Advanced imaging reveals the last bite of a 465-million-year-old trilobite

A recent research by paleontologists from the Faculty of Science at Charles University in Prague and their colleagues details the preserved intestinal contents of a 465-million-year-old trilobite. The study was released in Nature.

Discovered almost a century ago, this exceptional fossil was discovered, preserved in three dimensions within a structure known as a Rokycany ball. However, it has only just come to light due to the state-of-the-art imaging techniques of synchrotron tomography. The study closes a critical knowledge gap on the ecology of trilobites and their place in Paleozoic ecosystems.

Since its discovery in 1908 by private collector Karel Holub, the fossilized trilobite has been kept in the Rokycany museum (now the Museum of B. Horák, a division of the Museum of West Bohemia in Pilsen). According to Petr Kraft, the study's first author from the CU Faculty of Science, "I remember this specimen from my childhood; it was my grandfather's favorite fossil." For this reason, its picture used to hang in the paleontology office of the Rokycany Museum, where he volunteered."

Paleontologists did not, however, recognize until the early 21st century, that the visible fragments of shell in the trilobite's peeled-off median axis may represent preserved contents of its digestive system. It was not feasible to inspect them at the time without damaging the unique fossil.

The scientists made significant progress when they employed synchrotron tomography, a potent instrument that allowed them to non-destructively and highly-resolutionly photograph every shell piece in the stomach. One of the earliest fossils from the Czech Republic to be studied at the European Synchrotron (ESRF) in Grenoble, France, was the Rokycany trilobite.

"Getting slice images—which are akin to what most people are familiar with from CT scans at hospitals—is only the first step. After that, each structure is manually segmented using reconstruction software. After the fossil's three-dimensional model has been rendered in a virtual photo studio, the image depth is increased and an incredibly informative figure is produced, according to Valéria Vaškaninová from the CU's Faculty of Science. Vaškaninová used this laborious but efficient combination of imaging techniques for the first time in a 2020 Science paper on the origin of vertebrate teeth.

The trilobite Bohemolichas incola's digestive system was densely populated with fragments of calcareous shells from marine invertebrates, including echinoderms, bivalves, and ostracods, some of which could be identified down to the species level. It is suggested by the authors that the trilobite was a light crusher, an opportunistic scavenger, and a chance feeder that consumed both live and dead animals that either fell apart easily or were tiny enough to be eaten whole without making an effort to reject the hard shells.

It is amazing that throughout the digestive tract, the calcareous shells with thin walls remain partly dissolved. This suggests that an acidic environment was not encountered by them. Horseshoe crabs and other contemporary crustaceans have gut environments that are nearly neutral or slightly alkaline, indicating that this may be an evolutionary trait of arthropods.

This scavenger became scavenged after death. In the murky sea floor, the researchers found many footprints of small scavengers that had sunk into the trilobite's corpse, which was buried at a shallow depth.

It is surprising that they bypassed the intestines and instead seemed to target soft tissue. The scavengers could have recognized that the digestive tract's inside was toxic and that some of its digestion enzymes were still active. However, they were also unlucky because, as escape trails were missing, a solid "ball" that was quickly developing around the deceased trilobite confined them.

Provided by Charles University