The sophisticated visual system of a tiny Cambrian crustacean: analysis of a stalked fossil compound eye
Brigitte Schoenemann1,*, Christopher Castellani2, Euan N. K. Clarkson3, Joachim T. Haug4, Andreas Maas2, Carolin Haug4 and Dieter Waloszek2
Author Affiliations
1Steinmann Institute of Geology, Mineralogy and Palaeontology, University of Bonn, Palaeontology, 53115 Bonn, Germany
2Biosystematic Documentation, University of Ulm, 89081 Ulm, Germany
3Grant Institute, School of Geosciences, University of Edinburgh,Edinburgh, EH9 3JW, UK
4Geology and Geophysics Department, Yale University, 210 Whitney Avenue, New Haven, CT 06511, USA
*Author for correspondence (bschoenem@t-online.de).
Abstract
Fossilized compound eyes from the Cambrian, isolated and three-dimensionally preserved, provide remarkable insights into the lifestyle and habitat of their owners. The tiny stalked compound eyes described here probably possessed too few facets to form a proper image, but they represent a sophisticated system for detecting moving objects. The eyes are preserved as almost solid, mace-shaped blocks of phosphate, in which the original positions of the rhabdoms in one specimen are retained as deep cavities. Analysis of the optical axes reveals four visual areas, each with different properties in acuity of vision. They are surveyed by lenses directed forwards, laterally, backwards and inwards, respectively. The most intriguing of these is the putatively inwardly orientated zone, where the optical axes, like those orientated to the front, interfere with axes of the other eye of the contralateral side. The result is a three-dimensional visual net that covers not only the front, but extends also far laterally to either side. Thus, a moving object could be perceived by a two-dimensional coordinate (which is formed by two axes of those facets, one of the left and one of the right eye, which are orientated towards the moving object) in a wide three-dimensional space. This compound eye system enables small arthropods equipped with an eye of low acuity to estimate velocity, size or distance of possible food items efficiently. The eyes are interpreted as having been derived from individuals of the early crustacean Henningsmoenicaris scutula pointing to the existence of highly efficiently developed eyes in the early evolutionary lineage leading towards the modern Crustacea.
Cambrian, compound eye, arthropoda, crustacea, Orsten, vision
Received September 15, 2011.
Accepted October 12, 2011.
This journal is © 2011 The Royal Society
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