Impact of Oligo-Miocene climate changes on Mongolian mammals

The Oligocene - Miocene sedimentary sequence of the Taatsiin Gol and Taatsiin Tsagaan Nuur area (Central Mongolia) is of unique importance: here, the exposed sediments of the Hsanda Gol and the Loh Formations display imbedded basalt layers and fossil concentrations along caliche- and paleosol horizons. In the frame of foregoing FWF-projects a statigraphic concept was elaborated which is based on the evolution of mammals and on radiometric ages of basalts. 40Ar / 39Ar-datings provide three groups of basalt ages, the Early Oligocene basalt I group around 31.5 million years, the Late Oligocene basalt II group around 28 million years, and the Middle Miocene basalt III group around 13 million years. Meanwhile the Taatsiin Gol and Taatsiin Tsagaan Nuur area serves as key area for Oligocene-Miocene stratigraphy of Mongolia and as tie point for international correlations. The new project aims at exploration of Oligocene-Miocene climate development in Mongolia and the impact of climate changes on paleoenvironments and mammal communities. To achieve these goals numerous stratified caliche and paleosol layers will be sampled and analysed. The information derived from pedological analyses and the interpretation of shifts in stable isotope signatures (?18O, ?13C) are expected to give important hints to development of paleoenvironments and paleoclimate in the study area. The well stratified and dated Oligocene and Miocene vertebrate assemblages are composed of amphibians, reptiles and mammals dominated by lagomorphs, insectivores, rodents and ruminants. From this rich fossil fund vertebrate-community analyses, phylogenetic studies and palecologic interpretations will be performed. Special attention will be paid to the development and functionality of small and large herbivore mammal dental structures (applied analyses: enamel microstructure, microwear, mesowear, micro CT-scanning and 3D-modeling). The dietary signals resulting from these analyses will allow conclusions on significant changes of paleoenvironment and fauna in the course of more than 20 million years. Fieldwork in Mongolia (two seasons) and the subsequent scientific work will be performed in national and international co-operations. The Mongolian and Austrian research institutions, and all persons involved will strongly profit from this integrated approach.

Mongolia is a fascinating country! Worldwide it is known for marvellous fossil findings, for beautiful nature and very kind people. Moreover, it is a hot spot of mammal evolution, from the Mesozoic up to the present. This project was an interdisciplinary international research programme carried out in the Taatsiin Gol and Taatsiin Tsagaan Nuur area, which is part of the Valley of Lakes in Central Mongolia. The project aimed at reconstruction of mammal community structures within certain time slices of the Oligocene and early Miocene, to find out dynamics of mammal diversities, periods of high extinction and first occurrence rates, and significant mammal turnovers. The informations deriving from the fossil record were combined with geochemical and isotope data of sediments. We also correlated our data with global events, such as the uplift of the Tibetan plateau, the late Oligocene warming and again the significant cooling in the early Miocene. Our team was built up by 25 researchers coming from 10 countries, from Bolivia, Russia, Mongolia and all over Europe.We identified and described almost 19.000 mammal fossils, which derive from 60 fossil layers out of 30 sections and fossil sites, respectively. Finally, 182 mammal species, 87 genera, 27 families and 9 orders were studied. The dominating mammal groups are the small mammal orders Rodentia (48%), Lagomorpha (21%) and Eulipotyphla (12%), followed by rather small sizhed Ruminantia (12 %). Other mammal groups, such as giant rhinos and the according carnivorous predators and small marsupials are represented in very low species and individual numbers. Anylses of mammal data from Mongolia confirm that almost all large sized mammals, which dominated the beginning Cenozoic went extinct before reaching the Eocene-Oligocene boundary, an event which was obviously driven by the uplift of the Himalayan Plateau and a worldwide dramatic cooling. After the initial Oligocene Antarctic Glaciation mammals with small body size underwent a remarkable evolution and diversification with a peak in the early Oligocene, it was about 29 million years ago. This trend dramatically changed towards lowest mammal diversities and high extinction rates in the late Oligocene, a time of increasing aridity as evidenced by carbon isotopes. After a short period of moderate humidity at the Oligocene/Miocene transition, again, dry conditions and a drop of temperature caused the early Miocene faunal turnover 23-22 Ma ago.