Carbon Isotopes In Tooth Enamel Research Articles

Shepherding the past: High-resolution data on Neolithic Southern Iberian livestock management at Cueva de El Toro (Antequera, Málaga).

The feeding strategies of the first domesticated herds had to manage the risks arising from the novelty of livestock practices in territories often distant from the animals' primary habitats. The Iberian Peninsula is characterised by a great diversity of environments, which undoubtedly influenced these dynamics. At the beginning of the Neolithic period these led the possibility to combine diverse livestock farming practices based on different animal feeding habits. This variability is also consistent with the rythms of adoption of domesticated animals, being later on the northern area. In order to address this issue, this work focuses on the dietary regimes of early sheep herds from southern Iberia, an area for which information is currently scarce. This study utilises high-resolution radiocarbon dating and stable isotope data on teeth to investigate sheep husbandry management strategies in Cueva de El Toro (Antequera, Málaga). The radiocarbon dates on the analysed remains evidenced they were deposited at the site over a short period, supporting the recurrent use of the cave. The sequential analysis of oxygen and carbon isotopes in tooth enamel reveals distinct livestock management strategies, reproduction patterns, feeding habits, and mobility during this short period. This variability demonstrates that livestock management practices in the western Mediterranean are more diverse than previously considered. Furthermore, these findings support the hypothesis that early Neolithic communities in the southern Iberian Peninsula were able to adopt different feeding strategies within the same herd, depending on their ecological and productive needs.

Coyotes Reveal Baseline Nitrogen Decline Across End-Pleistocene Ecosystem Collapse

The end Pleistocene was a time of ecological turmoil, coincident with environmental change, extinctions, and anthropogenic impacts on the landscape. As one of the few persisting predators from the Pleistocene, La Brea’s exceptional record of coyotes (Canis latrans) provides a unique opportunity to clarify how a recently documented ecosystem state-shift impacted survivors. Through a multiproxy analysis of Rancho La Brea coyotes from the past 50,000 years to present, we analyzed over 100 individuals for radiocarbon chronologies, stable isotopes, dental microwear, and morphology to assess the consequences of megafaunal extirpation on these predators. Most notably, coyotes demonstrate a significant decline in δ15Nbone collagen values immediately after the extirpation of megafauna. While this decline is suggestive of a change in diet from more to less meat, stable isotopes of amino acids from a subset of samples instead provide evidence of a baseline shift in nitrogen—indicating large scale changes in the availability of nutritional resources. While coyotes do not demonstrate notable changes in diet across the extirpation boundary, as inferred from stable carbon isotopes in tooth enamel and dental microwear texture analysis, significant shifts in stable oxygen isotopes in δ18Oenamel and δ13Cbone collagen indicate more nuanced changes in potential prey-resources. Coyotes also demonstrate a linear decline in body size that begins prior to the local extirpation of megafauna (~20,000 years ago) and may be in response to competition with larger canids, the decline in large prey, and/or concurrent increases in aridity during this interval. A dramatic increase in scavenging of forested prey (e.g., deer) during the past century stands out as significantly distinct from the dietary niches occupied over the past 50,000 years—implying dramatic impacts of human behavior on coyotes, a recent shift in their ecological role, and the highly adaptable nature of these carnivores.

Seasonal Cyclicity in Trace Elements and Stable Isotopes of Modern Horse Enamel.

The study of stable isotopes in fossil bioapatite has yielded useful results and has shown that bioapatites are able to faithfully record paleo-environmental and paleo-climatic parameters from archeological to geological timescales. In an effort to establish new proxies for the study of bioapatites, intra-tooth records of enamel carbonate stable isotope ratios from a modern horse are compared with trace element profiles measured using laboratory micro X-Ray Fluorescence scanning. Using known patterns of tooth eruption and the relationship between stable oxygen isotopes and local temperature seasonality, an age model is constructed that links records from six cheek upper right teeth from the second premolar to the third molar. When plotted on this age model, the trace element ratios from horse tooth enamel show a seasonal pattern with a small shift in phase compared to stable oxygen isotope ratios. While stable oxygen and carbon isotopes in tooth enamel are forced respectively by the state of the hydrological cycle and the animal’s diet, we argue that the seasonal signal in trace elements reflects seasonal changes in dust intake and diet of the animal. The latter explanation is in agreement with seasonal changes observed in carbon isotopes of the same teeth. This external forcing of trace element composition in mammal tooth enamel implies that trace element ratios may be used as proxies for seasonal changes in paleo-environment and paleo-diet.

