Tympanoperiotic Complex Research Articles

The tympanoperiotic complex of the blue whale, Balaenoptera musculus.

The tympanoperiotic complex of a blue whale Balaenoptera musculus is described and compared to the homologous structures in the other extant and fossil baleen whale species. The periotic and the tympanic bulla represent informative anatomical regions in both functional and phylogenetic studies and for this reason a micro-CT scan of the bones was performed in order to better characterize their external aspect and to reconstruct the inner structures. In particular, the cochlea, the semicircular canals and associated portions of the periotic are reconstructed so that these structures may be used in phylogenetic analyses. We observed that the blue whale periotic is characterized by the presence of a strong dorsal protrusion which is posteriorly bordered by a previously undescribed morphological character that we name the posterotransverse fossa. The peculiar shape of the anterior process and the en echelon organization of the posterior foramina of the pars cochlearis are also described and compared. From a phylogenetic perspective, the blue whale is confirmed to be closely related to the fin whale, Balaenoptera physalus, but it is suggested, based on ear bone characters only, that it diverged before the other balaenopterid species in the phylogeny of Balaenopteridae. This placement supports a series of morphological observations suggesting that the extant blue whale was an early-diverging member of Balaenoptera. Our results help to decipher the evolutionary origin of the blue whale, the largest living animal, by allowing new and more detailed morphological analyses of the balaenopterid fossil record.

Resonance of the tympanoperiotic complex of fin whales with implications for their low frequency hearing.

The tympanoperiotic complex (TPC) bones of the fin whale skull were studied using experimental measurements and simulation modeling to provide insight into the low frequency hearing of these animals. The study focused on measuring the sounds emitted by the left and right TPC bones when the bones were tapped at designated locations. Radiated sound was recorded by eight microphones arranged around the tympanic bulla. A finite element model was also created to simulate the natural mode vibrations of the TPC and ossicular chain, using a 3D mesh generated from a CT scan. The simulations produced mode shapes and frequencies for various Young's modulus and density values. The recorded sound amplitudes were compared with the normal component of the simulated displacement and it was found that the modes identified in the experiment most closely resembled those found with Young's modulus for stiff and flexible bone set to 25 and 5 GPa, respectively. The first twelve modes of vibration of the TPC had resonance frequencies between 100Hz and 6kHz. Many vibrational modes focused energy at the sigmoidal process, and therefore the ossicular chain. The resonance frequencies of the left and right TPC were offset, suggesting a mechanism for the animals to have improved hearing at a range of frequencies as well as a mechanism for directionality in their perception of sounds.

