Enamel Carbonate Research Articles

Kangaroo tooth enamel oxygen and carbon isotope variation on a latitudinal transect in southern Australia: implications for palaeoenvironmental reconstruction

Tooth enamel apatite carbonate carbon and oxygen isotope ratios of modern kangaroos (Macropus spp.) collected on a 900-km latitudinal transect spanning a C(3)-C(4) transition zone were analysed to create a reference set for palaeoenvironmental reconstruction in southern Australia. The carbon isotope composition of enamel carbonate reflects the proportional intake of C(3) and C(4) vegetation, and its oxygen isotope composition reflects that of ingested water. Tooth enamel forms incrementally, recording dietary and environmental changes during mineralisation. Analyses show only weak correlations between climate records and latitudinal changes in δ(13)C and δ(18)O. No species achieved the δ(13)C values (~-1.0 ‰) expected for 100 % C(4) grazing diets; kangaroos at low latitudes that are classified as feeding primarily on C(4) grasses (grazers) have δ(13)C of up to -3.5 ‰. In these areas, δ(13)C below -12 ‰ suggests a 100 % C(3) grass and/or leafy plant (browse) diet while animals from higher latitude have lower δ(13)C. Animals from semi-arid areas have δ(18)O of 34-40 ‰, while grazers from temperate areas have lower values (~28-30 ‰). Three patterns with implications for palaeoenvironmental reconstruction emerge: (1) all species in semi-arid areas regularly browse to supplement limited grass resources; (2) all species within an environmental zone have similar carbon and oxygen isotope compositions, meaning data from different kangaroo species can be pooled for palaeoenvironmental investigations; (3) relatively small regional environmental differences can be distinguished when δ(13)C and δ(18)O data are used together. These data demonstrate that diet-isotope and climate-isotope relationships should be evaluated in modern ecosystems before application to the regional fossil record.

OXYGEN AND CARBON ISOTOPE ANALYSIS OF HUMAN DENTAL ENAMEL FROM THE CARIBBEAN: IMPLICATIONS FOR INVESTIGATING INDIVIDUAL ORIGINS

This study explores the potential of carbon and oxygen isotope data from human enamel carbonate (n = 50) to contribute to mobility studies in the Caribbean. Most oxygen and carbon isotope results display limited variation, with substantial overlap between islands. However, a few individuals from El Chorro de Maíta, Cuba possess relatively low δ18O and high δ13C. Two of these individuals were previously identified as possible non-Antillean immigrants on the basis of strontium isotopes, and bioarchaeological and mortuary evidence. The carbon and oxygen isotope results provide additional evidence supporting the proposed non-local origins of these individuals and contribute to explorations of their potential natal origins.

The Distribution of Carbonate in Enamel and its Correlation with Structure and Mechanical Properties.

The correlation of carbonate content with enamel microstructure (chemical and crystal structure) and mechanical properties was evaluated via linear mapping analyses using Raman microspectroscopy and nanoindentation. Mappings started at the outer enamel surface and ended in the inner enamel near the dentin-enamel junction (DEJ) in lingual and buccal cervical and cuspal regions. The carbonate peak intensity at 1070 cm-1 gradually increased from outer to inner enamel. Moreover, the phosphate peak width, as measured by the full width at half maximum (FWHM) of the peak at 960 cm-1, also increased, going from ~9 cm-1 in outer enamel to ~13 cm-1 in enamel adjacent to the DEJ, indicating a decrease in the degree of crystallinity of hydroxyapatite from outer to inner enamel. In contrast, Young's modulus decreased from 119±12 to 80±19 GPa across outer to inner enamel with a concomitant decrease in enamel hardness from 5.9±1.4 to 3.5±1.3 GPa. There were also significant correlations between carbonate content and associated crystallinity with mechanical properties. As carbonate content increased, there was an associated decrease in crystallinity and both of these changes correlated with decreased modulus and hardness. Collectively, these results suggest that enamel carbonate content and the associated change in the crystal structure of hydroxyapatite, i.e. degree of crystallinity, may have a direct effect on enamel mechanical properties. The combination of Raman microspectroscopy and nanoindentation proved to be an effective approach for evaluating the microstructure of enamel and its associated properties.

