Taphonomic experiments on damaged leaves: implications for interpreting insect-damaged leaves in the fossil record

Abstract

Ancient interactions between plants and insect herbivores are primarily understood through investigations of insect feeding damage on fossil leaves. Such damage is assigned to a damage type on the basis of its morphology. The damage type system is a valuable tool for comparing insect herbivory between different sites; however, for such comparisons to be quantitatively robust requires that the fossilization process does not significantly alter the morphology of herbivore damage on leaves. Here we test the effect of decay in water on leaves with simulated hole or margin feeding damage through controlled laboratory experiments. Crataegus intricata leaves were artificially damaged with hole punches and then left to decay in river water for 50 days. The morphology of the damage was checked on days 0, 3, 5, 7, 10, 12, 14, 17, 21, 24, 27, 31, 34, 37, 44, and 50, and each leaf was assigned to a damage type. Although the leaves underwent many decay-related changes, the damage did not change in any noticeable way in any experimental replicate, and the assigned DTs did not change. These results indicate that decay in standing water does not alter the morphology of damage on leaves. Further studies are needed to assess if other components of the fossilization process, such as transport, decay in sediment, or diagenetic alteration can alter herbivore damage on leaves.