Enamel δ18O Research Articles

Ecology of large ungulates in the northeastern Iberian Peninsula during the Upper Palaeolithic through stable isotopes and tooth wear analysis

The northeastern Iberian Peninsula acted as a refuge zone during the Late Pleistocene where the persistence of terrestrial ecosystems could provide hunter-gatherers with large prey, mainly horse (Equus ferus) and red deer (Cervus elaphus). Isotopic (δ13C, δ18O, δ15N) and dental wear (mesowear and microwear) analyses have been applied on the remains of both species from the archaeological sites of Arbreda and Bora Gran at Serinyà (Girona), where evidence of human occupation from the Mousterian to the Magdalenian has been attested. The incremental enamel analysis on horse teeth revealed seasonal variation in carbonate δ18O but no detectable change in carbonate δ13C values, reflecting a rather stable diet and habitat over the year. Nevertheless, higher inter-individual than intra-individual contrast in carbonate δ13C indicate different environmental conditions from one individual to another for each stratigraphic unit. In red deer teeth, seasonal signals in enamel carbonate δ13C and δ18O demonstrated mirrored trends. Further, red deer show higher δ13C values than those of horses, both in enamel carbonate and bone collagen, as well as higher variability in mesowear and microwear scores, reflecting a mixed-feeding habit. Despite a strong grazing signal in mesowear and microwear, the lower δ13C values for horses suggest a higher dependence on relatively more humid habitats than red deer, which likely foraged in dryer environments with xeric plants during winter. These differences in ecological partitioning are particularly well illustrated in distinct collagen δ13C and δ15N values during the harsh climatic conditions of the Final Gravettian coeval to the GS-3 or Last Glacial Maximum. The capacity of red deer to adapt to fluctuating environmental conditions contrasts with the niche persistence of horse allowed by the availability of mosaic habitat.

Stable isotope evidence for resource partitioning in extinct marine carnivores

Living pinnipeds play essential roles in marine ecosystems and display divergent lineage-specific foraging and habitat preferences. The origin of these ecological strategies remains unclear. We analyzed original (n = 22) and published (n = 93) stable carbon (δ13C) and oxygen (δ18O) isotope compositions of tooth enamel from fossil pinnipeds and coeval marine and terrestrial mammals from the late Early Miocene to early Middle Miocene Temblor Formation, the early Middle Miocene Round Mountain Silt Formation at Sharktooth Hill Bonebed, the Middle Miocene of lower levels of the Monterey Formation, and the late Middle Miocene Santa Margarita Formation from the eastern North Pacific Ocean; and original (n = 43) δ13C and δ18O values from the Early Pliocene Yorktown Formation in the western North Atlantic. As expected for aquatic mammals, pinnipeds and control marine mammals had low δ18O variability relative to coeval terrestrial mammals, indicating minimal diagenetic alteration. Among late Early Miocene and Middle Miocene pinnipeds, Allodesmus had lower δ13C values than coeval taxa indicating offshore foraging, in agreement with predictions based on skeletal morphology. However, Allodesmus from the late Middle Miocene Santa Margarita Formation had overlapping δ13C values with co-occurring cetaceans and pinnipeds suggesting preferential nearshore habitat. The stem otariid Pithanotaria had higher enamel δ13C values than co-occurring pinnipeds, indicating nearshore foraging. The stem odobenid Neotherium had intermediate δ13C values supporting foraging between nearshore and offshore predators. Conversely, the stem odobenid cf. Imagotaria had lower enamel δ18O but comparable δ13C values to coexisting pinnipeds, suggesting the exploitation of estuarine resources. At least two ecologically distinct pinniped groups also occurred in the Yorktown Formation. In this unit, the odobenid Ontocetus and some monachinae phocids were predominantly nearshore foragers, with higher enamel δ13C and δ18O values than simultaneously occurring marine mammals. The second group was exclusively composed of phocids, which had comparatively low δ13C and δ18O values, compatible with northward foraging movements along the western North Atlantic coast. The paleoecological profiles of fossils bear strong similarities to the life modes of extant pinniped communities, implying that extant foraging modes appeared early in pinniped evolution and that resource partitioning contributed to their community structure over time.

