010.26081                

Abstract

The role of mental foramens in dolphin hearing was studied in the present work. To this effect the mental foramens’ morphology features which are essential from acoustical viewpoint have been studied. The patterns of relationship between the location of mental foramens and their sizes are found. The affinity of the mental foramens’ morphology and acoustics that the nature had created testify acoustical expediency of the mental foramens’ architecture. This natural inference in the main is confirmed in this work by the experimental data. The mean values of detection thresholds of short broadband stimuli with spectral maximum on frequencies 8, 16, 30 and 100 kHz at acoustical shielding the mental foramens increased on 30, 34, 40 and 50 dB, respectively. Results obtained testify that the mental foramens are the unique sound-conducting pathway into the fat body of the mandibular canal for the sounds of all frequencies used in the experiment, approximately 6?150 kHz (in view of stimuli broadbandness). The left and right row of the mental foramens together with respective mandibular canal plays the role of pinna and external auditory meatus if to use conventional terminology of a land mammal ear. But it is already qualitatively the new external ear implemented by the nature as the receive array and acoustical horn. The new external ear has apparently appeared in result of the dolphins’ ancestors’ adaptation to new environment conditions, as evolutionary adaptation of the ear to the water and as functional adaptation of the ear in order that to fulfill the new more sophisticated functions in the structure of sonar. The findings give good reason to suppose existence of the same external ear in Odontoceti.

Keywords

Dolphin; Hearing; Architecture of Mental Foramens; Lower Jaw; Unique Pathway; Sound Conduction; The Traveling Wave Antenna; External Ear

Conflicts of Interest

The authors declare no conflicts of interest.

