Evolutionary trends in land vertebrate hearing organs

The last several decades of research have seen a burgeoning of data on the morphology, physiology, and evolutionary history of vertebrate auditory organs. This chapter briefly describes the status of our understanding of ear structure and function and their origins in fish, which hear using their vestibular epithelia, and land vertebrates that early evolved dedicated hearing structures. The various major lineages of land vertebrates-amphibians, lepidosaurs, archosaurs, and mammals-each have unique hearing organs. From humble beginnings as a small epithelium in their common ancestor, each lineage evolved specialized hair-cell populations and divisions of labor that led to highly sensitive and frequency-selective hearing. This chapter covers the origins, morphology, and physiological characteristics of the ears of all major groups.