A 20 MA RECORD OF PALEOCLIMATE FOR CENTRAL EUROPE AND MAMMALIAN PALEODIET ON THE BASIS OF STABLE ISOTOPE COMPOSITIONS OF OLIGOCENE/MIOCENE MAMMAL TEETH FROM THE NORTHERN ALPINE FORELAND BASIN

The oxygen and carbon isotopic compositions of fossil mammalian tooth enamel are valuable proxies for reconstructions of the paleodiet of mammals as well as the paleoclimate during their lifetime. Such reconstructions have been made using a multi-species, multi-locality approach of Tertiary mammal teeth from the North Alpine Foreland Basin on the basis of their carbon (δ¹³C) and oxygen isotope compositions (δ¹⁸O_CO3). Sympatric proboscid, equid, rhinocerotid, cervid, and suid teeth from biostratigraphically well-dated Swiss and German localities, which cover a period of about 20 Ma (MP 25: 28 Ma to MN 11: 8 Ma) with a time resolution of 0.5 to 2 Ma were chosen.

The enamel δ¹⁸O_CO3 and δ¹³C values of all Oligocene and Miocene large mammal teeth (n = 270) vary over a large range from –11.9‰ to –0.5‰, respectively, –14.5‰ to –7.5‰. The δ¹⁸O_CO3 values parallel the composite δ¹⁸O curve of benthic foraminifera and reflect well the major global climatic changes such as the Late Oligocene warming, Mid-Miocene climate optimum and the Middle to Late Miocene cooling trend. Thus, during the Neogene the terrestrial climate in the Molasse Basin realm is strongly coupled to the global climate. The Alps and their tectonic upliftment thus appear not have influenced the local climate and atmospheric circulation patterns significantly. Tertiary MAT calculated with a modern-day MAT-δ¹⁸O_H2O relation for Switzerland using meteoric δ¹⁸O_H2O values derived from enamel δ¹⁸O values range from 10 to 20°C with peak temperatures during the Mid-Miocene climate optimum and the upper Late Oligocene. These MAT are similar to other Tertiary temperature records for Central Europe (North Sea SST, MAT derived from fossil leaf floras).

The mean δ¹³C value of –10.9±1.2‰ indicates that all taxa fed in a C₃ plant dominated ecosystem and confirm the absence of C₄ plants in Central Europe. During the Middle to Late Miocene cooling enamel δ¹³C and δ¹⁸O_CO3 values decreased in all taxa and the low-crowned browsing horse Anchitherium was replaced by the high-crowned, graze-adapted Hipparion, immigrating to Europe from North America around 10.5 Ma. Lower enamel δ¹³C values for Hipparion (δ¹³C = –13.3±1.2‰, n = 17) than for Anchitherium (δ¹³C = –10.7±1‰, n = 22) probably reflect lower δ¹³C values of atmospheric CO₂ but still support a C₃ grass diet.