A model of the odontocete middle ear

Hemilä, Simo; Nummela, Sirpa; Reuter, Tom

doi:10.1016/s0378-5955(99)00055-6

Cited by 50 publications

(62 citation statements)

References 18 publications

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“…It remains unknown if the sensation level is increased by a similar magnitude or if the increase is partly compensated for by an AGC on the receiving side as is the case for bats (Henson, 1965;Suga and Jen, 1975). The role of the cetacean middle ear in hearing is debated (Hemila et al, 1999;Ketten, 1997;Ridgway et al, 2001). The large mass of odontocete middle ear bones does not suggest rapid and strong middle ear reflexes (Au and Benoit-Bird, 2003), as seen in bats with AGC on the receiving side (Suga and Jen, 1975).…”

Section: Discussionmentioning

confidence: 99%

Biosonar performance of foraging beaked whales (Mesoplodon densirostris)

Madsen

Johnson

Soto

et al. 2005

Journal of Experimental Biology

270

259

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Toothed whales (Cetacea, odontoceti) emit sound pulses to probe their surroundings by active echolocation. Noninvasive, acoustic Dtags were placed on deep-diving Blainville's beaked whales (Mesoplodon densirostris) to record their ultrasonic clicks and the returning echoes from prey items, providing a unique view on how a whale operates its biosonar during foraging in the wild. The process of echolocation during prey capture in this species can be divided into search, approach and terminal phases, as in echolocating bats. The approach phase, defined by the onset of detectable echoes recorded on the tag for click sequences terminated by a buzz, has interclick intervals (ICI) of 300-400·ms. These ICIs are more than a magnitude longer than the decreasing two-way travel time to the targets, showing that ICIs are not given by the two-way-travel times plus a fixed, short lag time. During the approach phase, the received echo energy increases by 10.4(±2)·dB when the target range is halved, demonstrating that the whales do not employ rangecompensating gain control of the transmitter, as has been implicated for some bats and dolphins. The terminal/buzz phase with ICIs of around 10·ms is initiated when one or more targets are within approximately a body length of the whale (2-5·m), so that strong echo returns in the approach phase are traded for rapid updates in the terminal phase. It is suggested that stable ICIs in the search and approach phases facilitate auditory scene analysis in a complex multi-target environment, and that a concomitant low click rate allows the whales to maintain high sound pressure outputs for prey detection and discrimination with a pneumatically driven, bi-modal sound generator.

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Section: Discussionmentioning

confidence: 99%

Biosonar performance of foraging beaked whales (Mesoplodon densirostris)

Madsen

Johnson

Soto

et al. 2005

Journal of Experimental Biology

270

259

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“…Although it has long been known that sound transmission through the cetacean ear differs from that of land mammals (e.g., Norris, 1968;Fleischer, 1978), the function of the middle ear was poorly understood until a generalized model for the hearing mechanism of modern odontocetes (toothed whales, including dolphins and porpoises) was designed (Nummela et al, 1999a,b;Hemilä et al, 1999Hemilä et al, , 2001). This study uses that model to evaluate sound transmission pathways in the Eocene whale ear.…”

Section: Sound Transmission Mechanisms In Mammalsmentioning

confidence: 99%

“…2C). The vibrations of the tympanic plate are transmitted through the middle ear ossicles to the oval window (Hemilä et al, 1999;Nummela et al, 1999a), similarly to the land mammal ear. The anatomy of the tympanic bone is different from that of other mammals; the lateral wall is thin, as in mammals in general, but the medial wall is a thick bulky structure, called the involucrum (Inv).…”

Section: Modern Odontocete Ear and Hearingmentioning

confidence: 99%

“…Previous studies of this evolutionary pattern (Fleischer, 1978;Lancaster, 1990;Thewissen and Hussain, 1993) were hampered by the paucity of Eocene whale ear ossicles and the lack of an understanding of the function of the middle ear in modern whales. We here use the functional model of Hemilä et al (1999Hemilä et al ( , 2001, and Nummela et al (1999a,b), and expand on the analysis of Nummela et al (2004a) to build a comprehensive evolutionary model of evolving sound transmission mechanisms during the period when cetaceans became aquatic. Our study does not address the functional changes in the inner ear (but see Ketten, 1992Ketten, , 2000Parks et al, 2007, this issue), and leaves open the question of the origin of low-frequency hearing in mysticetes.…”

