PALEOECOLOGY OF THE CENOZOIC RHINO FAUNA OF LINXIA BASIN, GANSU, NW CHINA, FROM CARBON AND OXYGEN ISOTOPES IN TOOTH ENAMEL

Cenozoic localities in the Linxia Basin have yielded an abundance of well-preserved rhino fossils, ranging in age from 30 to 2.5 Ma and include individuals from 12 genera within the families Hyracodontidae and Rhinocerotidae. Stable carbon and oxygen isotopic compositions were determined for 49 individuals of these genera in order to examine paleodiet and ecology. First, three general conclusions were made regarding paleodiet and environmental change: 1) The d¹³C values of tooth enamel from all individuals indicate a primary diet of C₃ browse and/or C₃ grasses; 2) The carbon isotope compositions of all rhinos suggests that the Linxia Basin was a savannah or a mixed woodland/C₃ grassland biome from the E. Oligocene to the L. Pliocene; and 3) The d¹⁸O values of the rhino tooth enamel for all individuals suggest that the climate in the area had not been stable from 30 to 2.5 Ma. Secondly, three more specific conclusions were drawn from this study: 1) d¹³C values suggest a generalized feeding habitfor Alicornops, whereas Parelasmotherium was found to have a more specialized diet. This was expected, given that Parelasmotherium had the most specialized dentition of all perissodactyls. Chilotherium was found to be a specialist at two time intervals, and a mixed feeder at three time intervals; 2) Allacerops and Indricotherium coexisted at 30 Ma and their average tooth enamel d¹³C and d¹⁸O values suggest that Indricotherium was more restricted to a closed habitat. Because Indricotherium was very large, it probably required a shaded or wet habitat to keep its body cooled; and 3) Chilotherium and Dicerorhinus coexisted at 6 Ma and isotopic analyses suggest that Chilotherium and Dicerorhinus shared similar feeding habits. Dicerorhinus dentition suggests it was a browser, and although Chilotherium had adaptations for grazing, it has been suggested that Chilotherium was not a true grazer. Isotopic results suggest that Chilotherium was a browser.