High-resolution taphonomic and palaeoecological analyses of the Jurassic Yanliao Biota of the Daohugou area, northeastern China

Abstract

The Yanliao Biota contains numerous exceptionally preserved fossils of evolutionary importance. However, the palaeoenvironment of this biota has not been fully studied. Here we present the first taphonomic and palaeoecological analysis of fossil abundance data from two newly excavated sites in the Daohugou area. In our study we have investigated the taxonomic composition, specimen abundance and size distribution patterns of invertebrate palaeocommunities, and corresponding taphonomic features, such as completeness, articulation and fossil orientation. Our results show that abundant aquatic and terrestrial organisms from various ecological niches are preserved in very thinly planar-laminated mudstone. Aquatic organisms of the two excavations are represented by low-diversity but high-density assemblages containing four species: the clam shrimp Triglypta haifanggouensis, the mayfly nymphs Fuyous gregarious and Shantous lacustris, and the water boatman Daohugocorixa vulcanica. Triglypta haifanggouensis dominates the fauna with carapace lengths ranging from 1.34 mm to 5.62 mm. Size distributions of different bedding planes vary between normal, bimodal and polymodal, implying multiple causes of death: reproductive senescence, and mass mortality events related to active volcanism or to rapid environmental fluctuations within the lake. Generally calm depositional conditions were repeatedly interrupted by weak currents, indicated by preferred plan-view orientations of aquatic insects on four out of nine investigated bedding planes. Changes in the community composition of aquatic arthropods relate to varying lake depth through time, or to different dispersal strategies after community breakdown. Terrestrial insects are highly diverse but less abundant. As a result of rapid burial, 49.8% of which are almost complete and articulated. The flora surrounding the comparatively shallow lake was rich, picturing a thriving forest-like ecosystem with moisture relation in a warm-temperate climate.