Isotopic tracking of large ungulate ecology in Middle Eocene Pondaung Formation (Myanmar)
Résumé
During the Cenozoic, Myanmar has been a key area for mammalian evolution, this region having seen the emergence and diversification of several major groups of eutherian mammals such as anthropoid primates as well as ruminant and hippopotamoid cetartiodactyls. While a very rich mammalian diversity has been described from this region, very few studies have focused on paleoecological and paleoenvironmental aspects related to these mammalian communities. The present study uses carbon (δ13C) and oxygen (δ18O) isotopic tracking in tooth enamel to reconstruct the paleoecology of Anthracotheriidae, Amynodontidae, Brontotheriidae and the chalicothere Eomoropus during the Middle Eocene of the Pondaung Formation. We investigated niche partitioning among the ungulate groups, forest cover in Central Myanmar, possible semi-aquatic ecology of Anthracotheriidae and Amynodontidae, as well as the occurrence of monsoon-like climatic pattern. The carbon isotopic results indicate that all the studied large ungulates were C3 browsers predominantly living in open woodland ecosystems. Niche partitioning occurred among ungulate families but also within them, pointing out to some ecological differences at a lower taxonomic level. A semi-aquatic ecology could not be confirmed for the analysed Anthracotheriidae, but is not excluded for some Amynodontidae with low oxygen-18 abundances. Furthermore serial isotopic analysis of tooth enamel provides evidence for a monsoon-like climatic pattern already during the Middle Eocene in this region, but the foraging strategy does not seem to be affected by the climatic seasonality.