Preservation of monoterpenoids in Oligocene resin: Insights into the evolution of chemical defense mechanism of plants in deep-time

Monoterpenoid class of compounds is well-known for the characteristic odor and their contribution in various ecological functions such as plant-insect interaction, defense, pollinator attraction etc. They are extremely volatile and labile by nature and therefore their preservation in geological samples is quite uncommon. In the present article we report, exceptionally preserved monoterpenoids in late Oligocene resin from offshore Shimokita, Japan. Compounds viz. fenchol, fenchone, camphor, borneol, isoborneol are detected in appreciable quantity while camphene, isocamphene and p-cymene are found in low amount. Such rare phenomenon suggests that the amber must have experienced some unique diagenetic condition which favored the preservation of these volatile compounds. These monoterpenes have distinct aroma and they actively contribute into the chemical defense mechanisms of extant plant species. Their excellent preservation in late Oligocene amber depicts that such chemical defense strategies had already been developed by plants during early Cenozoic.