A trilobite preserves exquisite fossils in Pompeii volcanic ash

Millions of years ago, trilobites could be found all over the Earth. Encased in hard exoskeletons, these animals have left behind countless fossils that paleontologists are studying today. Despite all these preserved shells, scientists have been unable to understand some aspects of trilobite anatomy even after centuries of study, particularly the soft internal structure of the ancient arthropods.

But a group of trilobite fossils buried in volcanic ash in Morocco may provide the best glimpse yet of the segmented sailors. In a paper published Thursday in the journal ScienceResearchers describe a group of trilobites that were turned to stone in a similar way to the Romans of Pompeii, who died in the eruption of Mount Vesuvius.

Abderrazak El Albani, a geologist at the University of Poitiers in France, led the excavation that discovered the new fossils in the High Atlas Mountains in 2015. During the Cambrian period, 510 million years ago, the region was a shallow marine environment surrounded by volcanic eruptions. One of those eruptions left a cream-colored layer of fine-grained volcanic ash that contained trilobite fossils.

When the researchers broke up the volcanic rock, they found incredibly detailed imprints of trilobites etched into the stone. “Volcanic ash is so fine, like talcum powder, that it can mold the smallest anatomical features of these animals onto their surface,” said John Patterson, a paleontologist at the University of New England in Australia and one of the co-authors of the new study.

Dr. El Albani and his team believe that a short and sudden burst of volcanic activity buried the trilobites, when ash debris filled the marine environment. The digestive tract of a buried trilobite is also filled with sediment that it may have ingested before death. As the ash turned to stone, it created three-dimensional molds of the buried trilobites.

This allowed the trilobites to be frozen in time in the same way as the doomed residents of Pompeii, who were buried in ash while fleeing the eruption of Vesuvius. Some of the trilobites are curled up like a ball while others look like they’re ready to scamper away. One specimen is even covered in tiny bivalves, which had clung to the animal’s shell using fleshy stalks.

“These brachiopods are still in their living state, which shows how quickly the burial happened,” Dr. El Albani said.

To get a closer look at the fossil anatomy, the scientists used micro-CT scans and X-ray imaging to create 3-D images of the specimens. This allowed them to see delicate structures such as the antennae, digestive tract and even the hair-like bristles on the trilobites’ walking legs.

The team also discovered previously unknown anatomical features. These included several small appendages that would have helped guide food into the trilobite’s mouth, and a soft tissue flap called the labrum that was attached to the trilobite’s hard mouth part and is now a common feature in living arthropods.

“The labrum is a kind of fleshy lip attached to the mouth that forms part of the oral chamber where food is processed,” Dr. Patterson said. “The labrum has long been thought to be present in trilobites, but has never been seen 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 were probably not shared equally across all trilobites. For example, some bug-eyed species of the genus Carolinaites “must have had to drag their eyes through the mud with their legs,” which were just as small as those in the Moroccan specimens, he said.

But he says the complex structures preserved in these “amazing” specimens will help place trilobites into the Arthropoda family tree.

“This discusses subtle aspects of anatomy, but this kind of debate becomes relevant when we want to figure out which group of living arthropods is most closely related to the extinct trilobites,” he said.

For Dr. El Albani, who hails from Morocco, the incredible trilobite specimens represent something more than a classification tool. He hopes they will inspire greater protection for Morocco’s fossil heritage, which has been exploited by commercial fossil traders to the extent that some call it “a fossil treasure.”Trilobite Economy,

“We want to preserve the place where this discovery was made to make it available for science,” he said.

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