Paleontologists have unearthed a well-preserved collection of Cambrian trilobite fossils in Morocco's High Atlas Mountains. The 510-million-year-old specimens are among the best-preserved three-dimensional trilobite fossils ever found.

Trilobites are extinct arthropods that dominated the marine fauna of the Paleozoic Era.

During their lifetime on Earth, which lasted much longer than the dinosaurs, they survived two major extinctions and dominated undersea ecosystems.

Trilobites are among the best-studied marine animal fossils because their hard, calcified exoskeletons are well preserved in the fossil record.

Over the past two centuries, paleontologists have described more than 20,000 species of organisms.

However, until now, comprehensive scientific understanding of this incredibly diverse group has been limited by the relative lack of soft tissue preservation.

“I've been studying trilobites for nearly 40 years but I've never felt as though I was looking at a living animal as I did in this case,” said Dr Greg Edgecombe, a palaeontologist at the Natural History Museum in London.

“I've seen a lot of representations of the soft-body anatomy of trilobites, but the 3D preservation here is truly astounding.”

“An unexpected outcome of our research is the discovery that shallow marine volcanic ash could be a huge repository for the preservation of exceptional fossils.”

The Moroccan trilobite was encased in hot ash in seawater, so its body fossilized very quickly as the ash turned to rock.

The ash molds preserved parts of their bodies, their legs, and even the hair-like structures running along their appendages.

The trilobite's digestive tract was also preserved after being buried in the ash.

Tiny “lamp shells” attached to the trilobite's exoskeleton also remained attached by fleshy stalks, just as they were when the animal was alive.

Microtomographic reconstruction of trilobite species. Zygothera mauretanica Ventral view. Image courtesy of Arnaud Mazurier, IC2MP, University of Poitiers.

Using CT scans and computer modelling of virtual X-ray slices, the researchers found that an appendage found at the edge of the mouth had a curved, spoon-like base, but was so small that it went undetected in the less well-preserved fossils.

In fact, while trilobites were previously thought to have three pairs of head appendages behind their long antennae, this study shows that both Moroccan species have four pairs.

The fleshy leaf-like part covering the mouth, called the labia, was recorded for the first time in a trilobite.

“The results reveal in incredible detail the clustering of specialised pairs of legs around the mouth, giving us a clearer picture of how trilobites fed,” said Dr Harry Burks, a palaeontologist at the University of Bristol.

“We found that the head and body appendages had rows of densely packed spines that pointed inwards, like those of today's horseshoe crabs.”

“As a scientist who has studied fossils from different times and places, finding such amazingly well-preserved fossils in a volcanic area was a very exciting experience for me,” said geologist Professor Abderrazak El Albani of the University of Poitiers.

“I believe that pyroclastic deposits should become new research subjects because of their excellent potential for capturing and preserving biological remains, including delicate soft tissues.”

“These discoveries are expected to lead to important discoveries about the evolution of life on Earth.”

The results of this study today are journal Science.

_____

Abderrazak El Albani others2024. Rapid volcanic ash deposition reveals 3D structure of Cambrian trilobite. Sciencein press.