Taxonomy and Paleoecological Significance of Insect Fossils from Member 6 of the Yanchang Formation in Huanglong, Shaanxi

The Triassic was a pivotal interval for the recovery of entomofaunas and the assembly of modern insect lineages following the end-Permian mass extinction. To address the scarcity of fossil records at the southeastern margin of the Ordos Basin, this study presents a systematic taxonomic and paleoecological investigation of insect fossils from Member 6 of the Yanchang Formation at the Baiyuchuan section in Huanglong, Shaanxi Province. The assemblage comprises specimens from the orders Hemiptera, Plecoptera, Blattodea, and Coleoptera. Within the Hemiptera—the primary focus of this research—four families (Hylicellidae, Surijokocixiidae, Granulidae, and Curvicubitidae) are recognized, and two new species (Brevilatum huanglongensis sp. nov. and Beaconiella huanglongensis sp. nov.) are established. Analyses of sedimentology and fossil assemblages indicate that during the deposition of Member 6 (Chang 6 period), the study area transitioned from a delta-front to a delta-plain environment. The presence of Ephemeroptera and Plecoptera nymphs suggests the proximity of well-oxygenated, clean freshwater habitats. Furthermore, preserved pigment bands and eyespot structures on hemipteran wings reveal sophisticated evolutionary coloration strategies, specifically cryptic mimicry and deictic (startle) displays utilized for environmental adaptation. Paleobiogeographical comparisons demonstrate that the Curvicubitidae and Surijokocixiidae link this assemblage to the contemporaneous Madygen entomofauna of Central Asia and Triassic faunas in Australia. Combined with the regional distribution of Odonata fossils, these findings suggest that interconnected paleodrainage systems served as dispersal corridors between the inland basins of East and Central Asia, facilitating faunal exchange. This study enriches the fossil record of the Ordos Basin and provides critical evidence for understanding Triassic insect evolution, paleoecology, and cross-regional biogeography.