465-Million-Year-Old Fossilized Trilobite Discovered by Scientists, Imaging Reveals the Last Meal Still Preserved in Its Gut

About 465 million years ago, a marine arthropod died near Prague. The final meal of the armored critter still lies in its guts as its body is buried in the sea floor, where it remained entombed for ages.

Preserved Gut Contents

The trilobite fossil was first discovered by a private collector in 1908. The fossil is contained in a small sphere of ancient sediment called siliceous nodules, which was weathered out of the shales of the Šárka Formation.

The rock deposit is all that remains of an ancient sea that once covered the Prague Basin in the Czech Republic. The nodules were created when sediment hardened rapidly around animals at very shallow depths. This process froze organisms in time and kept their 3D structures nearly intact.

Upon opening the siliceous nodules, it unveiled a fossilized specimen of the trilobite Bohemolichas incola. The fossil was handed over to Dr. Bohuslav Horák Museum, where Petr Kraft first saw it as a boy. Decades later, Kraft became a paleontologist at Charles University, working with another paleontologist, Valéria Vaškaninová.

The two researchers further studied the trilobite fossil, and something unusual caught their eyes. They spotted tiny, visible shells in the middle of the fossil, where the exoskeleton was a bit broken. The paleontologists decided to investigate the 3-centimeter object using synchrotron microtomography, a medical imaging technique that works like a CT scan but with much better resolution.

Scanned images of the tiny, fossilized shells reveal the final meal of the trilobite. Vaškaninová spent another one and a half years analyzing the scan to further understand the unusual gut content.

It was found that the meal consisted of ostracods or small crustaceans with vaulting shells. The shells were remarkably preserved, and scientists figured out that some of them belonged to Conchoprimitia osekensis, a tiny animal now extinct. Aside from this, the team also discovered a conical conch that belongs to a hyolith, a small bottom dweller that no longer exists. Other contents of the trilobite gut include the remains of an extinct echinoderm related to modern-day starfish and sea urchins and fragments of bivalves like today's clams and oysters.

Trilobite's Ancient Lifestyle Revealed

Based on how the shells are preserved, the researchers concluded that this specimen was a bottom dweller and most likely a scavenger. Predators are typically selective and mostly eat the soft parts of prey, so the fact that the guts contained a variety of shells indicates that they were not picky. As Vaškaninovád describes, they were like vacuum cleaners that eat almost everything.

Although the guts were not included in the preserved fossil, their contents reveal significant insight into the physiology of the trilobite. The shells from its last meal are made of calcium carbonate, which dissolves in acidic conditions. This means that the animal's gut had a neutral or alkaline pH. It was also assumed that the trilobite had two stomachs based on the imprint of the shape of the digestive tract.

These features probably evolved at the beginning of arthropod evolution since they are also found in other living arthropods. The new findings also strengthened the suspicion that trilobites might be related to chelicerates or crustaceans.