Small mammal tooth enamel carbon isotope record of C4 grasses in late Neogene China

The spatiotemporal pattern of the late Cenozoic spread of C4 vegetation is an important indicator of environmental change that is intertwined with the uplift of the Himalaya and Tibetan Plateau, and the development of the East Asian monsoons. To explore the spread of C4 vegetation in China and shed new light on regional climatic evolution, we measured δ13C values of more than 200 small mammal teeth (primarily rodents and lagomorphs) using a laser ablation isotope ratio mass spectrometry approach. Small mammals are highly sensitive indicators of their environment because they have limited spatial ranges and because they have minimal time-averaging of carbon isotope signatures of dietary components. The specimens originate from four classic Late Miocene fossil localities, Lufeng, Yuanmou, Lingtai, and Ertemte, along a southwest-northeast transect from Yunnan Province to Inner Mongolia. In Yunnan (Lufeng, Yuanmou) and on the Loess Plateau (Lingtai), the small mammal δ13C values record nearly pure C3 ecosystems, and mixed but C3-based ecosystems, respectively, in agreement with previous studies based on carbon isotopes of large herbivores and soil carbonates. In Inner Mongolia, the micromammalian tooth enamel δ13C record picks up the presence of C4 vegetation where large mammal samples do not, indicating a mixed yet C3-dominated ecosystem at ~6Ma. As a whole, the results support a scenario of northward increasing C4 grass abundance in a pattern that mirrors northward decreasing precipitation of the summer monsoon system. The results highlight differences between large and small mammals as indicators of C4 vegetation in ancient ecosystems, particularly the ability of small mammal δ13C values to detect the presence of minor components of the vegetation structure.

Using isotopic evidence to assess the impact of migration and the two-layer hypothesis in prehistoric Northeast Thailand.

The nature of the agricultural transition in Southeast Asia has been a topic of some debate for archaeologists over the past decades. A prominent model, known as the two-layer hypothesis, states that indigenous hunter-gatherers were subsumed by the expansion of exotic Neolithic farmers into the area around 2000 BC. These farmers had ultimate origins in East Asia and brought rice and millet agriculture. Ban Non Wat is one of the few archaeological sites in Southeast Asia where this model can potentially be tested. The site is located in the Mun River valley of Northeast Thailand, and divided into 12 phases that span over 2,000 years, from about 1750 BC to the end of the Iron Age (ca. 500 AD). These phases exhibit successive cultural changes, and current interpretation of the site is of an early hunter-gatherer population, with agriculturalists immigrating into the later phases. We analyzed strontium, oxygen, and carbon isotopes in tooth enamel from over 150 individuals, dating from the Neolithic to Iron Age, to assess extrinsic origins and differences in diet between early and later phases. We find evidence of dietary and cultural differences between groups at Ban Non Wat during its early occupation, but little evidence for immigration from distinct environments beyond the Khorat Plateau of Northeast Thailand. The lack of consistent isotopic differences between early and later Neolithic occupants at Ban Non Wat means that the site does not conclusively support the two-layer hypothesis.

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.