Humpback Vocalizations

Humpback Vocalizations Rajiv Mohabir (bio) Rajiv Mohabir, poem, humpback, whales, Hal Whitehead, Luke Rendell, whale song In any birthing area, humpbacks sing the same, slowly evolving song. Learning strains from one another, they sing across the fathoms, their phrases and themes shifting in a pattern of small changes until they stitch new songs of older material. Songs at the end of the summer transform from the beginning of the season. Biologists Hal Whitehead and Luke Rendell write that, in Hawaiian waters, groups of the North Pacific variety alter their own songs in response to songs they have heard from other, very distant, humpbacks. This suggests music carries across thousands of miles. When apart the songs of different socializing groups evolve at similar rates. Or at some meeting place mid-migration do humpbacks gather? ________ Mysticetes do not have phonic lips or a museau de singe as with whales like odontocetes Larynges large as British call boxes emit frequencies Megaptera novaeangliae's U- folds between upper and lower respiratory systems vibrate [End Page 93] ________ To hear sound and song and noise alike, scientists must dig further into the biology of a humpback's curved bulla. They know it attaches to the cetacean's jaw. The bulla looks like a conch shell or a giant clam that's been warped into a cave. Or it looks like a sliced mushroom or the mouth of a cowrie shell, but delicate. For sound to be realized in the tympanic plate, fat and soft tissue must vibrate against the jaw. The cochlea joins to the periotic by a thin membranelike bone. This formation, the tympanoperiotic complex, processes soundthrough bone conduction. ________ No one knows the why or where of it, but most agree whale song is moving. Why else send recordings in the Voyager spacecraft on the Golden Record? Is it the slow erasure of a species that wails out? Humans look for meaning and aesthetics in what they cannot understand— Biologists Whitehead and Rendell wonder why whale song rhymes or is perceived as rhyming through pattern repetition. Is it lyrical? Is it cetacean rhetoric? How human language breaks apart at the point of conception. The echo is amniotic. We, once aquatic, heard as whales do. ________ Megaptera novaeangliae's tympanoperiotic complex is designed to hear songs across great distances at frequencies below what the human ear can discern. It is a delicate instrument of song and divination, an environment under threat of shipping lanes [End Page 94] and naval sonar pulses. Songs are made of notes, or base units that humpbacks emit at 30–4,000 hertz, which is in the range of human hearing. Acoustic trauma will rupture the process— whales no longer able to tell how deep they dive. The pressure crushes— ________ In representations of the structure of humpback vocalizations, bioacousticians chart the anatomy of the line. Repetition, irregularity, looseness, and deft shifts of breath and phrase magic the water column. aaa bcb cbc ded eff ded eff g The rhyme sense in a complete song leaves the listener in a sonically unfamiliar place. In fact, the g cascades, a grand departure—a kind of poetic anticlosure asking for riff and response. Perhaps this is an eight-stanza poem, mediated through human interpretation of what we can only imagine, not living in a three-dimensional water column. ________ O O O O O O O O O O O O O O O O ________ OAccording to cetacean biologists, a unit may be imagined tO be nOtes of humpback song.| | | O | O | O | A collection of units is called a phrase (Of up tO ten seconds). Modulated O frequency O| | O | | | | and amplitude, the nOtes are wrOught into phrases humpbacks repeat into a theme. Whales,| O O O | | | | | which scientists postulate sing for aesthetics' sake (hence poetry), add theme to theme, they| | | | | | weave songs that last for up to twenty to thirty minutes each. Some, they repeat for days. [End Page 95] ________ Whale song constantly evolves though the extinction event looms—That great god. Whales in the same regions sing similar, if not the same, songs during the same times, each whale shifting tune and phrasing to...

Developing echolocation: distinctive patterns in the ontogeny of the tympanoperiotic complex in baleen and toothed whales (Cetacea)

Developing echolocation: distinctive patterns in the ontogeny of the tympanoperiotic complex in baleen and toothed whales (Cetacea)

Developing echolocation: distinctive patterns in the ontogeny of the tympanoperiotic complex in baleen and toothed whales (Cetacea)

Abstract Cetaceans (baleen and toothed whales) present a unique set of adaptations for life in water. Among other abilities, the two living groups can hear and produce different sound frequencies: baleen whales use low frequencies primarily for communication, whereas toothed whales acquired the ability to echolocate using high-frequency sounds. Both groups exhibit modifications to the morphology of the ear bones (tympanic bulla and periotic) that closely track their behaviour and ecology. The evolution of sound reception in whales is being investigated thoroughly, whereas the changes in prenatal development (ontogeny) that generate these disparate ear bone morphologies remain mostly unknown. In this study, we characterize the ontogeny of the ear bones in Cetacea by looking at the progression of ossification and associated changes in morphology using a combination of traditional measurements and an innovative landmark-free method to quantify shape on a newly assembled three-dimensional dataset spanning the ontogeny and phylogeny of extant Cetacea. We have found that the two groups of Cetacea share some aspects of ear ontogeny, such as a common growth trajectory of the periotic. However, differences in ossification, allometry and growth trajectory, particularly in the periotic bone, reflect their divergent inner ear morphology and hearing abilities.

