Bizarre 465-Million-Year-Old Creature Found With Gut Contents Preserved

Scientists have discovered a bizarre fossilized creature that lived 465 million years ago with the content of its gut still preserved.

In a study published in the journal Nature, a team of researchers describe a unique trilobite fossil that was found in Czech Republic's western Bohemia region.

"This is the first ever discovery of a trilobite gut where we can actually see what the animal has been eating. Until now we have had no direct evidence at all for the diets of these very abundant, diverse and ecologically important animals," Per Ahlberg, an author of the latest study from Uppsala University, Sweden, told Newsweek.

Trilobites are extinct marine arthropods with a shape and overall appearance rather like a woodlouse, or roly-poly bug. Arthropods are an extremely diverse group of invertebrate animals that have exoskeletons and a segmented body.

The specimen that the researchers studied is small, measuring under 2 inches in length. The upper surface of the body is covered by a jointed, hard carapace. The soft underside would have carried numerous pairs of legs, but these are not preserved. This trilobite lived on the seafloor and probably walked around fairly slowly.

Trilobites are among the most iconic and common fossil arthropods. These creatures formed a prominent part of marine ecosystems during most of their 270-million-year history, which spanned from the early Cambrian period to the end of the Permian—roughly 541–252 million years ago.

More than 20,000 trilobite species have been described to date. But despite the fact that scientists have documented numerous trilobite fossils, the feeding habits of these animals had to be inferred indirectly. This is because no one had reported a fossil specimen with its internal gut contents preserved.

"This is the only known example out of probably several hundred thousand trilobites that have been collected over the past couple of centuries," said Per Ahlberg.

According to the study, the trilobite specimen has a tightly packed gut full of fragmented shells that belonged to a variety of marine creatures. The findings shed light on the feeding habit and lifestyle of these extinct arthropods.

The researchers found that the trilobite had been eating small animals that were common in its environment, including ostracods (small, shell-bearing crustaceans), stylophorans (an extinct kind of echinoderm—a group that includes starfish and sea urchins), hyoliths (cone-shaped animals with no living relatives) and bivalves (a group that includes clams, oysters and mussels).

While these results are not necessarily very surprising, the authors propose that this species of trilobite, Bohemolichas incola, was an opportunistic scavenger. It likely ate dead or living animals, which either disintegrated easily or were small enough to be swallowed whole.

"It seems to have been a fast and uncritical feeder, just shoveling down whatever it came across that was small enough to fit in the mouth," Ahlberg said.

"We suspect this voracious feeding may have been to do with preparing the animal for moulting: some modern arthropods do similar things, filling the gut to help expand the body, and in fact we can see evidence that the carapace is starting to come apart."

Ahlberg said the most "surprising and interesting" result from studying the fossil was that it provided insights into the physiology of this extinct animal's digestion. The shell fragments would originally have been made of calcium carbonate, which is easily dissolved by acid. But the researchers did not see any evidence of acid dissolution on the shells.

This suggests that the gut pH was high, which is also what scientists have seen in modern crabs and horseshoe crabs. "The evidence from the trilobite suggests that this could be an ancestral trait for the whole of the arthropods," Ahlberg said.

The trilobite specimen documented in the study was first collected in 1908 and was kept in a local museum, although the fossil was never formally described until the latest study.

After the trilobite died, the evidence suggests that the scavenger itself became scavenged. The fossil shows signs that other animals had burrowed into its carcass in order to target the soft tissue, although they avoided the gut. This implies that the conditions in the trilobite's digestive system may have been noxious to these scavengers.