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| Artistic reconstruction of two species of trilobite an instant before burial in a flow of volcanic ash 510 million years ago. Gigoutella mauretanica (Ortega-Hernández, Azizi, Hearing, Harvey, Edgecombe, Hafid & El Hariri, 2017) in El Albani, Mazurier, Edgecombe, Azizi, El Bakhouch, ... et Paterson, 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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| Microtomographic reconstruction of the trilobite species Gigoutella mauretanica in ventral view |
Gigoutella mauretanica (Ortega-Hernández, Azizi, Hearing, Harvey, Edgecombe, Hafid & El Hariri, 2017)
Abderrazak El Albani, Arnaud Mazurier, Gregory D. Edgecombe, Abdelfattah Azizi, Asmaa El Bakhouch, Harry O. Berks, El Hafid Bouougri, Ibtissam Chraiki, Philip C. J. Donoghue, Claude Fontaine, Robert R. Gaines, Mohamed Ghnahalla, Alain Meunier, Alain Trentesaux and John R. Paterson. 2024. Rapid Volcanic Ash Entombment reveals the 3D Anatomy of Cambrian Trilobites. SCIENCE. 384, 6703; 1429-1435. DOI: doi.org/10.1126/science.adl4540
Editor’s summary: Trilobites are probably the best known denizens of the Cambrian Period. Their distinctive fossilized external forms are well recognized from an extensive fossil record spanning the early Cambrian to the Permian extinction. The vast majority of trilobite fossils display only external morphology, however, leaving much unknown about their internal morphology. El Albani et al. describe several trilobite fossils created by rapid death and preservation due to an underwater pyroclastic flow. This preservation created three-dimensional fossils with a remarkably well-preserved anatomy. This enhanced understanding of trilobite anatomy has revealed several new features and provided key insights into crown group euarthropods. —Sacha Vignieri
COVER: This reconstruction of a shallow marine environment shows trilobites being rapidly engulfed by volcanic ash from an eruption that occurred more than 500 million years ago. Recently discovered trilobite fossils from Cambrian-aged rocks in Morocco have revealed three-dimensional soft-tissue anatomy, including features not previously observed in these extinct arthropods. This find highlights marine volcanic ash deposits as important sites of exceptional fossil preservation. || Image: A. El Albani