Numerical-modeling-based investigation of sound transmission and reception in the short-finned pilot whale (Globicephala macrorhynchus)

The sound-transmission, beam-formation, and sound-reception processes of a short-finned pilot whale (Globicephala macrorhynchus) were investigated using computed tomography (CT) scanning and numerical simulation. The results showed that sound propagations in the forehead were modulated by the upper jaw, air components, and soft tissues, which attributed to the beam formation in the external acoustic field. These structures owned different acoustic impedance and formed a multiphasic sound transmission system that can modulate sounds into a beam. The reception pathways composed of the solid mandible and acoustic fats in the lower head conducted sounds into the tympano-periotic complex. In the simulations, sounds were emitted in the forehead transmission system and propagated into water to interrogate a steel cylinder. The resulting echoes can be interpreted from multiple perspectives, including amplitude, waveform, and spectrum, to obtain the acoustic cues of the steel cylinder. By taking the short-finned pilot whale as an example, this study provides meaningful information to further deepen our understanding of biosonar system operations, and may expand sound-reception theory in odontocetes.

Topography of vibration frequency responses on the bony tympano-periotic complex of the pilot whale Globicephala macrorhynchus

In modern Cetacea, the ear bone complex comprises the tympanic and periotic bones forming the tympano-periotic complex (TPC), differing from temporal bone complexes of other mammals in form, construction, position, and possibly function. To elucidate its functioning in sound transmission, we studied the vibration response of 32 pairs of formaldehyde-glutaraldehyde-fixed TPCs of Globicephala macrorhynchus, the short-finned pilot whale (legally obtained in Taiji, Japan). A piezoelectric-crystal-based vibrator was surgically attached to a location on the cochlea near the exit of the acoustic nerve. The crystal delivered vibrational pulses through continuous sweeps from 5 to 50 kHz. The vibration response was measured as a function of frequency by Laser Doppler Vibrometry at five points on the TPC. The aim of the experiment was to clarify how the vibration amplitudes produced by different frequencies are distributed on the TPC. At the lowest frequencies (<12 kHz), no clear differential pattern emerged. At higher frequencies the anterolateral lip of the TP responded most sensitively with the highest displacement amplitudes, and response amplitudes decreased in orderly fashion towards the posterior part of the TPC. We propose that this works as a lever: high-frequency sounds are most sensitively received and cause the largest vibration amplitudes at the anterior part of the TP, driving movements with lower amplitude but greater force near the posteriorly located contact to the ossicular chain, which transmits the movements into the inner ear. Although force (pressure) amplification is not needed for impedance matching in water, it may be useful for driving the stiffly connected ossicles at the high frequencies used in echolocation.

Morphological and Pathological Findings in the Middle and Inner Ears of Harbour Porpoises (Phocoena phocoena)

Hearing represents the major sense in harbour porpoises (Phocoena phocoena) and impairment of hearing has a great impact on the survival of these animals. In this communication, some anatomical and histological aspects of the tympanoperiotic complex of harbour porpoises are presented. In addition, the ears of 21 incidentally bycaught or stranded freshly dead harbour porpoises of different age groups and sex were investigated histologically. At the entrance to the middle ear cavity, mucosa-associated lymphoid tissue was present that was often hyperplastic in juvenile (9/10) and adult individuals (7/8). Solitary lymphoid follicles were additionally found in the corpus cavernosum and adjacent to the stapedius muscle in single porpoises. The nematode Stenurus minor represented the most common pathogen observed in the middle ear cavity of juvenile and adult harbour porpoises and the parasite was associated with chronic inflammation with metaplastic and hyperplastic epithelial changes. An unusual bone formation at the attachment of the corpus cavernosum to the perioticum was a common finding, even in young individuals. Whether this represents a normal structure or a metaplastic change remains undetermined. Acute haemorrhages in the cochlea and/or the tympanic cavity occurred in all animals and were most likely agonal changes. Single porpoises suffered from purulent otitis media, mycotic otitis media with osteolysis or chronically fractured tympanic bones, likely causing impairment of hearing that may have contributed to by-catch. There was no evidence that stranding in five porpoises was associated with the aural changes. Histological examination of the ears in harbour porpoises is a valuable part of the assessment of their health status. Damage to hearing structures may explain starvation due to impaired ability to catch prey or unusual behaviour such as stranding or entanglement in nets.

