Most intact trilobite fossils ever found shake up scientific knowledge of long-extinct group

Scientists 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 Mountains of Morocco, and scientists refer to them as “Pompeian” trilobites due to their remarkable preservation in ash.

The paper, “Burial of fast volcanic ash reveals 3D anatomy of Cambrian trilobites”, was published in the journal Science.

Trilobites from the Cambrian period were the subject of research by an international team of scientists led by Professor Abderrazak El Albani, a geologist working at the University of Poitiers and originally from Morocco. The team included Dr. Greg Edgecombe, 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 living animals as much as with these. I’ve seen a lot of trilobite soft anatomy.” but it’s the 3D preservation that’s truly stunning here.

“An unexpected result of our work is the discovery that volcanic ash in shallow marine environments could be a bonanza 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. Paleontologists have described over 20,000 species over the past two centuries.

Until now, however, a comprehensive scientific understanding of this phenomenally diverse group has been limited by the relative lack of soft tissue preservation. Because Moroccan trilobites were encased in hot ash in seawater, their bodies petrified very quickly as the ash turned to rock—and they met a similar end to the inhabitants of Pompeii after the eruption of Vesuvius.

Ash molds preserved every segment of their bodies, their legs, and even the hair-like structures that ran along the appendages. The digestive tract of trilobites was preserved even after it was filled with ash. Even the small “lampshells” attached to the trilobite exoskeleton remained attached by fleshy stalks as in life.

Lead author Professor 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 an extremely exciting experience for me.

“I think that pyroclastic deposits should become new targets for study, given their exceptional potential for trapping and preserving 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 on the edge of the mouth had curved spoon-like bases, but were so small that they went undetected in less perfectly preserved fossils.

In fact, trilobites were previously thought to have three pairs of cephalic appendages behind their long antennae, but both Moroccan species in this study showed that 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 the grouping of specialized pairs of legs around the mouth, giving us a clearer picture of how trilobites fed. The head and body appendages were found to have inward-facing batteries of dense spines, like today’s skunks have.’