Niche partitioning and competition between different rabbit breeds using stable isotopes

Stable isotope analysis (SIA) is an evolving method for determining diet, understanding food web and resolving biogeochemical issues in the ecosystem. This study aims to trace out ecological niche preferences/partitioning and competition among the lagomorphs, including two different breeds of European rabbit (Oryctolagus cuniculus), New Zealand rabbit and American Dutch rabbit, using SIA. Thirty-two samples of tooth enamel were analysed, which were collected from different districts of Punjab, Pakistan, including Okara, Sahiwal and Kasur. Among these samples, 16 belonged to the New Zealand breed (08 male and 08 female rabbits) and 16 to the American Dutch breed (08 male and 08 female rabbits). Significant (P<0.001) intergender differences in the isotope content of δ13C in the enamel for New Zealand and American Dutch rabbit were found. The European rabbits showed significant differences for both genders in the stable isotope of oxygen in the enamel (δ18O) values (P=0.05). Nitrogen stable isotope results showed no significant intergender differences between American Dutch and New Zealand rabbits (P=0.24). The stable isotope results for δ13C, δ15N, and δ18O indicate that the trophic niche partitioning of both breeds overlaps, which can potentially cause competition for resources, whereas the water intake may differ among different genders, which may reflect differential gender-related activities. The archaeological and fossilised data of lagomorphs is present, but there is no significant literature available for living lagomorphs (rabbits). In general, this study provides a basic and first dataset for δ13C, δ15N, and δ18O of living lagomorphs, which can serve as a comparative dataset for future studies.

Past rainfall patterns in Southeast Asia revealed by microanalysis of δ18O values in human teeth

Variations in human subsistence and settlement patterns have been documented at Holocene archaeological sites across Island and Mainland Southeast Asia. Although climate is frequently invoked as a causal mechanism underlying this variation, direct evidence of ancient rainfall variability on the scale of human lifetimes has thus far been elusive. Here we use a novel time-resolute method for in situ measurement of human tooth enamel δ18O values (n = 2629 near-weekly measurements sampling 51 years) to assess past rainfall seasonality patterns in Southeast Asia. Seasonal fluctuations in enamel δ18O values of ancient humans from several different periods are compared to modern rainfall recorded in Vietnam, Philippines, and Indonesia by the Global Network in Isotopes in Precipitation (GNIP). The likelihood that the ancient humans reflect local precipitation patterns is established through measurement of bulk enamel 87Sr/86Sr ratios. Comparison of the archaeological individuals and the modern rainfall datasets shows that the seasonal variabilities in ancient δ18Oenamel are consistent with seasonal variabilities in modern δ18Oprecip across the study locations (highest in Vietnam, lowest in Indonesia, intermediate in the Philippines). Strong seasonal δ18Oenamel trends in four of five hunter-gatherers from Con Co Ngua, Vietnam, facilitate the inference of birth approximately six months prior to the onset of monsoons, consistent with tropical subsistence societies where food availability correlates with rainfall. High-resolution analysis of human tooth enamel represents a powerful new tool for seasonality reconstructions across different regional and climatic settings.

The Impact of Contact: Isotope Geochemistry Sheds Light on the Lives of Indigenous Australians Living on the Colonial Frontier in Late 19th Century Queensland

Here, we report the first attempt to use isotope geochemistry to improve understanding of the experiences of Indigenous Australians living on the colonial frontier in late 19th century CE Australia. In the study, we analysed strontium (87Sr/86Sr), carbon (δ13C), and oxygen (δ18O) isotope ratios from the tooth enamel and dentine of six individuals who died in Normanton, Queensland, in the 1890s. The study was a collaboration between scientists and the local Traditional Owners, the Gkuthaarn and Kukatj people, and was carried out to promote truth and reconciliation. The enamel 87Sr/86Sr results suggest that the individuals moved to Normanton from three geologically distinct regions during the period of European expansion into the Gulf of Carpentaria, Cape York. This is consistent with the oral histories and historical documents, which suggest that many Indigenous people in the Gulf Country were displaced to camps on the outskirts of towns like Normanton because of European settlement. The δ13C values we obtained indicate that the individuals mostly ate C4 plants and/or C4-plant-consuming herbivores. When combined with the fact that some of the individuals’ teeth had dental caries, this suggests that the individuals may have had regular access to introduced foods. The enamel δ18O values are high compared to an international comparative sample, at 0.72–4.69‰ VPDB. We suspect the elevated values are due to a combination of a high degree of preferential loss of 16O through evaporation of surface water, the amount effect associated with the Australian monsoon, and high prevalence of introduced infectious diseases. Together, the results of our study demonstrate that isotopic analysis of human remains has the potential to further illuminate the effects of European colonisation on Indigenous people in Australia. Perhaps most importantly in connection with this, our study’s results show that isotopic analyses of human remains can provide surprisingly detailed information about the lives of a category of Indigenous Australians who rarely appear in the documents written by early ethnographers and colonial officials—subadults. That the analysis of the skeletal remains of Indigenous Australians can now contribute to the truth and reconciliation process is an unexpected, interesting, and welcome development in the story of bioarchaeology in Australia.

