Paleoecology of Aphelops and Teleoceras (Rhinocerotidae) through an interval of changing climate and vegetation in the Neogene of the Great Plains, central United States

Abstract

The Rhinocerotidae was one of most widespread and abundant mammalian groups in North America during the Oligocene and Miocene but were extinct by the early Pliocene. Potential drivers of extinction include the expansion of C4 grasslands, cooling climate, and increased seasonality. Here we examine potential changes in the relative abundance of two common genera, Aphelops and Teleoceras, from the middle Miocene to the Pliocene of the Great Plains. We also use stable isotopes in tooth enamel to test whether Great Plains rhinoceroses were able to incorporate C4 vegetation into their diet after the expansion of C4 grasslands. Relative abundance of rhinoceroses fluctuates during the middle to late Miocene but then rapidly declines at the end of the Miocene around 6.5 Ma, coinciding with the expansion of C4 grasslands on the Great Plains. Stable carbon isotopes indicate that both Aphelops and Teleoceras were predominantly C3 feeders for most of their history. During C4 expansion some individuals were able to adapt to modest C4 consumption but were not as successful as contemporaneous horses. Our results suggest that the extinction of rhinoceroses was associated with environmental stress related to diminishing food resources following the expansion of C4 vegetation, possibly coupled with a shorter growing season as climate cooled. In addition, tooth enamel δ18O values in rhinoceroses do not support the interpretation that Teleoceras, a “hippo-ecomorph”, had a semi-aquatic lifestyle. Tooth enamel δ18O values reflect a strong latitudinal temperature gradient, suggesting that rhinoceroses effectively track δ18O values in surface waters and are potentially useful for paleoclimatic reconstructions.