Over the past decade, we recorded exact locations of in situ fossils and measured calcareous nodules in paleosols of the Oligocene and lower Miocene (Whitneyan–Arikareean) John Day Formation of Oregon. These data enable precise biostratigraphy within an astronomical time scale of Milankovitch obliquity cycles and also provide mean annual precipitation and vegetation for each species. Fossils in paleosols of the John Day Formation alternated between semiarid shrubland and subhumid woodland communities every 41 ka. Land snails ‘Polygyra’ expansa and Monadenia dubiosa were found in semiarid paleosols, but Vespericola dalli and Monadenia marginicola were found in subhumid paleosols. Cicada burrows (Naktodemasis bowni) were found in semiarid paleosols, whereas dung beetle balls (Pallichnus dakotensis) and earthworm castings (Edaphichnium lumbricatum) were found in subhumid paleosols. Among hypertragulids, Hypertragulus hesperius was found in semiarid paleosols and Nanotragulus planiceps in subhumid paleosols. Among glires, the aplodontiid Haplomys liolophus, geomyids Pleurolicus sulcifrons and several species of Entoptychus, castorid Palaeocastor peninsulatus, and leporid Archaeolagus ennisianus were found in semiarid paleosols. Large ungulates were found primarily in subhumid paleosols, including the agriochoere Agriochoerus antiquus, oreodonts Eporeodon occidentalis and Promerycochoerus superbus, equid Miohippus annectens, and rhinos Diceratherium annectens and Diceratherium armatum. The inferred niches of fossil mammals are consistent with interpretations based on their morphology; taxa with adaptations for life in open, arid habitats, such as high-crowned teeth and semifossorial or cursorial limb structure, were mainly in semiarid paleosols, but taxa with arboreal adaptations were only found in subhumid paleosols.

在过去的十年中，我们记录了俄勒冈州渐新世和中新世（惠特尼－阿里卡瑞斯）下约翰新时代古土壤中原位化石的精确位置并测量了钙质结节。这些数据可以在米兰科维奇倾角周期的天文时间尺度内进行精确的生物地层学研究，还可以为每个物种提供年平均降水量和植被。每隔41 ka，John Day组古土壤中的化石在半干旱灌木丛和半湿润的林地群落之间交替。在半干旱古土壤中发现了蜗牛“ Polygyra ” expansa和Monadenia dubiosa，但在半湿古土壤中发现了Vespericola dalli和Monadenia marginicola。蝉洞穴（在半干旱的古土壤中发现了Naktodemasis bowni，而在半湿的古土壤中发现了粪甲虫球（Pallichnus dakotensis）和and铸件（Edaphichnium lumbricatum）。其中hypertragulids，异鼷鹿hesperius在半干旱的古土壤中发现和Nanotragulus planiceps在半湿润古土壤。在刺线中，刺线虫Haplomys liolophus，土鼠类Pulurolicus sulcifrons和几种钩足类动物，蓖麻类古猿半岛和类孢子虫古菌ennisianus在半干旱古土壤中被发现。大型有蹄类动物主要存在于半湿润的古土壤中，包括土壤小球藻Agriochoerus antiquus，齿齿兽Eporeodon occidentalis和Promerycochoerus superbus，Miohippus annectens以及犀牛Diceratherium annectens和Diceratherium armatum。化石哺乳动物的推测生态位与基于它们形态的解释是一致的。在开放，干旱的生境中具有生命适应能力的分类单元，例如高冠牙齿和半窝或半肢肢体结构，主要存在于半干旱古土壤中，而具有树状适应性的分类单元仅在半湿润的古土壤中发现。