Ultrasonic hearing and echolocation in the earliest toothed whales

Park, Travis; Fitzgerald, Erich M. G.; Evans, Alistair R.

doi:10.1098/rsbl.2016.0060

Cited by 63 publications

(98 citation statements)

References 15 publications

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“…A slight tympanal recess is observed near the end of the first half turn of the basal turn of the cochlea of the Oligocene odontocete (ChM PV2776), but no other odontocete examined here possesses such a structure (Fig. ) nor has an expanded tympanal recess been identified in other early diverging Oligocene odontocetes (Park et al, ).…”

Section: Resultsmentioning

confidence: 68%

Morphological variation among the inner ears of extinct and extant baleen whales (Cetacea: Mysticeti)

Ekdale

2016

Journal of Morphology

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Living mysticetes (baleen whales) and odontocetes (toothed whales) differ significantly in auditory function in that toothed whales are sensitive to high-frequency and ultrasonic sound vibrations and mysticetes to low-frequency and infrasonic noises. Our knowledge of the evolution and phylogeny of cetaceans, and mysticetes in particular, is at a point at which we can explore morphological and physiological changes within the baleen whale inner ear. Traditional comparative anatomy and landmark-based 3D-geometric morphometric analyses were performed to investigate the anatomical diversity of the inner ears of extinct and extant mysticetes in comparison with other cetaceans. Principal component analyses (PCAs) show that the cochlear morphospace of odontocetes is tangential to that of mysticetes, but odontocetes are completely separated from mysticetes when semicircular canal landmarks are combined with the cochlear data. The cochlea of the archaeocete Zygorhiza kochii and early diverging extinct mysticetes plot within the morphospace of crown mysticetes, suggesting that mysticetes possess ancestral cochlear morphology and physiology. The PCA results indicate variation among mysticete species, although no major patterns are recovered to suggest separate hearing or locomotor regimes. Phylogenetic signal was detected for several clades, including crown Cetacea and crown Mysticeti, with the most clades expressing phylogenetic signal in the semicircular canal dataset. Brownian motion could not be excluded as an explanation for the signal, except for analyses combining cochlea and semicircular canal datasets for Balaenopteridae. J. Morphol. 277:1599-1615, 2016. © 2016 Wiley Periodicals, Inc.

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Section: Resultsmentioning

confidence: 68%

Morphological variation among the inner ears of extinct and extant baleen whales (Cetacea: Mysticeti)

Ekdale

2016

Journal of Morphology

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“…A simulated mysticete audiogram was generated by Cranford & Krysl [26] which estimated that the lowest frequency detected for a juvenile fin whale was 10 Hz, slightly lower but still consistent with the estimated low-frequency limits of the extant mysticetes examined in this study. The estimated maximum frequencies for the mammalodontids and Zygorhiza are also within the limits of modern mysticetes, but are notably much lower than odontocetes, including the xenorophid inner ear described by Park et al [6], which we calculate here to have an estimated maximum frequency limit similar to some modern species (approx. 86 kHz), but not as high as more specialized taxa (electronic supplementary material, figure S5 and table S5).…”

Section: (B) Hearing Across the Archaeocete -Mysticete Transitionmentioning

confidence: 66%

“…Arguments for possessing both high-frequency [5,9 -11] and low-frequency [3,6,25] [5]), which strongly correlate to low-frequency hearing [18], are also highly congruent in archaeocetes and mysticetes (table 1). Lowfrequency limit estimates for archaeocetes and toothed mysticetes calculated using the equation of Manoussaki et al [18] were also all very low frequencies (less than 54 Hz), contrasting to a considerably higher low-frequency limit of 378.31 Hz for the odontocete Steno (table 1).…”

Section: (B) Hearing Across the Archaeocete -Mysticete Transitionmentioning

confidence: 97%

“…Additionally, preliminary results of a quantitative shape analysis of cetacean cochleae by Ekdale [4] indicate that Zygorhiza and an indeterminate species of toothed mysticete (ChM PV5720) plot within the cochlear morphospace of mysticetes. A final point to note is that virtually all studies to date [3][4][5][6]9,[18][19][20][21][22] on the diversity/evolution of cetacean inner ear anatomy have sampled different taxa/specimens for scanning/analyses under differing protocols. This has resulted in datasets that may not overlap taxonomically or analytically, which hampers comparison of results across multiple studies.…”