Seasonality of precipitation in the southwestern United States during the late Pleistocene inferred from stable isotopes in herbivore tooth enamel

The late Pleistocene was a climatically dynamic period, with abrupt shifts between cool-wet and warm-dry conditions. Increased effective precipitation supported large pluvial lakes and long-lived spring ecosystems in valleys and basins throughout the western and southwestern U.S., but the source and seasonality of the increased precipitation are debated. Increases in the proportions of C4/(C4+ C3) grasses in the diets of large grazers have been ascribed both to increases in summer precipitation and lower atmospheric CO2 levels. Here we present stable carbon and oxygen isotope data from tooth enamel of late Pleistocene herbivores recovered from paleowetland deposits at Tule Spring Fossil Beds National Monument in the Las Vegas Valley of southern Nevada, as well as modern herbivores from the surrounding area. We use these data to investigate whether winter or summer precipitation was responsible for driving the relatively wet hydroclimate conditions that prevailed in the region during the late Pleistocene. We also evaluate whether late Pleistocene grass C4/(C4+ C3) was higher than today, and potential drivers of any changes.Tooth enamel δ18O values for Pleistocene Equus, Bison, and Mammuthus are generally low (average 22.0 ± 0.7‰, 2 s.e., VSMOW) compared to modern equids (27.8 ± 1.5‰), and imply lower water δ18O values (−16.1 ± 0.8‰) than modern precipitation (−10.5‰) or in waters present in active springs and wells in the Las Vegas Valley (−12.9‰), an area dominated by winter precipitation. In contrast, tooth enamel of Camelops (a browser) generally yielded higher δ18O values (23.9 ± 1.1‰), possibly suggesting drought tolerance. Mean δ13C values for the Pleistocene grazers (−6.6 ± 0.7‰, 2 s.e., VPDB) are considerably higher than for modern equids (−9.6 ± 0.4‰) and indicate more consumption of C4 grass (17 ± 5%) than today (4 ± 4%). However, calculated C4 grass consumption in the late Pleistocene is strikingly lower than the proportion of C4 grass taxa currently present in the valley (55–60%). δ13C values in Camelops tooth enamel (−7.7 ± 1.0‰) are interpreted as reflecting moderate consumption (14 ± 8%) of Atriplex (saltbush), a C4 shrub that flourishes in regions with hot, dry summers.Lower water δ18O values, lower abundance of C4 grasses, and the inferred presence of Atriplex are all consistent with general circulation models for the late Pleistocene that show enhanced delivery of winter precipitation, sourced from the north Pacific, into the interior western U.S. but do not support alternative models that infer enhanced delivery of summer precipitation, sourced from the tropics. In addition, we hypothesize that dietary competition among the diverse and abundant Pleistocene fauna may have driven the grazers analyzed here to feed preferentially on C4 grasses. Dietary partitioning, especially when combined with decreased pCO2 levels during the late Pleistocene, can explain the relatively high δ13C values observed in late Pleistocene grazers in the Las Vegas Valley and elsewhere in the southwestern U.S. without requiring additional summer precipitation. Pleistocene hydroclimate parameters derived from dietary and floral records may need to be reevaluated in the context of the potential effects of dietary preferences and lower pCO2 levels on the stability of C3 vs. C4 plants.