Were European steppe bison migratory? 18O, 13C and Sr intra-tooth isotopic variations applied to a palaeoethological reconstruction

This paper focuses on the palaeoethological study of steppe bison (Bison priscus), a Eurasiatic species that disappeared at the end of the Pleistocene. In the Southern steppe of Eastern Europe, this large bovid seems to have been a keystone species during the late Pleistocene, where it is omnipresent in archaeozoological assemblages and can constitute spectacular bone accumulations. Based on the principles of actualism, which assume that modern animal biology and their behavioural adaptations can be applied to the past, different models of bison palaeoethological reconstructions have been proposed to explain this important occurrence of bison in East European archaeological records. Considering the variability of extant bison behaviour, it appeared necessary to undertake a direct reconstruction of the behaviour of fossil bison, to assess how they were targeted.In order to reconstruct steppe bison ecology and habits stable isotope analyses were conducted of tooth enamel carbonate of 25 individuals from Amvrosievka, a Late Pleistocene (∼18,500 BP) archaeological site complex from Eastern Ukraine. Intra- and inter-individual variations in the stable oxygen, carbon and strontium isotope composition of tooth enamel were analysed to reconstruct the feeding behaviour and seasonal movements of steppe bison. This is the first large scale multi-proxy study of its kind for a Pleistocene cohort.The results show that bison δ13C values are wholly consistent with an exclusively C3 plant diet, typical of steppe/grassland environments, with a likely consumption of lichen during the cold season. δ18O, δ13C and 87Sr/86Sr values are typical of sedentary bison herds, with limited inter-seasonal movement. These results challenge the previous assumption that Pleistocene bison of the East European steppe were migratory, demonstrating instead that they occupied limited ranges, with no long distance seasonal movement, and that they occasionally incorporated low nutrient foods in their diet.These new palaeobiological results confirm the ecological and behavioural plasticity of bison and have important implications for archaeologists studying hunter-gatherers since human acquisition strategies are directly related to the social, seasonal and spatial behaviour of prey species. This research demonstrates that direct reconstructions of the eco-ethology of fossil prey species are essential, therefore, before attempting to make inferences about the hunting tactics and subsistence strategies developed by Prehistoric hunters.

A Comparative Study of Carbonate Determination in Human Teeth Using Raman Spectroscopy

Carbonate determination in dental apatites such as dentine and enamel is important for studying the dynamics of dental caries and developmental defects of these tissues. Traditionally, these determinations have been performed by acidic digestion with the subsequent measurement of released carbon dioxide gas. As an alternative, Raman spectroscopy has been used for the determination of carbonate in synthetic carbonated apatites with at least four analytical methods published thus far. However, these methods have not been applied to biological apatites. The aim of this comparative study was to test the suitability of these four methods for the determination of B-type carbonate in human enamel and dentine. A method for determining the A-type carbonate content of enamel using the Raman technique is also presented. Raman spectra were obtained from 10 human enamel and dentine samples and analysed with each of the four methods using either a single or multiple ν₁(PO₄^3–) band spectral fitting model. Each of the methods resulted in a different determination for the carbonate content when using the same measurement data. The method that used the full-width-at-half-maximum of the ν₁(PO₄^3–) band to determine the B-type carbonate concentration was found to be in best agreement with (i) the results (using the acid digestion method) of teeth collected from the same sample population and (ii) previously reported values for both enamel and dentine. The use of a multiple-band spectral fitting model produced the highest determination precision (particularly in the case of dentine).

Diet and death in times of war: isotopic and osteological analysis of mummified human remains from southern Mongolia

This study presents the results of an isotopic analysis of nine naturally mummified individuals—three adults, two adolescents, one juvenile, and three infants—recovered from the Hets Mountain Cave site in southern Mongolia, where they had been secondarily deposited. All of the individuals show evidence of violent perimortem trauma, but no skeletal indicators of nutritional or disease-related stress. Multi-isotopic data (δ13C, δ15N, δ18O, 87Sr/86Sr, and 20nPb/204Pb) were characterized in multiple tissues from each individual when possible, in order to reconstruct diet composition and residential origin at different points in life. Specifically, δ13C and δ15N in bone carbonate and collagen (N = 8) and hair keratin (N = 4) were coupled with enamel carbonate δ18O and δ13C (N = 3) and enamel 87Sr/86Sr, and 20nPb/204Pb (N = 3) to assess diet and residential mobility in relation to skeletal indicators of health and trauma. Results are consistent with a persistence of mixed C3/C4 pastoral subsistence and general stability of diet composition over the life course, in contrast to contemporary accounts of widespread famine and a dependence on grains imported from China throughout the region. However, results also suggest that at least some individuals may have migrated to this region of southern Mongolia from elsewhere during life, meaning that their dietary isotopic profiles may not represent local subsistence patterns near the Hets Mountain Cave site. Overall, these results speak to the utility of life course oriented multi-isotopic analysis in complementing more top-down historical analyses in understanding variation in subsistence, nutrition, and migration in regions undergoing significant political and economic turmoil.

