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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 sea creatures called trilobites, revealing anatomical details scientists had never seen before. first.
Within moments, a rapid stream of hot ash and volcanic gases, called a pyroclastic flow, engulfed the trilobites and then cooled and solidified into solid rock. The trilobites disappeared from the site – just 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 trilobite burials. Analysis revealed nearly pristine 3D footprints of vaporized animal carcasses inside chunks of volcanic rock, scientists reported June 27 in the journal Science.
From scans of these prehistoric casts, scientists reconstructed 3D digital models, showing the trilobite’s anatomy in unprecedented detail. The hot volcanic flow that buried the trilobites preserved imprints of soft tissues that don’t usually fossilize, including gut organs, antennae, feeding structures, and clusters of sensory hairs and tiny spines on trilobite appendages.
“It’s incredible to have this in 3D without any change or distortion,” said lead study author Dr. Abderrazak El Albani for CNN. The detailed preservation showed that trilobites were anatomically sophisticated animals, with many specialized adaptations for feeding and moving along the seabed, 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 as the animals drowned in clouds of ash in seawater, the study authors wrote.
The pressures of sediment layers often flatten delicate fossils. But after the eruption buried the trilobites, the cold seawater mixed with the hot ash and quickly solidified the pyroclastic flow into a tomb of solid rock. It kept the trilobites’ shapes from distorting and preserved a virtually perfect imprint of their bodies, said El Albani, a professor of geosciences at the University of Poitiers in France.
The findings also underscore 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 safeguards help ensure that buried remnants of Earth’s distant past remain accessible for future study, El Albani said.
Over the past 200 years, paleontologists have identified over 22,000 species of trilobites from places 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 becoming extinct about 252 million years ago. Most trilobite species are no longer than 1 inch (2.5 centimeters), but some, such as Hungoides bohemicus, grew to more than 12 inches (30.5 centimeters).
Trilobites had strong exoskeletons that are usually well fossilized. However, preservation of soft tissue in newly found trilobites is extremely rare, said Dr. Melanie Hopkins, curator in charge of invertebrate paleontology at the American Museum of Natural History in New York City.
“Only a small fraction of trilobite species are preserved long enough for us to observe the appendages at all,” 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 several features that have not been observed before,” she said. Such characteristics are critical for understanding how new traits and new species evolve, and for tracing relationships among arthropod groups, Hopkins added.
“The more anatomical details we have, the better we can draw conclusions about how fossil arthropods were related to each other.”
Scientists found four trilobite specimens 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. Specimens ranged from about 0.4 inches (11 millimeters) to 1 inch (26 millimeters) long.
“This is the first time we have preserved the labrum,” a bulbous structure above the mouth sometimes referred to as the upper lip in insects, El Albani said. Behind the labrum, the oral cleft was also excellently preserved. Surrounding it were thin curved appendages, likely used for feeding, which were also previously undetected 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 suddenness of the Cambrian volcanic eruption even preserved evidence of neighbors sharing the marine habitat of the trilobites. The research team found that a 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 record, El Albani said.
“It’s a unique window into the history of life for this specimen from 515 million years ago,” he said. “I hope that with further 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 appeared in Live Science magazine, Scientific American, and How It Works.