Mammals at Ashfall Fossil Beds State Historical Park (NE Nebraska) offer a unique opportunity to test for the preservation of primary isotopic signatures in fossilized materials. At this site, large herbivores such as rhinoceroses, horses and camels are buried in volcanic ash sourced from an eruption of the Bruneau-Jarbridge caldera (Idaho/Nevada) ca. 11.8 million years ago. Most fossils from Ashfall display pathologic bone symptomatic of a lung disease (hypertrophic osteopathy or HPOA) likely related to inhalation of volcanic ash. In this study, we compare the stable oxygen isotopic composition (δ 18 O) of pathologic bone with that of normal cortical bone to determine if elevated body temperatures associated with HPOA can be reconstructed. Our results show consistently lower δ 18 O values in pathologic bone, suggesting it may have formed at a higher body temperature. While the direction of offset between normal and pathologic bone (  N-P) is consistent, the magnitude of the offset is variable and sometimes larger than can be explained solely by elevated body temperature. A change in body water δ 18 O related to physiology and/or HPOA could be an additional factor influencing   N-P. For example, an increase in drinking water contribution to the body water reservoir could help to explain the observed δ 18 O offset for animals whose behavioral response to disease includes increased water consumption. This interpretation is supported by the high number of individuals concentrated in and around a shallow paleo-water body at Ashfall. Isotopic exchange during diagenesis may be another variable affecting the magnitude of   N-P, and can be examined further through intra-individual δ 18 O comparisons of different skeletal tissues (e.g., enamel and bone, phosphate and carbonate) or through δ 18 O comparisons between different members of the Ashfall fauna.

Oreopithecus bambolii is a Late Miocene hominoid with an extensive fossil record in the Baccinello Basin (Tuscany, Italy), and was the only western European hominoid to survive a major extinction event ca. 9.6 Ma (millions of years ago). Oreopithecus lived in the insular Tusco-Sardinian paleobioprovince, where it evolved many unique anatomical specializations that make it important for understanding the mechanisms and history of Late Miocene hominoid evolution. The eventual extinction of Oreopithecus and its associated fauna ca. 6.5 Ma has generally been attributed to interaction with species that arrived from continental Europe following tectonic collision of the Tusco-Sardinian province with mainland Italy, but palynological, paleontological, and sedimentological records indicate an environmental shift toward more variable climate across the extinction event. To explore the possibility of environmental change as a contributing factor in the extinction of Oreopithecus, we developed a stable carbon and oxygen isotope record from organic matter in paleosols from the Baccinello Basin. These data show very low temporal and spatial variability (indicating plant ecosystem stability through time and space) and provide no evidence for ecologically significant changes in floral composition spanning the extinction event, suggesting that environmental change was not an underlying cause for the extinction of Oreopithecus and its associated fauna. The carbon isotope values fall entirely within the range of isotopic variability for modern plants following the C(3) photosynthetic pathway (trees, shrubs, cool-season grasses), indicating that C(4) vegetation (warm-season grasses) was not an important component of biomass. When corrected for temporal variation in the carbon isotopic composition of atmospheric carbon dioxide, the paleosol carbon isotope values are consistent with predicted values based on modern plants and the Baccinello palynoflora, supporting the reliability of paleosol isotopic records as paleoecological proxies.

The late Neogene of the Mediterranean region is marked by significant faunal and floral turnover in terrestrial ecosystems, paleogeographic and paleoceanographic changes associated with the Messinian Salinity Crisis (MSC), and regional climate transition associated with the onset of northern hemisphere glaciation. In this paper we report stable oxygen isotope compositions (δ18O) of terrestrial mammal faunas from the Late Miocene, Pliocene and Pleistocene of Spain, and compare these data with Late Miocene mammal δ18O values from northern Libya. Since tooth enamel δ18O from modern horses has been demonstrated to be a reasonable proxy for the δ18O of local meteoric water, which is in turn strongly dependent on mean annual temperature (MAT), we use the δ18O of fossil horse tooth enamel to estimate MAT. Our paleotemperature reconstructions are consistent with global cooling during the late Cenozoic, with MAT for the Late Miocene that is warmer than today by ∼1–2°C in NE Spain and by ∼4–5°C in SE Spain. The difference of ∼8–9°C between NE and SE Spain for the Late Miocene is ∼60% greater than the MAT difference between these same areas today. The δ18O values from Libya are lower than those for southern Spain, and may suggest cooler and/or wetter climates in northeastern Africa during the latest Miocene and early Pliocene. We examined intrafaunal δ18O patterns to make interpretations about paleoecology and to qualitatively assess paleoaridity. Comparisons of δ18O values between clades are consistent with a semi-aquatic lifestyle for anthracotheres, hippopotamids, and castorids. We also compare intra-tooth samples of enamel and dentine to examine possible diagenetic alteration of these materials. Comparisons of enamel and dentine δ18O suggest slight diagenetic alteration of dentine, but we demonstrate that these δ18O values can be used to reconstruct reasonable values of diagenetic water δ18O. Overall, our data do not support large climatic changes in the Iberian Peninsula during the MSC, but are consistent with long-term global cooling and sharper latitudinal climate gradients in Spain during the Neogene.

Abstract A substantial complication to using the oxygen isotope composition (δ18O) of vertebrate bioapatite in paleoclimate studies is the need to distinguish variation due to temporal changes in the δ18O of surface waters from that due to temperature-dependent fractionation during biomineralization. One solution is multiple-taxon comparisons using data from coexisting homeothermic and heterothermic animals. Fossil emydid turtles have been suggested to be potentially useful as functional homeotherms because (1) modern emydids employ behaviors, such as basking, to restrict skeletal growth to a narrow temperature range; (2) their aquatic habitat constrains the isotopic variability of dietary inputs; and (3) emydids have a dense fossil record. But because turtles lack teeth and therefore tooth enamel, sampling must focus on bone, which is potentially more susceptible to diagenetic alteration. This study examines the δ18O of carbonate (δ18Oc) and phosphate (δ18Op) in hydroxylapatite from co-occurring emydids and heterotherms (crocodilians and gars) from the Paleocene–Eocene of the Clarks Fork Basin, Wyoming. Previous isotopic studies of this area provide an extensive data set for comparison with the results of this study. Bone and enamel δ18Oc values measured here exhibit a greater range (16‰–32‰ Vienna Standard Mean Ocean Water) than previously observed, suggesting alteration, while the range of δ18Op values (9‰–15‰) is within that predicted by presumably unaltered mammalian tooth enamel δ18Oc. While high crystallinity indices (0.28–0.55) and a lack of covariation between δ18Oc and δ18Op suggest alteration of one or both of these constituents, a strong correlation between crocodilian enamel and bone δ18Op suggests bone phosphate may be reliable.1