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About half a billion years ago, a volcanic eruption near a shallow sea in present-day Morocco preserved some of the most complete specimens ever found of bug-like sea creatures called trilobites, revealing anatomical details scientists had never seen before.
Moments later, a fast-moving flow of hot ash and volcanic gases called a pyroclastic flow engulfed the trilobites and then cooled and solidified into solid rock. The trilobites perished on the spot – much like the humans who were similarly buried in ash at Pompeii in AD 79, 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 mountain range. But an international team of researchers recently used high-resolution X-ray microtomography to peer through the layers of the trilobite tombs. The analysis revealed nearly pristine 3D prints of the animals’ vaporized bodies in chunks of volcanic rock, the scientists reported June 27 in the journal Science.
From scans of these prehistoric forms, the scientists reconstructed 3D digital models showing the anatomy of the trilobite in unprecedented detail. The hot volcanic flow that buried the trilobites preserved imprints of soft tissues that do not normally fossilize, including intestinal organs, antennae, feeding structures, and clusters of sensory setae and small spines on the trilobite appendages.
“It’s just amazing to have this in 3D without any change or deformation,” lead study author Dr. Abderrazak El Albani told CNN. The detailed preservation showed that trilobites were anatomically complex animals, with many specialized adaptations for feeding and locomotion on the sea floor, he said.
Chemical analysis of oxygen levels in the sediments in and around the specimens revealed that the trilobites’ guts were filled with ash, likely ingested when the animals suffocated from ash clouds in seawater, the study authors wrote.
Arnaud Mazurier/Institut de Chimie des Milieux et Matériaux de Poitiers/University of Poitiers
The trilobite Protolenus is shown in side view. The digestive system is visible in blue, the hypostoma or mouth structure in green (far left), and the labrum, a bulbous structure above the mouth sometimes called the upper lip in insects, in red.
The pressure of sedimentary layers often flattens delicate fossils. But after the eruption buried the trilobites, cool seawater mixed with the hot ash and quickly solidified the pyroclastic flow into a tomb of solid rock. It keeps the trilobites’ shapes from being distorted and preserves a virtually perfect imprint of their bodies, said El Albani, a 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 the Tatelt, the Burgess Shale, an important Cambrian fossil site in Canada, is recognized as a UNESCO World Heritage Site. Such protections help ensure that buried remains from Earth’s distant past remain accessible for future research, El Albany said.
Over the past 200 years, paleontologists have identified more than 22,000 species of trilobites from places around the world that were once covered by oceans. Trilobites were arthropods, like modern insects, spiders, centipedes and crustaceans, and evolved into a wide range of shapes and sizes before becoming extinct about 252 million years ago. Most trilobite species are no more than 1 inch (2.5 centimeters) long, but some, such as Hungoides bohemicus, have grown to more than 12 inches (30.5 centimeters).
Arnaud Mazurier/Institut de Chimie des Milieux et Matériaux de Poitiers/University of Poitiers
A microtomographic reconstruction shows the newly discovered trilobite species Gigoutella mauretanica found in the Tatelt Formation of the High Atlas Mountains.
Trilobites had robust exoskeletons that usually fossilize well. Soft-tissue preservation in newly discovered trilobites, however, is extremely rare, said Dr. Melanie Hopkins, associate curator of invertebrate paleontology at the American Museum of Natural History in New York.
“Only a small fraction of trilobite species are well enough preserved that we can observe appendages at all,” said Hopkins, who studies trilobites but was not involved in the new study. “The level of detail preserved in the Tatelt specimens is extremely unusual, so much so that there are some features that have not been seen before,” she said. Such characteristics are critical for understanding how new traits and new species evolve and for tracing the relationships between arthropod groups, Hopkins added.
“The more anatomical details we have, the better inferences we can make about how fossil arthropods were related to each other.”
The scientists found four specimens of the trilobite and identified two species new to science: Gigoutella mauretanica and Protolenus (Hupeolenus) — the latter a still unnamed species in a known genus and subgenus. Specimens range in length from about 0.4 inches (11 millimeters) to 1 inch (26 millimeters).
“This is the first time we have preserved the labrum,” a bulbous structure above the mouth sometimes called the upper lip in insects, El Albani said. Behind the labrum, the mouth slit was also excellently preserved. Surrounding it were thin curved appendages, probably used for feeding, which also had not been previously found in trilobite fossils, according to the study authors.
The discovery of the structures raises new questions about the diversity in trilobite food 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 suddenness of the Cambrian volcanic eruption even preserved evidence of neighbors who shared the trilobites’ marine habitat. The research team found that one G. mauretanica trilobite had small shelled animals called brachiopods, about 0.04 inches (1 millimeter) long, still attached to its face. This example of commensalism — different types of animals living together — is also extremely rare in the trilobite fossil, El Albani said.
“This is a unique window into the life history of this specimen from 515 million years ago,” he said. “I hope that with other discoveries – by our team, by 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 been published in Live Science, Scientific American, and How It Works magazine.
