The Randeck Maar: Palaeoenvironment and habitat differentiation of a Miocene lacustrine system

Abstract The Randeck Maar in S. Germany is a well-known fossil lagerstatte with exceptionally preserved fossils, particularly insects and plants, which thrived in and around the maar lake during the Mid-Miocene Climatic Optimum (late Early/early Middle Miocene, mammal zone MN5). We provide the first critical and detailed overview of the fauna and flora with lists of 363 previously published, partially revised, and newly identified taxa. Plant remains are the most diverse group (168 taxa), followed by insects (79). The flora points towards subhumid sclerophyllous forests and mixed mesophytic forests, the former being an indication for the occurrence of seasonal drought. Three main sections can be differentiated for the habitats of the Randeck Maar lake system: (1) Deep- and open-water lake habitats with local and short-termed mass occurrences of insect larvae, amphibians, and/or gastropods, while fish is particularly scarce. The interpretation of the water chemistry is problematic because contradictive palaeoenvironmental indicators for both brackish and freshwater conditions exist. (2) Shallow parts of the lake comprise a narrow reed-belt with insects and gastropods living on the exposed plant stems as well as turtles. (3) Crater slopes and surrounding plateaus were mainly covered by subhumid sclerophyllous to mixed mesophytic forests depending on sun exposition and soil conditions. Horses and other forest-dwellers preferably lived in forested habitats while proboscideans and rhinoceratids occupied more open habitats. Our study also brings up contradictive results that cannot be untangled with the current state of knowledge and thus directions for future studies are discussed.