Geographic variation in bone carbonate and water δ18O values in Mendoza, Argentina and their relationship to prehistoric economy and settlement

Questions of mobility, settlement pattern, and their relation to economic organization and resource use are central to ongoing work in central-western Argentina. Here we analyze geographic patterns in the distribution of 178 human bone carbonate δ18O samples, 46 human tooth enamel carbonate δ18O samples, and 48 water δ18O samples from throughout the Andean Cordillera and Monte Desert and evaluate their implications for prehistoric mobility and economy. We confirm and refine previous generalizations regarding a highland/lowland dichotomy in water δ18O values and show that the range of human carbonate δ18O values generally reflect available water sources. While there is little within-lifetime change in patterns of water use, we show that most individuals have stable isotope signatures consistent with water use from multiple areas or areas other than where they were ultimately interred. These data indicate high levels of residential mobility, and we conclude by discussing their implications for our understanding of regional prehistory.

Stable isotopes reflect the ecological stability of two high-elevation mammals from the late Quaternary of Colorado

The vertebrate fossil record of Cement Creek Cave, Colorado, spans from >45,000yr ago to the present and represents the richest stratified series of high-elevation (>2900m) mammal remains known from the late Quaternary of North America. Stable carbon and oxygen isotope analyses of tooth enamel were used to assess potential ecological responses of two species found commonly throughout the cave, Yellow-bellied marmots (Marmota flaviventris) and Bushy-tailed woodrats (Neotoma cinerea), to late Quaternary climate and environmental changes of the Southern Rocky Mountains. Results indicate that despite such perturbations, the dietary ecologies of both species were maintained across this period. Neither taxon shifted to consuming C4 taxa or different C3 functional groups; similarly, no significant shifts in surface water use were detected. Variations in enamel δ13C were observed, however, that represent the physiological responses of high-elevation plants to changing levels of late Quaternary atmospheric CO2. While our findings extend both the geographic and elevational record of this plant CO2 response, they simultaneously highlight the ecological stability of high-elevation M. flaviventris and N. cinerea during climate changes of late Quaternary magnitude.

EXAMINING CHILDHOOD DIETS AT KAMINALJUYU, GUATEMALA, THROUGH STABLE ISOTOPIC ANALYSIS OF SEQUENTIAL ENAMEL MICROSAMPLES*

Stable carbon and oxygen isotope ratios of tooth enamel provide a means to examine nutritional changes during childhood. To date, such studies have used large enamel samples, often spanning the developmental period of the tooth. This paper reports the results of small samples drilled from first molars and premolars of human teeth from Kaminaljuyu, a Classic period city in highland Guatemala. Carbon isotopes show considerable increase between cuspal and cervical enamel for both teeth, indicating an increase in maize consumption during childhood. Oxygen isotope trends are more variable, and suggest some seasonal fluctuation. While the oxygen isotope data confirm the identification of foreign skeletons among the samples, they illustrate a need for caution when sampling teeth due to variable δ18O composition of enamel within a tooth.

Small mammal carbon isotope ecology across the Miocene–Pliocene boundary, northwestern Argentina

The late Miocene expansion of plants using the C4 photosynthetic pathway in South America has been documented by tooth enamel carbon isotope ratios (δ13Cen). However, a more detailed understanding of this ecological event is hampered by poor chronological control on the widespread fossil localities from which isotopic data are derived. This study develops a δ13Cen record from a single 2500m-thick stratigraphic section in subtropical South America. Strata at Puerta de Corral Quemado (PCQ), northwestern Argentina, span 9 to 3.5Ma in age, and existing paleosol carbonate data (δ13Cpc) document C4 expansion across the Miocene–Pliocene boundary. Comparison of δ13Cen data with δ13Cpc data at high stratigraphic resolution refines understanding of this ecological event in South America. Small mammal δ13Cen data in particular are complementary to that of large mammal and paleosol δ13C data. Small mammal teeth integrate isotopic data over much shorter temporal and spatial scales than large mammal teeth, providing a sensitive measure of local vegetation and placing constraints on the landscape distribution of C3 and C4 plants. Explicit consideration of the distinctive carbon isotope enrichment factor between enamel and diet for rodents (ε*en–diet=11‰, as opposed to 14‰ for large mammals) allows for unequivocal inference of C4 vegetation ~1Ma prior to that inferred from large mammal δ13Cen data, and ~2Ma prior to δ13Cpc data. This multiproxy record demonstrates that C4 plants were a stable component of the ecosystem hundreds of thousands of years prior to their major ecological expansion, and that the expansion of C4 plants was pulsed at PCQ. Two periods of ecological change are demonstrated by δ13C and δ18O data at ~7Ma and 5.3Ma (coincident with the Miocene–Pliocene boundary). Development of small mammal δ13Cen records on other continents may provide similar insight into the early stages of the global C4 event.

