GSA Connects 2021 in Portland, Oregon

Paper No. 212-11
Presentation Time: 10:45 AM


SILANO, Miranda, Department of Geosciences, Auburn University, 2050 Beard Eaves Coliseum, Auburn, AL 36849; Department of Geological Sciences, University of Florida, 241 Williamson Hall, Gainesville, FL 32611, MORAN, Sean M., Department of Vertebrate Paleontology, Florida Museum of Natural History, 1659 Museum Road, Gainesville, FL 32611; Department of Biology, University of Florida, 220 Bartram Hall, Gainesville, FL 32611; Vertebrate Paleontology, North Carolina Museum of Natural Sciences, 11 West Jones Street, Raleigh, NC 27601 and ROSS, Mackenzie, Department of Geology, University of Florida, University of Florida, 3309-A, Gainesville, FL 32601; Department of Vertebrate Paleontology, Florida Museum of Natural History, 1659 Museum Road, PO Box 117800, Gainesville, FL 32611

Stable isotope ratios of carbon and oxygen, δ13C and δ18O, have been used to elucidate the paleoecology of mammalian herbivores, but are underutilized in the study of predator-prey relationships in the fossil record. This is especially true in the White River Group (WRG) of the Great Plains across the Eocene-Oligocene climatic transition, where several studies investigate stable isotope paleoecology of herbivores, but not of carnivores. This study tests the hypothesis that common WRG carnivore taxa can be differentiated isotopically in accordance with δ13C values of preferred prey taxa. Thirty-one individuals of four common EOT carnivore families (eight nimravids, seven canids, eight hyaenodontids, and eight amphicyonids) were sampled for δ13C and δ18O values. Isotopic data from the carnivores were compared to all previously published herbivore data (245 samples of 14 genera). All samples included in this study are from Sioux or Dawes County, Nebraska, and represent individuals from both the Chadronian (late Eocene) and Orellan (early Oligocene) North American Land Mammal Ages. Statistically, canids have significantly higher δ13C (mean δ13C= -8.9‰) when compared to nimravids (Welch’s t-test, t(12.3) = 2.9, p = 0.014) and hyaenodontids (Welch’s t-test, t(12.7) = 3.8, p = 0.002). Nimravids have the lowest δ13C (mean δ13C= -10.7‰). Amphicyonids have the largest interquartile range of δ13C values from -11.8‰ to -7.9‰, averaging -9.8‰. Hyaenodontids have the smallest interquartile range of δ13C values, from -10.4‰ to -9.7‰, averaging -10.1‰. Overall, across the Chardonian and Orellan, there is an increase in both δ13C and δ18O values. High δ13C values in canids suggest omnivory, as seen in modern canids and supported by microwear evidence. The low δ13C values in nimravids support a hyper-carnivorous diet and consumption of larger herbivores, a hypothesis speculated in previous publications. The large range of δ13C for amphicyonids implies a generalist diet, while the narrow δ13C values for hyaenodontids imply dietary specialization. Using δ13C analysis as a method to understand ecological relationships between carnivores and their preferred prey allows an understanding of how the changing climate of the EOT affected the large mammals of Nebraska.