Enamel Carbonate Research Articles

Herbivore paleodiet and paleoenvironmental changes in Chad during the Pliocene using stable isotope ratios of tooth enamel carbonate

Chad is a key region for understanding early hominid geographic expansion in relation to late Miocene and Pliocene environmental changes, owing to its location 2500 km west from the Rift Valley and to the occurrence of sites ranging in age from about 6 to 3 Ma, some of which yield fossil hominids. To reconstruct changes in herbivore paleodiet and therefore changes in the paleoenvironment, we measured the carbon and oxygen isotope composition of 80 tooth-enamel samples from three time horizons for nine families of Perissodactyla, Proboscidea, and Artiodactyla. The absence of significant alteration of in vivo isotopic signatures can be determined for carbon, thus allowing paleodietary and paleoenvironmental interpretations to be made.While the results generally confirm previous dietary hypotheses, mostly based on relative crown height, there are some notable surprises. The main discrepancies are found among low-crowned proboscideans (e.g., Anancus) and high-crowned rhinocerotids (Ceratotherium). Both species were more opportunistic feeders than it is usually believed. This result confirms that ancient feeding ecology cannot always be inferred from dental morphology or extant relatives.There is an increase in the average carbon isotope composition of tooth enamel from the oldest unit to the youngest, suggesting that the environment became richer in C4 plants with time. In turn, more C4 plants indicate an opening of the plant cover during this period. This increase in carbon isotope composition is also recorded within genera such as Nyanzachoerus, Ceratotherium, and Hexaprotodon, indicating a change from a C3-dominated to a C4-dominated diet over time. It appears that, unlike other middle Pliocene hominid sites in eastern and southern Africa, this part of Chad was characterized by very open conditions and that savanna-like grasslands were already dominant when hominids were present in the area.

Correspondence Between Stable Carbon, Oxygen and Nitrogen Isotopes in Human Tooth Enamel and Dentine: Infant Diets at Kaminaljuyú

We have previously shown that records of the history of dietary supplementation and weaning can be recovered from isotopic analyses of enamel carbonate in permanent human teeth which form during early childhood. Here, we describe a parallel and complementary record of dietary change in the δ13C and δ15N composition of dentine collagen from the same teeth (a first permanent molar, M1; a premolar, P; a third molar, M3), which are from the archaeological site of Kaminaljuyú, in highland Guatemala. In this smaller sample, enamel δ13C and δ18O show the same patterns that we described previously (Wright & Schwarcz, 1998). Enamel δ13C increases from M1 to P and M3, owing to the introduction of solid foods to the milk diet by 2 years of age. Enamel δ18O decreases from M1 and P to M3 owing to a reduced intake of18O-rich breast milk at an older age, perhaps 4 years.Although limited in scope by the poor preservation of dentine at this site, we observed that first molars, which are first to form, show higher dentine δ15N than do teeth developing at older ages, paralleling the pattern that has been described for bone collagen of deceased children. For most individuals, this drop occurs early, owing to the introduction of solid protein foods before 2 years of age. Dentine δ13C shows two widely divergent intertooth patterns. Some individuals show an increase in later developing teeth, a pattern which parallels the enamel δ13C data. Others show a decline in dentine δ13C, suggesting a shift to an isotopically lighter protein source in later childhood. Despite these divergent trends, differences in δ13C between enamel and dentine are significantly greater in teeth developing in later childhood (P, M3) than in those forming in infancy (M1), a trend which appears to be a trophic effect, but is largely determined by enamel δ13C. Together, the use of enamel and dentine isotopic ratios allows greater precision for reconstructing the culturally variable nature of the dietary shift from breast milk through complementary feeding and weaning to an adolescent diet.

