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About half a billion years ago, a volcanic eruption near a shallow sea in what is now Morocco preserved some of the most complete specimens ever found of insect-like sea creatures called trilobites, revealing anatomical details that scientists had never seen before. .
Within moments, a rapid torrent of hot ash and volcanic gases, called pyroclastic flow, engulfed the trilobites and then cooled and hardened into solid rock. The trilobites died on the spot – just like the people who were also buried in the ash at Pompeii in 79 AD during the eruption of Mount Vesuvius.
For 515 million years, all evidence of these trilobites remained hidden, buried in a place called the Tatelt Formation in the High Atlas Mountains. But an international team of researchers recently used high-resolution X-ray microtomography to peer through the layers of trilobite graves. The analysis revealed nearly pristine 3D prints of the animals’ vaporized bodies inside chunks of volcanic rock, the scientists reported in the June 27 journal. Science.
From scans of these prehistoric casts, scientists reconstructed 3D digital models, displaying the trilobite anatomy in unprecedented detail. The hot volcanic flow that buried the trilobites preserved impressions of soft tissues that do not normally fossilize, including intestinal organs, antennae, feeding structures and clusters of sensory bristles, and small spines on trilobite appendages.
“It’s simply incredible to have this in 3D without any alteration or deformation,” lead author of the study Dr. Abderrazak El Albani he told CNN. Detailed preservation has shown that trilobites were anatomically sophisticated animals, with many specialized adaptations for feeding and movement along the seafloor, he said.
Trilobites caught in a flash of volcanic activity
Chemical analysis of oxygen levels in the sediments in and around the specimens revealed that the trilobites’ intestines were filled with ash, likely swallowed as the animals suffocated in ash clouds in seawater, the study authors wrote.
Pressures from sediment layers often flatten delicate fossils. But after the eruption buried the trilobites, cold seawater mixed with the hot ash and quickly hardened the pyroclastic flow into a tomb of solid rock. It prevented the trilobite casts from distorting and preserved a virtually perfect impression of their bodies, said El Albani, professor of geosciences at the University of Poitiers in France.
The findings also highlight the urgency of protecting fossil-rich sites in Africa, such as the Tatelt Formation, El Albani added. Unlike Tatelt, the Burgess Shale, an important Cambrian fossil site in Canada, is recognized as a UNESCO World Heritage Site. These protections help ensure that the buried remains of Earth’s distant past remain accessible for future study, El Albani said.
‘Extremely unusual’ discovery
Over the past 200 years, paleontologists have identified more than 22,000 species of trilobites in locations around the world that were once covered by oceans. Trilobites were arthropods, like modern insects, spiders, millipedes and crustaceans, and evolved into a wide variety of shapes and sizes before becoming extinct about 252 million years ago. Most trilobite species are no more than 2.5 centimeters long, but some, such as Hungoides bohemicus, have reached more than 30.5 centimeters in length.
Trilobites had tough exoskeletons that typically fossilize well. However, soft tissue preservation in the newly discovered trilobites is exceptionally rare, he said. Dr.curator responsible for invertebrate paleontology at the American Museum of Natural History in New York City.
“Only a small fraction of trilobite species are well preserved enough for us to observe appendages,” said Hopkins, who studies trilobites but was not involved in the new research. “The level of detail preserved in the Tatelt specimens is extremely unusual, so much so that there are some features that have not been observed before,” she said. Such traits are critical for understanding how new traits and new species evolve, and for tracking relationships between groups of arthropods, Hopkins added.
“The more anatomical details we have, the better inferences we can make about how fossil arthropods were related to each other.”
Trilobites had a stiff upper lip
Scientists found four specimens of trilobites and identified two species new to science: Gigoutella mauretanica and Protolenus (Hupeolenus) — the second is an as-yet unnamed species in a known genus and subgenus. The samples ranged from about 0.4 inches (11 millimeters) to 1 inch (26 millimeters) in length.
“This is the first time we have preserved the labrum,” a bulbous structure over the mouth that is sometimes called the upper lip in insects, El Albani said. Behind the lip, the mouth slit has also been exquisitely preserved. Surrounding it were slender, curved appendages, likely used for food, that had also not previously been detected in trilobite fossils, according to the study authors.
The discovery of the structures raises new questions about the diversity in trilobite feeding appendages; how this may have affected what trilobites ate and where they lived; and their vulnerability to changing environmental conditions if they had highly specialized diets, Hopkins said.
The rapidity of the Cambrian volcanic eruption even preserved evidence of neighbors that shared the trilobites’ marine habitat. The research team discovered that a trilobite G. mauretanica had small shelled animals called brachiopods, measuring about 1 millimeter long, still clinging to its face. This example of commensalism – different types of animals living together – is also extremely rare in the fossil record of trilobites, El Albani said.
“It’s a unique window into the life history of this specimen from 515 million years ago,” he said. “I hope that with other discoveries — from our team, from other teams in Morocco — we will find more or different specimens, which will give us the opportunity to see more about their life history and evolution.”
Mindy Weisberger is a science writer and media producer whose work has appeared in Live Science, Scientific American, and How It Works.
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