“Trilobite Pompeii” discovered

Artist’s impression of the process that once led to the formation of trilobite fossils. © Prof. A. El Albani, Univ. Poitiers.

Volcanic ash enclosed their body structures and preserved them in great detail: Paleontologists report on three-dimensionally preserved trilobite fossils that were formed during a coastal volcanic eruption around 500 million years ago. The finds from the Atlas Mountains in Morocco have now also provided new insights into the anatomy of these famous prehistoric aquatic animals. The discoveries also suggest that paleontological treasures could also lie dormant in other Pompeii-like deposits around the world, say the researchers.

They are among the most prominent of the extinct creatures in the history of the earth: from the Cambrian period around 521 million years ago to the end of the Permian period around 251 million years ago, the world’s seas were teeming with trilobites. This is evidenced by countless fossils of representatives of this very species-rich group of arthropods. Trilobites are therefore considered to be the best-studied marine animals in the history of evolution. But that does not mean that they have already revealed all their secrets. As a rule, only their hard shells have been well preserved. Fine structures of the original body structure, on the other hand, have mostly been lost in the processes of fossilization. There is still some uncertainty about the characteristics of the delicate body structures and the internal organs of trilobites.

New light is now being shed on the fine physical structure of these prehistoric creatures by special finds reported by the international research team led by Abderrazak El Albani from the University of Poitiers. They come from the so-called Tatelt Formation in the Atlas Mountains of Morocco, which dates back to the Cambrian period around 500 million years ago. The researchers discovered astonishingly detailed fossils of two species of trilobites there. “I have been studying trilobites for almost 40 years, but I have never had such an intense feeling of looking at living animals. The 3D preservation in this case is truly astonishing,” says co-author Greg Edgecombe from the Natural History Museum in London.

Bedded in ashes

As the team reports, the examination of the material in which the fossils are embedded shows that it is of volcanic origin. Certain silicate compounds and other substances indicate that the rock was formed from hot ash that had come into contact with salt water. The team therefore assumes that the fossils were formed by a pyroclastic ash flow that covered a shallow area of ​​the sea after a volcanic eruption. When it entered the water, it formed a dense cloud of fine material that enveloped and buried all life. The trilobites thus suffered a similar fate around 500 million years ago to the inhabitants of the Roman city of Pompeii after the eruption of Vesuvius. In the case of the prehistoric aquatic animals, the subsequent fossilization processes led to astonishingly detailed fossils that also show no distortions or crushing, explain the researchers.

In order not to destroy the delicate structures, the team recorded them using computer tomography scans. Based on the data, they then made virtual X-ray sections that led to three-dimensional representations. This revealed how detailed the animals had once been preserved: Even hair-like structures that ran along their appendages can be seen, as well as tiny mollusks that had once attached themselves to the trilobites’ shells. The structures of the digestive tract have also been preserved, the researchers report. In some cases, the ash has apparently even reached these internal structures.

Video: The results of the CT scans allow the detailed 3D structures of the fossils to be represented in the model. © Greg Edgecombe

New insights into trilobite anatomy

The investigations also revealed structures that had not previously been discovered in less well-preserved fossils. For example, it was assumed that trilobites had three pairs of head appendages behind their long antennae. But as the discovery of tiny structures in the area of ​​the mouth has now shown, there were actually four pairs. For the first time, the researchers were also able to identify a structure in the prehistoric arthropods that covered the mouth – a so-called labrum.

“The results also revealed in exquisite detail a cluster of specialized leg pairs around the mouth, giving us a clearer picture of how trilobites fed. It also showed that the head and body appendages had inward-facing spine formations, similar to those of modern horseshoe crabs,” says co-author Harry Berks of the University of Bristol.

In addition to the new insights into the anatomy of trilobites, the team also sees a fundamental message in the study results: “These findings make it clear that marine volcanic ash deposits are a previously little-explored source of exceptionally preserved organisms,” write the authors. First author El Albani says: “I think that pyroclastic deposits should become a new target for study because they have an extraordinary potential for preservation. Such findings could lead to important discoveries about the evolution of life on our planet,” says the scientist.

Source: University of Bristol, scientific article: Science, doi: Science, doi: 10.1126/science.adl4540

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