Critical Cranial and Cochlear Structures in Echolocators

TitleCritical Cranial and Cochlear Structures in Echolocators
Publication TypeConference Proceedings
Year of Publication2012
AuthorsKetten, D. R., J. Simmons, H. Riquimaroux, S. R. Cramer, and J. J. Arruda
Conference Name11th European Conference on Underwater Acoustics 2012
Series TitleProceedings of the Institute of Acoustics
EditionPt. 3
Date Published07/2013
PublisherInstitute of Acoustics
ISBN Number978-1-62276-192-0
Keywordsbat inner ear, cochlea, dolphin inner ear, ear topography, echolocation, echolocators, inner ear morphometrics, middle ear, pinna, underwater acoustics

Although microchiropteran bats (largely insectivorous predators) and odontocete cetaceans (toothed whales which prey on fish and invertebrates) have different target species and operate in radically different media, both have sophisticated sonar capabilities and evident similarities in their ability to produce, detect and analyze ultrasonic signals. We expect because of the similarity of tasks and information that odontocetes and microchiropteran bats obtain acoustically from their environments that there are some commonalities in their fundamental biosonar reception and processing mechanisms but also differences related to potentially alternative echolocation strategies and especially to media dependent elements of their auditory system structure and analyses and related behaviours. These include features particularly related to wavelength and speed of sound in each medium with habitat and prey parameters that evolutionarily shaped hearing abilities. These are manifested in differences in the structure and peak spectra of echolocation signals and their representation and in the features that have been shown to be critical for analysis at the peripheral and central levels. In addition, there are niche and task dependent signal elements, such as detection in clutter in bats (1) and the structural variations between Type I and Type II ears associated with upper and lower ultrasonic signal dependence (2,3) that impose critical differences for the extraction of features in air vs water. The objective of the present study was to understand the similarities and differences of dolphin and bat inner ear topography and morphometrics related to these issues. This paper compares similarities and differences of pinnal, middle ear, and cochlear architecture and the implications for ultrasonic encoding and acuity amongst these groups.