The Pampean region (Argentina) underwent larger variation in aridity than in temperature during the late Pleistocene: New evidence from the isotopic analysis of mammalian taxa

During the Pleistocene intense climatic changes occurred corresponding with the alternation of interglacial and glacial periods. By means of stable isotope analysis on fossil mammals, this research allows the assessment of the palaeoecological and palaeoclimatic conditions, including the possible scenarios for the atmospheric circulation pattern during three key phases of the late Pleistocene in the Pampean region of Argentina: Last Interglacial (LIG, MIS 5e; unpublished data), Last Glacial Maximum (LGM; 28,170–19,849 cal BP yrs), and post-Last Glacial Maximum (post-LGM, 17,281–11,500 cal BP yrs). Tooth enamel δ13C values of mammals from the Last Glacial Maximum showed an increase in C4 plants consumption compared to the other two phases studied, which may be related to a reduction in forest cover due to a combination of environmental factors such as decreased pCO2atm and increased aridity. We evaluated mean annual precipitation (MAP) and mean annual temperature (MAT) variability from tooth enamel δ13C and δ18O values, which showed a greater variation in precipitation between phases than in temperature. This result enabled us to propose two climate regimes for the studied temporal sequence, an arid-temperate regime, and a humid-temperate regime, which were mostly regulated by variations in atmospheric circulation.

Middle Pleistocene paleoclimate and paleoenvironment of central Italy and their relationship with hominin migrations and evolution

To investigate the paleoclimate and paleoenvironment of central Italy during the Middle Pleistocene, we analyzed the carbon and oxygen stable isotope composition of the carbonate component of sequential enamel samples from twenty-four rhinoceros (Stephanorhinus spp.) teeth. The samples come from two key archeological and paleontological sites located in the Molise region: Isernia La Pineta (ILP; ∼600 ka) and Guado San Nicola (GSN; ∼400 ka).Carbon isotope ratios of enamel from both ILP and GSN indicate feeding in a pure C3 ecosystem that consisted predominantly of woodlands and/or mesic C3 grasslands with the possible sparse presence of closed canopy forests at or near ILP ∼600 ka. The average (± 1 σ) enamel δ13C for ILP (−13.6 ± 0.6‰) is lower than that for GSN (−12.1 ± 0.4‰), suggesting higher mean annual precipitation and lesser aridity ∼600 vs. ∼400 ka. Average intra-tooth variability in enamel δ13C from both sites is low (∼1‰), likely indicating seasonally uniform diets, plant carbon isotope compositions, and precipitation amounts. However, the low intra-tooth variability in enamel δ13C may also reflect amplitude attenuation of the isotopic signal of the plants into tooth enamel.With respect to oxygen isotopes, the average (± 1 σ) enamel δ18O for ILP (24.2 ± 0.7‰) is slightly lower than that for GSN (25.0 ± 0.7‰), likely reflecting the higher elevation of ILP as well as lesser aridity and/or slightly lower mean annual temperature in the region ∼600 vs. ∼400 ka. The δ18O values of meteoric precipitation (∼-7‰) calculated from enamel compositions are indistinguishable from the modern values, suggesting that mean annual temperatures were broadly similar to today (∼13°C). Both sites exhibit a moderate average intra-tooth variability in enamel δ18O (∼2‰), likely indicating a temperature seasonality similar or slightly decreased relative to today. The temperate climate and the increase in aridity that occurred sometime between ∼600 and ∼400 ka were potentially important factors for the human colonization of the Italian peninsula and for the cultural and behavioral evolution of the early hominins during the Middle Pleistocene.

Climatic quantification and seasonality of the late MIS 3 in North China: A perspective from carbon and oxygen isotopes of fossil mammal teeth

