The different reproductive strategies of males and females underlie differences in behavior that may also lead to differences in nutrient use between the two sexes. We studied sex differences in the utilization of two essential amino acids (EAAs) and one non-essential amino acid (NEAA) by the Carolina sphinx moth (Manduca sexta). On day one post-eclosion from the pupae, adult male moths oxidized greater amounts of larva-derived AAs than females, and more nectar-derived AAs after feeding. After 4 days of starvation, the opposite pattern was observed: adult females oxidized more larva- derived AAs than males. Adult males allocated comparatively small amounts of nectar-derived AAs to their first spermatophore, but this allocation increased substantially in the second and third spermatophores. Males allocated significantly more adult-derived AAs to their flight muscle than females. These outcomes indicate that adult male and female moths employ different strategies for allocation and oxidation of dietary AAs.

Isotopic analyses of d18O and d2H of water through the hydrologic cycle have allowed hydrologists to make better interpretations related to climate and relationships between precipitation, surface water, and groundwater. In this study 394 precipitation samples 1917 surface water samples and 1405 groundwater samples across Massachusetts was used to create an isoscape for each respective water. All samples have been collected by volunteers throughout Massachusetts. A state meteoric water line: d2H = 7.7*d18O + 9.8, surface water line: d2H = 5.7*d18O – 4.2, and groundwater line: d2H = 6.5*d18O + 2.9 was created for the state of Massachusetts. The d18O isoscape for each of the above-mentioned waters shows an isotopic separation along an east-west topographic gradient where isotopes were enriched in the eastern portion of Massachusetts and depleted in the western portion of Massachusetts. Precipitation, surface water, and groundwater show unique isotopic variability. The isotopic variability of precipitation is primarily due to seasonality, moisture source and differences in topography across Massachusetts. The d18O and d2H isotopic variability of surface water is due to a biasing of precipitation as well an enrichment due to an open water system as the surface water dataset correlates with surface water type and precipitation isotopic values. The d18O and d2H isotopic variability of groundwater is due to the dampening of surface water and precipitation because of hydrogeologic processes and the biasing of surface waters that have gone through open water isotopic variability.

The Cassenha Hill copper-gold prospect is situated in the Catabola area, Huambo Province, southwestern Angola. Geologically, the prospect is part of the Angolan Central Eburnean Zone (CEZ) and consists of Paleoproterozoic metasedimentary rock sequences which have been intruded by Eburnean granitoids at ± 2.1 Ga. The prospect itself comprises an area of 180 Km2 and has been intermittently explored since 2005 by Rift Valley Resources (RVR) and its associates. The Cassenha Hill prospect is characterized by the occurrence of partially altered and highly oxidized metasedimentary rocks (meta-mudstone, meta-siltstone, carbonate-rich rock, meta-sandstone, breccia, and quartzite), and altered isolated granitoids. This study represents the first detailed study of the prospect and aims to shed light on the characteristics of the various rock types (i.e., host and barren rocks), their source/provenance, styles of alteration, and the origin and/or type of the fluid responsible for the mineralization. Techniques applied include borehole core logging, petrography, whole-rock geochemistry (XRF and ICP-MS), and stable isotope geochemistry on samples collected on the surface and from exploration boreholes drilled as part of RVR exploration program. Overall, the petrographic and geochemical studies undertaken in the rocks of the Cassenha Hill prospect indicate the following: (1) The rocks are moderately to strongly fractured; (2) The rocks have experienced weak to moderate chemical weathering; (3) The rocks are compositionally immature and originated from felsic provenance; (4) The rocks are sulfur-poor, and lacking in sulfide minerals (5) The rocks are enriched in LREE and LILE elements and depleted in HREE and HFSE elements; (6) The mineralization is associated with chloritization alteration and predominantly occurs within and/or at the edges of quartz/chlorite-rich veins/fractures and is not restricted to any rock type. Two ore stages could be identified, namely, hypogene ore (stage I) consisting of pyrite ± chalcopyrite ± other copper sulfides, and supergene ore (stage II) consisting of malachite ± azurite ± chrysocolla, which represents the prevalent mineralization at the prospect. The δ 18O value of quartz veins range from +12.81 to +13.53‰, while the δD of chlorite minerals range from -51 to -45‰. Therefore, assuming fluid-rock interaction took place at ≈ 350oC, due to the presence of quartz, the fluid had δ 18OH20 values of about +8‰, which are typical of magmatic waters. On the other hand, at a temperature of ≈ 350oC, and with the difference between chlorite and water being -33.5‰, such fluids would have had δDH20 values of about -20‰ (δ 18OH20= -4‰), which are typical of meteoric waters. Although the various mineral phases have yielded different isotopic signatures, this study suggests that water is ultimately of meteoric origin but exchanged with hydrogen-poor magmatic rock, thus maintaining the meteoric signature. The continuous influx of meteoric waters within the fracture system led to the development of copper oxides such as malachite, azurite and chrysocolla, which possibly originated from the insitu oxidation of the hypogene sulfides. This signature, together with other field, petrographic and geochemical observations allows one to, tentatively, suggest that the Cassenha Hill prospect represents an extension of a polymetallic vein-type of porphyry Cu deposit that has been subjected to supergene processes at the weathering profile.

