Sound localization in the alligator

• Physiological and behavioral data support sound localization in crocodilians.
• Directional hearing is affected by skull pneumaticity and coupled eardrums.
• Evolutionary changes in middle-ear pneumaticity affect localization cues.
• Changes in auditory periphery may be reflected in neuroanatomical circuitry.

In early tetrapods, it is assumed that the tympana were acoustically coupled through the pharynx and therefore inherently directional, acting as pressure difference receivers. The later closure of the middle ear cavity in turtles, archosaurs, and mammals is a derived condition, and would have changed the ear by decoupling the tympana. Isolation of the middle ears would then have led to selection for structural and neural strategies to compute sound source localization in both archosaurs and mammalian ancestors. In the archosaurs (birds and crocodilians) the presence of air spaces in the skull provided connections between the ears that have been exploited to improve directional hearing, while neural circuits mediating sound localization are well developed. In this review, we will focus primarily on directional hearing in crocodilians, where vocalization and sound localization are thought to be ecologically important, and indicate important issues still awaiting resolution.This article is part of a Special Issue entitled < Annual Reviews 2015 >.