Comparative and functional morphology of the middle ear in Zambezian mole-rats (Coetomys – Cryptomys, Bathyergidae)

The present issue of the Belgian Journal of Zoology contains the proceedings of the 9th International African Small Mammal Symposium (ASMS), held at the Sokoine University of Agriculture, Morogoro, Tanzania from 14-18 July 2003Within the family Bathyergidae, the genus Coetomys (Cryptomys) is the most speciose. However, an unambiguous morphological or morphometrical species diagnosis has not been feasible to date. The middle ear structures involved in sound transmission were examined and measured in six species of Zambezian mole-rats of varying body sizes : Coetomys amatus, C. anselli, C. darlingi, C. kafuensis, C. mechowi and C. whytei. Compari- sons revealed many differences in the shape of the middle ear ossicles allowing species differentiation. Bullar vol- ume, eardrum area and cross-sectional area of the bony meatus were positively correlated with body size (as repre- sented by condylo-basal length) whereas the size of middle ear ossicles was rather independent of body size. Middle ears shared typical features with those found in low-frequency hearing mammals. Contrary to the findings in heter- omyids and the Spalax ehrenbergi species complex, within the genus Coetomys, those species occupying more mesic habitats had more efficient tympano-ossicular systems (suggesting more sensitive hearing) than species from drier habitats