Si la relation entre l’enregistrement géochimique au sein de ces travertins et les paramètres environnementaux semble admise, le détail des processus, notamment cinétique et dégazage, ainsi que leur poids respectifs dans les reconstitutions paléoenvironnementales ne sont clairement établis. Afin de mieux contraindre ces processus, un travail minutieux de reconnaissance des mécanismes de précipitation et d’enregistrement de la signature géochimique a été effectué sur les travertins –récents et fossiles- d’une source carbogazeuse située dans le Massif Central (France). Il couple expériences de laboratoire innovantes et travail sérié sur le terrain.Le taux de dégazage du CO2 dans les sources carbogazeuses est l’un des facteurs principaux conduisant aux conditions de précipitation via la modulation du taux de précipitation de la calcite et par conséquent, sa composition en 18O et 13C. Les tests en laboratoire ont été conduits en deux étapes : (1) caractérisation des mécanismes de dégazage seuls, et (2) des expériences combinant dégazage et précipitation pour mieux appréhender les processus cinétiques lors de la précipitation des travertins. En parallèle, un travail de terrain spécifique par pose de plaques de plexiglas le long de différents écoulement de la source, nous a permis de connaitre la résolution de précipitation des travertins et d’obtenir une meilleure estimation des facteurs de fractionnement.Les tests en laboratoire confirment que, lors d’un dégazage important, i.e. conduisant à la précipitation de travertins, la spéciation des espèces du carbone inorganique dissout (CID) et les flux entre ces espèces sont des paramètres primordiaux à considérer. Le facteur de fractionnementεDIC-CO2(g) qui dépend du pH suit alors une distillation de Rayleigh dans un système cinétique. Les évolutions des espèces carbonées en solution ont ainsi pu être modélisées à l’aide d’une équation de diffusion faisant intervenir les paramètres propres à l’expérience.Les résultats de terrain permettent de démontrer que les variations de conditions de précipitation sont principalement dues aux variations de conditions hydrodynamiques et, secondairement, aux variations de température, ce qui a pu être modélisé à l’aide de l’équation définie par Plummer en 1968 et qui a montré la variabilité des conditions de précipitation in-situ. Dans le cas des expériences de précipitation en laboratoire et par comparaison avec les données de terrain, le facteur de fractionnement εCID-calcite va dépendre des concentrations de chaque espèce de CID mais aussi de la partition du carbone entre phase gaz et phase solide. Pour l’oxygène 18, de 0°C à 10°C, les résultats acquis sur les travertins actuels nous ont permis d’utiliser la droite définie récemment par Coplen (2007) pour lier de façon fiable la température au moment de la précipitation et le facteur de fractionnement. Toutefois, pour des températures plus élevées, le facteur de fractionnement est plus important que ce qu’il devrait et confirmant ainsi la non-représentativité des droites de Coplen pour la détermination de la température de précipitation. Lors des expériences de précipitation la tendance est inverse à celle observée pour les travertins confirmant l’influence de la vitesse de dégazage et de l’indice de saturation sur le fractionnement isotopique. Nous avons également confirmé avec les expérimentations, l’impact de la vitesse de précipitation sur les teneurs isotopiques enregistrées dans les travertins.Ce travail a mis en lumière des mécanismes cinétiques complexes et qui ne sont pas complètement contraints par la seule utilisation des outils isotopiques. L’utilisation du partitionnement des éléments traces est un outil