Accuracy, precision, and error in age estimation of Florida manatees using growth layer groups in earbones.

Ages of Florida manatees (Trichechus manatus latirostris) can be estimated by counting annual growth layer groups (GLGs) in the periotic dome portion of the tympanoperiotic complex of their earbones. The Florida Fish and Wildlife Conservation Commission manages an archive of more than 8,700 Florida manatee earbones collected from salvaged carcasses from 1989 to 2017. Our goal was to comprehensively evaluate techniques used to estimate age, given this large sample size and changes to processing protocols and earbone readers over time. We developed new standards for estimating ages from earbones, involving two independent readers to obtain measurements of within- and between-reader precision. To quantify accuracy, precision, and error, 111 earbones from manatees with approximately known ages (first known as calves: “KAC”) and 69 earbones from manatees with minimum known ages (“MKA,” based on photo-identification sighting histories) were processed, and their ages were estimated. There was greater precision within readers (coefficient of variation, CV: 2.4–8.5%) than between readers (CV: 13.1–13.3%). The median of age estimates fell within the true age range for 63.1% of KAC cases and was at least the sighting duration for 75.0% of MKA cases. Age estimates were generally unbiased, as indicated by an average raw error ± SD of −0.05 ± 3.05 years for the KAC group. The absolute error (i.e., absolute value of raw error) of the KAC data set averaged 1.75 ± 2.50 years. Accuracy decreased and error increased with increasing known age, especially for animals over 15 years old, whose ages were mostly underestimated due to increasing levels of resorption (the process of bone turnover that obscures GLGs). Understanding the degree of uncertainty in age estimates will help us assess the utility of age data in manatee population models. We emphasize the importance of standardizing and routinely reviewing age estimation and processing protocols to ensure that age data remain consistent and reliable.

Directional Hearing and Head-Related Transfer Function in Odontocete Cetaceans.

The head-related transfer function (HRTF) is an important descriptor of spatial sound field reception by the listener. In this study, we computed the HRTF of the common dolphin Delphinus delphis. The received sound pressure level at various locations within the acoustic fats of the internal pinna near the surface of the tympanoperiotic complex (TPC) was calculated for planar incident waves directed toward the animal. The relative amplitude of the received pressure versus the incident pressure was the representation of the HRTF from the point of view of the animal. It is of interest that (1) different locations on the surface of the TPC resulted in different HRTFs, (2) the HRTFs for the left and right ears were slightly asymmetric, and (3) the locations of the peaks of the HRTF depended on the frequency of the incident wave.

Auditory anatomy of beaked whales and other odontocetes: Potential for cochlear stimulationviaa “vibroacoustic duct mechanism”

AbstractComputed tomography (CT) and microcomputed tomography (microCT) were used to examine the structures involved in cochlear stimulation in odontocetes and terrestrial mammals. Cranial CT examined the osseous attachment of the skull to the tympanoperiotic complex (TPC) and the path of the endocranial foramen of the vestibulocochlear nerve (EFVN), which was assumed to contain the perilymphatic duct. Additional CTs of TPC were taken postextraction to examine the gross morphology of this structure. MicroCT was used to examine the acoustic windows of the cochlea, including the round and oval windows and the apertures of the cochlear and vestibular aqueducts. Cranial CT scans demonstrated an osseous connection between the skull and TPC in beaked whales andPhyseter macrocephalus. EFVN traveled through a greater length of cranial bone and communicated more closely with the periotic bone in beaked whales than in other species.Ziphius cavirostriswas observed to have a reduced medial sulcus of the mallear ridge (MSMR) and tympanic plate and an enlarged aperture of the cochlear aqueduct, respectively. The potential significance of these findings, including the role of the perilymphatic duct as a novel route of cochlear stimulation referred to as the “vibroacoustic duct mechanism,” are discussed.

