Abstract Intra-tooth stable isotope variations have been used to interpret seasonality and aridity in paleoenvironmental reconstructions of paleontological and archeological sites. However, most intra-tooth datasets only permit qualitative interpretations of seasonality, because the measured signal is attenuated due to the duration of enamel mineralization process and sampling geometry. The common warthog (Phacochoerus africanus) is an ideal organism to investigate stable isotope variation in enamel. Their canines grow continuously through the life of the individual and are therefore excellent candidates for mathematical modeling of seasonal signals and of signal attenuation; further, their isotope profiles (a series of isotope measurements) can be compared to isotope profiles of third molars (M3) to provide insights into environmental reconstructions. We first obtained paired intra-tooth enamel samples from ever-growing canines and hypsodont M3s of two extant common warthog specimens from Laikipia, Kenya. Second, from a different set of specimens, we collected data on enamel growth patterns and geometry using histological thin sections and transmitted light microscopy, and enamel mineralization parameters using micro-CT scans in each tooth type. Third, we reconstructed the timeline of unattenuated seasonal δ18O signal from canine enamel using growth rate estimates and the inverse model of Passey et al. (2005). Our results demonstrate that canines, which capture ~1.5 years of time, exhibit near-constant growth rates and simple enamel maturation geometry, whereas M3s, which also represent ~1.5 years of time, exhibit linearly decreasing growth rates and more complex maturation patterns. We compare the timelines of unattenuated seasonal δ18O signal and measured M3 profiles and find an average signal reduction of ~50% in the M3s, providing interpretations of the duration of seasonal cycles that are consistent 75% of the time. We conclude that warthog canines are well suited for the inverse model approach, and we established the model parameters for the forward and inverse methods. Timeline reconstructions based on M3 histology are promising for investigating the pattern of rainfall seasonality in the past. Finally, we found an unexpected carbon isotopic spacing of ~2‰ between canine and M3 enamel, which suggests caution in interpreting δ13C results from suid canine or molar enamel alone.

中文翻译：

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疣猪犬齿和第三磨牙的牙内稳定同位素分布：对古环境重建的影响

摘要 牙内稳定同位素变化已被用于解释古生物和考古遗址古环境重建中的季节性和干旱性。然而，大多数牙内数据集只允许对季节性进行定性解释，因为测量的信号由于牙釉质矿化过程和采样几何的持续时间而衰减。普通疣猪 (Phacochoerus Africanus) 是研究牙釉质中稳定同位素变异的理想生物。它们的犬齿在个体的一生中不断生长，因此是季节性信号和信号衰减数学建模的绝佳候选者；更多，它们的同位素分布（一系列同位素测量）可以与第三磨牙 (M3) 的同位素分布进行比较，以提供对环境重建的见解。我们首先从肯尼亚莱基皮亚（Laikipia）的两种现存常见疣猪标本的不断生长的犬科动物和斜齿动物 M3 中获得配对的牙内釉质样本。其次，从一组不同的标本中，我们使用组织学薄片和透射光显微镜收集了有关牙釉质生长模式和几何形状的数据，以及使用微 CT 扫描每种牙齿类型的牙釉质矿化参数。第三，我们使用增长率估计和 Passey 等人的逆模型重建了来自犬牙釉质的未衰减季节性 δ18O 信号的时间线。(2005)。我们的结果表明，捕获约 1.5 年时间的犬科动物 表现出近乎恒定的增长率和简单的牙釉质成熟几何形状，而 M3s 也代表约 1.5 年的时间，表现出线性下降的增长率和更复杂的成熟模式。我们比较了未衰减的季节性 δ18O 信号和测量的 M3 剖面的时间线，发现 M3 中的平均信号减少了约 50%，提供了对 75% 时间一致的季节性周期持续时间的解释。我们得出结论，疣猪犬非常适合逆向模型方法，并且我们为正向和逆向方法建立了模型参数。基于 M3 组织学的时间线重建有望用于调查过去的降雨季节性模式。最后，我们在犬牙釉质和 M3 牙釉质之间发现了一个意想不到的~2‰的碳同位素间距，