primordial pour appuyer l’étude de ces mécanismes. / The response of continental groundwater systems to recent climate fluctuations can be reconstructed via the continuous measurement of groundwater level, spring flow and climatic chronicles. When any data exist, recent reconstructions of groundwater dynamics may be reached through various recorders of environmental and hydrological conditions such as travertine. Although the relationship between geochemical records in travertine and environmental parameters seems to be accepted, the details of processes and their respective weight in the paleo-information are not clearly established.Rate of CO2 degassing in CO2-rich spring likely influences calcite precipitation rate and the related δ18O and δ13C composition. Isotopic equilibrium is rarely maintained during travertine deposition and the degassing rate is the main controlling factor of the disequilibrium. Due to the lack of knowledge, fractionation processes, either kinetic or equilibrium, occurring between CO2-rich water, gas and travertine required specific pH and temperature-controlled laboratory tests. These tests were conducted on synthetic water at different pH to focus only on the degassing processes. Other tests were conducted on trace elements partitioning during calcite precipitation, to identify the origin of isotopic signature variability, and to constraint the way of recording past conditions.All these tests confirmed that during a degassing leading to travertine precipitation, the speciation of dissolved inorganic carbon species is a major parameter to be tackled since a linear relationship between εDIC-CO2(g) and pH is observed. Indeed, we highlighted that for a high degassing rate, the isotopic equilibrium is not reached because the reaction greater involves light isotopes than heavy ones. There is thus different reaction rate between the species of dissolved inorganic carbon, the reactions occurring faster in the water than the one between water and gas, the latter being controlled by diffusion.

Global carbon cycle dynamics and fluxes of CO2 between biosphere and atmosphere have been progressed through the use of Keeling Plots. Processes that control and effect the isotopic composition of soil-respired CO2, soil CO2, and equilibrated soil carbonate are specifically addressed in this study through the use of Keeling Plots. Replicate grassland soil profiles containing either C3 or C4 homogenized organic matter were constructed and maintained under controlled settings to encourage the production of soil-respired CO2 and the precipitation of pedogenic carbonate. Soil CO2 was sampled over five months and analyzed with IRMS. Keeling Plots illustrated source CO2 affected by mixing with atmospheric CO2 near the surface and equilibration with ¹³C-depleted CO2 at depth in the zone of likely carbonate precipitation. The δ13C Keeling Plot intercepts for the surface horizons (~ -24.7 per mil for C3 profiles and ~ -11.1 per mil for C4 profiles) follow the diffusion-production model when corrected with a constant 4.4 per mil diffusional fractionation, but the Keeling Plot intercepts for developing Bk horizons were curved towards depleted values (~ -36.2 per mil for C3 profiles and ~ -18.4 per mil for C4 profiles). This change in isotopic composition with depth deviates from the usual interpretations of Keeling Plots (steady-state, source to background diffusional mixing). δ13C Keeling Plot intercepts indicated evaporative enrichment in the surface horizons of C3 and C4 profiles). This study uses Keeling Plots as a measure of mixing to assess the efficacy of steady-state diffusion-production models of soil CO2 equilibration with soil carbonate.