The oxygen isotope relationship between the phosphate and structural carbonate fractions of human bioapatite

Oxygen isotope analysis of archaeological human dental enamel is widely used as a proxy for the drinking water composition (δ(18)O(DW)) of the individual and thus can be used as an indicator of their childhood place of origin. In this paper we demonstrate the robustness of structural carbonate oxygen isotope values (δ(18)O(C)) in bioapatite to preserve the life signal of human tooth enamel by comparing it with phosphate oxygen isotope values (δ(18)O(P)) derived from the same archaeological human tooth enamel samples. δ(18)O(C) analysis was undertaken on 51 archaeological tooth enamel samples previously analysed for δ(18)O(P) values and strontium isotopes. δ(18)O(C) values were determined on a GV IsoPrime dual inlet mass spectrometer, following a series of methodological tests to assess: (1) The reaction time needed to ensure complete release of CO(2) from structural carbonate in the enamel; (2) The effect of an early pre-treatment with dilute acetic acid to remove diagenetic carbonate; (3) Analytical error; (4) Intra-tooth variation; and (5) Diagenetic alteration. This study establishes a direct relationship between δ(18)O(C) and δ(18)O(P) values from human tooth enamel (δ(18)O(P) = 1.0322 × δ(18)O(C) - 9.6849). We have combined this equation with the drinking water equation of Daux et al. (J. Hum. Evol. 2008, 55, 1138) to allow direct calculation of δ(18)O(DW) values from human bioapatite δ(18)O(C) (δ(18)O(DW) = 1.590 × δ(18)O(C) - 48.634). This is the first comprehensive study of the relationship between the ionic forms of oxygen (phosphate oxygen and structural carbonate) in archaeological human dental enamel. The new equation will allow direct comparison of data produced by the different methods and allow drinking water values to be calculated from structural carbonate data with confidence.

Diagenesis in bone and enamel apatite carbonate; the potential of density separation to assess the original composition

This paper presents a new approach to the isotopic measurement of diagenetically altered archaeological bone apatite carbonate. We describe how the existing differential dissolution method may be combined with a new approach to remove diagenetically reformed material on the basis of its greater specific gravity. We show that heavier, more diagenetically altered fraction has a higher (altered) δ13C and also increased crystallinity within one individual. In addition, we proposed one potential tool to check the validity of bone carbonate by comparing bone collagen, enamel carbonate and bone carbonate values of δ13C and radiocarbon content from the same individual. In the case of Danebury cattle, we estimated the biogenic δ13Capa value for DC83 and DC89, although it is still difficult to overcome diagenesis in order to meet the expected value, which is shown to be 1.9‰ (DC83) and 3.5‰ (DC89).

Paleoclimate during Neandertal and anatomically modern human occupation at Amud and Qafzeh, Israel: the stable isotope data

The δ 13C(en) and δ 18O(en) values of goat and gazelle enamel carbonate indicate that Neandertals at Amud Cave, Israel (53–70 ka) lived under different ecological conditions than did anatomically modern humans at Qafzeh Cave, Israel (approximately 92 ka). During the Last Glacial Period, Neandertals at Amud Cave lived under wetter conditions than those in the region today. Neither faunal species ate arid-adapted C 4 plants or drought-stressed C 3 plants. The variation in gazelle δ 18O(en) values suggests multiple birth seasons, which today occur under wetter than normal conditions. The magnitude and pattern of intra-tooth variation in goat δ 18O(en) values indicate that rain fell throughout the year unlike today. Anatomically modern humans encountered a Qafzeh Cave region that was more open and arid than Glacial Period Amud Cave, and more open than today's Upper Galilee region. Goat δ 13C(en) values indicate feeding on varying amounts of C 4 plants throughout the year. The climate apparently ameliorated higher in the sequence; but habitats remained more open than at Amud Cave. Both gazelles and goats fed on C 3 plants in brushy habitats without any inclusion of C 4 plants. The magnitude of intra-tooth variation in goat δ 18O(en) values, however, suggest that some rain fell throughout the year, and the relative representation of woodland dwelling species indicates the occurrence of woodlands in the region. Climate differences affecting the distribution of plants and animals appear to be the significant factor contributing to behavioral differences previously documented between Neandertals and anatomically modern humans in the region. Climate forcing probably affected the early appearances of anatomically modern humans, although not the disappearance of Neandertals from the Levant.

