文章基本信息

标题：Magnesium stable isotope ecology using mammal tooth enamel
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作者：Jeremy E. Martin ; Derek Vance ; Vincent Balter 等
期刊名称：Proceedings of the National Academy of Sciences
印刷版ISSN：0027-8424
电子版ISSN：1091-6490
出版年度：2015
卷号：112
期号：2
页码：430-435
DOI：10.1073/pnas.1417792112
语种：English
出版社：The National Academy of Sciences of the United States of America
摘要：SignificanceThe diet of fossil organisms can be inferred through isotopic analysis of skeletal tissues, largely assessed using isotopic and elemental systems such as carbon isotopes ({delta}13C) and strontium/calcium (Sr/Ca) and barium/calcium (Ba/Ca) concentration ratios. In the case of complex dietary habits such as omnivory, these systems must be used jointly together with new proxies. Based on the expectation that fractionation of bio-essential metals occurs during metabolism, we explore the isotopic variability of magnesium ({delta}26Mg) in tooth enamel sampled from an assemblage of modern mammals. We demonstrate that {delta}26Mg increases from herbivores to higher-level consumers, discriminating most of the identified trophic steps. This, combined with {delta}13C, Ba/Ca, and/or {delta}44Ca might prove useful in paleodietary studies. Geochemical inferences on ancient diet using bone and enamel apatite rely mainly on carbon isotope ratios ({delta}13C) and to a lesser extent on strontium/calcium (Sr/Ca) and barium/calcium (Ba/Ca) elemental ratios. Recent developments in nontraditional stable isotopes provide an unprecedented opportunity to use additional paleodietary proxies to disentangle complex diets such as omnivory. Of particular relevance for paleodietary reconstruction are metals present in large quantity in bone and enamel apatite, providing that biologically mediated fractionation processes are constrained. Calcium isotope ratios ({delta}44Ca) meet these criteria but exhibit complex ecological patterning. Stable magnesium isotope ratios ({delta}26Mg) also meet these criteria but a comprehensive understanding of its variability awaits new isotopic data. Here, 11 extant mammal species of known ecology from a single locality in equatorial Africa were sampled for tooth enamel and, together with vegetation and feces, analyzed for {delta}26Mg, {delta}13C, Sr/Ca, and Ba/Ca ratios. The results demonstrate that {delta}26Mg incorporated in tooth enamel becomes heavier from strict herbivores to omnivores/faunivores. Using data from experimentally raised sheep, we suggest that this 26Mg enrichment up the trophic chain is due to a 26Mg enrichment in muscle relative to bone. Notably, it is possible to distinguish omnivores from herbivores, using {delta}26Mg coupled to Ba/Ca ratios. The potential effects of metabolic and dietary changes on the enamel {delta}26Mg composition remain to be explored but, in the future, multiproxy approaches would permit a substantial refinement of dietary behaviors or enable accurate trophic reconstruction despite specimen-limited sampling, as is often the case for fossil assemblages.
关键词：stable isotopes ; magnesium ; carbon ; equatorial mammals ; paleoecology