Early Cretaceous amber from south-western France: insight into the Mesozoic litter fauna

The Albian amber of Archingeay (Charente-Maritime, SW France) shows a unique ecological feature among worldwide Cretaceous ambers: a large part of the arthropods trapped in this resin are representatives of the litter biota (i.e. the fauna living on the ground surface). This selective trap sampled the in situ fauna, important for the knowledge of the Early Cretaceous forest ecosystem. This exceptional fossilization could be explained by an important fluidity of the resin, which allowed flows from the branches or the trunk to directly contact the soil, instantaneously entrapping organisms crawling on the soil surface as well as the associated plant remains. The plant source of the resin was probably a member of the Araucariaceae, as suggested by SEM analysis of both plant remains trapped in the resin and the abundant lignite associated with the amber in the same strata. This litter-bearing amber exhibits a high diversity of taxa, encompassing 14 of 21 arthropod groups included in this resin: Isopoda, Myriapoda, Acari, Araneae, Pseudoscorpionida, Collembola, Blattodea, Psocoptera, Coleoptera, Homoptera, Heteroptera, Orthoptera, Hymenoptera, and Diptera. In addition to a unique insight into the diversity of a Cretaceous subtropical forest floor, this litter fauna provides valuable paleoclimatic data for the west European Albian coast, suggesting xeric conditions with a probable dry season within the globally warm and wet period of the mid-Cretaceous.