Summary Juniperus spp. are keystone shrubs in western North America and important climatic indicators in paleo‐records. However, a lack of taxonomic resolution among fossil species limits our ability to track past environmental changes. Plant macrofossils at Rancho La Brea (RLB) allow for reconstructions of juniper occurrence to species across 60 000 yr. We use microscopy, image analysis, species distribution modeling (SDM), and radiocarbon dating to identify an unknown Juniperus species at RLB and put it into chronological context with fossil Juniperus californica at the site to infer past environmental conditions. We identify the unknown taxon as Juniperus scopulorum Sargent, 1897. The Pleistocene occurrence of this species in California expands its known distribution and documents its extirpation. Temporal ranges of the two fossil junipers alternate, revealing a pattern of differential climatic sensitivity throughout the end of the Pleistocene. Occurrence patterns suggest sensitivity to temperature, moisture availability, and the presence of two mega‐droughts at c. 48–44.5 ka and c. 29.3–25.2 ka. Extirpation of both taxa by c. 13 ka is likely driven by climate, megafaunal extinction, and increasing fire. The extirpation of fossil junipers during these past climatic events demonstrates vulnerability of juniper species in the face of global change.

中文翻译：

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来自 Rancho La Brea（美国加利福尼亚州）的杜松种子化石鉴定：晚更新世的干旱和灭绝


摘要 Juniperus spp. 是北美西部的关键灌木，也是古记录中的重要气候指标。然而，化石物种之间缺乏分类学分辨率限制了我们追踪过去环境变化的能力。Rancho La Brea （RLB） 的植物大型化石可以重建 60 000 年内杜松的出现。我们使用显微镜、图像分析、物种分布建模 （SDM） 和放射性碳测年法来识别利比的未知杜松物种，并将其与现场的杜松化石放在时间背景下，以推断过去的环境条件。我们将未知的分类群确定为 Juniperus scopulorum Sargent， 1897。该物种在加利福尼亚的更新世出现扩大了其已知的分布并记录了它的灭绝。两种杜松化石的时间范围交替出现，揭示了整个更新世末期气候敏感性不同的模式。发生模式表明对温度、水分可用性的敏感性，以及在 c. 48-44.5 ka 和 c. 29.3-25.2 ka 存在两次特大干旱。大约 13 ka 导致这两个类群的灭绝可能是由气候、大型动物灭绝和火灾增加驱动的。在过去的这些气候事件中，杜松化石的灭绝表明杜松物种在面对全球变化时的脆弱性。