Earliest record of rhinocerotoids (Mammalia: Perissodactyla) from Switzerland: systematics and biostratigraphy

Earliest rhinocerotoids from Switzerland are reviewed on the basis of dental remains from the earliest Oligocene north-central Jura Molasse localities of Bressaucourt (MP21/22) and Kleinblauen (top MP22). The record in Bressaucourt is restricted to Ronzotherium and Cadurcotherium, representing Switzerland's oldest, well-dated post-"Grande Coupure" large mammal association, the only occurrence of Cadurcotherium, and the earliest occurrence of rhinocerotoids in Switzerland. The correlation with high-resolution stratigraphy of this locality permitted a dating of the fauna to ca. 32.6 Ma, less than a million years after the "Grande Coupure" event. The rhinocerotoids of Kleinblauen are represented by Epiaceratherium, Ronzotherium and Eggysodon. With the presence of Plagiolophus ministri, they are the only well-dated Swiss post-"Grande Coupure" large mammal assemblage with the persistence of an endemic pre-"Grande Coupure" taxon. Moreover, the coexistence of Epiaceratherium magnum and E. aff. magnum could indicate a new speciation within the Epiaceratherium lineage around the top of MP22. The rhinocerotoid associations of Bressaucourt with Ronzotherium – Cadurcotherium on the western side of the southernmost Rhine Graben area, and Kleinblauen with Epiaceratherium – Ronzotherium – Eggysodon on the eastern side, respectively, reveal a possible environmental barrier constituted by the Early Oligocene Rhenish sea and its eventual connection with the Perialpine sea. This one could have separated an arid area in central-eastern France from a humid area in Switzerland and Germany. These results, combined with the repartition of similar rhinocerotoid associations in Western Europe, also give new insights into an alternative earliest Oligocene dispersal route of rhinocerotoids from Asia towards Western Europe via North Italy.