Herbivorous large mammals from the late Middle Miocene Gratkorn locality (Styria, Austria) Taxonomy and Isotopic Tracking of Palaeoecology (δ18OCO3, δ13C, 87Sr/86Sr)

Abstract

During transition from Middle to Late Miocene strong geographic, climatic, and biotic changes had a strong impact on aquatic and terrestrial ecosystems in Central Europe. Large-scale erosion in the Central Paratethys realm caused a lack of terrestrial sediments from this time period and thus resulted in a remarkable palaeobiological “blackout” for the record on land in this region from late Sarmatian to early Pannonian. The here presented Gratkorn locality, well dated to an age of 12.2/12.0 Ma (early late Sarmatian) provides a rich vertebrate assemblage (species diversity as well as total number of specimens) with 65 recorded species up to date. It represents a unique window to the terrestrial record of this time period and helps to understand the evolution of vertebrate faunas during the Middle-Late Miocene transition. Remains of herbivorous large mammals were morphologically described and assigned to the following taxa (Suidae not part of this thesis): Deinotherium levius vel giganteum, Aceratherium sp., Brachypotherium brachypus, Lartetotherium sansaniense, Chalicotherium goldfussi, Anchitherium sp., Listriodon splendens, Parachleuastochoerus steinheimensis, Dorcatherium naui, Micromeryx flourensianus, ?Hispanomeryx sp., Euprox furcatus, Palaeomerycidae gen. et sp. indet., and Tethytragus sp.. Except of Dorcatherium naui, presence and evolutionary stage of the large mammals are well in accordance with a late Middle Miocene assemblage. The records of Euprox furcatus and Micromeryx flourensianus comprise the first for the Styrian Basin and Hispanomeryx has not been recorded for Central Europe so far besides the locality Steinheim a. A.. Dorcatherium naui is considered a typical faunal element of the Late Miocene and has been described only recently from Middle Miocene localities. With the rich material from Gratkorn assignation of this species to a more selenodont phylogenetic lineage together with Dorcatherium guntianum and well distinct from Dorcatherium crassum can be verified and the descent of the species from the latter thus shown to be unlikely. The fossil assemblage from Gratkorn is considered an autochthonous taphocoenosis without any significant time averaging or faunal mixing. Most likely the accumulation did not last longer than a few years or decades and local accumulation of large mammal bones was the result of scavenging. Based on the taxonomic record, morphology of skeletal and dental elements, and especially isotope analyses (δ18OCO3, δ13C, 87Sr/86Sr), dominance of C3 vegetation, semi-arid and subtropical climate with distinct seasonality, and too little precipitation for closed canopy woodlands can be reconstructed for the wider area around the locality. The landscape provided diversity in plant resources to allow occupation of different niches by herbivorous large mammals: subcanopy browsing, rooting, top canopy browsing, facultative frugivory, and mixed feeding. Comparison with data from other Miocene localities from different areas and time slices showed rather stable niche partitioning for the herbivorous large mammal species. Thus these seem to be affected only to a minor degree by climatic conditions but rather represent a typical partitioning for a Middle Miocene ecosystem.