First high-intensity glossopterid herbivory index assessment from Indian Gondwana: Insights into global Permian plant-insect interactions

Abstract

The Permian sediments of the East Bokaro Coalfield, Jharkhand, within the Damodar Basin, are renowned for their abundant Lower Gondwana plant fossil record. The megafloral assemblages, recovered from the Barakar Formation (late Artinskian-Kungurian; late Early Permian), particularly from the Open Cast Projects of Kathara, Karo, and Khasmahal, reveal diverse insect-mediated damage. The flora is dominated by Glossopteridales (Glossopteris, Gangamopteris), followed by Cordaitales (Noeggerathiopsis, Euryphyllum) and Equisetales (Schizo-neura). Of 974 examined specimens, 89 (9.13%) exhibit traces of insect activity. These traces offer critical insights into early insect behaviour and ecological interactions. Documented feeding types include galling, blotching, midrib feeding, hole feeding, margin feeding, surface abrasion, and complete surface obliteration-primarily affecting glossopterid leaves, scale leaves, and stems. Margin feeding emerges as the most prevalent damage type, accounting for 28.09% of recorded instances. Additionally, the presence of egg sacs along leaf midribs and laminae suggests oviposition behaviour. This investigation represents the first quantitative Herbivory Index (HI) study from Indian Gondwana, providing a benchmark dataset for understanding Permian plant-insect dynamics in the Southern Hemisphere. The HI was applied to quantify feeding intensity, revealing a peak value of 31.97% for surface feeding, indicating significant insect activity. Comparative analysis with contemporaneous Permian floras from Gondwana and Laurasia demonstrates that the East Bokaro assemblage exhibits relatively diverse herbivory levels in a global context, highlighting its ecological distinctiveness. These findings substantially contribute to our understanding of insect feeding strategies, plant-insect coevolution, and their evolutionary implications during the late Early Permian, offering a critical reference point for global deep-time herbivory studies.