Trilobites preserved in incredible detail by Pompeii-style eruption

A fossil site in Morocco has been called the “Pompeii of trilobites” as it contains sublimely detailed fossilised moulds of the creatures, preserved after a pyroclastic ash flow from a volcanic eruption around 509 million years ago.

“My jaw fell onto the desk,” says John Paterson at the University of New England in Armidale, Australia. “I have never seen the level of detail preserved in these fossil trilobites. They are absolutely, no question, the best-preserved trilobites ever found.”

Trilobites are marine arthropods that existed from around 520 million years ago until nearly 252 million years ago. We know of more than 22,000 species and countless fossils have been discovered, but these are normally just their tough exoskeleton. The creatures’ soft parts are only found on rare occasions, and are always flattened and damaged.

However, the moment Paterson saw scans and images of trilobite fossils collected in 2022, from south-west of Marrakesh, in Morocco, he knew they were something special.

“On one of the more complete specimens, all of the appendages are preserved in 3D, right down to the bristles on their walking legs,” he says.

So far, Paterson and his colleagues have collected four specimens, each only around a centimetre long, representing two species from the Tatelt formation in Morocco. Two of the four trilobite specimens belong to the genus Protolenus, but the researchers are unsure whether they belong to a new species. The other specimens are Gigoutella mauretanica.

Pompeii is prized by archaeologists because ash from Mount Vesuvius quickly descended on the Roman city, preserving its structures and inhabitants. Once the ash cooled and formed into rock, each of the bodies decomposed, leaving a cavity that represents a perfect mould. The same thing happened to the trilobites, says Paterson.

The team scanned the moulds with a micro CT scanner and was able to create perfect 3D images of the creatures. “With these specimens, you can see anything you want at any angle,” says Paterson.

The scans have allowed the team to resolve some important details of trilobite anatomy that have been long debated, such as the structure of its feeding apparatus. For one of the individuals, it must have swallowed ash as it died because its digestive tract is filled with volcanic material and, hence, clearly preserved.

Another insight was how the creatures used their legs. “They have very gnarly-looking spines on the inner side of their legs,” says Paterson. “These would have acted like a shredding tool on whatever was their prey. In other words, they chewed with their legs and pushed the food from their legs up to their mouth.”

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