Marine Isotope Stage 3 (MIS 3, at 60–25 ka B.P.) was a short interstadial within the Last Glacial period. A generally warm and wet climatic condition during the MIS 3 period has been suggested by many previous studies. Quantitative climatic reconstruction and studies of seasonality, however, have been seldom attempted given the scarcity of useful proxy indicators. A full understanding the climatic characteristics during this period is hampered by their absence. This is especially the case in the East Asian monsoon region in North China, which is very sensitive to climatic change. To help fill this knowledge gap, we have determined the stable carbon (δ13C) and oxygen isotope (δ18O) compositions of tooth enamel from fossil mammals (Bubalus sp [buffalo] and Cervus elaphus [red deer], dated at ∼33–31 ka B.P.) recovered from Longquan Cave in North China. We use these data to constrain ecology, local air temperature and precipitation amounts during the late MIS 3. The average δ13C (VPDB) of tooth enamel (−14.4‰ and −8.8‰, respectively for buffalo and red deer) indicate that C3 plants comprised the main diet of animals living in this area. Pollen assemblages demonstrated that vegetation mainly consisted of grasses and herbs (∼64%) with trees only accounting for about 26%. These results indicate a landscape of open steppe with sparsely distributed trees. The reconstructed climate derived from tooth enamel δ18O was relatively colder and drier than present-day condition, with mean annual air temperature ranging from 4 to 13 °C and mean annual precipitation ranging from 360 to 670 mm. Moreover, the inferred summer and winter half-year temperatures were respectively 8–24 °C and −2 to 5 °C, which represents either similar or weaker seasonality than at the present time. The inferred cold and dry climate suggested by our study contrasts with the warm and wet conditions previously reconstructed using proxy indicators from bulk soil samples in North China. In comparison to the long-term, time-averaged climatic condition reflected by those soil proxies, the stable isotope compositions of fossil more likely recorded climatic conditions at annual or seasonal time-scale. The inferred annual cold/dry climate at Luanchuan Cave suggested by our data may indicate a short climatic cooling event from Greenland Interstadial (GIS) 5 to its following stadial. Mean annual temperature fluctuated by ∼8 °C during this interstadial-stadial cycle.

Stable isotopes confirm the Banwell Bone Cave Mammal Assemblage Zone represents an MIS 5 fauna

Abstract The position of the Banwell Bone Cave mammal assemblage zone (MAZ) in the mammalian biostratigraphy of the British Isles has been the focus of debate for decades. Dominated by fauna typical of cold environments it was originally linked to the marine oxygen isotope stage (MIS) 4 stadial (ca. 72–59 ka). Subsequently it was argued that the Banwell Bone Cave MAZ more likely relates to the temperate interstadial of MIS 5a (ca. 86–72 ka). It is envisioned that “cold fauna” such as bison and reindeer moved into Britain during stadial MIS 5b (ca. 90 ka) and were subsequently isolated by the rising sea level during MIS 5a. Here we investigate environmental conditions during the Banwell Bone Cave MAZ using bone collagen δ13C and δ15N and tooth enamel δ18O and δ13C isotope analysis. We analyse bison and reindeer from the MAZ type-site, Banwell Bone Cave. Our results show unusually high δ15N values, which we ascribe to arid conditions within a temperate environment. Palaeotemperature estimates derived from enamel δ18O indicate warm temperatures, similar to present day. These results confirm that the Banwell Bone Cave MAZ relates to a temperate interstadial and supports its correlation to MIS 5a rather than MIS 4.

Correlation between \u03b418Ow and \u03b418\u039fen for estimating human mobility and paleomobility patterns

In this study a methodology for identifying the geographic origin of unidentified persons, their residence and moving patterns while providing information on lifestyle, diet and socio-economic status by combining stable isotopic data, with the biological information (isotopic composition of the skeleton), is presented. This is accomplished by comparing the oxygen isotopic composition of the spring water that individuals were drinking, during their living period, with the oxygen isotopic composition of their tooth enamel bioapatite. Spring water and teeth samples were collected from individuals from three different areas of Greece: North Greece, Central Greece and South Greece and isotopic analysis of δ13C and δ18O of tooth enamel bioapatite and δ18O of spring water were conducted. For these three areas the isotopic methodology is a promising tool for discriminating the provenance. Furthermore, as a case study, this methodology is applied to two archeological sites of Greece (Medieval-Thebes and Roman-Edessa) in order to determine paleomobility patterns.

