Evidence of insect leaf mining on Late Triassic (Carnian) gymnosperms from Argentina

Abstract

We describe two ichnotaxa —Cuniculonomus parallelus Givulescu emend. Robledo et al. and Foliomacula diffussus ichnogen. et ichnosp. nov.— of insect leaf mines from the Late Triassic of Mendoza, Argentina. The specimens, from the Potrerillos Formation at the Quebrada del Durazno locality, consist of a linear mine on a Yabeiella leaf, and a blotch mine on a Heidiphyllum leaf. The earliest convincing records of leaf mining are all linear mines, dating back to the middle-late Triassic, with the first blotch mines appearing from the Cretaceous onwards. The discovery presented here therefore represents the earliest record of a blotch mine, and demonstrates that strategies of endophytic herbivory diversified considerably earlier than previously thought. The abundant associated paleoentomological fauna from the locality provides a rare opportunity to consider possible producers of these interactions. A definitive identification of the miners however, remains highly speculative, partly due to the paucity of direct analogues of insect lineages with leaf mining larvae this early in the fossil record. The exceptional abundance and quality of fossil preservation of both plants and associated insects at the Quebrada del Durazno locality also provides an opportunity to re-evaluate plant host diversity and possible adaptations to mitigate insect herbivory. The insect mine on Yabeiella is the first, and to date only, record of this type of interaction on a gnetalean host. We consider the presence of dense pubescence on Yabeiella and its affiliated Fraxinopsis seeds, as a potential passive defense mechanism against insect herbivory rather than as an adaptation to environmental conditions.