The earliest signs of cannibalism appear in 514-million-year-old trilobite fossils from Emu Bay, off the coast of South Australia. Researchers from Australia and Europe found numerous bite marks on trilobite shells and traces of fossilized excrement containing shell fragments from nearby relatives. This combination of damage and coprolites suggests that cannibalism emerged in the early Cambrian, about 50 million years earlier than previously estimated. An article on these findings appeared in the journal Paleogeography, Paleoclimatology, Paleoecology.
Cannibalistic behavior is observed in many living arthropod groups today. For example, female mantises sometimes eat their mates after mating, termites feed on kin, and some mosquitoes target larvae in crowded environments. Earlier work had placed the origin of cannibalism in the late Ordovician, roughly 450 million years ago, but recent evidence points to an earlier Cambrian event around 514 million years ago, when even the dominant trilobite species consumed anything nearby, including armored relatives.
The preserved gut contents and fossil injuries are considered among the strongest indicators of predation or scavenging between species. Yet such fossils are rare. In this case, the Emu Bay region provided ideal preservation conditions, allowing researchers to observe both healed wounds and fossilized feces that preserve dietary traces. Trilobites possessed hard exoskeletons, similar to modern armored crustaceans, which helped them leave lasting marks of struggle. When attacks occurred, the shells recorded telltale bite marks and signs of body-part loss that endured through fossilization.
Researchers conducted a detailed study of two trilobite species, Redlichia takoensis and Redlichia rex, by examining 38 fossils collected from Emu Bay and material held in museum collections. The team looked for patterns in injury and distribution to infer the aggressor and the sequence of events. Wounds on smaller individuals were scarce because they had already appeared in coprolites, while the most formidable predator left a substantial record in the fecal material attributed to the large 25-centimeter king of the group. Much of the fragmentary material from smaller specimens surfaced in these coprolites, providing a window into a cannibalistic landscape that favored the larger predator.
Despite these findings, trilobites could not have relied solely on cannibalism without risking their own survival. The interpretation suggests episodic cannibal attacks driven by resource scarcity rather than a constant behavior, with relatives becoming targets when other food sources dwindled. This picture helps explain how a lineage with such a robust, armored body plan could persist while occasionally turning on kin in an environment where opportunities and sustenance were unevenly distributed.
In sum, the amalgamation of bite marks, fossilized feces, and the distribution of injuries supports a scenario in which early Cambrian ecosystems featured cannibalistic interactions that shaped the survival strategies of trilobites. The discovery adds a new dimension to the timeline of social and feeding behaviors among ancient arthropods and invites further study into how early Cambrian communities organized themselves in the face of scarce resources. The broader significance lies in understanding how predation and competition influenced early animal life—insights drawn from the Emu Bay deposits and their extraordinary preservation. Attributions: Paleogeography, Paleoclimatology, Paleoecology