Palaeoecological and palaeoenviromental reconstruction of the upper Miocene vertebrate karstic site of Corral de Lobato, central-eastern Spain

We report stable isotopic analyses for dental enamel of fossil mammals from the Miocene (~7.1 Ma, MN13, middle Turolian) Corral de Lobato locality, Guadalajara, Spain, and compare it with adjacent localities of the Iberian Range. This multidisciplinary research allows the assessment of the palaeoenvironmental, palaeoecological and palaeoclimatic conditions that were in place in the central-eastern area of the Iberian Peninsula at this time. Herbivore tooth enamel δ13C values point to the presence of two environments: open woodland/arid C3 grassland and woodland/mesic C3 grassland. We infer the most probable diets of the two carnivores analysed, indicating a partition of resources and habitats. Tooth enamel δ18O values from the obligate drinkers indicate that all of them would have drunk water with similar evaporation rates except for the suid Hippopotamodon major, although its distinct δ18O values may be influenced by its omnivorous diet. Comparing Corral de Lobato taxa with those from other semi-contemporaneous (MN12–MN13) localities of the nearby Teruel Basin, δ13O values point to more arid conditions in Corral de Lobato while lower values of δ18O are most likely related to the karst origin of water bodies. Possibly, the difference between the isotopic compositions of Corral de Lobato and adjacent localities results from the combined effect of palaeotopography and a global climate pulse about 7 Ma.

Assessing weaning stress – Relations between enamel hypoplasia, δ18O and δ13C values in human teeth obtained from early modern cemeteries in Wroclaw, Poland

ObjectivesThe aim of this paper is to assess linear enamel hypoplasia (LEH) on canines of adults from early modern Wroclaw cemeteries to compare δ13C and δ18O values in enamel formed before, during and after LEH formation, and to attempt to find a link between the selected indicators of the weaning process. Material and methods15 permanent canines with visible LEH were selected for analysis. Age at LEH formation was estimated using the Reid and Dean method. The perikymata count was used to estimate the duration of LEH formation. Incremental stable oxygen and carbon isotopes analysis was performed on tooth enamel to infer stress related to weaning and dietary patterns. Kruskal–Wallis ANOVA, Mann–Whitney U test and Spearman correlation were used in statistical inference. ResultsThe average age of LEH formation was 3.14 years, with an average duration of 111 days. Stable carbon isotope values consistently increase in 73% of the individuals sampled. The values of δ18O do not show a dominant pattern. The average value of δ13C increases over the time of enamel formation. The δ13C values collected below LEH were negatively correlated with δ18O values and the duration of LEH termination. ConclusionsMarking of carbon and oxygen isotopes indicates different stages of weaning. Advancements in diet change (determined by higher δ13C) corresponds with faster recovery after physiological stress episode. There is no evidence for different breastfeeding models between distinct parishes in early modern Wroclaw.

OXYGEN ISOTOPE PROFILES OF UPPERMOST JURASSIC VERTEBRATE TEETH AND OYSTER SHELLS: A RECORD OF PALEOENVIRONMENTAL CHANGES AND ANIMAL HABITATS

ABSTRACTHigh resolution oxygen isotopes profiles of well-preserved uppermost Jurassic oyster shells and vertebrate (ichthyosaur and fish) teeth from Central Poland were obtained using a microdrill and an ion microprobe (SHRIMP IIe/MC). Internal variability of δ18O values of oyster shells (-1.7 to 1.3‰ VPDB) collected from the offshore interval of the studied section is greater than that determined previously from bulk oysters. Relatively high δ18O values of the studied oysters may be linked to a slight increase in the salinity of the mid-Polish basin. Low δ18O values of co-occurring ichthyosaur tooth enamel substantiate endothermy of these reptiles. An observed ontogenetic increase in the ichthyosaur enamel δ18O values (from ∼ 19.4 to ∼ 21.6‰ VSMOW) may be a result of long distance migrations although the effect of metabolic factors at rising body mass cannot be completely excluded. It is postulated that δ18O values of the latest portion of the ichthyosaur tooth enamel can be used for the calculation of ancient water oxygen isotope composition and verification of oxygen isotope temperatures. High δ18O values of the enameloid of Caturus lungfishes (23.6 to 26.5‰ VSMOW) collected from an upper part of the studied section, which was deposited in a restricted lagoonal environment after a marine regression, are probably a result of a high evaporation rate. The fishes could have breathed atmospheric air and withstood episodes of water hypoxia. Internal oxygen isotope records of the shells and teeth are promising proxies for studies of the paleoenvironment and activity of animals.

