A trilobite preserves exquisite fossils in Pompeii volcanic ash

Hundreds of millions of years ago, trilobites were found all over the Earth. Covered in hard exoskeletons, the animals left countless fossils that are studied by paleontologists today. Despite the preserved shells, scientists have been unable to understand certain aspects of trilobite anatomy after centuries of study, particularly the delicate internal structures of ancient arthropods.

But a group of trilobite fossils buried in volcanic ash in Morocco may offer the best glimpse of a dismembered seafarer. In an article published Thursday in the journal ScienceThe researchers describe a group of trilobites that were devastated like the Romans of Pompeii, who were frozen to death by the eruption of Mount Vesuvius.

A 2015 excavation in the High Atlas Mountains led to the discovery of new fossils led by geologist Abdelrazak El Albany of the University of Poitiers in France. During the Cambrian period, 510 million years ago, the region was a shallow marine environment. Surrounded by fiery volcanoes. One of those eruptions left behind a cream-colored layer of fine volcanic ash in which trilobites had fossilized.

When the researchers opened up the volcanic rock, they found incredibly detailed records of trilobites etched into the stone. “Volcanic ash is a fine grain, like talcum powder, that can form very small anatomical features on the surface of these animals,” said John Patterson, a paleontologist at the University of New England in Australia and one of the new co-authors. study

Dr. El Albani and his team found that the trilobites were buried as a result of a short and sudden volcanic activity when the ash debris flooded the marine environment. A trilobite’s digestive tract is filled with sediments ingested before death. As the ash turned into stone, it formed three-dimensional molds of the buried trilobites.

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This froze the trilobites in time, like the extinct inhabitants of Pompeii, who escaped the eruption of Vesuvius and were buried in the ash. Some trilobites are curled up in a ball, while others look like they’re ready to scatter. One specimen even covered minuscule bivalves that rode the animal’s shell using fleshy stems.

“These brachiopods are still alive, which shows how quickly they were buried,” Dr El Albany said.

To get a closer look at the fossil’s anatomy, the scientists created 3-D images of the specimens using micro-CT scans and X-ray imaging. This allowed us to see delicate structures such as antennae, digestive tracts and the hairlike bristles on the walking legs of trilobites.

The team also discovered previously unknown anatomical features. Common features among living arthropods now include several small appendages that help stuff food into the trilobite’s slit-like mouth, and a soft-tissue flap called a labrum attached to the trilobite’s hard mouthparts.

“The labrum is a kind of fleshy lip associated with the mouth, which is part of the oral cavity where food is processed,” Dr. Patterson said. “The labrum has long been hypothesized to exist in trilobites but has never been observed in fossils.”

According to Thomas Hegna, a paleontologist at the State University of New York at Fredonia who was not part of the study, the appendages seen in the new specimens are often not shared in the same form by all trilobites. For example, he said, some bug-eyed species of the genus Carolinides “have to drag their eyes through the mud with their feet,” which are as narrow as in the Moroccan specimens.

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But the complex structures preserved in these “breathtaking” specimens help place trilobites within the arthropod family tree, he says.

“It goes into anatomical nuances, but such discussions are relevant when we want to discover that a group of living arthropods is closely related to extinct trilobites,” he said.

Dr. from Morocco. For El Albani, the incredible trilobite specimens represent something more than a taxonomic tool. He hopes they will encourage greater protection for Morocco’s ancient heritage, which has been exploited by commercial fossil dealers, who some call “The trilobite economy.”

“We want to preserve the discovery site to make it available to science,” he said.

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