Most pristine trilobite fossils ever found, shaking up scientific understanding of long-extinct group

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 have been dubbed “Pompeii” trilobites by scientists because of their remarkable preservation in ash.

The article, “Rapid volcano ash entombment reveals the 3D anatomy of Cambrian trilobites,” was published in the journal Science.

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

Dr Greg Edgecombe said: “I’ve been studying trilobites for nearly 40 years but I’ve never felt like I was looking at living animals as much as I do with this one. I’ve seen a lot of soft anatomy in trilobites but it’s the 3D preservation that’s really amazing here.

“An unexpected outcome of our work is the discovery that volcanic ash in shallow marine environments could be a boon for exceptional fossil preservation.”

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

However, to date, comprehensive scientific understanding of this phenomenally diverse group has been limited by the relative paucity of soft tissue preservation. Because the Moroccan trilobites were encased in hot ash in seawater, their bodies fossilized very quickly as the ash transformed into rock, which meant a similar end to the inhabitants of Pompeii after the eruption of Mount Vesuvius.

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

Lead author Prof. Abderrazak El Albani says: ‘As a scientist who has worked on fossils from different ages and locations, discovering fossils in such a remarkable state of preservation in a volcanic environment was a very exciting experience for me.

“I think pyroclastic deposits should become new research targets because they have an exceptional potential for capturing and preserving biological remains, including vulnerable soft tissues.

“We expect that these findings will lead to important discoveries about the evolution of life on our planet Earth.”

Using CT scans and computer models of virtual X-rays, the researchers found that the appendages at the edge of the mouth had a curved, spoon-shaped base. However, they were so small that they had not been noticed in less well-preserved fossils.

Trilobites were previously thought to have three pairs of head appendages behind their long antennae, but in both Moroccan species in this study there were four pairs.

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

Co-author Harry Berks from the University of Bristol added: “The results revealed in exquisite detail a clustering of specialized pairs of legs around the mouth, giving us a clearer picture of how trilobites feed. The head and body appendages appeared to be an inward-facing battery of having dense spines, like those of today’s horseshoe crabs.”