Rapid volcanic ash entombment reveals the 3D anatomy of Cambrian trilobites
by: 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.

Summarized by Erin Potter: Erin lives in the Binghamton, NY area. She is a lecturer in the Geography Department at Binghamton University, where she hopes to also pursue her Ph.D. in Earth Sciences. Erin holds a Master’s degree in geosciences with a concentration in teaching, as well as a Masters in atmospheric science. She has one daughter, a scientist in the making, and knows the importance of being a role model and a representative of women in science.

What data were used? The authors examined trilobites, which are extinct creatures that lived from 521 to 252 million years ago. They primarily lived in ocean environments and are related to things like the pill bugs alive today. Two trilobite species were retrieved from volcanic ash in Morocco. Authors collected the ash as well. The species are Protolenus (Hupeolenus) and Gigoutella mauretanica which are both from the Cambrian Period, about 538 to 485 million years ago.

What was the hypothesis being tested? The goal of this study was to examine the specific processes of fossilization of trilobites from rapid cooling of volcanic ash as it entered a shallow marine environment, preserving fine details of trilobite anatomy. 

Methodology: The authors used a type of X-ray imaging to capture internal structures from the two species of trilobites. They also assessed the fossilization process of the volcanic ash and the minerals in the ash responsible for the preservation. Three-dimensional images created by the X-ray imaging were analyzed to show the fine anatomy preservation.  

Results: Several intricate features were found, many previously unknown for these species (Figure 1). Among these anatomy features found were antennae and the related appendages (much like other arthropods, like insects have antennae). Appendages for moving and feeding were clearly visible in the X-ray images, including claws. The digestive system–such as the esophagus, intestines, and digestive glands– is preserved with great detail in one of the species. The mouthparts (called the hypostome and labrum) were examined in the 3D imagery. The Gigoutella mauretanica specimen was found to have been preserved with smaller organisms attached to the hard exoskeleton. The rapid burial allowed for these small organisms, called brachiopods (two shelled organisms that were common 538 to 252 million years ago), to be preserved attached to the trilobite specimen. Even soft tissue, like the pedicle (the fleshy attachment structure on the brachiopod) can be seen on the preserved specimens. The ash that was studied showed various sizes and mineral composition. Grain size ranged from larger grains called lapilli to very fine-grained ash. The organization of grain sizes indicated a single event was responsible for this volcanic rapid burial. Minerals that made up the volcanic material included quartz/silica, calcite, and chlorite. The mineral composition around the trilobites (quartz/silica, albite, and iron chlorite) shows evidence of an interaction of the volcanic material with the shallow marine environment that the trilobites would have lived in. 

Why is this study important? There is limited information on the internal anatomy of creatures that existed during the Cambrian, 538 to 485 million years ago. The researchers described the fine, soft tissue features of the organisms, something so rare in the fossil record. Typically, the hard parts of an organism, like shells and bones, are what get preserved in greater detail in the fossil record. Animal fossils from this time are often incomplete. This research fills in the gaps of the soft-anatomy features of trilobites in the Cambrian. These preserved features were previously undescribed for these particular species, adding to the current knowledge of trilobite anatomy. 

Broader Implications beyond this study: The way these soft parts of the body have been preserved so well by rapid volcanic ash leads to the possibility of exploring this type of fossilization process further. Perhaps more can be learned about other organisms by looking for other fossils in this source. Ash is known to preserve well, as it does not crush the organism. Volcanic events like the one in this paper involve a pyroclastic flow, typical in large stratovolcanoes. These flows are fast and hot, and result in various sized grains like the researchers describe. This leads to the rapid burial and the ash acts like cement for the organisms trapped. This has been noted in other research papers for other organisms, like an ancient vulture found near Rome, Italy (Dawid et al.). By documenting these cases in volcanic regions, future research can look to these areas for more examples of fine-detailed, soft-body anatomical feature preservation.  

Citation: 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.  Rapid volcanic ash entombment reveals the 3D anatomy of Cambrian trilobites. Science 384,1429–1435(2024).DOI:10.1126/science.adl4540

Dawid A. Iurino, Luca Bellucci, Danielle Schreve, Raffaele Sardella. Exceptional soft tissue fossilization of a Pleistocene vulture (Gyps fulvus): new evidence for emplacement temperatures of pyroclastic flow deposits. Quaternary Science Reviews, 96, 180–187 (2014). DOI: 10.1016/j.quascirev.2014.04.024.