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Researchers have described some of the best-preserved three-dimensional trilobite fossils ever discovered. The fossils, which are more than 500 million years old, were collected in the High Atlas of Morocco and are called by scientists the “Pompeii” trilobites because of their remarkable preservation in the ash.

The paper, “Rapid Burial of Volcanic Ash Reveals 3D Anatomy of Cambrian Trilobites,” is published in the journal, Science.

The Cambrian trilobites have been the subject of research by an international team of scientists led by Prof. Abderrazak El Albani, a geologist from the University of Poitiers and originally from Morocco. The team included Dr Greg Edgecombe, a paleontologist at the Natural History Museum.

Dr Greg Edgecombe said: “I’ve been studying trilobites for almost 40 years, but I’ve never felt like I was looking at live animals like I did with these. I’ve seen a lot of trilobite soft anatomy, but the 3D preservation here is truly astounding.

“An unexpected result of our work is the discovery that volcanic ash in shallow marine settings can be gold for exceptional fossil preservation.”

Because of their hard, calcified exoskeleton, which is often well-preserved in the fossil record, trilobites are some of the best-studied fossil marine animals. Over 20,000 species have been described by paleontologists over the past two centuries.

However, until now comprehensive scientific understanding of this phenomenally diverse group has been limited by the relative paucity of soft tissue preservation. Due to the fact that the Moroccan trilobites were encased in hot ash in seawater, their bodies petrified very quickly while the ash transformed into rock – meeting a similar fate to the inhabitants of Pompeii after the eruption of Mount Vesuvius.

Ash forms retain every segment of their bodies, their legs, and even the hair-like structures that run along their appendages. The trilobite digestive tract was also preserved after it was filled with ash. Even the tiny “lamp shells” attached to the trilobite exoskeleton remained attached by fleshy stalks as they had been in life.

Lead author Prof. Abderrazak El Albani said: “As a scientist who has worked on fossils from different eras and locations, discovering fossils in such a remarkable state of preservation in a volcanic environment was an extremely exciting experience for me.

“I think that pyroclastic deposits should become new targets for research, given their extraordinary potential to trap and preserve biological remains, including delicate soft tissues.”

“These findings are expected to lead to significant discoveries about the evolution of life on our planet Earth.”

Using CT scans and computer modeling of virtual X-ray sections, the researchers found that the appendages found at the edge of the mouth had curved bases, similar to spoons, but were so small that they went unnoticed in less perfectly preserved fossils.

In fact, trilobites were previously thought to have three pairs of head processes behind their long antennae, but both Moroccan species in this study showed that there were four pairs.

A fleshy lobe covering the mouth, called the labrum, was first documented in trilobites.

Co-author Harry Burks, from the University of Bristol, added: “The results reveal in extraordinary detail the grouping of specialized pairs of legs around the mouth, giving us a clearer picture of how trilobites feed. The head and body appendages were found to have an inward-facing battery of dense spines, like those of today’s horseshoe crabs.”