Stable isotope analyses are powerful tools for reconstructing ancient ecologies and ecosystems, as they are independent of morphology and directly reflect dietary ecology. The application of stable isotope analyses, however, is not without limitations, as determination of food web dynamics using these methods often relies on poorly tested assumptions. The guiding thread of this thesis is the testing of foundational cornerstones on which these methods rely, in order to validate the suitability of applying these techniques to different mammalian clades, and to more reliably and confidently interpret the isotopic signals preserved in extinct organisms. The first chapter of this thesis tests the validity of an important assumption behind the interpretation of stable carbon isotope analyses for understanding diet in terrestrial mammalian herbivores: if, as assumed for almost two decades, mammalian bioapatite δ¹³C is enriched by 14‰ relative to dietary δ¹³C. By analyzing new isotopic data from a never before assessed herbivorous group spanning a broad range of body masses—sloths (Xenarthra, Mammalia)— and other mammals with experimentally controlled or observationally known diets, I discovered considerable variation in diet–bioapatite δ¹³C enrichment among mammals. Statistical tests (ordinary least squares, quantile, robust regressions, Akaike information criterion model tests) documented independence from phylogeny, and a previously unrecognized strong and significant correlation of δ¹³C enrichment with body mass for all mammalian herbivores. A single-factor body mass model outperformed all other single-factor or more complex combinatorial models evaluated, including for physiological variables (metabolic rate and body temperature proxies), and indicated that body mass alone predicts δ¹³C enrichment. These analyses, spanning more than 5 orders of magnitude of body sizes, yield a size-dependent prediction of isotopic enrichment across Mammalia and for distinct digestive physiologies, permitting reconstruction of foregut versus hindgut fermentation physiologies for fossils and refined mean annual paleoprecipitation estimates based on δ¹³C of mammalian bioapatite. Second, I sought to evaluate the existing paradigm governing identification of closed canopy rainforests in the fossil record using mammalian δ¹³C data: the presence of mammals with dietary δ¹³C <-31‰, which has only been observed in closed canopy rainforests in Equatorial Africa, the only other tropical ecosystem sampled extensively. This chapter provides a characterization of δ¹³Cbioapatite, δ¹³Chair and δ¹⁵Nhair of a modern mammalian community in western Amazonia, in Peru, to test if the isotopic structure of mammals in this Neotropical ecosystem is similar to those in African tropical rainforests. The results indicate that despite their marked geographical and taxonomic differences, median δ¹³Cdiet values from closed canopy rainforests in Amazonia (-27.4‰) and equatorial Africa (-26.9‰) are not significantly different. Amazonian mammals, however, seem to exploit a narrower spectrum of dietary resources than equatorial African mammals, as depicted by the absence of highly negative δ¹³Cdiet values previously proposed as indicative of rainforests (<-31‰). I hypothesize that differential effects of late Pleistocene extinction may be responsible for the ecological disparities among the two rainforests, by significantly reducing evolutionary time and dietary breadth reflected in the modern Amazonian mammalian community. Finally, the third chapter of this dissertation evaluates assumptions behind δ¹⁵N amino acid compound specific analyses in order to test the controversial hypothesis of carnivory and consumption of proteins of animal origin in fossil sloths. This analytical technique relies on three main assumptions. First, that the offset between the δ¹⁵N of glutamic acid (δ¹⁵NGlx) and phenylalanine (d15NPhe) in the organism under study will increase with increasing trophic level. Second, that the offset between δ¹⁵NGlx and δ¹⁵NPhe at the base of the food chain is relatively constant and has a value of -8.4‰ for C3 ecosystems. Third, that the trophic discrimination factor in all ecosystems (the difference in δ¹⁵NGlx relative to δ¹⁵NPhe with increasing trophic level) is 7.6‰. The results of my experiments conducted on extant xenarthrans (sloths and anteaters) with controlled diets document that only the first assumption holds true. Rather than relying on an equation with constants introducing uncertainties and that are not applicable to organisms feeding on a combination of items of different origin (e.g., C3 + C4 plants), δ¹⁵NGlx and δ¹⁵NPhe values by themselves can accurately reconstruct the trophic position of organisms. Indeed, the results on δ¹⁵NGlx and δ¹⁵NPhe herein obtained for five xenarthran species in controlled feeding experiments, combined with mammalian data available from the literature, show strong and significant correlations between these two AAs and with trophic positions. Both the TP equation and the regression analyses of δ¹⁵NGlx and δ¹⁵NPhe suggest that the Pleistocene fossil ground sloths 𝘔𝘺𝘭𝘰𝘥𝘰𝘯 𝘥𝘢𝘳𝘸𝘪𝘯𝘪𝘪 and 𝘕𝘰𝘵𝘩𝘳𝘰𝘵𝘩𝘦𝘳𝘪𝘰𝘱𝘴 𝘴𝘩𝘢𝘴𝘵𝘦𝘯𝘴𝘪𝘴 were not pure herbivores as commonly presumed, but rather that they were both mixed feeders/omnivores, incorporating items of animal origin in their diets.