Oxygen Isotopes in Enamel Carbonate and their Ecological Significance

Stable carbon isotope analysis of fossil tooth enamel carbonate, and oxygen isotope analysis of bone or enamel phosphate, are established tools for palaeodietary and palaeoclimatic reconstruction, respectively.13C/12C ratios provide evidence of an animal’s diet and phosphate-based18O/16O values are used to establish palaeotemperature proxies. Recent studies of fossil enamel suggest that biogenic18O/16O signals are also retained in the carbonate compartment, despite assumptions that18O/16O ratios from apatite carbonate are highly susceptible to exchange during fossilization. Here, we re-examine existing enamel carbonate18O/16O data from the rich fossil assemblages of Swartkrans and Equus Cave. We find patterns that can be interpreted in terms of drinking behaviour, diet, and physiology. In general, herbivores that drink little are more enriched than those that drink frequently, while carnivores are depleted compared with herbivores. Thus, we can increase our knowledge of the ecology of fossil taxa by coupling carbon and oxygen isotope ratio data.

Methodological and Archaeological Implications of Intra-tooth Isotopic Variations (δ13C, δ18O) in Herbivores from Ain Ghazal (Jordan, Neolithic)

Tooth enamel is considered very stable against post-mortem alteration and therefore is a preferred study material for isotopic analyses in the context of palaeoecology. The range of isotopic variation within one given tooth has important implications for the sampling procedure especially if microsamples are used. Thus, the awareness of intra-tooth isotopic variability is undeniable for the study of palaeoclimate as well as for the reconstruction of palaeodiet and the inferred use of ecological niches in the past. In Neolithic tooth enamel (Bovidae and Equidae from Ain Ghazal, Jordan) carbonate was analysed for δ13C and δ18O in order to trace intra-tooth variation. Up to 13 enamel samples were taken per tooth from crown to root in horizontal layers with a drill. The variation of isotopic values is higher in equid than in bovid tooth enamel. Results for δ13C in a given tooth vary within a range up to 2·9 per mil (PDB) in equid enamel, but remain within the frame of either C3or C4feeders, and do not indicate a clear shift from C3or C4plant consumption for a given individual. Results for δ18O vary up to 6·9 per mil (PDB) within one given tooth in equids. This approach offers several methodological perspectives. First, the sampling of many individuals of one species at a given site over a longer time period should permit a comparison of stable isotope variations, both synchronically and diachronically. From the high time resolution possible via intra- and inter-tooth isotopic variability we may better monitor seasonality or reconstruct climatic changes. Information on short-term climatic variation could provide important arguments for the discussion of cultural developments at a given archaeological site. Here we emphasize the methodological aspect and its implications. A better understanding of the site of Ain Ghazal and its development reflected in settlement size, artefacts, and architecture will be possible, however, here we present preliminary data.

Alteration of Enamel Carbonate Environments during Fossilization

An understanding of enamel diagenesis is necessary to ensure sound isotopic palaeodietary and palaeoenvironmental reconstructions. Although carbon isotope signals of browsing and grazing herbivores remain distinct in enamel even after millions of years, subtle alteration of isotopic signatures does occur. To better understand this change we analysed modern and fossil enamel from a number of South African sites using Fourier Transform Infra-Red spectroscopy. Our results indicate that while there is little evidence of increased crystallinity in fossil enamel, there is a small but significant change in the proportion of carbonate ions occupying hydroxyl and phosphate sites. This seems to occur early in the process of fossilization, after which there is no noticeable change. It is also important to note that the degree of alteration varies significantly within and between sites. We suggest that this change results from one or some combination of three mechanisms: exogenous carbonate incorporation, endogenous carbonate loss, and endogenous carbonate reorganization. Determining which mechanism(s) contribute to this alteration is important because all three are likely to affect biogenic carbon isotope ratios differently. FTIR spectroscopy promises to increase our knowledge of diagenesis, and in so doing, should improve our palaeodietary and palaeoenvironmental reconstructions.

The isotopic ecology of late Pleistocene mammals in North America: Part 1. Florida

Mammoths and mastodons are common in Pleistocene deposits, yet these proboscideans and many other animals disappeared suddenly ≈10,000 years ago. In this study, we reconstruct the diets of proboscideans and associated mammals through isotopic analysis of carbonate in tooth enamel apatite in order to test nutritional hypotheses for late Pleistocene extinction. We analyzed specimens from six sites in Florida, ranging from full glacial (>21,000 BP) to late glacial (14,750 to 10,000 BP) age. The oxygen isotope composition of mammalian apatite covaries with meteoric water composition, which in turn varies with climate. Consequently, oxygen isotope analysis can be used to assess the potential for time-averaging or mixing of specimens from different geographic regions within fossil assemblages. The carbon isotope composition of an herbivore is controlled by the isotopic composition of the plants that it ingests. Carbon isotope analysis reveals that mastodons ate chiefly C 3 plants, presumably trees, shrubs and herbs, whereas mammoths consumed chiefly C 4 grass. Several nutritional hypotheses for late Pleistocene extinction entail the assumption that extinct taxa had specialized diets. The resource partitioning and focused feeding preferences of Florida's proboscideans corroborate this assumption, but they do not, in themselves, prove that nutritional stress was the cause of the late Pleistocene extinction.

