Dramatic change in the diet of a late Pleistocene Elasmotherium population during its last days of life: Implications for its catastrophic mortality in the Saratov region of Russia

Abstract The late Pleistocene site of Irgiz 1 (Saratov Region, Russia) has yielded an accumulation of giant rhinoceros (Elasmotherium sibiricum) within the deposits of an oxbow lake. Irgiz 1 is one of the few sites in the world with a significant amount of elasmothere individuals of different age groups. Tooth mesowear and microwear are used to characterize the dietary traits of the giant rhinoceros on two temporal scales, the annual average diet and the diet at the time of death, respectively. Tooth mesowear, analyzed on 20 specimens, suggests a highly abrasive diet similar to that of extant grazers (similar to the extant white rhinoceros). Tooth microwear analyzed on 16 specimens, conversely, indicates that E. sibiricum was a browser (feeding on leaves from shrubs and trees) at the time of death. The strong discrepancy between the results from the two dietary proxies and the very low variability of the microwear signal suggest that these animals may have died in an event of short duration. The elasmotheres from the area around Irgiz 1 were grazers, but a catastrophic event, perhaps related to the sudden accumulation of snow and ice coating (‘dzud’), limited the availability of grass and forced them to shift toward shrub /tree foliage that was still accessible. The combination of the two proxies, mesowear and microwear, allows the reconstruction of the dietary traits of E. sibiricum, but also to propose a hypothesis for death. This first study of tooth meso- and microwear on elasmotheres provided unique data which allows us to broaden our knowledge about the diet of these animals. The findings indicate that the Irgiz 1 population of elasmotheres died in a single catastrophic event and that the fossil assemblage is not time-averaged.