https://www.nature.com/articles/s41586-023-06567-7

Abstract:

"Trilobites are among the most iconic of fossils and formed a prominent
component of marine ecosystems during most of their
270-million-year-long history from the early Cambrian period to the end
Permian period1. More than 20,000 species have been described to date,
with presumed lifestyles ranging from infaunal burrowing to a planktonic
life in the water column2. Inferred trophic roles range from
detritivores to predators, but all are based on indirect evidence such
as body and gut morphology, modes of preservation and attributed feeding
traces; no trilobite specimen with internal gut contents has been
described3,4. Here we present the complete and fully itemized gut
contents of an Ordovician trilobite, Bohemolichas incola, preserved
three-dimensionally in a siliceous nodule and visualized by synchrotron
microtomography. The tightly packed, almost continuous gut fill
comprises partly fragmented calcareous shells indicating high feeding
intensity. The lack of dissolution of the shells implies a neutral or
alkaline environment along the entire length of the intestine supporting
digestive enzymes comparable to those in modern crustaceans or
chelicerates. Scavengers burrowing into the trilobite carcase targeted
soft tissues below the glabella but avoided the gut, suggesting noxious
conditions and possibly ongoing enzymatic activity."

The gut contents of this particular little monster is mainly calcarous
stuff. Hyolithids (some identified by species!), echinoderm stereom and
ostrocods. This isn't to say that other trilobites wouldn't have
preferred less crunchy dinners.