Prehistoric trilobite fossils reveal unprecedented soft tissue details
Researchers have made an extraordinary discovery that has provided a unique opportunity to learn more about the past and acquire previously inaccessible knowledge. This discovery was made possible by a fortunate turn of events and a prehistoric volcanic eruption.
A volcanic eruption occurred during the Cambrian period. The pyroclastic flow and ash from this eruption entered a shallow marine environment inhabited by ancient arthropods known as trilobites. The ash ensured the preservation of these trilobites, including their soft tissues, which typically degrade or are destroyed in other fossilisation processes.
Now, hundreds of millions of years later, researchers have had the unprecedented chance to study the three-dimensional anatomy of these trilobites and the smaller creatures that were attached to their bodies at the time.
Cambrian ellipsocephaloid trilobites from Morocco are articulated and undistorted, revealing exquisite details of the appendages and digestive system, according to members of the team led by sedimentologist Abderrazzak El Albani from the University of Poitiers in France, as quoted by the portal sciencealert.com.
Researchers suggest that this discovery highlights that volcanic ash deposits in the marine environment could be a source of exceptionally well-preserved organisms.
We know that such pyroclastic flows can capture and preserve a snapshot of what they cover. The most famous example is Pompeii, where inhabitants were buried and encased in millions of tonnes of ash that fell on the ancient Roman city, preserving their final moments in vivid detail.
Such a discovery is rare
Despite over 22,000 known species of trilobites described and documented over 300 million years from the beginning of the Cambrian, the number of fossil specimens with intact internal anatomy is extremely limited and usually incomplete. This is because soft tissues cannot survive the temperature and pressure changes that accompany fossilisation.
In the Tatelt Formation in Morocco, a fossil deposit with many layers spanning centuries, there is a thick layer containing volcanic ash and debris. Within this layer, El Albani and his collaborators found specimens of two species of trilobites.
The characteristics of this ash layer suggest that it was deposited during a single large pyroclastic flow, during which hot ash and gas travelled across the ground away from the volcanic eruption. Minerals indicate rapid interaction between hot volcanic material and salty seawater.
This had never been observed before
To understand the impact this had on the fossilisation process of the trilobite specimens, researchers used micro-CT X-ray imaging to reconstruct the animals' internal anatomy in three dimensions. The results were simply spectacular.
They observed trilobite skeletons that had not been distorted by time. They also examined their antennae, digestive systems, and complex anatomy around the mouth. Their uniqueness is that some of the discovered elements had never been identified.
The pyroclastic flow even preserved tiny brachiopods – small creatures resembling clams, which clung to the shells of trilobites in an epibiotic relationship. These brachiopods appear relaxed, suggesting that both species perished together, either buried alive or shortly after death.
We have gained more insight into one of the most numerous groups of animals that ever existed on our planet. This research has also revealed an untapped paleontological resource.
