Comparative anatomy of the mammalian bony cochlea and its ontogenetic development in humans

Wannaprasert, Thanakul
Comparative anatomy of the mammalian bony cochlea and its ontogenetic development in humans. Doctor of Philosophy thesis, University of Liverpool.

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The cochlea is the organ for sound reception. Mammals place varied functional demands on their sense of hearing to meet the requirements of a broad range of ecological niches and diverse behaviours. However, documenting potentially related adaptations of the cochlea to eco-behavioural traits is difficult due to its complex geometry. The present study aims to determine whether the bony cochlea carries eco-behavioural traits that can be used to contextualize our understanding of the fossil record and evolutionary transitions. This study also includes work on ontogenetic changes since these can yield important insights into evolutionary processes resulting in differences of the adult phenotypes. Advanced techniques in micro-CT imaging, 3D image visualization, geometric morphometrics and statistical methods were used to study morphological variations of the bony cochlea across 45 adult eutherian species. Also, the same set of techniques was used to study 12 human fetal (approximately four to nine months of gestation) cochleae in comparison with five adult cochleae. Results revealed that there was a considerable range of variation in form of the mammalian bony cochlea. Potential links between the bony cochlear morphology and hearing, ecology and behaviour were found. Dimensions of the bony cochlea may be indicative of the eco-behavioural niche that a mammal occupies; e.g., fewer than two spiral turns is associated with obligate marine species. Rodents also showed remarkable variation in the cochlear morphology, more so than any other group of mammals studied, reflecting their diverse eco-behavioural traits. Results from the human developmental study showed that whilst the general coiled shape was achieved at the midgestational age, there was size related morphological change during the postnatal period. The round window size reached mature state prior to birth, by approximately the second trimester, whereas the oval window continued to change in size after birth. The postnatal enlargement may be determined by functional requirements of air-borne hearing, particularly with respect to frequency range and sensitivity.

Item Type: Thesis (Doctor of Philosophy)
Additional Information: Date: 2013-10 (completed)
Uncontrolled Keywords: comparative anatomy, bony cochlea, mammals, ontogenetic development, humans
Depositing User: Symplectic Admin
Date Deposited: 11 Feb 2014 11:32
Last Modified: 17 Dec 2022 01:41
DOI: 10.17638/00014173
  • Jeffery, Nathan