New Insights to Ancient Eyes – The Sensory Structure of Trilobite Eyes
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1
University of Cologne, Dep. Neurobiology/Comparative Physiology, Germany
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2
University of Edinburgh, Grant Institute, United Kingdom
The nature of fossilised sensory structures, such as of compound eyes is hitherto unknown. The only structure known so far is that of a dipteran in Eocene amber, which shows the structure of a superposition eye like in recent flies (Tanaka et al 2009), thus compound eye systems older than of ~35Ma. are not understood so far. Trilobites are the dominat arthropods of the Palaeozoic, and equipped with excellent compound eyes from the very beginning. Such trilobites of the suborder of Phacopina investigated here appeared between the early Ordovician (488.4Ma) and lasted up to the late Devonian (416-359.2MA). They show huge compound eyes relatively to the body, with large lenses standing separately rather than hexagonally packed (schizochroal eyes). Worldwide exist several locations where these trilobites are excellently preserved. Using x-ray ct-scanning (µ-ct) and synchrotron techniques the construction of original sensory structures in the eyes of phacopine trilobites is revealed for the first time. They are preserved as mineral coatings on the original components, and they form rosettes of cells lying within sublensar capsules. This is in contrast to the hypotheses formulated before, that the sublensar capsules were flored by a tiny retina below an extended vitreous body (Clarkson 1975, Clarkson & Levi-Setti 1975). The arrangement of the sensory cells is very similar to that of modern apposition eyes, revealing this eye structure to have been effective since almost half a billion years. They resemble especially the apposition eyes of Limulus, which has obviously retained an ancient visual system, which successfully holds itstown today among the modern visual principles (Schoenemann & Clarkson 2013).
Figure legend: A Head of a trilobite with compound eye, Geesops schlotheimi (Bronn 1825) Middle Devonian, Eifelium, Ahrdorf Fm., Gees/Gerolstein, Germany. B Fossilised rosette of the sensory structure of a ~390million year old compound eye (G. schlotheimi). C Schematic drawing of B interpreting as: sc sensory cell, r rhabdom, ec excentric cell, central process of the excentric cell.
Acknowledgements
Greatest thank to C. Adams Phoenix/x-ray for his help using the µct at Munich, P. Tafforeau and W. Ludwig, and to the ESRF Grenoble.
References
Clarkson E.N.K. (1975) The evolution of the eyes in trilobites. Fossils and Strata 4, 7-31.
Clarkson E.N.K. & Levi-Setti R. (1975) Trilobite Eyes and the optics of Descartes and Huygens. Nature 254, 663-666.
Schoenemann B. & Clarkson E.N.K. (2013) Discovery of a some 400 million year-old sensory structure, in the compound eyes of trilobites. Nature Scientific Reports, | 3:1429 DOI:10.1038/srep01429.
Tanaka G., Parker A.R., Siveter D.J., Maeda H. & Furutani M (2009) An exceptionally well-preserved Eocene dolichopodid fly eye: function and evolutionary significance. Proceedings of the Royal Society London, Biological Sciences, 276, 1015-1019.
Keywords:
Vision,
Compound eye,
arthropod,
evolution,
receptor cell,
trilobite,
Palaeozoic
Conference:
International Conference on Invertebrate Vision, Fjälkinge, Sweden, 1 Aug - 8 Aug, 2013.
Presentation Type:
Poster presentation preferred
Topic:
Development and evolution
Citation:
Schoenemann
B and
Clarkson
EN
(2019). New Insights to Ancient Eyes – The Sensory Structure of Trilobite Eyes.
Front. Physiol.
Conference Abstract:
International Conference on Invertebrate Vision.
doi: 10.3389/conf.fphys.2013.25.00100
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Received:
23 Apr 2013;
Published Online:
09 Dec 2019.
*
Correspondence:
Dr. Brigitte Schoenemann, University of Cologne, Dep. Neurobiology/Comparative Physiology, Köln, D-50674, Germany, B.Schoenemann@uni-koeln.de