References

[1]	De Haan, F.V.R. (1957) Hearing in whales. Acta Otolaryngologica Supplementum, 134, 1-14.
[2]	Fraser, F.C. and Purves, P.E. (1960) Hearing in the cetaceans: Evolution of the accessory air sacs and the structure and function of the outer and middle ear in recent cetaceans. Bulletin of the British Museum (Natural History), Zoology, 7(1), 1-140.
[3]	Van Heel, W.H.D. (1962) Sound and cetacean. Netherlands Journal of Sea Research, 1(4), 407-507.
[4]	Yamada, M. (1953) Contribution to the anatomy of the organ of hearing of whales. The Scientific Reports of the Whales Research Institute, 8(1), 1-79.
[5]	Fleischer, G. (1973) Structural analysis of the tympanicum complex in the bottlenose dolphin (Tursiops truncatus). Journal of Auditory Research, 13, 178-190.
[6]	McCormick, J.G., Wever, E.G., Palin, J. and Ridgway, S.H. (1970) Sound conduction in the dolphin ear. Journal of the Acoustical Society of America, 48(6), 1418-1428.
[7]	Bullock, T.H., Grinell, A.D., Ikezono, E., Kameda, K., Katsuki, J., Nomota, M., Sato, O., Suga, N. and Yanagisawa, K. (1968) Electrophysiological studies of central auditory mechanisms in cetaceans. Zeitschrift für Vergleichende Physiologie, 59(2), 117-156.
[8]	Airapetiantz, E.S., Voronov, V.A., Ivanenko, U.V., Ivanov, M.P., Ordovsky, D.L., Popov, V.V., Sergeev, B.F. and Chilingiris, V.I. (1973) The physiology of the sonar system in Black Sea dolphins. Zhurnal Evoliutsionnoǐ Biokhimii i Fiziologii, 9(4), 416-422.
[9]	Dubrovsky, N.A. (1990) On the two auditory subsystems in dolphins: Sensory abilities of cetaceans. Plenum Press, New York, 233-254.
[10]	Norris, K.S. (1964) Some problems of echolocation in cetaceans. In: Tavolga, W., Ed., Marine Bio-Acoustics, Pergamon Press, New York, 316-336.
[11]	Norris, K.S. (1968) The evolution of acoustic mechanisms in odontocete cetaceans. In: Drake, E.T., Ed., Evolution and Environment, Yale University Press, New Haven, 297-324.
[12]	Popov, V.V., Supin, A.Y., Klishin, V.O., Tarakanov, M.B. and Pletenko, M.G. (2008) Evidence for double acoustic windows in the dolphin, Tursiops truncates. Journal of the Acoustical Society of America, 123(1), 552-560.
[13]	Ketten, D.R. (1997) Structure and function in whale ears. Bioacoustics, 8(1-2), 103-135.
[14]	Nummela, S., Reuter, T., Hemila, S., Holmberg, P. and Paukku, P. (1999) The anatomy of the killer whale middle ear (Orcinus orca). Hearing Research, 133(1-2), 61-70.
[15]	Hemilä, S., Nummela, S. and Reuter, T. (1999) A model of the odontocete middle ear. Hearing Research, 133(1-2), 82-97.
[16]	Koopman, H.N., Budge, S.M., Ketten, D.R. and Iverson, S.J. (2006) Topographical distribution of lipids inside the mandibular fat bodies of Odontocetes: Remarkable complexity and consistency. Journal of Oceanic Engineering, 31(1), 95-106.
[17]	Møhl, B., Au, W.W.L., Pawloski, J. and Nachtigall, P.E. (1999) Dolphin hearing: Relative sensitivity as a function of point of application of a contact sound source in the jaw and head region. Journal of the Acoustical Society of America, 105(6), 3421-3424.
[18]	Brill, R.L., Moore, P.W.B., Helweg, D.A. and Dankiewicz, L.A. (2001) Investigating the dolphin’s peripheral hearing system: Acoustic sensitivity about the head and lower jaw. Technical Report–1865, 1-14.
[19]	Brill, R.L. (1988) The jaw-hearing dolphin: Preliminary behavioral and acoustics evidence. In: Nachtigal, P. and Moore, P., Ed., Animal Sonar. Processes and Performance, Plenum Press, New York, 281-287.
[20]	Rimskaya-Korsakova, L.K. and Dubrovsky, N.A. (1998) Two sound conduction pathways to the cochlea participate information of spatial auditory image in the dolphin. Sensory Systems, 12(4), 497-506.
[21]	Ryabov, V.A. (2004) Lower jaw–peripheric part of the dolphin echolocation hearing. In: Belkovich, V.M., Ed., Marine Mammals of the Holarctic, Collection of Scientific Papers, KMK Scientific Press, Moscow, 483-489.
[22]	Ryabov, V.A. (2007) Mechanisms of a dolphin’s echolocation hearing. In: Dible, S., Dobbins, P., Flint, J., Harland, E. and Lepper, P., Ed., Bio-Acoustics 2007, Proceedings of the Institute of Acoustics, 29(3), 283-293.
[23]	Ryabov, V.A. (2008) Acoustic clutter field and echo reception by the dolphin. Biophysics, 53(3), 237-242.
[24]	Ryabov, V.A. (2003) A dolphin lower jaw is a hydroacoustic antenna of the traveling wave. Journal of the Acoustical Society of America, 114(4), 2414-2415.
[25]	Ryabov, V.A. (2008) Properties of the dolphin’s mandible horn. In: Boltunov, A.N., Ed., Marine Mammals of the Holarctic, Collection of Scientific Papers, Astroprint Publishing House, Odessa, 468-473.
[26]	Schusterman, R.J. (1980) Behavioral methodology in echolocation by marine mammals. In: Busnel, R.-G. and Fish, J.F., Ed., Animal Sonar Systems, Plenum Publishing Corporation, New York, 11-41.
[27]	Agarkov, G.B., Homenko, B.G. and Hadjinsky, V.G. (1974) Morphology of dolphins. Naukova Dumka, Kiev, 1-167.
[28]	Varanasi, U. and Malins, D.C. (1971) Unique lipids of the porpoise (Tursiops gilli): Differences in triacyclglycerols and wax esters of acoustic (mandibular and melon) and blubber tissues. Biochimica et Biophysica Acta, 231, 415-418.
[29]	Johnson, C.S. (1967) Sound detection thresholds in marine mammals. In: Tavolga, W.N., Ed., Marine Bio-Acoustics II, Pergamon Press, Oxford, 247-260.
[30]	Johnson, C.S. (1968) Maskes tonal thresholds in the bottlenose porpoise. Journal of the Acoustical Society of America, 44(4), 965-967.
[31]	Babushina, E.S. (1999) Sound reception in marine mammals: Effects of stimulus parameters and transmission pathways. Biophysics, 44(6), 1064-1071.