The oldest evidence of cannibalism was found among the remains of trilobites aged 514 million years off the coast of South Australia, in Emu Bay. A group of Australian and European scientists found not only many wounds on the shells of trilobites, but also fossil excrement, apparently produced by the same trilobites, containing fragments of the shells of their relatives. From all this it follows that the emergence of cannibalism must be attributed to the early Cambrian – more than 50 million years earlier than previously thought. An article about this was published in the journal Palaeogeography, Palaeoclimatology, Palaeoecology.
Cannibalism is widespread among the million modern species of arthropods. So, the female praying mantis eats her partner after copulation, termites suck blood from wounded relatives, and mosquitoes feast on larvae. Previous studies have attributed the earliest cannibalism to the late Ordovician period, about 450 million years ago. However, now it turns out that already 514 million years ago, in the Cambrian period, the “king” of trilobites ate everything that he could get his hands on, including armored creatures of his own kind.
The characteristic fossilized food left inside the guts of extinct organisms is considered by paleontologists to be the best evidence that one animal ate another. However, such fossils are rare. In this case, the scientists were lucky: the fossil-rich site in Emu Bay had the optimal conditions for preserving this kind of evidence—fossil injuries and fossilized feces. Trilobites had a hard exoskeleton, like modern armored arthropods like horseshoe crabs or lobsters. When the trilobites managed to fight off the attack, their shells retained bite marks and places of missing body fragments.
Russell Bicknell, a paleontologist at the University of New England in Australia, and colleagues focused on studying such healed wounds in two trilobite species, Redlichia takooensis and Redlichia rex. After collecting 38 fossils of the two species during fieldwork in Emu Bay and in the collection of the Museum of South Australia, scientists began looking for patterns that could tell about the nature of the attacks – who, in one case or another, was the attacker, who managed to fight back. Small trilobites with scars were not found at all – they were already found in fossilized excrement, also called coprolites. The most active cannibal at the same time was the 25-cm “king of trilobites” R. Rex, it was in his feces that most of the remains of small trilobites were found.
However, trilobites could not be exclusively cannibals, otherwise this species would not have existed for a long time. They probably attacked their relatives in conditions of a shortage of other resources.