Traces of a limnic food web in the Eocene Lake Messel — a preliminary report based on fish coprolite analyses

The extraordinary fossil preservation of a wide variety of organisms (i.e. algae, arthropods, vertebrates) in the Eocene Lake Messel locality partly allows the reconstruction of an autochthonous food web. Investigations on over 150 fish coprolites from different stratigraphic horizons reveal for the first time cuticular remains of different arthropod taxa including Branchiopod Crustacea (Cladocera, Conchostraca) and Nematocere Diptera (Culicidae, Chaoboridae). The picture of the “hostile” Lake Messel must be revised with these new finds, as there is now evidence for diverse and abundant autochthonous life in the upper water layers. The organisms identified here were part of a complex food web, and thus close the gap between primary producers and fish in the Lake Messel ecosystem. By coprolite analysis, the food web reconstruction presented here is based on evidence of actually eaten oragnisms. Primary producers were pelagic, floating or benthic algae, the latter growing on a substrate (Messel Waterlily and other higher plants). A number of Arthropoda described here (e.g. Culicidae) fed on these algae as primary consumers. Second level consumers include Chaoboridae (described here for Messel for the first time) and Heteroptera. Juvenile and small fish, which in turn were captured by adult predatory fish, crocodiles, turtles, and piscivore mammals represent higher order trophic levels.