Given its crucial role in atmospheric chemistry and its global warming potential, methane(CH4) deserves to be accurately budgeted. However, the recent renewed rise in atmosphericCH4 growth rates from 2007 on, after a few years of slow-down, attests that sources are notcompensated anymore by sinks, and calls for a better assessment of the processes contributingto the global CH4 budget. Among natural sources, oceanic emissions are still subject tomany uncertainties, due to the lack of sampling. This is particularly relevant in polar regions,where the role of sea ice on CH4 sea-air fluxes is largely unknown.In an effort to contribute to a better characterisation of CH4 dynamics in oceanic environments,we investigated very contrasted settings during a journey from temperate to polarregions and applied the concentration and stable isotope approach.We start by evaluating the performance of a commercially available in situ CH4 sensor(CONTROS HydroC® CH4 from Kongsberg Contros) in controlled and natural environments,with the hope of using it in the framework of our various field campaigns. Although thissensor has the potential to significantly increase the spatial and temporal resolution comparedto discrete sampling, the long response time prevents from using its measurements as absolutevalues in dynamic natural environments and calls for progress in the field of technologies forcontinuous in situ dissolved CH4 measurements. However, the sensor turns out to be veryuseful during cruises to observe relative changes in dissolved CH4 concentrations and guidethe discrete sampling episodes.Our journey starts in the Scheldt estuary, at the transition between land and sea. Stableisotope analyses reveal that the unusual enrichment of dissolved CH4 in 13C and D in theupper estuary could result from intense microbial oxidation or an unknown source upstream.In the lower part of the estuary, this enriched CH4 mixes with depleted CH4 produced bymethanogenesis in the sediments, before entering the North Sea.In the shallow coastal Wadden Sea, we highlight the dominant contribution of coastal areasto oceanic CH4 emissions. The progressive increase in dissolved CH4 concentrations coincidedwith a 2°C warming of seawater. Submarine groundwater discharge, controlled by thespring-neap tide cycle, and tidal pumping might also have contributed to temporal variationsin dissolved CH4 concentrations and isotopic composition.In the Barents Sea, sailing towards polar latitudes, we find that the fractional sea-ice coverdid not induce a significant change in CH4 concentration nor isotopic composition at theocean-atmosphere interface. Local CH4 seepages at the seafloor might be a relict of gashydrate dissociation after the retreat of the Scandinavian Ice Sheet from the continental shelfafter the Last Glacial Maximum.Trapped in landfast sea ice at Barrow (Arctic) and Cape Evans (Antarctic), we find thatthe processes governing CH4 dynamics in sea ice happen to be dependent on the season andthe regional setting, and can be unravelled thanks to stable isotope analyses. At Barrow,the range of delta-13C values points towards in-ice microbial oxidation of CH4 produced bymethanogenesis in the underlying sediments. At Cape Evans, the much higher delta-13C valuessuggest a hydrothermal origin of CH4 trapped in sea ice and/or aerobic production withinsea ice.The journey ends in the Ross Sea, where the high variability and supersaturation observed indissolved CH4 concentrations, as well as carbon isotope signatures typical of a thermogenicorigin, suggest that gas seepages on the continental shelf might be the main source of CH4 tothe water column.This unique dataset of CH4 concentration and stable isotope composition in seawater, in seaice and in the atmosphere, highlights the spatial and temporal variability of the processesgoverning CH4 dynamics across the various oceanic environments investigated. This thesisprovides an example of how the isotopic approach can be successfully applied to disentanglethe biogeochemical cycle of CH4. To better constrain oceanic emissions, we recommend theimplementation of an extensive monitoring network to measure dissolved CH4 continuously,particularly in shallow coastal regions, which contribute the most. Eventually, further studiesshould focus on the Southern Ocean, which has yet to reveal its secrets with regard to CH4dynamics. / Doctorat en Sciences / info:eu-repo/semantics/nonPublished

Despite high taxonomic diversity elsewhere in North America during the Pleistocene, vertebrate faunas are exceedingly rare in the region of northern Mexico. Térapa, a unique fossil site located in the present-day desert of Northcentral Sonora, Mexico (29°41́N, 109°39́W, 605. m elevation), contributes to our understanding of the paleoecology and paleoclimate of the region during the Late Pleistocene, ca. 43,000-40,000. cal.yr BP. At least 60 vertebrate taxa, including amphibians, turtles, a crocodilian, snakes, birds and many mammals, have been recovered from an 11-m thick sequence of fossiliferous sediments. The diversity and tropical affinity of these taxa suggest a more-forested environment than the thornscrub desert habitat present in this region today.Isotopic analyses of tooth enamel carbonate from ancient mammalian herbivores suggest that the Sonoran desert has undergone considerable climate change since the Late Pleistocene. Bulk carbon (́13C) and oxygen (́18O) isotopes from nine mammalian fossils indicate a habitat mosaic with variations in diet that include browsers, mixed feeders and C4 hyper-grazers (́13C range of -10‰ to 2‰). Unique to this site are 13C tooth enamel values of -6.1 and -5.6 ‰ for the deer Odocoileus, which suggest a more variable diet than strict browsing, including possibly feeding on CAM and/or C4 plants. Serial sampling of carbon (δ13C) and oxygen (δ18O) isotopes for ancient mammal teeth with hypsodont dentitions (fossil Equus and Bison,) as well as δ18O meteroric water estimates from well-supported climatic models suggest a cooler and more equable environment at Térapa during the Late Pleistocene. These results also support previous habitat reconstructions inferred from the macrobotanical and packrat midden records of northern Sonora (Mexico). High-resolution stable isotope geochemistry indicates that: 1) ancient Térapa was covered with forest and grassland habitats that extended northward into Mexico by about 350km relative to their present-day northern limits during the Late Pleistocene; and 2) an Amount Effect (AE) is demonstrated in the fossil record at Térapa even though the climate was less seasonal compared to the modern desert habitat.

