Trilobite ‘Pompeii’ reveals 500-million-year-old animals preserved in exquisite detail (2024)

Create a list of articles to read later. You will be able to access your list from any article in Discover.

You don't have any saved articles.

Trilobites were one of our planet’s most successful groups of animals.

First appearing roughly 521 million years ago, they split into an incredible diversity of species ranging from just a few millimetres to over 90 centimetres long. Their hard, calcified exoskeleton is frequently well preserved in the fossil record, making trilobites some of the best studied fossil marine animals.

Palaeontologists have been able to figure out a lot about trilobites from their exoskeletal ‘shell’, but their understanding has been limited by the relative scarcity of soft tissue preservation, including of the arthropods’ legs, mouthparts and internal organs.

Now, researchers have described some of the best-preserved trilobite fossils ever discovered.

The fossils represent two species that were rapidly buried by volcanic ash as they walked or rested on the floor of a shallow sea some 500 million years ago. The speed at which they were preserved and the fine nature of the ash means that the resulting three-dimensional moulds show details as small as the filaments on the trilobites’ legs and tiny commensal animals attached to their backs.

The trilobites formed natural moulds within the ash which turned to stone, in the same way in which the eruption of Mount Vesuvius buried the unfortunate inhabitants of Pompeii and Herculaneum in 79 AD.

Dr Greg Edgecombe is a palaeontologist at the Natural History Museum who specialises in trilobites and was involved in describing these incredible new specimens.

“I’ve been studying trilobites for nearly 40 years, but I never felt like I was looking at live animals as much as I have with these ones”, says Greg. “It’s pretty mind blowing. I’ve seen a lot of soft anatomy of trilobites, but it’s the 3D preservation here that really does it.”

“Everybody who’s seen these images are just gobsmacked. It’s extraordinary.”

The paper describing these incredible fossils has been published in Science.

Perfect casts of ancient arthropods

The fossils formed on what was once a shallow, sandy sea floor over which a whole host of trilobite species would have been scurrying about. Suddenly, a volcano on the coast erupted, sending ash plumes and molten lava into the air and a pyroclastic flow pummelling down its slopes.

As this silica-rich current of hot gas and volcanic matter hit the sodium-rich sea, the reaction caused the water to become more acidic and new minerals to crystalline and rapidly turn to rock - or lithify.

The trilobites were likely encased within a matter of seconds. Their burial was so rapid that even the tiny animals living on them are preserved as in life. These tiny lamp shells, which were a type of brachiopod, attached to the outer surface and legs of the trilobites using a little soft tissue stalk.

“The trilobites are encased even before the brachiopods could collapse, so the lithification was fast,” explains Greg. “There is this unappreciated discovery that volcanic ash in shallow marine settings could be a bonanza for exceptional fossil preservation.”

As the trilobites were smothered, their final act was swallowing a mouthful of slurry, filling their guts with the volcanic ash. Over time, their bodies decayed, leaving near-perfect three-dimensional hollow moulds within the rock. The material in their guts also turned to rock, preserving a perfect cast of their digestive tract running through the natural mould.

The specimens were imaged in a CT scanner, allowing their 3D form to be reconstructed from X-rays.

The fine grain of the volcanic ash means that the casts show us incredible details - not only each body segment and leg, but even the hair-like structures that run along the appendages. These details have been observed in other fossil trilobites, but rarely in three-dimensions and as they would have been positioned in life.

It is the extraordinary preservation of the mouth parts that has really excited Greg.

“We’ve never had this level of information about the appendages around the mouth,” he says. The fossils show that these trilobites had a previously unknown pair of modified appendages that sat right next to the mouth to help pass food into it. These small structures have a short antenna-like branch.”

“The specialisation of these appendages around the mouth is something we’ve not known in trilobites previously. I think that’s partly because we’ve got this 3D preservation and see everything in situ.”

The rarity of these fossils can’t be overstated. Whilst soft tissue from trilobites is known from around 30 of the 22,000 known species, typically they are squashed flat and often mispositioned. But even returning to the rock formation in which these specimens were discovered has so far yielded only the four studied examples with this exceptional preservation.

“It takes a lot of work to find them,” explains Greg. “Our lead author Abderrazak El Abani has done numerous field trips in Morocco since he became aware of these fossils, working long days in the field but still not found any more. So these trilobites are very scarce.”

Crucially, it shows us that incredibly well-preserved fossils from volcanic ash in shallow marine environments exist. Other trilobite fossils with soft tissue are thought to have formed in deeper seas, whilst these ones came from nearshore environments.

Greg is hopeful that other rock formations that have similar origins could contain fossils with comparable levels of preservation and that people will now know to look for them.

Read more

Discover oceans

Explore life underwater and read about the pioneering work of our marine scientists.