Possible courtship behaviour of Devonian fish: Evidence from large radial trace fossils in northwestern China

One kind of mysterious underwater circle observed on the seafloor near southern Amami-Oshima Island in subtropical Japan has attracted widespread attention, but its origin has long been unknown. In recent years, based on successive underwater photography, they were shown to represent the patterned structures constructed by male pufferfishes. Here we present a large radial trace fossil from the Upper Devonian Hongguleleng Formation in western Junggar, Xinjiang, northwestern China. They are circular or near-circular patterned structures consisting of numerous radial grooves and ridges. Based on morphological analysis of these specimens and comparison with the modern patterned structures made by pufferfish for courtship, we suggest that this trace fossil may be patterned structure made by male fish in the Devonian to attract females. If true, these structures would be the first reported example of courtship behaviour in the trace fossils of fish, and suggest that animal courtship behaviour has existed for at least 360 million years. These trace fossils provide new material for research on the breeding strategies and sexual selection of Devonian animals, and new insight on the origin and evolution of courtship behaviour.