Peering into the eyes of trilobites using EBSD

Torney, C., Lee, M.R. and Owen, A.W. (2008) Peering into the eyes of trilobites using EBSD. In: Rollett, A.D. (ed.) Materials processing and texture : a collection of papers presented at the 15th International Conference on Textures of Materials (ICOTOM 15) June 1-6, 2008, Pittsburgh, Pennsylvania. Hoboken. ISBN 9780470408346

Abstract

The compound eyes of trilobites, an extinct group of marine arthropods, contain many sub-millimeter sized calcium carbonate lenses whose microstructures are the key to understanding how this ancient visual system functioned. The lenses had to be constructed by the animal very precisely in order to avoid double refraction but the mechanisms by which they focused light remain controversial. Optical models of the schizochroal eyes that typify phacopine trilobites, accepted since the 1970s, have assumed that the calcite of each lens had a uniform crystallographic orientation and light was focused onto underlying photoreceptor cells via intralensar structures. These models, and others that have been developed subsequently, were tested by mapping the lenses of different trilobite species by Electron Backscatter Diffraction (EBSD) and using both carbon-coated and uncoated cross-sections of the lenses; the latter within the SEM operated in low vacuum mode. Some species did indeed form their lenses from calcite of a uniform orientation and focusing was assisted by using intralensar structures of different chemical compositions. Other species had lenses with a very different and highly intriguing microstructure whereby light may have been ‘guided’ to a central single crystal using an outer lens unit composed of calcite with a radially arranged c axis. This study highlights a novel application of EBSD to the flourishing field of biomineralization and illustrates how crystallography can be used to help understand functional morphology.

• Item Type: Book Sections
• Keywords: Electron Backscatter Diffraction, Calcite, Lenses, Trilobite
• Status: Published
• Refereed: Yes
• Glasgow Author(s) Enlighten ID: Torney, Clare and Owen, Dr Alan and Lee, Professor Martin
• 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
• Publisher: Hoboken
• ISBN: 9780470408346