Isotope Paleobiology of the Vertebrates: Ecology, Physiology, and Diagenesis

Isotopic studies of vertebrate material have a short history, while isotopic analyses of invertebrates originated in the 1940's. Interestingly, the driving force behind Harold Urey's desire to derive a carbonate paleotemperature scale in the 1940's and 1950's was the hope that it would solve the mystery of dinosaur extinction by demonstrating temperature changes at the K/T boundary. The most useful and commonly investigated stable isotopes for paleobiologic studies of vertebrates are carbon, nitrogen and oxygen. Oxygen is available from the inorganic bone or tooth apatite phase. Carbon is most often derived from tooth enamel carbonate or organic collagen, and nitrogen is derived from collagen. Each of these stable isotopes provides information on different aspects of an animal's biology and when combined, provide powerful analyses for ecological and evolutionary reconstructions. In the 1970's, much work was done describing the carbon and nitrogen variations in plants. This period was followed in the late 1970's and early 1980's by research on these isotopic variables in mammals (e.g., DeNiro and Epstein, 1978, 1981; Vogel, 1978; Van der Merwe, N.J., 1982). The utility of these isotopes for dietary recognition led to their extensive investigation in archeological studies. Not until the mid to late 1980's and 1990's have these isotopes been utilized in both the inorganic component of teeth and bones as well as the organic component of bones in Pleistocene and older paleobiologic studies. The 1980's also saw the emergence of research on the oxygen isotopic variations in mammals. However, the focus of isotopic studies on vertebrates was not for paleobiologic purposes, but rather, for attempts to derive paleohydrologic or paleoclimatic information from them (e.g., Longinelli, 1984; Luz et al., 1984).

Stable carbon and oxygen isotopes in human tooth enamel: Identifying breastfeeding and weaning in prehistory. Am. J. Phys. Anthropol.106: 1–18.

ERRATUM: Wright LE and Schwarcz HP (1998) Stable Carbon and Oxygen Isotopes in Human Tooth Enamel: Identifying Breastfeeding and Weaning in Prehistory. Am. J. Phys. Anthropol. 106: 1–18. Isotopic ratios were incorrectly printed as percentages (%) rather than units permil (‰). Wherever “breast feeding” and “breast fed” occur, the words should be combined into “breastfeeding” and “breastfed” respectively. The correct information on isotopic ratios is the following: p. 1, Abstract: all % signs should be “‰”; p. 2, column two, last line: “… δ13C values1, have been …”; p. 2, Footnote 1 should read: “Isotope ratios of carbon and oxygen are expressed in δ notation as follows, δ = [(Rsample/Rstandard) − 1] × 1000, where R = 13C/12C for δ13C, and R = 18O/16O for δ18O, and are in units permil, ‰.”; p. 3, column two: all % signs should be “‰”, except for the 23rd line from the bottom, which reads: “… provided 95% of water intake by all infants …”; p. 5: all % signs should be “‰”; p. 6, column one: 8th and 9th line from bottom should be “… mean deviations were 0.029‰ for δ13C and 0.024‰ for δ18O …”; p. 6, column one: 2nd line from bottom should be “… only 0.208‰ for δ13C and only 0.091‰ for δ18O …”; p. 6, column two: top line: “… of 0.5‰ in δ13C and 0.2‰ in δ18O …”; p. 8, 9 and 10: all % signs should be “‰”; p. 11, column two: 7th line from top: “… the lipids are 4-6‰ lighter …”; p. 12, 13 and 14: all % signs should be “‰.”

