Unearthing ancient secrets: Trilobites preserved by volcanic ash
Researchers have stumbled upon an extraordinary discovery, giving them the opportunity to learn about the past and gain knowledge that was previously inaccessible. This breakthrough would not have been possible without a series of coincidences and a prehistoric volcanic eruption.
In the Cambrian era, a volcano erupted. The resulting pyroclastic flow and ash flowed into a shallow marine environment inhabited by a population of ancient arthropods called trilobites. The ash preserved them to this day, along with soft tissues, which usually degrade or are destroyed during other fossilization processes.
Now, hundreds of millions of years later, we have had the chance to observe an unprecedented record of their three-dimensional anatomy, as well as the smaller creatures that clung to their bodies at that 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 say this discovery suggests that volcanic ash deposits in a marine environment could be a source of exceptionally well-preserved organisms.
We know that such pyroclastic flows can preserve a snapshot of what they bury. The most famous example is Pompeii, where inhabitants were buried and encased in millions of tons of ash that fell on the ancient Roman town, preserving their last moments in horrifying detail.
Such a discovery is rare
Despite over 22,000 known species of trilobites described and documented over 300 million years since the beginning of the Cambrian, the number of fossil specimens with intact internal anatomy is exceedingly limited, and they are usually incomplete. Soft tissues cannot survive the temperature and pressure changes that cause fossilization.
In the Tatelt Formation in Morocco, a fossil deposit with many layers spanning centuries, a thick layer contains volcanic ash and debris. El Albani and his collaborators found specimens of two species of trilobites within these layers.
The characteristics of this ash layer indicate that it was deposited during a single large pyroclastic flow, during which hot ash and gas moved across the ground away from the volcanic eruption. The minerals indicated a quick interaction between the hot volcanic material and salty seawater.
This has never been observed before
To determine the impact on the fossilization process of trilobite specimens, researchers used X-ray microtomographic imaging to reconstruct the interior anatomy of the animals in three dimensions. What they discovered was simply spectacular.
They observed trilobite skeletons that were not distorted by time. They also examined their antennae, digestive system, and complex anatomy around the mouth. Their discovery was unique because some of the elements had never been identified.
The pyroclastic flow even preserved tiny brachiopods — small creatures resembling clams that clung to the trilobite shells in an epibiotic relationship. These brachiopods assume a relaxed position, suggesting that both species died together, either buried alive or shortly after death.
We know very little more about one of the most numerous groups of animals that ever existed on our planet. However, the research has also revealed an untapped paleontological resource.
