An electron backscatter diffraction study of geesops: a broader view of trilobite vision?

Torney, C., Lee, M.R. and Owen, A.W. (2008) An electron backscatter diffraction study of geesops: a broader view of trilobite vision? In: Fourth International Trilobite Conference, Toledo, Spain, 16 - 24th June 2008,

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The calcite eyes of trilobites have been studied for over 100 years using methods including light microscopy (e.g. Clarke 1889; Campbell 1975; Towe 1973; Clarkson 1979 and Bruton and Haas 2003) and more recently cathodoluminescence (CL) imaging coupled with scanning electron microscopy (SEM) of samples etched in EDTA (Miller and Clarkson 1980). This work has provided a great deal of information on the mechanisms by which lenses collected light, drawing attention to the importance of the crystallographic orientation of lens calcite for focusing, and leading to sophisticated models of trilobite vision (Clarkson and Levi-Setti, 1975; Gál et al., 2000). The morphology and mode of life of phacopids, in particular Geesops, are well understood (Bruton and Haas, 2003a; 2003b) but observations on the internal structure of their lenses contradict the generally accepted models for image formation by schizochroal eyes. Recent technological advances have given new impetus to the analysis of crystalline materials and especially important has been electron backscatter diffraction (EBSD). This is a SEM-based technique that can be used to accurately ‘map’ variations in the crystallographic orientation of a sample down to the sub-micrometre scale by recording on a sensitive camera Kikuchi patterns that are formed by diffraction of an electron beam when focused on a polished sample tilted at 70°. Although this technique has been understood for over 50 years (Alam et al., 1954) and has been extensively used in disciplines such as metallography (Humphreys, 2001), until recently its Earth Science applications were limited to studies of structural geology and petrology (Nuchter and Stockhert, 2007). Recent applications of EBSD to biomineralisation research (Dalbeck and Cusack, 2006; Griesshaber et al., 2007) have mapped the crystal orientation and microstructure of calcite shells and in 2006 Lee et al. were able to apply this technique to investigating the microstructure of lenses in the schizochroal eye of Dalmanites. This paper describes results of an EBSD study of eyes of Geesops schlotheimi (Bronn, 1825) combined with more traditional microscopy techniques to reveal new aspects of trilobite lens structure.

Item Type:Conference Proceedings
Keywords:EBSD, Schizochroal eye, Phacopids, Geesops
Glasgow Author(s) Enlighten ID:Owen, Dr Alan
Authors: Torney, C., Lee, M.R., and Owen, A.W.
Subjects:T Technology > T Technology (General)
Q Science > QD Chemistry
College/School:College of Science and Engineering > School of Geographical and Earth Sciences
Copyright Holders:Copyright © 2008 The Author
First Published:First published in Proceedings of Fourth International Trilobite Conference
Publisher Policy:Reproduced with permission of the author
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