Stable carbon and oxygen isotopes in human tooth enamel: Identifying breastfeeding and weaning in prehistory

This paper investigates the utility of stable carbon and oxygen isotopes in human dental enamel to reveal patterns of breastfeeding and weaning in prehistory. Enamel preserves a record of childhood diet that can be studied in adult skeletons. Comparing different teeth, we used δ13C to document the introduction of solid foods to infant diets and δ18O to monitor the decline of breastfeeding. We report enamel carbonate δ13C and δ18O of 33 first molars, 35 premolars, and 25 third molars from 35 burials from Kaminaljuyú, an early state in the valley of Guatemala. The skeletons span from Middle Preclassic through Late Postclassic occupations, ca. 700 B.C. to 1500 A.D. Sections of enamel were removed from each tooth spanning from the cusp to the cemento-enamel junction. Stable isotope ratios were measured on CO2 liberated by reaction of enamel with H3PO4 in an automated carbonate system attached to a VG Optima mass spectrometer. Within a skeleton, teeth developing at older ages are more enriched in 13C and more depleted in 18O than teeth developing at younger ages. Premolars average 0.5% higher in δ13C than first molars from the same skeleton (P = 0.0001), but third molars are not significantly enriched over premolars. The shift from first molars to premolars may be due to the shift to solid foods from lipid-rich milk. After 2 years, when premolars begin to mineralize, the δ13C in childhood diets did not change systematically. First molars and premolars are similar in δ18O, but third molars average 0.7% lower than first molars (P = 0.0001) and 0.5% lower than premolars (P = 0.0003). First molar and premolar δ18O is heavier, because breast milk is more enriched in 18O than is drinking water. Hence, many children continued to nurse during the period of premolar formation. Together, these results indicate that Kaminaljuyú children had begun to eat solid maize foods before the age of 2 years but continued to drink breast milk until much later. Am J Phys Anthropol 106:1–18, 1998. © 1998 Wiley-Liss, Inc.

Stable carbon and oxygen isotopes in human tooth enamel: identifying breastfeeding and weaning in prehistory.

This paper investigates the utility of stable carbon and oxygen isotopes in human dental enamel to reveal patterns of breastfeeding and weaning in prehistory. Enamel preserves a record of childhood diet that can be studied in adult skeletons. Comparing different teeth, we used delta13C to document the introduction of solid foods to infant diets and delta18O to monitor the decline of breastfeeding. We report enamel carbonate delta13C and delta18O of 33 first molars, 35 premolars, and 25 third molars from 35 burials from Kaminaljuyú, an early state in the valley of Guatemala. The skeletons span from Middle Preclassic through Late Postclassic occupations, ca. 700 B.C. to 1500 A.D. Sections of enamel were removed from each tooth spanning from the cusp to the cemento-enamel junction. Stable isotope ratios were measured on CO2 liberated by reaction of enamel with H3PO4 in an automated carbonate system attached to a VG Optima mass spectrometer. Within a skeleton, teeth developing at older ages are more enriched in 13C and more depleted in 18O than teeth developing at younger ages. Premolars average 0.5/1000 [corrected] higher in delta13C than first molars from the same skeleton (P = 0.0001), but third molars are not significantly enriched over premolars. The shift from first molars to premolars may be due to the shift to solid foods from lipid-rich milk. After 2 years, when premolars begin to mineralize, the delta13C in childhood diets did not change systematically. First molars and premolars are similar in delta18O, but third molars average 0.7/1000 [corrected] lower than first molars (P = 0.0001) and 0.5/1000 [corrected] lower than premolars (P = 0.0003). First molar and premolar delta18O is heavier, because breast milk is more enriched in 18O than is drinking water. Hence, many children continued to nurse during the period of premolar formation. Together, these results indicate that Kaminaljuyú children had begun to eat solid maize foods before the age of 2 years but continued to drink breast milk until much later.

