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El Albani A, Mazurier A, Edgecombe GD, Azizi A, El Bakhouch A, Berks HO, Bouougri EH, Chraiki I, Donoghue PCJ, Fontaine C, Gaines RR, Ghnahalla M, Meunier A, Trentesaux A, Paterson JR. Rapid volcanic ash entombment reveals the 3D anatomy of Cambrian trilobites. Science 2024; 384:1429-1435. [PMID: 38935712 DOI: 10.1126/science.adl4540] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/18/2023] [Accepted: 05/23/2024] [Indexed: 06/29/2024]
Abstract
Knowledge of Cambrian animal anatomy is limited by preservational processes that result in compaction, size bias, and incompleteness. We documented pristine three-dimensional (3D) anatomy of trilobites fossilized through rapid ash burial from a pyroclastic flow entering a shallow marine environment. Cambrian ellipsocephaloid trilobites from Morocco are articulated and undistorted, revealing exquisite details of the appendages and digestive system. Previously unknown anatomy includes a soft-tissue labrum attached to the hypostome, a slit-like mouth, and distinctive cephalic feeding appendages. Our findings resolve controversy over whether the trilobite hypostome is the labrum or incorporates it and establish crown-group euarthropod homologies in trilobites. This occurrence of moldic fossils with 3D soft parts highlights volcanic ash deposits in marine settings as an underexplored source for exceptionally preserved organisms.
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Affiliation(s)
| | - Arnaud Mazurier
- University of Poitiers, UMR CNRS 7285 IC2MP, 86000 Poitiers, France
| | | | - Abdelfattah Azizi
- Laboratory of Geo-resources, Geo-environment and Civil Engineering, Department of Geosciences, Faculty of Sciences and Technics, Cadi Ayyad University, Marrakesh 40000, Morocco
| | - Asmaa El Bakhouch
- Laboratory of Geo-resources, Geo-environment and Civil Engineering, Department of Geosciences, Faculty of Sciences and Technics, Cadi Ayyad University, Marrakesh 40000, Morocco
| | - Harry O Berks
- Bristol Palaeobiology Group, School of Earth Sciences, University of Bristol, Bristol BS8 1TQ, UK
| | - El Hafid Bouougri
- DLGR Laboratory, Department of Geology, Cadi Ayyad University, Faculty of Sciences-Semlalia, Marrakesh 40000, Morocco
| | - Ibtissam Chraiki
- DLGR Laboratory, Department of Geology, Cadi Ayyad University, Faculty of Sciences-Semlalia, Marrakesh 40000, Morocco
| | - Philip C J Donoghue
- Bristol Palaeobiology Group, School of Earth Sciences, University of Bristol, Bristol BS8 1TQ, UK
| | - Claude Fontaine
- University of Poitiers, UMR CNRS 7285 IC2MP, 86000 Poitiers, France
| | - Robert R Gaines
- Department of Geology, Pomona College, Claremont, CA 91711, USA
| | | | - Alain Meunier
- University of Poitiers, UMR CNRS 7285 IC2MP, 86000 Poitiers, France
| | - Alain Trentesaux
- University of Lille, UMR CNRS 8187 LOG, ULCO, 59655 Villeneuve d'Ascq, France
| | - John R Paterson
- Palaeoscience Research Centre, School of Environmental and Rural Science, University of New England, Armidale, NSW 2351, Australia
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Schoenemann B, Clarkson ENK. The median eyes of trilobites. Sci Rep 2023; 13:3917. [PMID: 36890176 PMCID: PMC9995485 DOI: 10.1038/s41598-023-31089-7] [Citation(s) in RCA: 3] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/14/2022] [Accepted: 03/06/2023] [Indexed: 03/10/2023] Open
Abstract
Arthropods typically possess two types of eyes-compound eyes, and the ocellar, so called 'median eyes'. Only trilobites, an important group of arthropods during the Palaeozoic, seem not to possess median eyes. While compound eyes are in focus of many investigations, median eyes are not as well considered. Here we give an overview of the occurence of median eyes in the arthropod realm and their phylogenetic relationship to other ocellar eye-systems among invertebrates. We discuss median eyes as represented in the fossil record e.g. in arthropods of the Cambrian fauna, and document median eyes in trilobites the first time. We make clear that ocellar systems, homologue to median eyes and possibly their predecessors are the primordial visual system, and that the compound eyes evolved later. Furthermore, the original number of median eyes is two, as retained in chelicerates. Four, probably the consequence of a gene-dublication, can be found for example in basal crustaceans, three is a derived number by fusion of the central median eyes and characterises Mandibulata. Median eyes are present in larval trilobites, but lying below a probably thin, translucent cuticle, as described here, which explains why they have hitherto escaped detection. So this article gives a review about the complexity of representation and evolution of median eyes among arthropods, and fills the gap of missing median eyes in trilobites. Thus now the number of median eyes represented in an arthropod is an important tool to find its position in the phylogenetic tree.
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Affiliation(s)
- Brigitte Schoenemann
- Department of Biology, Institute of Zoology (Neurobiology, Animal Physiology), University of Cologne, 50674, Cologne, Germany.
| | - Euan N K Clarkson
- Grant Institute, School of Geosciences, University of Edinburgh, West Mains Road, Edinburgh, EH9 3JW, UK
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