Functional Morphology of the Ear of the Lesser Bamboo Rat (Cannomys badius)

Abstract

Abstract. The outer, middle, and inner ears were studied in the lesser bamboo rat (Cannomys badius), a subterranean rodent in Indochina. Stereoscopic dissection and micro-computed tomography were used. The middle ear of the bamboo rat was characterized by a round eardrum without pars flaccida, “freely mobile” ossicles with a reduced transversal lamina and no orbicular apophysis, an enlarged stapedial footplate, absence of the stapedial artery, no unusual inflated bulla and retention of middle-ear muscles. The inner ear exhibited an elongated and highly coiled cochlea. Some features are associated with improved low-frequency hearing but decreased hearing sensitivity, as seen in other subterranean species. Hearing frequency limits calculated based on the middle ear dimensions were 0.5–40 kHz with best sensitivity at 6–8 kHz. It seems that the ear morphology and hearing ability of the lesser bamboo rat are typically adapted for underground habitat, even though some structures deviate from the pattern of subt...