Tale of two rhinos: isotopic ecology, paleodiet, and niche differentiation of Aphelops and Teleoceras from the Florida Neogene

Abstract Carbon (δ13C) and oxygen (δ18O) isotopic results are presented from 42 tooth enamel carbonate samples of rhinos (Family Rhinocerotidae) from a sequence of Florida Neogene localities between 9.5 and 4.5 Ma. These data are used to interpret ancient diets and test previous hypotheses of terrestrial/aquatic adaptations of two sympatric rhinos, Aphelops and Teleoceras. The long-limbed, shorter-crowned Aphelops traditionally has been reconstructed as an open-country browser (similar to the modern black rhino), whereas short-limbed, higher-crowned Teleoceras traditionally has been reconstructed as an amphibious grazer (similar to the modern hippo). Between about 9. 5 and 7 Ma the δ13C values (all <−11.0‰) from Florida Aphelops and Teleoceras indicate that both rhinos were feeding on C3 plants. This diet probably included a combination of browse and C3 grasses, although the exact proportions for each genus cannot be distinguished isotopically. In contrast, after the late Miocene global carbon shift as represented at 4.5 Ma in Florida, Aphelops was a browser (mean δ13C = −11.9‰), whereas Teleoceras was a mixed feeder/C4 grazer (mean δ13C = −7.0‰). Oxygen isotopic values indicate that neither Aphelops nor Teleoceras was principally aquatic. Given these new isotopic data, more plausible modern analogs for these two extinct rhinos are, respectively, the terrestrial browsing black rhino (Diceros bicornis) and the terrestrial grazing white rhino (Ceratotherium simum), which are sympatric today in Africa.

Quantitative Determination of Type A and Type B Carbonate in Human Deciduous and Permanent Enamel by Means of Fourier Transform Infrared Spectrometry

Caries progression has been shown to be faster in the deciduous than in the permanent dentition. Several factors influence caries progression. Among these are variations in the chemical composition of the two enamel types. The carbonate ion is known to occupy two different positions in the hydroxyapatite structure of the enamel, the hydroxide position (A) and the phosphate position (B). Carbonate may be of different chemical importance in the two lattice positions. In the present study, a quantitative determination of the carbonate in the two different positions (type A and type B) in deciduous and permanent enamel was performed by FTIR spectrometry. Calibration curves, made with synthesized hydroxyapatites with carbonates in either position, were used to determine the quantity of type A and type B carbonates in both enamel types. The deciduous enamel contained significantly more type A carbonate than permanent enamel. The total carbonate content (sum of type A and type B carbonates) was also significantly higher in deciduous than in permanent enamel. TG analysis of enamel samples confirmed the quantitative carbonate determinations by FTIR spectrometry. The difference in carbonate content between deciduous and permanent enamel may be one of several factors contributing to faster caries progression in deciduous teeth.

A stable isotope study of fossil mammal remains from the Paglicci cave, Southern Italy. N and C as palaeoenvironmental indicators

A set of 102 tooth and bone samples of Pleistocene age (32,600-13,300 yr BP) belonging to the species Cervus elaphus, Bos primigenius and Equus caballus and coming from the Paglicci cave (Southern Italy) was studied for the carbon (δ 13C) and nitrogen (δ 15N) isotopic composition of bone and dentine collage and for the carbon (δ 13C c) isotopic composition of tooth enamel carbonate. The amount of collagen extracted from bone and tooth samples (mg/g) was rather variable, representing approximately only 0.5–15% of the collagen present in a fresh bone. However, the loss of an important fraction of the original collagen during diagenesis did not change the in vivo isotopic composition. In general, when the δ 13C of both collagen and carbonate and the δ 15N of collagen obtained from each level for the three species are compared, wild ox shows the most increased values, deer the most decreased values and horse shows intermediate results. These differences are probably related to distinct diets or to differences in their physiological behaviour. However, the isotopic results suggest that the three species considered lived in an open environment with a diet based on C 3 plants. The stratigraphic sequence of light and heavy nitrogen isotope values between 19,000 and 15,000 may be related to shifts from arid to humid conditions, while the overall trend shown by δ 13C toward lighter values may be related to a progressive development of a forest habitat.

