Evidence of specialised agglomeratic galling by Psyllidae on Semecarpus L.f. (Anacardiaceae) leaves since the Pliocene

Galling, a common form of endophytic leaf damage in angiosperms, is characterised by the abnormal growth of plant cells and tissues induced by specialist herbivores. Here, we document the first evidence of unique fossil agglomerate galls along with corresponding midrib-flanking oviposition scars of psyllids (Hemiptera: Psyllidae) on leaf impressions of Semecarpus L.f. (Anacardiaceae) from the latest Neogene (Pliocene) strata of the Chotanagpur Plateau, Jharkhand, eastern India. Each gall is characterised by a hemispherical or sub-globose shape, resembling small nodules or beads, and is uniquely positioned on opposite sides of the secondary veins. When these galls are clustered together, they form compact agglomerates. This indicates a novel galling morphotype that has not been described previously and does not align with any established damage types (DTs) reported in the literature. Based on surveys of modern forests adjacent to the fossil locality and published literature, we suggest that the probable gall inducers were Psyllidae, which produce similar clustered galls on extant leaves of Semecarpus . This evidence indicates that agglomerate gall-inducing insects in the genus have maintained long-term host fidelity since the Pliocene. These findings also broaden the known diversity of fossil galls and offer insights into the evolutionary history of galling behaviours, highlighting how galls diversified through deep geological time.