Lowland–upland migration of sauropod dinosaurs during the Late Jurassic epoch

Sauropod dinosaurs were the largest vertebrates ever to walk the Earth, and as mega-herbivores they were important parts of terrestrial ecosystems. In the Late Jurassic-aged Morrison depositional basin of western North America, these animals occupied lowland river-floodplain settings characterized by a seasonally dry climate. Massive herbivores with high nutritional and water needs could periodically experience nutritional and water stress under these conditions, and thus the common occurrence of sauropods in this basin has remained a paradox. Energetic arguments and mammalian analogues have been used to suggest that migration allowed sauropods access to food and water resources over a wide region or during times of drought or both, but there has been no direct support for these hypotheses. Here we compare oxygen isotope ratios (δ(18)O) of tooth-enamel carbonate from the sauropod Camarasaurus with those of ancient soil, lake and wetland (that is, 'authigenic') carbonates that formed in lowland settings. We demonstrate that certain populations of these animals did in fact undertake seasonal migrations of several hundred kilometres from lowland to upland environments. This ability to describe patterns of sauropod movement will help to elucidate the role that migration played in the ecology and evolution of gigantism of these and associated dinosaurs.

Isotopic paleoecology of Clovis mammoths from Arizona

The causes of megafaunal extinctions in North America have been widely debated but remain poorly understood. Mammoths (Mammuthus spp.) in the American Southwest were hunted by Clovis people during a period of rapid climate change, just before the regional onset of Younger Dryas cooling and mammoth extirpation. Thus, these mammoths may provide key insights into late Pleistocene extinction processes. Here we reconstruct the seasonal diet and climatic conditions experienced by mammoths in the San Pedro Valley of Arizona, using the carbon ((13)C/(12)C) and oxygen ((18)O/(16)O) isotope compositions of tooth enamel. These records suggest that Clovis mammoths experienced a warm, dry climate with sufficient summer rainfall to support seasonal C(4) plant growth. Monsoon intensity may have been reduced relative to the preceding time period, but there is no isotopic evidence for severe drought. However, it is possible that the "Clovis drought", inferred from stratigraphic evidence, occurred suddenly at the end of the animals' lives and thus was not recorded in the enamel isotopic compositions. Unlike mammoths that lived before the Last Glacial Maximum, Clovis mammoths regularly increased C(4) grass consumption during summer, probably seeking seasonally green grasslands farther from the river valley. This predictable seasonal behavior may have made mammoths easier to locate by Clovis hunters. Furthermore, Clovis mammoths probably had no previous experience of such sudden climatic change as is believed to have occurred at the time of their extinction.

Investigating climate at the Upper Palaeolithic site of Kraków Spadzista Street (B), Poland, using oxygen isotopes

Between 50,000 and 20,000 years ago, Europe experienced a series of rapid climate change events known as the Dansgaard–Oeschger cycles, which may have made areas of northern Europe more attractive for occupation by early modern humans at certain times than at others. This paper investigates when humans were occupying northern Europe in relation to these climatic changes at the archaeological site of Kraków Spadzista Street (B), by applying oxygen isotope analysis of mammoth tooth enamel carbonates (δ18O and δ13C) found at the site. The new isotopic data suggest that mean annual temperatures at Kraków Spadzista were 4–9 C° colder than present and, based on comparisons with previously published isotopic data for mammoth in Europe, the Kraków assemblage most likely formed during a cold Dansgaard–Oeschger event. This suggests modern humans were able to occupy and survive in this area of northern Europe during the harsh cold phases that affected Europe at this time.