Stable‐isotope studies on the collagenic and hydroxylapatite components of fossils: Palaeoecological implications

Collagenic material has been extracted and analysed for stable carbon- and nitrogen-isotope ratios from Henschke Cave, a Late Pleistocene fossil locality, South Australia. The carnivore Thylacoleo carnifex most likely consumed omnivores (Parameles spp.) with a palaeodiet of C3 plant material under a forest canopy, which was also recorded in the herbivores analysed (Macropus spp., Sthenurus spp. and Diprotodon spp.). A forested environment supports previous interpretations of extant fauna and their modern habitats. The presence of negative nitrogen-isotope ratios in herbivores has been interpreted as non-diagenetic on the basis of carbon/nitrogen ratios and amino acid spectra, and in fact may be indicative of acidic soils. Analyses on bone and enamel carbonate hydroxylapatite from the same species support the conclusion that bone is unreliable for palaeoecological and palaeoclimatological research. However, bone carbonate hydroxylapatite may prove valuable in assessing the extent of isotopic fractionation during diagenesis. A review of carbon-isotope analyses on fossil collagenic material and enamel carbonate hydroxylapatite suggests a carnivore-herbivore boundary. The application of this boundary in palaeoecological research requires further investigation. Future palaeoecological research on fossils needs to incorporate stable-isotope analyses on the carbonate hydroxylapatite and collagenic components of fossils.

Oxygen isotope partitioning between phosphate and carbonate in mammalian apatite

The oxygen isotope compositions of phosphate and structural carbonate in mammalian enamel and bone apatite are linked to that of body water at constant body temperature near 37°C, but the isotope systematics of oxygen in structural carbonate are not well understood. Using coupled measurements of the oxygen isotope composition of structural carbonate and phosphate from horse tooth enamel, the apparent oxygen isotope fractionation factor between structural carbonate and body water is estimated to be 1.0263 ± 0.0014. These estimates provide a quantitative basis for using the oxygen isotope composition of structural carbonate in mammalian biogenic apatite for ecological, climatological, and physiological reconstruction.

Magnesium and carbonate in enamel and synthetic apatites.

This study aimed to: determine the Mg and CO3 distribution in the outer (surface), middle, and inner (closest to the enamel-dentin junction, EDJ) layers of human enamel; and determine the factors affecting the incorporation of Mg into synthetic apatites and the consequence of such incorporation on the properties of the apatites. Results demonstrated that the concentrations of Mg, CO3, and organic components increased from the surface to the inner layers close to the EDJ and a difference in crystallinity from the outer to the inner layers. Initial results indicated that the extent of dissolution of the inner layer enamel is greater than that in the outer or surface enamel. Results on synthetic apatites showed the following: (1) Limited Mg incorporation into apatite was dependent on solution [Mg/Ca] molar ratio, temperature, pH, and the presence of CO3 or fluoride (F); (2) incorporation of Mg causes reduction in crystallinity and an increase in the extent of dissolution of the apatite; (3) the negative effect of Mg on the properties of apatites is synergistic to that of CO3 and antagonistic to that of F; and (4) exposure to acid of Mg-containing apatites causes the dissolution of Mg-rich apatite and precipitation of Mg-poor apatite. The observed decrease in the [Mg/Ca] of enamel and synthetic apatites after acid exposure may explain the observed 'preferential loss' of Mg and CO3 in the initial stages of caries.

Stable carbon and oxygen isotope analysis of fossil tooth enamel using laser ablation

A technique is described whereby the δ13C and δ18O values of fossil tooth enamel can be measured in situ using laser ablation techniques. The laser heats the sample and forms CO2 from structural carbonate apatite. The δ18O values obtained with this method are equal to those of the phosphate oxygen due to the high temperature of reaction during ablation. Analytical precision is approximately 0.5‰ for both δ13C and δ18O. The spatial resolution is 200 μm or less, which may be reduced as the technical modifications are made. This method allows the analysis of samples that previously could not be analyzed due to difficulty with sample preparation, size, or rare nature. The apparent oxygen isotope fractionation between the carbonate and laser derived oxygen (αCO3-laser) is 1.0071 for biogenic apatite at 38°C determined using the in situ laser. Comparison of δ18O(CO3) and δ18O(laser) analyses with δ18O(laser) and δ18O(PO4) results suggest a fractionation factor α(CO3)-PO4) of 1.0083. Variations in the δ18O and δ13C values of single teeth can be easily determined with the in situ technique. This will allow the study of changes in diets or water sources during the period of tooth growth, which for larger mammals can be several years for the tooth row. The δ13C and δ18O values are important in paleodiet and paleoecology studies. They can be used to study resource partitioning within an ecosystem and can shed light on the life history strategies within living and extinct species.

