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., Lucas, S.J., Wise, E.R., Stein, R.S. & Duer, M.J. (2006) Ossicular density in golden moles (Chrysochloridae). Journal of Comparative Physiology A 192: 1349-1357.
As I have shown in some of my previous work (Mason 2003a,b, 2004), golden moles from southern Africa have enormously hypertrophied middle ear ossicles, which are believed to be used in the transmission of seismic vibrations by bone conduction. Although known to be large and heavy, in this study we addressed the question of whether these ossicles are also more dense than typical bone. Using diiodomethane and chloroform mixtures, we used a simple buoyancy test to determine ossicular density, finding that the mallei of the desert golden mole Eremitalpa granti are made of the densest bone yet documented in any terrestrial mammal, averaging 2.44 g/cm3. Using solid-state NMR, we demonstrated that this bone is particularly well mineralized, and micro-CT scans show that the ossicles contain relatively few vascular channels. Other golden moles did not have unusually dense ossicles: we suggest that Eremitalpa, being the smallest golden mole, might be under particular selective pressure to increase ossicular density rather than absolute size of its ear bones.
During the course of this project, we unexpectedly found that the malleus morphology in Eremitalpa granti granti is rather different from that of Eremitalpa granti namibensis: this difference between the two subspecies is described here for the first time.
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