Postnatal development of franciscana's (Pontoporia blainvillei) biosonar relevant structures with potential implications for function, life history, and bycatch

AbstractFranciscana dolphins (Pontoporia blainvillei) are the most endangered species of the western South Atlantic Ocean. The major cause of their vulnerability is incidental bycatch in fishery gill nets. Ontogenetic changes of biosonar relevant structures in Pontoporia were analyzed in five specimens (one female neonate, two male neonates and two male adults) using digital imaging technology (MRI, CT) and macroscopic dissections to compare structures involved in sound production and reception. These data were compared to an ontogenetic series of 69 macerated skulls of Pontoporia in order to elucidate the correlation between soft tissue structures and bones of the epicranial complex and to describe the development‐related changes in the mandible. Postnatal developmental shape changes of the posterior part of the right vestibular air sac followed bone formation and the melon with its right branch elongated, paralleling the flatter facial depression of adults. Minor postnatal developmental modifications were verified in the tympano‐periotic complex but a shape change of the mandible was visible by a ventral deviation of the posterior part of the mandible in adults. These results reveal postnatal changes in allometry and shape of biosonar relevant structures that may be one of the causes that increase bycatch of neonate and young Pontoporia individuals.

Precocious Ossification of the Tympanoperiotic Bone in Fetal and Newborn Dolphins: An Evolutionary Adaptation to the Aquatic Environment?

The present study, performed with a dual-energy X-ray (DXA) bone densitometer on a series of fetal and newborn striped and short-beaked common dolphins, shows that the bone density of the area of the tympanic bulla within the tympanoperiotic complex starts with 0.483 g cm(-2) in 5- to 6-month-old specimens of striped (or common) dolphin fetuses and reaches 1.841 g cm(-2) in newborn striped dolphins, with values consistently higher than in other parts of the skull or elsewhere in the skeleton. The same results apply to the common bottlenose dolphins, in which the area of the tympanic bulla has a density of 0.312 g cm(-2) in 5-month-old specimens and becomes four times as much in newborns. Regardless of the areal bone density results correlated to the DXA-technique, comparisons with DXA-bone density data in the literature referred to other mammals emphasize the presence of very high mineral deposition in the area of the tympanoperiotic bone in fetal and newborn dolphins and the most dense part of it belongs to the tympanic bulla. The early osseous maturation of the tympanic bulla area may be compared to what described in fin whales and may represent an unique ontogenetic and phylogenetic feature of cetaceans, possibly related to the development of essential acoustic sense and establishment of immediate post-natal mother-calf relationship.

Precocial development within the tympanoperiotic complex in cetaceans

Marine Mammal ScienceVolume 31, Issue 1 p. 369-375 Notes Precocial development within the tympanoperiotic complex in cetaceans Winston C. Lancaster, Corresponding Author Winston C. Lancaster Department of Biological Sciences, California State University, Sacramento, California 95819-6077, U.S.ACorresponding author ([email protected]).Search for more papers by this authorWilliam J. Ary, William J. Ary Department of Biology, 5500 Campanile Drive, San Diego State University, San Diego, California 92182-4614, U.S.ASearch for more papers by this authorPetr Krysl, Petr Krysl Jacobs School of Engineering, University of California at San Diego, 9500 Gilman Drive, La Jolla, California 92093-0085, U.S.ASearch for more papers by this authorTed W. Cranford, Ted W. Cranford Department of Biology, 5500 Campanile Drive, San Diego State University, San Diego, California 92182-4614, U.S.ASearch for more papers by this author Winston C. Lancaster, Corresponding Author Winston C. Lancaster Department of Biological Sciences, California State University, Sacramento, California 95819-6077, U.S.ACorresponding author ([email protected]).Search for more papers by this authorWilliam J. Ary, William J. Ary Department of Biology, 5500 Campanile Drive, San Diego State University, San Diego, California 92182-4614, U.S.ASearch for more papers by this authorPetr Krysl, Petr Krysl Jacobs School of Engineering, University of California at San Diego, 9500 Gilman Drive, La Jolla, California 92093-0085, U.S.ASearch for more papers by this authorTed W. Cranford, Ted W. Cranford Department of Biology, 5500 Campanile Drive, San Diego State University, San Diego, California 92182-4614, U.S.ASearch for more papers by this author First published: 26 June 2014 https://doi.org/10.1111/mms.12145Citations: 14Read the full textAboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Citing Literature Volume31, Issue1January 2015Pages 369-375 RelatedInformation

The auditory anatomy of the minke whale (Balaenoptera acutorostrata): a potential fatty sound reception pathway in a baleen whale.