Section: Hearing Through Bone-conduction Mechanismmentioning

confidence: 99%

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Sound transmission in archaic and modern whales: Anatomical adaptations for underwater hearing

Nummela

Thewissen

Bajpai

et al. 2007

The Anatomical Record

Self Cite

104

111

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The whale ear, initially designed for hearing in air, became adapted for hearing underwater in less than ten million years of evolution. This study describes the evolution of underwater hearing in cetaceans, focusing on changes in sound transmission mechanisms. Measurements were made on 60 fossils of whole or partial skulls, isolated tympanics, middle ear ossicles, and mandibles from all six archaeocete families. Fossil data were compared with data on two families of modern mysticete whales and nine families of modern odontocete cetaceans, as well as five families of noncetacean mammals. Results show that the outer ear pinna and external auditory meatus were functionally replaced by the mandible and the mandibular fat pad, which posteriorly contacts the tympanic plate, the lateral wall of the bulla. Changes in the ear include thickening of the tympanic bulla medially, isolation of the tympanoperiotic complex by means of air sinuses, functional replacement of the tympanic membrane by a bony plate, and changes in ossicle shapes and orientation. Pakicetids, the earliest archaeocetes, had a land mammal ear for hearing in air, and used bone conduction underwater, aided by the heavy tympanic bulla. Remingtonocetids and protocetids were the first to display a genuine underwater ear where sound reached the inner ear through the mandibular fat pad, the tympanic plate, and the middle ear ossicles. Basilosaurids and dorudontids showed further aquatic adaptations of the ossicular chain and the acoustic isolation of the ear complex from the skull. The land mammal ear and the generalized modern whale ear are evolutionarily stable configurations, two ends of a process where the cetacean mandible might have been a keystone character.

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“…The T-P complex, which is suspended through ligaments outside the skull in a peribullar cavity, is surrounded by air filled sinuses, allowing the acoustic isolation from the skull (Reysenbach de Haan, 1957;Fleischer, 1976;Ketten and Wartzok, 1990;Nummela et al, 1999b). While some authors expressed doubts about the functionality of the middle ear (Fraser and Purves, 1954;Reysenbach de Haan, 1957;McCormick et al, 1970;Fleisher, 1978;Ridgway et al, 1997) others presented morphological evidences supporting the active role of the middle ear in sound transmission (Nummela et al, 1999a,b;Hemila et al, 1999Hemila et al, , 2001Ketten, 2000;Morell et al, 2007).…”

Section: Introductionmentioning

confidence: 99%

Decalcifying odontocete ears following a routine protocol with RDO®

Degollada

Alonso

Jauniaux

et al. 2009

Journal of Experimental Marine Biology and Ecology

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The study of the organ of Corti is essential to assess the impact of underwater noise on cetaceans. While classical histology techniques (including EDTA decalcification) have been previously considered, the process is time consuming. Independently from the histological technique, one of the challenging steps after extraction and fixation of the samples is to decalcify the bone envelope to access the cochlea without damaging the soft tissues. Here, we propose to use a fast commercial decalcifier (RDO®). 93 ears from 11 different odontocetes species stranded in the Mediterranean, Spanish North Atlantic and North Sea were used to precisely determine the decalcification time. Depending on the tympanic-periotic volume of the species, the decalcification time ranged from several hours to a few days, allowing a subsequently faster observation of the cochlear structures through routine microscope techniques.

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A model of the odontocete middle ear

Cited by 50 publications

References 18 publications

Biosonar performance of foraging beaked whales (Mesoplodon densirostris)

Biosonar performance of foraging beaked whales (Mesoplodon densirostris)

Sound transmission in archaic and modern whales: Anatomical adaptations for underwater hearing

Decalcifying odontocete ears following a routine protocol with RDO®

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