Vegetation and Seasonality Shifts during the Late Quaternary Deduced from 13C/ 12C Ratios of Grazers at Equus Cave, South Africa

Season of rainfall can be a major influence on the relative proportions of C 3 and C 4 grasses in a landscape, since their relative distribution is essentially constrained by temperatures during the growing season; cool growing seasons favor C 3 grasses, whereas warm ones favor C 4 grasses. 13C/ 12C ratios in tooth enamel carbonate of grazers from the site of Equus Cave, northern Cape Province, South Africa, were used to determine vegetation and rainfall seasonality shifts during the late Quaternary. The results show shifts in the relative proportion of C 3 and C 4 grasses during the latter stages of the Pleistocene, and domination by C 4 grasses in the Holocene. The data show that the northwestern Cape did not fall within a winter rainfall zone during this period as has been postulated in recent climate models. Instead, a more complex situation is suggested in which at least two periods of enhanced winter rainfall occurred within a predominantly summer rainfall regime.

Paleodietary reconstruction of Miocene faunas from Paşalar, Turkey using stable carbon and oxygen isotopes of fossil tooth enamel

Abstract Miocene-age (∼ 15 Ma) deposits at Pasalar in northwest Turkey contain abundant and well-preserved dental remains from a variety of herbivores. We used the carbon and oxygen isotopic compositions of inorganic carbonate in enamel from these teeth to reconstruct the paleodiet and sources of body water, respectively, of Miocene mammals. The δ13C (PDB) values of carbonate in the enamel fall between -13·5 and -9·0%, indicating a diet dominated by C3 plants for all mammals. Some species are distinctly different isotopically from others, likely reflecting on variation in the δ13C values of the plants being consumed. Giraffokeryx and Caprotragoides display the most depleted δ13C values, probably indicating they were feeding upon C3 plants experiencing low water stress and/or CO2 recycling, such as in a forest. Hypsodontus and Conohyus, on the other hand, consistently display the most enriched δ13C values. They were therefore consuming isotopically enriched C3 plants or a small quantity of C4 grasses. In either case, a more open habitat is indicated. The other species we measured, including Griphopithecus , yielded intermediate values. The δ18O (PDB) values of the carbonate in fossil enamel also differ substantially between some taxa, and probably show that mammals such as Giraffokeryx, like East African giraffes today, were drawing their water from sources enriched in 18O, such as from the top of a forest canopy.

Trophic Structure and Climatic Information From Isotopic Signatures in Pleistocene Cave Fauna of Southern England

The preservation of trophic structure and climatic information in Kent's Cavern Upper Pleistocene mammal bones and teeth was assessed by comparing the isotopic composition of modern and fossil equivalents. Yields of collagen from both bone ( N=19) and tooth ( N=49) were extremely variable, with values relative to modern bone ranging from 0% to 100%. No evidence of preferential preservation of tooth collagen was detected. The carbon and nitrogen isotopic differences in the herbivore versus carnivore collagen from Kent's Cavern fauna were consistent with those observed in modern faunas. Moreover, an enrichment of 0·4-1·7‰ in 15N was observed in tooth collagen of both deer and hyena as compared to bone collagen. This enrichment presumably reflects a trophic shift from the consumption of milk during infancy. Herbivores and carnivores had distinct differences in the carbon isotopic composition of enamel carbonate hydroxylapatite, similar to those measured in modern specimens from similar climatic environments. The spacing between the Δ 13C values (difference between isotopic composition in collagen and carbonate hydroxylapatite) of Kent's Cavern herbivores and carnivores is similar to that measured in modern mammals from a single locality. The preservation of primary oxygen isotopic composition of enamel carbonate hydroxylapatite was more difficult to assess, however. Oxygen isotopic compositions of Kent's Cavern enamel are systematically lower than those of contemporaneous faunas from Southern France, which is consistent with a latitudinal effect on rainfall oxygen isotopic compositions. Although the Kent's Cavern specimens have been subjected to extensive diagenetic alteration, the biological isotopic signals seem to have utility for paleoecological reconstructions.