Stable isotope ecology of Hippotherium from the Late Miocene Pannonian Basin system

Abstract

The retreat of the Paratethys Sea in the Middle to Late Miocene left behind a series of intermontane lakes across Central Europe. Ancient Lake Pannon, which existed in present-day Hungary and surrounding countries, was gradually filled in by fluvial sedimentation from 10 to 4Ma. This infilling allowed for the migration of mammals such as the horse Hippotherium into the Pannonian Basin System (PBS). Stable carbon and oxygen isotope records from Hippotherium are used here to reconstruct changing environmental conditions of the Late Miocene in this region. Our emphasis is on understanding the vegetation and surface water of the basin because these in turn affected the isotopic composition of Lake Pannon. We analyzed the enamel of 68 Hippotherium teeth from 23 localities in the PBS for carbon and oxygen isotope composition. Carbon isotope records indicate that Hippotherium in the central regions of the basin were feeding in more open habitats than those in the northwest. We find no evidence of the expansion of C4 grasses into the PBS. Oxygen and carbon isotope values from the Vienna Basin (NW part of the PBS) generally covary, whereas those from more central regions do not. The oxygen values of the central PBS are generally lower than those of the Vienna Basin. These data suggest that the interior of the PBS was generally dry, which forced Hippotherium to use water sources that were not strongly evaporated, such as rivers originating from outside the basin. The dry interior was likely caused by a rain shadow east of the Alps and north of the Dinarides. Consequently, much of the surface inflow into Lake Pannon would have been influenced by runoff from high elevations around or outside the basin. By understanding the terrestrial environment, better constraints can be placed on lake conditions in future work.