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. (2016) Structure and function of the mammalian middle ear. I: Large middle ears in small desert mammals. Journal of Anatomy 228: 284-299.
It has been known for many years that small desert mammals often have relatively enormous middle ear cavities, visible as very prominent auditory bullae. These are believed to subserve acute low-frequency hearing, a number of adaptive benefits for which have been proposed. The enlarged middle ears of kangaroo rats and gerbils in particular have been well-described, but other desert mammals have received much less attention. In this paper, I describe the middle ear structures of three species of gerbils (Meriones unguiculatus, Desmodillus auricularis and Gerbillurus setzeri), two jerboas (Jaculus orientalis and J. jaculus) and two elephant shrews or sengis (Macroscelides flavicaudatus and Elephantulus rupestris), based on micro-CT reconstructions and the results of dissection under light microscopy. All of these species have markedly enlarged ear cavities with the exception of Elephantulus. The sengi Macroscelides has relatively the largest, the two ear cavities combined well exceeding brain cavity volume! I discuss here the different patterns of bullar composition and expansion in the different species and the functional meaning of these differences, and present a critical review of the literature concerning why small desert mammals often have such enlarged middle ears. The fact that Elephantulus, found in the same region of Namibia as Macroscelides, Desmodillus and Gerbillurus, has much smaller ears than these other species shows that desert life alone is not sufficient evolutionary pressure for the development of hypertrophied middle ears.
A companion paper to this article introduces middle ear function to those with little background, and explains how we can infer that the large ear cavities of these species augment sound transmission at low frequencies.
This article is available on the Journal of Anatomy website: please click here to access it.
Please contact me if you would like to be sent a reprint copy of this paper.
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