Plant–insect interactions from the Late Oligocene of Spain (La Val fossil site, Estadilla, Huesca) and their palaeoclimatological implications

Abstract

Trace fossils of insect herbivory are an important tool, which provide evidence for palaeoecological and palaeoclimatic interpretations, as well as being a unique and direct record of the plant–insect interactions in the geologic past. In the Iberian Peninsula, these types of surveys have been scarce and purely descriptive. The La Val fossil site is an interesting, new megaflora assemblage from the Late Oligocene of Spain, which encompasses numerous plant–insect interactions and their palaeoclimatic and palaeoecological implications. A total of 1337 fossil specimens from 13 stratigraphic levels were analyzed for this study. We identified 28 different types of plant–insect interactions belonging to seven Functional Feeding Groups (FFGs). Hole feeding was the most common category of external-feeding insect damage, followed by margin feeding, skeletonization, and surface feeding. Among the internal-feeding FFGs, galling was the richest and most abundant FFG. All other internal-feeding FFGs were relatively uncommon: piercing/sucking, and incertae sedis (DT114). Among stratigraphic levels, the mean herbivory frequency was significantly greater at lower levels compared to the upper levels. La Val presents a marked drop in the diversity of plant–insect interactions through time, possibly due to changes in temperature or humidity levels. A marked decrease in galling diversity and a generalized decrease in interactions are observed at the youngest levels. This could be related to an increase in humidity though time in the La Val palaeoforest, since modern xeric environments favour the proliferation of galls. • Reports plant–insect interactions from an Iberian Peninsula Oligocene deposit. • Herbivore interactions decrease in number and richness in the youngest horizons. • A decrease in galling diversity is also observed in the youngest horizons. • Changes in herbivory across horizons may reflect an increase in humidity through time. • The data provide context for previously reported European plant–insect associations.