Reconstructing water availability in terrestrial ecosystems is key to understanding past climate and landscapes, but there are few proxies for aridity that are available for use at terrestrial sites across the Cenozoic. The isotopic composition of tooth enamel is widely used as a paleoenvironmental indicator and recent work suggests the potential for using the triple oxygen isotopic composition of the carbonate component of mammalian tooth enamel (Δ′¹⁷O_enamel) as an indicator of aridity. However, the extent to which Δ′¹⁷O_enamel values vary across environments is unknown and there is no framework for evaluating past aridity using Δ′¹⁷O_enamel data. Here we present Δ′¹⁷O_enamel and δ¹⁸O_enamel values from 50 extant mammalian herbivores that vary in physiology, behavior, diet, and water-use strategy. Teeth are from sites in Africa, Europe, and North America and represent a range of environments (humid to arid) and latitudes (34°S to 69°N), where mean annual δ¹⁸O values of meteoric water range from –26.0‰ to 2.2‰ (VSMOW). Δ′¹⁷O_enamel values from these sites span 162 per meg (–252 to –90 per meg), where 1 per meg = 0.001‰). The observed variation in Δ′¹⁷O_enamel values increases with aridity, forming a wedge-shaped pattern in a plot of aridity index vs. Δ′¹⁷O_enamel that persists regardless of geographic region. In contrast, the plot of aridity index vs. δ¹⁸O_enamel for these same samples does not yield a distinct pattern. We use these new Δ′¹⁷O_enamel data from extant teeth to provide guidelines for using Δ′¹⁷O_enamel data from fossil teeth to assess and classify the aridity of past environments. Δ′¹⁷O_enamel values from the fossil record have the potential to be a widely used proxy for aridity without the limitations inherent to approaches that use δ¹⁸O_enamel values alone. In addition, the data presented here have implications for how Δ′¹⁷O_enamel values of large mammalian herbivores can be used in evaluations of diagenesis and past pCO₂ and past gross primary productivity.

重建陆地生态系统中的水资源可用性是了解过去气候和景观的关键，但在整个新生代的陆地上，很少有干旱的替代指标可供使用。牙釉质的同位素组成被广泛用作古环境指标，最近的工作表明使用哺乳动物牙釉质碳酸盐成分（Δ' ¹⁷ O_牙釉质）的三重氧同位素组成作为干旱指标的潜力。然而，Δ′ ¹⁷ O_釉质值在不同环境中的变化程度是未知的，并且没有使用Δ′ ¹⁷ O_釉质数据评估过去干旱的框架。这里我们介绍 Δ′ ¹⁷来自 50 种生理、行为、饮食和用水策略的现存哺乳动物食草动物的O_牙釉质和 δ ¹⁸ O_{牙釉质值。}牙齿来自非洲、欧洲和北美洲，代表了一系列环境（潮湿到干旱）和纬度（34°S 到 69°N），其中大气水的年平均 δ ¹⁸ O 值范围为 –26.0‰至 2.2‰ (VSMOW)。来自这些位点的 Δ′ ¹⁷ O_牙釉质值跨越 162/meg（–252 到 –90/meg），其中 1/meg = 0.001‰）。观察到的 Δ' ¹⁷ O_{牙釉质值的变化随着干旱而增加，在干旱指数与 Δ'} ¹⁷ O的关系图中形成楔形图案无论地理区域如何，_{珐琅质都能持久存在。}相比之下，这些相同样品的干燥指数与 δ ¹⁸ O_釉质的关系图并没有产生明显的模式。我们使用这些来自现存牙齿的新 Δ′ ¹⁷ O_{牙釉质数据来为使用来自化石牙齿的 Δ′} ¹⁷ O_牙釉质数据来评估和分类过去环境的干燥度提供指导。来自化石记录的Δ′ ¹⁷ O_牙釉质值有可能成为广泛使用的干旱指标，而没有使用 δ ¹⁸ O_{牙釉质的方法所固有的限制}单独的价值观。此外，此处提供的数据对大型哺乳动物食草动物的 Δ′ ¹⁷ O_釉质值如何用于评估成岩作用和过去p CO ₂以及过去的总初级生产力具有重要意义。