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. (1999) The Functional Anatomy of the Middle Ear of Mammals, with an Emphasis on Fossorial Forms. PhD Thesis, University of Cambridge, U.K.
Project supervisor: Dr. Adrian Friday, Department of Zoology, University of Cambridge. Thesis examiners: Prof. Jenny Clack, Dr. Bob Presley.
The middle ears of 59 species of mammals, including seventeen fossorial (burrowing) species, were examined and described (see species list for more information). A detailed anatomical description was produced of the ear region of the European mole, Talpa europaea, and intraspecific variation in the middle ear structures of the mole and of the hedgehog Erinaceus europaeus was investigated. It was found that the sizes of the measured middle ear parameters are strongly correlated with skull length in Talpa, remaining roughly isometric with each other as absolute size changes. Male moles, which are larger than females, were found to have larger middle ear structures. No bilateral asymmetry was identified. In Erinaceus, middle ear structures do not appear to show significant correlations with skull length and there was little evidence of differences in middle ear structures between sexes, but only preliminary data were available for this species.
An extensive interspecific data set was assembled, combining middle ear measurements from this study with measurements from the literature. It was found that the middle ear structures of mammals generally increase in size with increasing body size, while remaining in approximately isometric proportions with each other. It was shown that mammals possessing the primitive, “microtype”, ossicular morphology typically have smaller middle ear structures than other mammals of similar body mass.
An existing model of the function of the middle ear was augmented, and a simple model of inertial bone conduction was applied to a range of mammals for the first time. The evolution of the middle ears of extant mammals was examined in the light of the predictions of the two models. The middle ears of most fossorial mammals do not appear to be tuned towards low frequencies, as has previously been supposed. In the majority of species, little anatomical evidence was found suggesting unusual vibratory sensitivity being conferred by the middle ear. The bizarre middle ear structures of some golden moles, on the other hand, seem to be ideally adapted towards the transmission of seismic vibrations through inertial bone conduction, at the expense of hearing in air, a hypothesis in accordance with behavioural observations from the literature.
The functional anatomy of the middle ear of fossorial mammals was reinterpreted, and the evolution of the middle ear apparatus in these species was discussed.
Chapters:
Chapter 1: Introduction.
Chapter 2: Material and Methods
Chapter 3: Anatomy of the Auditory Region of Talpa europaea
Chapter 4: Statistical Analyses
Chapter 5: Modelling Middle Ear Function
Chapter 6: Evolution of the Middle Ear in Mammals: a Functional Perspective
Chapter 7: Functional Anatomy of the Middle Ear in Fossorial Mammals
Chapter 8: Summary
Appendices:
- Specimens obtained for use in this study
- The auditory anatomy of mammals examined in this study
- Talpa europaea data table
- Measurements of middle ear parameters in mammals
- Functional anatomy of the middle ear in some non-fossorial mammals (elephants, gerbils & heteromyids, seals, shrews, tenrecs, hedgehogs)
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