Unlike earlier workers who tended to take an anthropocentric view of the evolution of the vertebrate auditory system, and emphasized specializations found in amniotes, and especially mammals, we tend to take an `ichthyocentric' approach to these issues and argue that
all vertebrates probably have very similar basic functional requirements for their auditory systems. As a consequence, all vertebrates investigated have evolved similar functional approaches to sound detection and analysis. Moreover, in a number of cases the structural
basis for detection and analysis, such as the heterogeneous sensory hair cell, serves as the mechanism for detection and initial analysis throughout the vertebrates. Moreover, we would argue that specializations found in certain vertebrates, such as the outer hair cell motor of mammals, and the ability to use the auditory system for echolocation, the detection of very high frequencies, and other properties are only modi¢cations on the basic themes that are as old as the vertebrates. Indeed, this has become particularly apparent with the discovery that some fishes, as many bats and toothed whales, are able to detect ultrasound to over 150 kHz