Oligocene trace fossils from temporary fluvial plain ponds: an example from the Freshwater Molasse of Switzerland

Numerous invertebrate trace fossils and small rare vertebrate tracks are reported and described from the Upper Oligocene deposits of the Lower Freshwater Molasse in eastern Switzerland. They are commonly accompanied by mud-cracks, raindrops, and plant remains, mostly leaves. The invertebrate trace fossils were produced by different animals, mostly insect larvae, nematodes, and probably by molluscs, in desiccating pools on a fluvial plain of a braided river. The trace fossil assemblage differs from the Scoyenia ichnofacies which is typical for terrestrial fluvial plain environment. Instead, it resembles the impoverished Mermia ichnofacies which is probably common but poorly known in this environment. This ichnofacies corresponds to a low energy environment, most probably to fluvial plain ponds.