An article published in the journal “Palaeogeography, Palaeoclimatology, Palaeoecology” describes a research of truly exceptional fossils because they kept in ancient ocean sediments the traces left in the Cambrian by trilobites and their prey, worm-like creatures. Their analysis reveals the trilobites’ predatory behavior, which was already sophisticated more than half a billion years ago.

Trilobites were arthropods that had considerable success in the course of the Paleozoic era, disappearing only in the devastating extinction at the end of the Permian period, when the Earth was reduced almost to a dead planet. There were several thousand species of trilobites classified in a class on their own called trilobite. In the Cambrian period, between 541 and 485 million years ago, instead, there was the largest spread of species seen in the history of the Earth and trilobites were among the protagonists.

Many geological and paleontological research has been conducted in the St. Francois Mountains, a mountain range in the south-east of the State of Missouri. In the Cambrian, they were islands in an ocean in which trilobites and creatures that resembled today’s worms lived. Sometimes, it’s possible to find not only these animals’ fossils but also fossil traces of their burrows and trails left in the sediments.

In this research, a crucial discovery concerned traces left by trilobites that intersected with those of their worm-like prey. Generally, in a site they are only some of these situations but one of them is different, with hundreds of points in which traces of trilobites intersected with worm-like creatures’ burrows. For that reason, 82 slabs were taken from the rocks in order to study the interactions between these ancient animals.

That’s how James and John Huntley Schiffbauer, assistant professors of geological sciences at the Missouri University (MU) College of Arts and Science, conducted a research to analyze the slabs taken from that site. Their team studied the rocks with sophisticated techniques such as three-dimensional laser scans and digital photographs analysis. They allowed to find the ancient burrows and the traces left by trilobites and their prey.

The discovery is interesting because the traces allowed the researchers to reconstruct the those trilobites’ predatory techniques. Previous studies conducted at MU revealed that trilobites had very large eyes so the researchers were also trying to find clues that revealed how they used them.

The statistical analysis of the traces suggest that trilobites were selective in their search for prey, preferring smaller ones. Their attack was conducted from above but with a low angle in order to take advantage of their many legs to improve their ability to grasp their prey firmly. Their large eyes probably improved their skills in finding traces of the their prey’s burrows.

The predatory behavior reconstructed is sophisticated and means that these trilobites were already evolved from this point of view. This research shows that half a billion years ago there were already animals that had developed some strategic skills in their attacks on their prey, confirming the importance of predation in evolution.