Plant-insect interaction from the Middle Jurassic Haifanggou Formaton in Huludao, western Liaoning and its geological implications

A total of 228 well-preserved fossil leaves have been discovered from the Middle Jurassic Haifanggou Formation in Baimashi Village, Lianshan District, Huludao, Liaoning. To gain insights into the plant-insect interaction during the Middle Jurassic in western Liaoning, this paper aims to identify and quantitatively analyse evidence of insect damages on fossil leaves from the Haifanggou Formation based on previous taxonomic research. Seven insect damage types (DTs) assigned to three functional feeding groups (FFGs) are identified. Margin feeding is the most prevalent FFG, followed by hole feeding and surface feeding, suggesting that Orthoptera and Hymenoptera with chewing mouthparts were dominant during the Middle Jurassic in this area, with Hemiptera and Coleoptera also playing a significant role. The primary plant groups targeted by insects are Ginkgophytes, followed by Pteridophytes, Cycadophytes and Czekanowskiales, with Cycadophytes exhibiting the highest average percentage of damaged leaf perimeter and area. This could be attributed to the physical insect resistance mechanism of conifers, as well as the chemical defense capabilities of Pteridophytes and Ginkgophytes during the Middle Jurassic. Plants and insects from the Haifanggou Formation are highly diverse, and approximately 17.54% of the observed fossil leaves show traces of insect damage, probably indicating the presence of active insects in the area and a close relationship between plants and insects during the Middle Jurassic. Considering the floristic composition and the climate-indicative plant groups, it can be inferred that the climate in the study area during the Middle Jurassic was warm and humid, potentially accompanied by intermittent droughts.