The interpretability of stable hydrogen isotopes in modern herbivore tooth enamel

Stable hydrogen isotopes (δD values) in animal organic tissues such as collagen and keratin typically correlate with local meteoric water, but little is known about δD in tooth enamel apatite. In this study, we analyzed comminuted tooth enamel for oxygen isotopes (δ18O) of the CO3 component and for δD of bulk enamel. We find positive correlations between enamel δD and δ18O (R2 = 0.70) and between enamel δD and local precipitation δD (R2 = 0.53). However, the slopes of these relationships are much shallower (less variation in tooth enamel δD) than expected from studies of other tissues. Based on mass spectrometric peak areas, H2 contents for enamel are 2–5 times higher than expected from chemical compositions, and we interpret as much as 50–90% of measured hydrogen from tooth enamel may be adsorbed water derived from laboratory water vapor. We tested this hypothesis by equilibrating tooth enamel with very high and very low δD values of water vapor, then exposing to laboratory air for different periods of time ranging from minutes to 8 hours. These experiments show that the apparent δD value of enamel converges to a nearly constant δD value in 1 to 2 hours. The large amount of adsorbed water and rapid approach to equilibrium will make it difficult to infer provenance from δD measurements alone, or to reproduce measured tooth enamel δD values among laboratories with different water vapor compositions. Heating at 70 °C for 48 hours in air does not remove adsorbed hydrogen, but does reduce δD values by c. 10‰ compared to unheated samples. Differences in δD values for heated vs. unheated enamel may reflect either a different, temperature-dependent partition coefficient between adsorbed water (on apatite) and water vapor, exchange of structural H at elevated temperatures, or subtle changes to crystal structure, such as loss of structural H.

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

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.

Oxygen isotope analyses of ungulate tooth enamel confirm low seasonality of rainfall contributed to the African Humid Period in Somalia

During the African Humid Period (AHP), between ~14 and 5 ka, north and eastern Africa were much wetter and greener than they are today. Although the AHP has long been attributed to an increase in rainfall driven by orbital forcing, many details regarding the timing, pacing, and contributing moisture sources remain to be determined, especially for eastern Africa. Recent research suggests that both Atlantic and Indian Ocean moisture contributed to the AHP in eastern Africa. Large mammalian faunas from two Late Pleistocene/Holocene rockshelter sites in southern Somalia, Gogoshiis Qabe and Guli Waabayo, provide an unusual opportunity to investigate the AHP in an area of eastern Africa that is orographically isolated from Atlantic Ocean moisture. To track changes in aridity at these sites, we used the oxygen isotope aridity index, which exploits the difference in tooth enamel oxygen isotope (δ18O) values between evaporation insensitive obligate drinkers and evaporation sensitive non-obligate drinkers to calculate a water deficit value. Water deficit values calculated from dik-dik (Madoqua spp.; non-obligate drinkers) and warthog (Phacochoerus spp.; obligate drinkers) tooth enamel δ18O values at Gogoshiis Qabe and Guli Waabayo are in agreement and progressively increase toward the present. Additionally, two of three direct dated serially-sampled warthog teeth (ID 4032 and 4033) from Guli Waabayo demonstrate low seasonality of rainfall during much of the AHP (range in δ18O ≤ 1.8‰). One tooth (ID 4035) with high amplitude variability in δ18O values (3.1‰) dates to 8470 ± 66 cal yr B.P., a period identified as a lowstand in several lake level records. Our results suggest that regions isolated from Atlantic Ocean moisture likely experienced a less-pronounced AHP than those receiving moisture from multiple sources but indicate less seasonal variability than present. Our findings also support the presence of climate variability within the AHP.

Isotopic analysis of the Blick Mead dog: A proxy for the dietary reconstruction and mobility of Mesolithic British hunter-gatherers

A single domestic dog (Canis familiaris) tooth was recovered from the Mesolithic site of Blick Mead in the Stonehenge landscape. As no human remains were recovered from the site, the dog tooth provides a potential proxy for reconstructing human diet. Previous studies have shown that domestic dogs often have similar δ13C and δ15N values to their human companions. Incremental dentine carbon and nitrogen isotope analysis and bulk enamel carbon, oxygen and strontium isotope analysis were obtained from the tooth to produce a life-history profile of the dog's diet and mobility. The δ13C and δ15N values indicate that there was little variation in the dog's diet between c.2 and 6 months of age. δ15N values range between +7.9 to +8.7‰, (mean +8.5‰), whereas δ13C values range between −21.3 and −20.5‰, (mean −20.9‰). These data suggest that the dog was consuming predominantly terrestrial herbivorous protein, with the possible inclusion of freshwater fish. The enamel 87Sr/86Sr ratio of 0.70796 can only be obtained from a chalk landscape, such as is found at Blick Mead and elsewhere in southern and southeastern Britain, or basalt terrains which are rare in southern Britain. The enamel δ18O(SMOW) value of 25.7‰ is not consistent with the dog residing at Blick Mead but appropriate contemporaneous data from dogs is currently lacking. The results are thus consistent with the dog originating in a chalk or possibly basaltic terrain elsewhere in Britain and Ireland or that the dog resided locally at a time when the climate was colder than present.

