EVIDENCE FOR INSECT AND ANNELID ACTIVITY ACROSS THE TRIASSIC-JURASSIC TRANSITION OF EAST GREENLAND

Abstract

During a study of macroflora from the Astartekloft locality in Jameson Land, East Greenland, endophytic insect ovipositions (egg traces) belonging to ichnogenus Paleoovoidus were recorded for the first time in ginkgoalean (Ginkgoites, Sphenobaiera, and Baiera) fossil leaves across the Triassic-Jurassic (Tr-J) transition (ca. 200 Ma). The ovipositions may have been produced by insects in the order Odonata (dragonflies and damselflies) and are relatively more abundant before than after the Tr-J transition, possibly reflecting changes in plant-insect association. Fossil clitellate annelid (leech) cocoons were also discovered in a macerated sample from a single bed within the Tr-J transition. The cocoons belong to two species: Dictyothylakos pesslerae and Pilothylakos pilosus, extending the range of the latter genus from the Early Cretaceous to the Early Jurassic. This new evidence suggests that the ecosystem and food webs were profoundly affected by the environmental degradation surrounding the end-Triassic event (ETE), which was marked by faunal mass extinctions and floral turnover. Invertebrate ichno- and body fossils may add significantly to paleoenvironmental information provided by plant fossil assemblages, and therefore a protocol for recording evidence of invertebrate activity in paleobotanical research is suggested, including analyzing a standardized number of specimens for fossil traces and bulk maceration for discovery of invertebrate body fossils. More well-designed studies on Mesozoic plant-invertebrate associations are needed and will provide deeper knowledge about the structure and evolution of complex ecosystems.