Enamel carbon isotope evidence of diet and habitat of Gigantopithecus blacki and associated mammalian megafauna in the Early Pleistocene of South China

Enamel stable carbon isotope analyses were conducted on the large fossil ape Gigantopithecus blacki and an associated mammalian megafauna from Longgudong Cave in Jianshi and Juyuandong Cave in Liucheng, South China. The range in delta (13)C values (-18.8aEuro degrees to -14.1aEuro degrees) indicates that G. blacki and other large mammals fed on solely C3 biomass, and lived in forest habitats, and not open country or savannas. These results are consistent with other faunal and floral analyses for that time. The diet and habitat of G. blacki were significantly different from those of early hominins (Australopithecus and Paranthropus) from South and East Africa. Extinction of G. blacki probably was a result of forest habitat fragmentation and deterioration.

Analysis of 14C and 13C in teeth provides precise birth dating and clues to geographical origin

The identification of human bodies in situations when there are no clues as to the person's identity from circumstantial data, poses a difficult problem to the investigators. The determination of age and sex of the body can be crucial in order to limit the search to individuals that are a possible match. We analyzed the proportion of bomb pulse derived carbon-14 ((14)C) incorporated in the enamel of teeth from individuals from different geographical locations. The 'bomb pulse' refers to a significant increase in (14)C levels in the atmosphere caused by above ground test detonations of nuclear weapons during the cold war (1955-1963). By comparing (14)C levels in enamel with (14)C atmospheric levels systematically recorded over time, high precision birth dating of modern biological material is possible. Above ground nuclear bomb testing was largely restricted to a couple of locations in the northern hemisphere, producing differences in atmospheric (14)C levels at various geographical regions, particularly in the early phase. Therefore, we examined the precision of (14)C birth dating of enamel as a function of time of formation and geographical location. We also investigated the use of the stable isotope (13)C as an indicator of geographical origin of an individual. Dental enamel was isolated from 95 teeth extracted from 84 individuals to study the precision of the (14)C method along the bomb spike. For teeth formed before 1955 (N=17), all but one tooth showed negative Δ(14)C values. Analysis of enamel from teeth formed during the rising part of the bomb-spike (1955-1963, N=12) and after the peak (>1963, N=66) resulted in an average absolute date of birth estimation error of 1.9±1.4 and 1.3±1.0 years, respectively. Geographical location of an individual had no adverse effect on the precision of year of birth estimation using radiocarbon dating. In 46 teeth, measurement of (13)C was also performed. Scandinavian teeth showed a substantially greater depression in average δ(13)C (-14.8) than teeth from subjects raised in Japan (-13.5), Middle East and North Africa (-12.7) and South America (-10.9). In summary, isotopic analysis of carbon in enamel from a single tooth can give a good estimate of the year of birth of an individual and also provide information about the geographical origin of the individual. This strategy can assist police and forensic authorities when attempting to solve unidentified homicide cases and may facilitate the identification work associated with mass disasters.

Intra-tooth oxygen isotope variation in a known population of red deer: Implications for past climate and seasonality reconstructions

Over the last decade oxygen isotopes from herbivore teeth have frequently been used as a proxy for palaeoclimatic conditions, yet our knowledge of how accurately the isotope signatures of an animal reflect seasonal climatic fluctuations remains limited. Our study on modern red deer from a known location aimed to assess the degree to which seasonal climate changes are reflected in red deer teeth. Our analyses of sequential sub-samples from red deer second and third molars showed that enamel carbonate δ 18O values vary within teeth and that the pattern of intra-tooth isotopic variation broadly corresponds to that observed in precipitation δ 18O over an annual cycle. The pattern of intra-tooth isotopic variation and absolute values are similar for individuals born in the same year. As the population range in intra-tooth δ 18O values closely matches that estimated for the local precipitation and the calculated range in temperature corresponds with that recorded on the Isle of Rum, we conclude that red deer intra-tooth oxygen isotope signatures are a good palaeoclimate and seasonality proxy. In addition, all deer have recorded the lowest δ 18O of the cycle (winter minimum) in the same location of the M3 crown, demonstrating the potential utility of this sampling protocol to infer birth seasonality in red deer.

Ancient forests and grasslands in the desert: Diet and habitat of Late Pleistocene mammals from Northcentral Sonora, Mexico

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°41′N, 109°39′W, 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 (δ 13C) and oxygen (δ 18O) isotopes from nine mammalian fossils indicate a habitat mosaic with variations in diet that include browsers, mixed feeders and C4 hyper-grazers (δ 13C range of − 10‰ to 2‰). Unique to this site are δ 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 (δ 13C) and oxygen (δ 18O) isotopes for ancient mammal teeth with hypsodont dentitions (fossil Equus and Bison,) as well as δ 18O 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 350 km 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.