Cetaceans possess highly derived auditory systems adapted for underwater hearing. Odontoceti (toothed whales) are thought to receive sound through specialized fat bodies that contact the tympanoperiotic complex, the bones housing the middle and inner ears. However, sound reception pathways remain unknown in Mysticeti (baleen whales), which have very different cranial anatomies compared to odontocetes. Here, we report a potential fatty sound reception pathway in the minke whale (Balaenoptera acutorostrata), a mysticete of the balaenopterid family. The cephalic anatomy of seven minke whales was investigated using computerized tomography and magnetic resonance imaging, verified through dissections. Findings include a large, well-formed fat body lateral, dorsal, and posterior to the mandibular ramus and lateral to the tympanoperiotic complex. This fat body inserts into the tympanoperiotic complex at the lateral aperture between the tympanic and periotic bones and is in contact with the ossicles. There is also a second, smaller body of fat found within the tympanic bone, which contacts the ossicles as well. This is the first analysis of these fatty tissues' association with the auditory structures in a mysticete, providing anatomical evidence that fatty sound reception pathways may not be a unique feature of odontocete cetaceans. Anat Rec, 2012. © 2012 Wiley Periodicals, Inc.

Live CT imaging of sound reception anatomy and hearing measurements in the pygmy killer whale, Feresa attenuata

In June 2008, two pygmy killer whales (Feresa attenuata) were stranded alive near Boca Grande, FL, USA, and were taken into rehabilitation. We used this opportunity to learn about the peripheral anatomy of the auditory system and hearing sensitivity of these rare toothed whales. Three-dimensional (3-D) reconstructions of head structures from X-ray computed tomography (CT) images revealed mandibles that were hollow, lacked a bony lamina medial to the pan bone and contained mandibular fat bodies that extended caudally and abutted the tympanoperiotic complex. Using auditory evoked potential (AEP) procedures, the modulation rate transfer function was determined. Maximum evoked potential responses occurred at modulation frequencies of 500 and 1000 Hz. The AEP-derived audiograms were U-shaped. The lowest hearing thresholds occurred between 20 and 60 kHz, with the best hearing sensitivity at 40 kHz. The auditory brainstem response (ABR) was composed of seven waves and resembled the ABR of the bottlenose and common dolphins. By changing electrode locations, creating 3-D reconstructions of the brain from CT images and measuring the amplitude of the ABR waves, we provided evidence that the neuroanatomical sources of ABR waves I, IV and VI were the auditory nerve, inferior colliculus and the medial geniculate body, respectively. The combination of AEP testing and CT imaging provided a new synthesis of methods for studying the auditory system of cetaceans.

A New Acoustic Portal into the Odontocete Ear and Vibrational Analysis of the Tympanoperiotic Complex

