Dr. Matthew Mason: Further Information...
University Physiologist Tel: +44 (0)1223 333829, Fax: +44 (0)1223 333840, E-mail: mjm68@cam.ac.uk
Mason, M.J. (2001) Middle ear structures in fossorial mammals: a comparison with non-fossorial species. Journal of Zoology 255: 467-486.
Dating back to the time of Cuvier, there have been many reports that fossorial (burrowing) mammals such as moles have enlarged middle ear structures, the better for low-frequency hearing. However, the great majority of these reports have been little more than anecdotal. This paper collects together a large amount of data relating to middle ear structures, both from the literature and from the author's own observations, and attempts to perform a rigorous analysis of the sizes of these structures in subterranean mammals (concentrating on talpid moles, golden moles and mole-rats), as compared to non-fossorial species. Body size is taken into account, since the ear scales non-isometrically among mammals. It is concluded that ear structures among fossorial species in general are not, in fact, unusual in size, but there are some exceptions. The stapes footplate area is typically enlarged in fossorial mammals, which (according to very simple models of middle ear function!) is expected to reduce the "area ratio" and reduce the efficiency of sound transmission: any benefit deriving from this is unknown. Low anatomical lever ratios and the loss of middle ear muscles are also commonly observed in subterranean species. Some genera of golden moles (Chrysospalax, Eremitalpa, Chrysochloris) have enormously hypertrophied ear ossicles: the largest, relative to body size, of any mammal, and it is suggested that these might be used to subserve a form of seismic sensitivity (see Mason, 2003b, and other papers on my publication list). By contrast, the marsupial mole Notoryctes has the smallest ear ossicles relative to body size of any mammal examined: these may well be degenerate.
To access this paper via the Wiley website, please click here.
Please note the following correction:
The stapes footplate area assigned to Parascalops breweri in the Appendix (0.205 mm2) proved to be based on a calculation error: the correct value should be 0.130 mm2.
Please contact me if you would like to be sent a reprint copy of this paper.