The Foundations of High-Frequency Hearing in Early Mammals

It has become common in the paleontological literature to assume that the presence of secondary bony laminae in the cochleae of early mammals indicates that these species were able to perceive high sound frequencies (> 20 kHz). This review examines the validity of this idea in the context of comparative physiological data from extant amniotes and surveys a number of unique features of mammalian cochleae that correlate with high-frequency hearing. As it is difficult to imagine how all of these features could have arisen simultaneously, high-frequency hearing probably had a more gradual origin. This suggests that the presence or absence of secondary laminae should be interpreted with greater caution.