Comparative cochlear morphology in echolocating cetaceans

Abstract

The anatomy of the cochlea of six species of odontocetes, or toothed whales (Physeter catadon, Grampus griseus, Lagenorhynchus albirostris, Phocoena phocoena, Tursiops truncatus, and Stenella longirostris) was compared using conventional micrography and radiographic techniques including edge enhancement x-ray, CT scan, magnification radiography, and digital subtraction. These species were selected for differences in frequency and patterning of normal and ultrasonic vocalizations in their natural environments. The cochlea were extracted post-mortem and preserved by injection. Whole cochlea were first examined radiographically for species-specific differences in gross morphology and topology, particularly for angular change of the scalae and torsion of membranal and neural components. Specimens were then decalcified and processed for SEM or thin section microscopy. Measurements obtained by both methods are presented and the advantages of the radiographic techniques discussed. The results are compared with the cetacean cochlear models of Wever [Wever et al., Proc. Natl. Acad. Sci. 68, 2381–2385 (1971)] and Fleischer [G. Fleischer, J, Paleon. 50 (1), 133–152 (1976)] and analyzed according to the dimension-frequency correlation techniques of Greenwood [D. D. Greenwood, J. Acoust. Soc. Am. 33, 1344–1356 (1961)] and Hinchcliffe and Pye [R. Hinchcliffe and A. Pye, Int. Audiol. 7, 259–288 (1968)]. [Work supported by NSF.]