Fish hunting trace Osculichnus and the oldest Sinusichnus sinuosus from the Upper Devonian of South China

Abstract

Trace fossils are special objects in the study of predator–prey interactions in the fossil record. Here we report on diverse morphological types of the gnathostome fish hunting trace Osculichnus from the Upper Devonian of South China. The studied Osculichnus specimens occur as groups of bilobate mounds on the sole of fine- to medium-grained quartz sandstones from the estuarine-embayment depositional system of the Upper Devonian Wutong Formation in Wuhan city. The fish feeding trace Osculichnus is closely associated with the highly regular, branched sinuous trace Sinusichnus sinuosus on the bedding plane. Previously, Sinusichnus sinuosus has been typically reported from Late Cretaceous to Miocene marginal-marine sediments, with two records in the Lower and Middle Triassic of South China, and is generally regarded as the burrows of decapod crustaceans. The discovery of Sinusichnus sinuosus in the Upper Devonian, though of relatively small diameter (0.4–4.3 mm) than its Mesozoic and Cenozoic counterparts, extends its stratigraphical distribution and is suggestive of some primitive, small-sized decapod crustacean producers. The Osculichnus makers possibly preyed upon the Sinusichnus makers or other small invertebrates in the sediments. The overall shape and morphological details of the Late Devonian Osculichnus suggest lungfish as candidate trace makers. The fish hunting traces and associated trace fossils from South China thus provide unique insights into the palaeoecology of Late Devonian fishes.