Section: (B) Hearing Across the Archaeocete -Mysticete Transitionmentioning

confidence: 99%

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Low-frequency hearing preceded the evolution of giant body size and filter feeding in baleen whales

et al. 2017

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Living baleen whales (mysticetes) produce and hear the lowest-frequency (infrasonic) sounds among mammals. There is currently debate over whether the ancestor of crown cetaceans (Neoceti) was able to detect low frequencies. However, the lack of information on the most archaic fossil mysticetes has prevented us from determining the earliest evolution of their extreme acoustic biology. Here, we report the first anatomical analyses and frequency range estimation of the inner ear in Oligocene (34 -23 Ma) fossils of archaic toothed mysticetes from Australia and the USA. The cochlear anatomy of these small fossil mysticetes resembles basilosaurid archaeocetes, but is also similar to that of today's baleen whales, indicating that even the earliest mysticetes detected low-frequency sounds, and lacked ultrasonic hearing and echolocation. This suggests that, in contrast to recent research, the plesiomorphic hearing condition for Neoceti was low frequency, which was retained by toothed mysticetes, and the highfrequency hearing of odontocetes is derived. Therefore, the low-frequency hearing of baleen whales has remained relatively unchanged over the last approximately 34 Myr, being present before the evolution of other signature mysticete traits, including filter feeding, baleen and giant body size.

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“…Recent evidence suggests that the ability to echolocate and for high-frequency hearing arose ∼28 million years ago on the odontocete stem lineage, shortly after the divergence from the mysticetes (Geisler et al, 2014;Park et al, 2016). Because all toothed whales examined possess some wax esters, and some type of shorter-chain (<16 carbons) or BCFA in the acoustic fat bodies, I propose that the synthesis of these unusual lipids originated in the cranial adipose tissues, as an adaptation to enhance echolocation and hearing.…”

Section: Evolution Of the Systemmentioning

confidence: 99%

Function and evolution of specialized endogenous lipids in toothed whales

Koopman

2018

Journal of Experimental Biology

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The Odontocetes (toothed whales) possess two types of specialized fat and, therefore, represent an interesting group when considering the evolution and function of adipose tissue. All whales have a layer of superficial blubber, which insulates and streamlines, provides buoyancy and acts as an energy reserve. Some toothed whales deposit large amounts of wax esters, rather than triacylglycerols, in blubber, which is unusual. Waxes have very different physical and physiological properties, which may impact blubber function. The cranial acoustic fat depots serve to focus sound during echolocation and hearing. The acoustic fats have unique morphologies; however, they are even more specialized biochemically because they are composed of a mix of endogenous waxes and triacylglycerols with unusual branched elements (derived from amino acids) that are not present in other mammals. Both waxes and branched elements alter how sound travels through a fat body; they are arranged in a 3D topographical pattern to focus sound. Furthermore, the specific branched-chain acid/alcohol synthesis mechanisms and products vary phylogenetically (e.g. dolphins synthesize lipids from leucine whereas beaked whales use valine). I propose that these specialized lipids evolved first in the head: wax synthesis first emerged to serve an acoustic function in toothed whales, with branched-chain synthesis adding additional acoustic focusing power, and some species secondarily retained wax synthesis pathways for blubber. Further research is necessary to elucidate specific molecular mechanisms controlling the synthesis and deposition of wax esters and branched-chain fatty acids, as well as their spatial deposition within tissues and within adipocytes.

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Ultrasonic hearing and echolocation in the earliest toothed whales

Cited by 63 publications

References 15 publications

Morphological variation among the inner ears of extinct and extant baleen whales (Cetacea: Mysticeti)

Morphological variation among the inner ears of extinct and extant baleen whales (Cetacea: Mysticeti)

Low-frequency hearing preceded the evolution of giant body size and filter feeding in baleen whales

Function and evolution of specialized endogenous lipids in toothed whales

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