An assemblage of large-sized insect traces in paleosols from the middle Miocene of northern Patagonia related to the climatic optimum

A new assemblage of large insect trace fossils is recognized in paleosols of the middle Miocene pyroclastic deposits from extra-Andean north Patagonia. This assemblage includes Racemusichnus jacobacciensis igen. isp. nov., the largest trace fossil in paleosols attributed to solitary insects. R. jacobacciensis is represented by clusters of two to seven thickly walled cylinders horizontally orientated in the paleosol. The cluster arrangement, its orientation, the large size and wall of the cylinders suggest a dung beetle, probably a representative of the Geotrupidae as the possible trace maker. The new ichnoassemblage, also comprising large-sized specimens of Coprinisphaera ispp., Teisseirei barattinia and Feoichnus challa, belongs to the Rosellichnus assemblage-SAPIA of the Coprinisphaera Ichnofacies. Mollic paleosols along with the trace fossils, mammal remains and previous data for this unit suggest an open grassy habitat compatible with high productive grass savannas, under a temperate-warm and seasonal subhumid climate. This assemblage of large-sized trace fossils is attributed to highly productive ecosystems related to the rise of temperature occurred during the Middle Miocene Climatic Optimum. •Racemusichnus jacobacciensis igen. isp. nov. is a new trace fossil from Patagonia.•It is the largest from paleosols produced by solitary insects, probably Geotrupidae.•It is part of an association of traces of large size that can be linked to the MMCO.•This association of the Rosellichnus assemblage-SAPIA occurs in mollic paleosols.•It is inferred a grass savanna developed under temperate-warm subhumid climate.