Ancient trilobites buried by a volcano 515 million years ago rise from the ashes in 3D

About half a billion years ago, a volcanic eruption near a shallow sea in what’s now Morocco preserved some of the most complete specimens ever found of buglike sea creatures called trilobites, revealing anatomical details that scientists had never seen before. Within moments, a fast-moving torrent of hot ash and volcanic gases, called pyroclastic flow, engulfed the trilobites and then cooled and hardened to solid rock. For 515 million years all evidence of those trilobites stayed hidden, buried at a site called the Tatelt Formation in the High Atlas mountain range. But an international team of researchers recently used high-resolution X-ray microtomography to peer through the layers of the trilobites’ tombs. The analysis revealed nearly pristine 3D imprints of the animals’ vaporized bodies inside chunks of volcanic rock. From scans of these prehistoric molds, the scientists reconstructed 3D digital models, displaying trilobite anatomy in unprecedented detail. The hot volcanic flow that buried the trilobites preserved impressions of soft tissues that typically don’t fossilize, including gut organs, antennae, feeding structures and clusters of sensory bristles, and tiny spines on the trilobites’ appendages. Trilobites caught up in a flash of volcanic activity Chemical analysis of oxygen levels in the sediments in and around the specimens revealed that the trilobites’ guts were stuffed with ash, likely swallowed as the animals suffocated on ash clouds in seawater. The pressures of sediment layers often flatten delicate fossils. But after the eruption buried the trilobites, cool seawater mixed with the hot ash and quickly hardened the pyroclastic flow into a tomb of solid rock. It kept the molds of the trilobites from distorting and preserved a virtually perfect imprint of their bodies. The findings also underscore the urgency of protecting fossil-rich locations in Africa such as the Tatelt Formation. Unlike the Tatelt, an important Cambrian fossil site in Canada is recognized as a UNESCO World Heritage Site. Such protections help to ensure that buried remnants of Earth’s distant past remain accessible for future study. ‘Extremely unusual’ discovery Over the past 200 years, paleontologists have identified over 22,000 species of trilobites from locations around the world that were once covered by oceans. Trilobites were arthropods, like modern insects, spiders, millipedes and crustaceans, and they evolved into a wide range of shapes and sizes before going extinct around 252 million years ago. Most trilobite species are no more than 1 inch (2.5 centimeters) long, but some grew to be more than 12 inches (30.5 centimeters) long. Trilobites had tough exoskeletons that typically fossilize well. However, the preservation of soft tissue in the newfound trilobites is exceptionally rare. ‘Only a small fraction of trilobite species are well-preserved enough for us to observe appendages at all,’ said one expert. ‘The more anatomical detail we have, the better inferences we can make about how fossil arthropods were related to one another.’ Trilobites had a stiff upper lip The scientists found four trilobite specimens and identified two species new to science: Gigoutella mauretanica and Protolenus (Hupeolenus) — the second is a still-unnamed species in a known genus and subgenus. ‘This is the first time we have preservation of the labrum,’ a bulbous structure over the mouth that is sometimes referred to as an upper lip in insects, said one of the scientists. Behind the labrum, the mouth slit was also exquisitely preserved. Surrounding it were slender curved appendages, likely used for feeding, that were also previously undetected in trilobite fossils, according to the researchers. The suddenness of the Cambrian volcanic eruption even preserved evidence of neighbors that shared the trilobites’ marine habitat. The research team found that one G. mauretanica trilobite had tiny shelled animals called brachiopods, measuring about 0.04 inch (1 millimeter) long, still clinging to its face. This example of commensalism — different types of animals living together — is also exceedingly rare in the trilobite fossil record. ‘It’s a unique window into the life history for this specimen from 515 million years ago,’ said one of the scientists. ‘I hope that with other discoveries — by our team, by other teams — we will find more or different specimens, which will give us the opportunity to see more about their life history and evolution.’