Predator-prey interactions in the Early Triassic ocean

The Permian−Triassic mass extinction punctuated the history of life by wiping out 81%−96% of marine species, enabling the establishment of modern ecosystems. Predator-prey interactions represent a significant driving force of evolutionary change in the history of life, but are scarce and heretofore little appreciated during the Early Triassic. We report exceptionally preserved Kouphichnium trackways, burrows and trails, and a previously undocumented compound trace from the Lower Triassic Daye Formation of South China. Kouphichnium is widely attributed to limulids (horseshoe crabs), whereas the simple traces and the compound trace are most probably produced by polychaete worms. The co-occurrence and specific spatial relationships of these traces are interpreted as an unusual case of predatory interaction preserved in the act between limulid predators and their polychaete prey. A dataset of ecospace utilization of infaunal communities in shallow carbonate settings demonstrates that infaunalization was also enhanced at that time, coinciding with the diversification of marine predators. We propose that enhanced infaunalization was driven either by predation or by the amelioration of environmental conditions during the late Early Triassic. Both the snapshot of predators caught in the act of hunting their prey and the diverse predator taxa may indicate prevalent predation pressures in the Early Triassic ocean of South China.