Abstract Intratooth stable isotope profiles in enamel provide time series of dietary and environmental information that if correctly interpreted, serve as archives of seasonal variability in past environments. A major challenge in interpreting these profiles arises from time averaging imparted by enamel mineralization and developmental geometry, whereby the primary (δ13C or δ18O) input signal is attenuated and shifted, which can potentially lead to incorrect interpretations of the magnitude or frequency of seasonal variability. Several forward and inverse models have been developed to reconstruct the primary input signal from intratooth profiles in continuously growing teeth. Here the models developed by Passey and Cerling (2002) and Passey et al. (2005) are extended to molars of Elephantinae, which grow over a long but finite interval of time. Proboscidean molars are particularly attractive for intratooth profiles because they may contain a decade or more of information and they are often well preserved in the fossil record because of their thick enamel and large size. Forward model parameters are established using histological analysis of molar thin sections of extant African elephants (Loxodonta africana) and a mammoth (Mammuthus columbi) and by micro-CT analysis of L. africana molar plates. The density of immature enamel is about 65% of the final density of mature enamel. The appositional length varies from approximately 35 to 55 mm, and the maturation length is about 70 mm. Histological methods are used to determine crown formation time (CFT) in elephant and mammoth molar plates. CFT for the elephant and mammoth molar plates studied in thin section are about 5–6 years and 11 years, which translate to mean growth rates of about 21 mm/year and 16 mm/year, respectively. Coeval molar and tusk profiles from a zoo elephant are compared. The tusk isotope profile serves as a proxy for the primary input signal, and thus provides an opportunity to evaluate the forward and inverse models. The results from the zoo elephant profiles demonstrate that the inverse model accurately reconstructs the amplitude and overall structure of the primary input signal. Inverse model results of mammoth molar profiles show double the range of δ13C in measured enamel profiles. Inversion model results illustrate that improved reconstruction of the primary input signal can lead to more accurate interpretations of the seasonal variability of diet and body water and by extension, vegetation and precipitation in past environments.

中文翻译：

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从长鼻磨牙的稳定同位素分布中提取气候和饮食信息的正向和反向方法

摘要 牙釉质中的牙内稳定同位素分布提供了饮食和环境信息的时间序列，如果正确解释，可作为过去环境中季节性变化的档案。解释这些剖面的一个主要挑战来自釉质矿化和发育几何学赋予的时间平均，其中主要（δ13C 或 δ18O）输入信号衰减和偏移，这可能导致对季节性变化的幅度或频率的错误解释。已经开发了几种正向和逆向模型来从连续生长的牙齿中的齿内轮廓重建主要输入信号。这里是 Passey 和 Cerling (2002) 以及 Passey 等人开发的模型。(2005) 扩展到 Elephantinae 的臼齿，它们在很长但有限的时间间隔内生长。长鼻磨牙对牙内轮廓特别有吸引力，因为它们可能包含十年或更长时间的信息，并且由于它们的厚牙釉质和大尺寸，它们通常在化石记录中保存完好。使用现存非洲象 (Loxodonta Africana) 和猛犸象 (Mammuthus columbi) 的磨牙薄切片的组织学分析和非洲象牙磨牙板的显微 CT 分析建立了正向模型参数。未成熟牙釉质的密度约为成熟牙釉质最终密度的65%。同位长度约35至55毫米，成熟长度约70毫米。组织学方法用于确定大象和猛犸象牙板的牙冠形成时间 (CFT)。大象和猛犸象磨牙板的 CFT 薄切片研究约为 5-6 年和 11 年，这意味着平均增长率分别约为 21 毫米/年和 16 毫米/年。比较了动物园大象的同时代臼齿和象牙轮廓。象牙同位素分布作为主要输入信号的代理，因此提供了评估正向和反向模型的机会。动物园大象剖面的结果表明，逆模型准确地重建了主要输入信号的幅度和整体结构。猛犸象摩尔分布的逆模型结果显示测量的牙釉质分布中 δ13C 的范围是两倍。反演模型结果表明，对主要输入信号的改进重建可以更准确地解释饮食和身体水分的季节性变化，进而更准确地解释过去环境中的植被和降水。