Kangaroos are the world's most diverse group of herbivorous marsupials. Following late-Miocene intensification of aridity and seasonality, they radiated across Australia, becoming the continent's ecological equivalents of the artiodactyl ungulates elsewhere. Their diversity peaked during the Pleistocene, but by approximately 45,000 years ago, 90% of larger kangaroos were extinct, along with a range of other giant species. Resolving whether climate change or human arrival was the principal extinction cause remains highly contentious. Here we combine craniodental morphology, stable-isotopic, and dental microwear data to reveal that the largest-ever kangaroo, Procoptodon goliah, was a chenopod browse specialist, which may have had a preference for Atriplex (saltbushes), one of a few dicots using the C4 photosynthetic pathway. Furthermore, oxygen isotope signatures of P. goliah tooth enamel show that it drank more in low-rainfall areas than its grazing contemporaries, similar to modern saltbush feeders. Saltbushes and chenopod shrublands in general are poorly flammable, so landscape burning by humans is unlikely to have caused a reduction in fodder driving the species to extinction. Aridity is discounted as a primary cause because P. goliah evolved in response to increased aridity and disappeared during an interval wetter than many it survived earlier. Hunting by humans, who were also bound to water, may have been a more decisive factor in the extinction of this giant marsupial.

Neogene land-mammal localities are very rare in the northeastern U.S.; therefore, the late Miocene/early Pliocene Gray Fossil Site in eastern Tennessee can clarify paleoecological dynamics during a time of dramatic global change. In particular, the identification of ancient forests and past climate regimes will better our understanding of the environmental context of mammalian evolution during the late Cenozoic. Stable isotope analyses of bulk and serial samples of fossil tooth enamel from all ungulates present at the Gray site elucidate paleoecological reconstructions. The herbivorous megafauna include taxa of likely North American and Eurasian ancestry including: the tapir Tapirus polkensis, rhino Teleoceras cf. T. hicksi, camel cf. Megatylopus sp., peccary Tayassuidae, and proboscidean Gomphotheriidae. The tapir, rhino, camel, and peccary yield mean stable carbon isotope (δ13C) tooth enamel values of - 13.0‰, - 13.3‰, - 13.8‰, and - 13.1‰, respectively, suggesting forest-dwelling browsers. This range of δ13C values indicates the presence of a C3 dominated ancient local flora. Because δ13C values decline with increasing canopy density, the ancient temperate forests from the Gray site were moderately dense. The lack of significant C4 plant consumption (i.e., tooth enamel δ13C values < - 9‰) suggests the presence of forests large enough to independently support the continued browsing of sustainable populations of browsers from the Gray site. In contrast, bulk and serial δ13C values ranging from - 0.7‰ to 0.3‰ from a gomphothere tusk support a diet consisting of C4 grasses, suggesting the presence of C4 grasslands within the individuals home range. The rare earth element (REE) analyses of the gomphothere tusk and the teeth of Tapirus and Teleoceras indicates that these individuals shared similar depositional environments; thus, demonstrating the concurrent presence of C3 forests and C4 grasslands in the northeast. Stable carbon and oxygen serial sample variation of the tapir, rhino, peccary, and gomphothere is less than 1.5‰, suggesting minor differences in seasonal temperature and/or precipitation. These data support the possibility of a North American forest refugium in the southern Appalachians during a time typified by more open environments.