Global concern over the possible deleterious effects of noise on marine organisms was catalyzed when toothed whales stranded and died in the presence of high intensity sound. The lack of knowledge about mechanisms of hearing in toothed whales prompted our group to study the anatomy and build a finite element model to simulate sound reception in odontocetes. The primary auditory pathway in toothed whales is an evolutionary novelty, compensating for the impedance mismatch experienced by whale ancestors as they moved from hearing in air to hearing in water. The mechanism by which high-frequency vibrations pass from the low density fats of the lower jaw into the dense bones of the auditory apparatus is a key to understanding odontocete hearing. Here we identify a new acoustic portal into the ear complex, the tympanoperiotic complex (TPC) and a plausible mechanism by which sound is transduced into the bony components. We reveal the intact anatomic geometry using CT scanning, and test functional preconceptions using finite element modeling and vibrational analysis. We show that the mandibular fat bodies bifurcate posteriorly, attaching to the TPC in two distinct locations. The smaller branch is an inconspicuous, previously undescribed channel, a cone-shaped fat body that fits into a thin-walled bony funnel just anterior to the sigmoid process of the TPC. The TPC also contains regions of thin translucent bone that define zones of differential flexibility, enabling the TPC to bend in response to sound pressure, thus providing a mechanism for vibrations to pass through the ossicular chain. The techniques used to discover the new acoustic portal in toothed whales, provide a means to decipher auditory filtering, beam formation, impedance matching, and transduction. These tools can also be used to address concerns about the potential deleterious effects of high-intensity sound in a broad spectrum of marine organisms, from whales to fish.

Vibration characteristics of the tympanoperiotic complex in the bottlenose dolphin, Tursiops truncatus.

Modal finite + boundary element analysis of a bottlenose dolphin’s bony tympanoperiotic complex, including the ossicles, was performed to determine the mode shapes and natural frequencies. The goal was to gain insight into the transmission of sound pressure waves arriving through the soft tissues and transmitted across the bony components into the oval window of the inner ear. The finite element model of the bones was derived from CT scans with a 360 μm voxel resolution. In the first approximation the soft tissue was considered to be acoustically equivalent to an incompressible inviscid liquid, taken as infinite in extent. The added mass terms were computed with a boundary element model. The computed frequencies cover the range up to 160 kHz. The capacity of the natural vibration modes to excite motion of the stapes footplate was assessed by measuring the relative motion of the incudostapedial joint normalized by the normal displacement of the wet‐surface of the ear bones. In addition to a quantitative assessment a number of qualitative observations may be made that could explain the function of the dolphin’s ear complex. For example, the vibrational patterns are nontrivial and frequency dependent. [Work supported by the U.S. Navy CNO45.]

“Rivers” of sound in Cuvier’s beaked whale (Ziphius cavirostris): Implications for the evolution of sound reception in odontocetes.

Industrial CT scanning technology was used to collect the first x‐ray tomograms from the head of an adult male Cuvier’s beaked whale. These scans and tissue property measurements were used to construct a finite element model. Simulations revealed pathways for sound propagation into and out of the head. One intriguing result concerns a newly described gular pathway by which sound reaches the hearing apparatus. Propagated sound waves enter the ventral aspect of the head and form an acoustic “river” that flows toward the bony ear complexes through the internal mandibular fat bodies. The precise pathway and dimensions of the sound river vary with frequency, but it converges on the bony tympanoperiotic complex. A combination of tissue structures and air spaces act like an internal acoustic pinna that filters and concentrates the incoming sound. The river of sound apparently functions in concert with the absence of the medial bony lamina of the posterior portion of the mandible, a condition that exists in all toothed whales and their ancestral archaeocetes. The gular pathway and river of sound suggests that this is the primordial pathway for underwater hearing in whales and that Norris’ jaw hearing mechanism was a more recent development.

Building on the shoulders of a giant: Using technology to extend biosonar research pathways first blazed by Sam H. Ridgway.

Underwater biosonar research began in the middle of the last century by a handful of pioneers. Among the debates that raged in the scientific literature for the first 30 years were (1) the origin of biosonar signals and their formation into a transmitted beam and (2) the pathways and mechanisms for sound reception. Ridgway and his colleagues (1980) provided definitive proof for the nasal origin of sonar signals using electromyography and small pressure catheters inserted into various airways. Ridgway also collaborated on a series of experiments that attempted to discern the structure and function of the tympanoperiotic complex. My colleagues and I have combined remote imaging technology, high-speed video endoscopy, and finite element analysis to pinpoint the site of sonar signal generation, posit novel sound propagation pathways into and out of the heads of various odontocetes, and uncover new elements of the structure and function of the tympanoperiotic complex. These results will be presented in light of Ridgway’s pioneering work.