The evolution of the early tetrapod middle ear and associated structures

• Main Author: Robinson, Jamie
• Published: University College London (University of London) 2006
• Subjects: 573.893816
• Online Access: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.431771

This thesis utilises modern techniques to investigate the origin and evolution of hearing in tetrapods with particular emphasis on the evolution of the middle ear region of early tetrapods and the proposed relatives of lissamphibians. Recent advances in computed tomography (CT) scanning and 3D computer reconstruction has allowed the re-examination of many important specimens in the early tetrapod fossil record. The combination of CT scanning and 3D reconstruction has permitted the detailed visualisation of many aspects of these fossil specimens that could not have been easily achieved by traditional means. These modern techniques have been used to model the middle ear region in a range of early tetrapods. This was undertaken to investigate the form of the middle ear region in stem group tetrapods and temnospondyls, a group frequently cited in the origin of lissamphibians. The high resolution models created by the modem techniques have been utilised to investigate the function of the middle ear region in early tetrapods. Additionally, fossil evidence for the origin of the varied middle ear structures observed in the extant lissamphibians has been elucidated from the new models. Furthermore, these models allow the quantitative measurements of many aspects of the middle ear. The analysis of the new models has demonstrated that the support function for the stapes in early tetrapods has been overstated. A crude but transitional hearing function for the stapes is proposed for a range of stem group tetrapods. It is shown that temnospondyls, which are thought to possess tympanic membranes also appear to have possessed numerous specialisations of the middle ear present in extant lissamphibians.