Evolution of the Sense of Hearing in Vertebrates

This paper briefly recapitulates work on the preterrestrialphase of the evolution of hearing which was published in detailelsewhere. Following this, the problem of the origin of theterrestrial middle ear is examined in some detail, and it isdemonstrated that Eusthenopteron, and probably other rhipidistiansas well, possessed an eardrum. This drum was formed by the fusionof the distal surface of a spiracular diverticulum and a ligamentbetween parietal shield and squamosal. It is further demonstratedthat the geometry of this eardrum in relation to the middle-earcavity was adequate to allow the fish to make the transitionfrom aquatic hearing to terrestrial hearing without loss ofsensitivity.