Late Middle Pleistocene ecology and climate in Northeastern Thailand inferred from the stable isotope analysis of Khok Sung herbivore tooth enamel and the land mammal cenogram

Paleoecological and paleoclimatic records based on the stable isotopes of mammalian tooth enamel are poorly known in mainland Southeast Asia during the Pleistocene. Khok Sung in Northeastern Thailand is a late Middle Pleistocene terrace deposit, tentatively dated either as 213 ka or 188 ka, yielding 15 described mammalian taxa with especially abundant and complete fossil remains. To investigate paleodiets and habitats of these ancient mammals and to understand the corresponding regional climate, we performed an analysis of stable carbon and oxygen isotopes extracted from tooth enamel carbonate of various mammalian taxa, coupled with the cenogram method. The enamel δ13C values of Khok Sung mammals indicate a variety of diets, ranging from pure C3 to C4 plants, suggesting that C4 grasses were a major component of local Thai ecosystems during the late Middle Pleistocene. The stable isotopic distinction between C3 and C4 plants suggests that the Pleistocene wildlife habitats ranged from closed forests to open grasslands for the Khok Sung area. Moreover, differences within sympatric Pleistocene herbivores such as proboscideans, rhinoceroses, and cervids characterize possible niche partitioning by minimizing interspecific overlap. Paleoclimatic interpretations based on the intra-tooth variability in enamel δ18O values from large mammals and on the cenogram analysis reflect significant seasonal variations in precipitation and temperature, and humid conditions, for the Khok Sung locality. Compared to modern environments in Thailand, it is apparent that C4-dominated grasslands were more widespread at that time when anthropic impacts on the ecosystems were presumably absent or minimal.

Multi-Isotope investigations of ungulate bones and teeth from El Castillo and Covalejos caves (Cantabria, Spain): Implications for paleoenvironment reconstructions across the Middle-Upper Palaeolithic transition

The Cantabrian region of Northern Spain was an important area of human occupation during the Middle and Upper Palaeolithic as the rich archaeological record demonstrates. The environmental conditions experienced by late Neanderthals and Anatomically Modern Humans (AMH) in the region during MIS3 are still poorly known, but are crucial to understand the role climatic instability could have had on the adaptations of these populations. In this study, a series of archaeological levels with Mousterian and Aurignacian artefact assemblages, dating between 49 and 35 ka uncal. BP, from the sites of El Castillo and Covalejos caves in Cantabria were studied using multi-isotope techniques including bone collagen δ13C, δ15N and δ34S analysis and a pilot study based on tooth enamel δ18O and δ13C. Results at Covalejos indicate a large range in δ15N values observable within both Mousterian Level D and Aurignacian Level B, suggesting the presence of different micro-environments within the local area at certain times during each temporal period. Within Aurignacian Level C and Mousterian Level J, the δ15N values range is much smaller, but shows consistency in the parts of the landscape being exploited during both times. Neanderthals and AMH appear to have been procuring animals from isotopically similar zones (isozones) when they occupied Covalejos. The variations in δ34S values between levels analysed at Covalejos also implies the use of a variety of hunting locations by both late Neanderthals and AMH. At El Castillo, δ13C and δ15N values show great consistency between levels, indicating that animals were being hunted from the same isozones when the site was presumably occupied by the two human species. The mosaic landscapes of Cantabria may have buffered the sharp environmental fluctuations that occurred during late MIS3 throughout Europe, providing suitable habitats for the key prey ungulate species that were routinely exploited throughout the Middle and Early Upper Palaeolithic. This environmental buffering may explain why this southerly, oceanic region was consistently occupied throughout this time of bio-cultural transition.