Abstract
During the Miocene (ca. 23.0–5.3 Ma), North America's Great Plains were a broad mosaic of savanna-woodlands inhabited by a diverse ungulate fauna. We investigated resource partitioning among ungulates at Ashfall Fossil Beds State Historical Park (henceforth “Ashfall”) in north-central Nebraska to establish how taxa shared the landscape. This mid-Miocene (11.86 ± 0.13 Ma) site preserves a watering-hole filled with volcanic ash that entombed hundreds of skeletons of medium- and large-bodied ungulates. We analyzed carbon (δ13C), oxygen (δ18O), and strontium (87Sr/86Sr) isotopes in enamel from seven species: the rhinoceros Teleoceras major (n = 13); three horses (Cormohipparion occidentale, Pliohippus pernix, and Pseudhipparion gratum; n = 3 each); two camels (Procamelus grandis and Protolabis heterodontus; n = 1 each); and one small ruminant artiodactyl (Longirostromeryx wellsi; n = 3). Carbon isotope data indicate that all seven ungulates foraged in open habitats dominated by C3 plants (enamel δ13CVPDB range from −9.6‰ to −6.9‰) with little to no evidence of C4 plant consumption. The overall range in δ18OVPDB values is ca. 6‰ (−7.6‰ to −1.3‰), while the range for 87Sr/86Sr is narrow (0.70864–0.70898). Horses have significantly higher δ18O and 87Sr/86Sr than T. major, which we suggest indicates horses foraged in relatively dry habitats, while T. major inhabited wet habitats with different strontium sources. Both camels isotopically resemble horses, and Longirostromeryx wellsi has intermediate 87Sr/86Sr and wide-ranging δ18O values. Plotting Teleoceras and co-occurring ungulates in a model that tests for semi-aquatic behavior using δ18O suggests that T. major from Ashfall was semi-aquatic; ecology and behavior may have varied among Teleoceras species living in different places at different times. This study exemplifies how 87Sr/86Sr data complement δ13C and δ18O analyses when reconstructing ancient environments; they can provide nuanced ecological information even in landscapes with homogeneous bedrock.
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