Geographic variation in diets of ancient populations of 5-million-year-old (early Pliocene) horses from southern North America

Using tooth morphology and carbon isotopes, geographic differences in diets are presented for four species of early Pliocene horses (late Hemphillian, Hh 4, between 5.8 and 4.8 Ma) from four localities in Florida, Texas, and Mexico. These four species include three-toed Nannippus aztecus, Neohipparion eurystyle, and one-toed Astrohippus stockii, and Dinohippus mexicanus. The amount of dental variation represented in local populations of these extinct species is similar to that seen in extant equid populations (coefficients of variation, Vs, between ~ 4 and 10). As such, the fossil accumulations of individual species from single localities can be treated as paleopopulations. All four of these horses have high-crowned teeth (hypsodonty indices between 2.6 and 3.1) and the question is addressed how these closely-related species partitioned their available resources to minimize competition. Comparisons of tooth morphology indicate negligible geographic differences between paleopopulations of the same species. Therefore local differences in diets evolved within a context of stasis in tooth morphology. Carbon isotopes of fossil equid tooth enamel indicate that most of the populations and species studied here were primarily C4 grazers, although with some exceptions: Nannippus aztecus tends to be more negative, indicating a higher proportion (~ 20%, or sometimes greater) of C3 plants in its diet. A few individuals within the paleopopulations demonstrate relatively negative tooth enamel carbon isotope values (between ~ − 3 and − 10‰), indicating a diet with some, to predominantly, C3 plants. The sources of isotopic variation result from a variety of factors including latitudinal and seasonal differences in C4 and C3 grass availability, local microhabitat differences, and possibly migration patterns. For the most part these four species of early Pliocene horses have similar diets consisting of predominantly C4 grasses. They therefore differentiated their niches through other evolutionary and ecological strategies, possibly including body size and local habitat differences.

Diet and habitat of toxodont megaherbivores (Mammalia, Notoungulata) from the late Quaternary of South and Central America

The toxodont megaherbivores Toxodon and Mixotoxodon were endemic to South and Central America during the late Quaternary. Isotopic signatures of 47 toxodont teeth were analyzed to reconstruct diet and ancient habitat. Tooth enamel carbon isotope data from six regions of South and Central America indicate significant differences in toxodont diet and local vegetation during the late Quaternary. Toxodonts ranged ecologically from C 3 forest browsers in the Amazon (mean δ 13C = −13.4‰), to mixed C 3 grazers and/or browsers living either in C 3 grasslands, or mixed C 3 forested and grassland habitats in Honduras (mean δ 13C = −9.3‰), Buenos Aires province, Argentina (δ 13C = −8.7‰), and Bahia, Brazil (mean δ 13C = −8.6‰), to predominantly C 4 grazers in northern Argentina (δ 13C = −4.4‰), to specialized C 4 grazers in the Chaco of Bolivia (δ 13C = −0.1‰). Although these toxodonts had very high-crowned teeth classically interpreted for grazing, the isotopic data indicate that these megaherbivores had the evolutionary capacity to feed on a variety of dominant local vegetation. In the ancient Amazon region, carbon isotope data for the toxodonts indicate a C 3-based tropical rainforest habitat with no evidence for grasslands as would be predicted from the Neotropical forest refugia hypothesis.

Vegetational ecotype of the Gyirong Basin in Tibet, China and its response in stable carbon isotopes of mammal tooth enamel

Carbon isotope analysis of modern herbaceous plants in the Gyirong Basin (Tibet, China) indicates that although C3 plants are dominant, C4 plants rarely comprise of the vegetation in the area at 4000 m above sea level. The C4 plants discovered in the Gyirong Basin areSalsola nepalensis of Chenopodiaceae andPennisetum flaccidum of Gramineae, affirming that C4 plants affected by high solar gain can be distributed at high altitude, which supports the opinion that some C4 plants can exist in areas of high elevation. Carbon isotope analysis of herbivore tooth enamel from the Gyirong Basin indicates that carbon isotopes of structural carbonate in biogenic apatite at high altitude still keep a stable enrichment relationship with those of plants in their diet. Carbon isotopes in tooth enamel are therefore an accurate proxy for vegetation ecotypes and should reflect climatic and environmental features.