Timing and ecological steps of the rise and expansion of grasslands differ not only geographically but also according to the type of available information. Patagonia (Argentina) was largely considered the region where grasslands and grazers early evolved in the Eocene, mostly based on functional morphology of mammals. However, recent paleobotanical studies question this traditional view and maintain that this occurred after early Miocene. To tackle this discrepancy, we conduct a multidisciplinary and integrative approach using diverse lines of evidence obtained from middle Eocene - middle Miocene tuffaceous deposits of central and northern Patagonia. Gathered data correspond to sedimentary facies, paleosols, insect trace fossils, opal phytoliths and fossil mammals (tooth morphology, body size). Long-lasting and frequent volcanic ashfalls caused permanent disturbances in physical scenarios, biotic systems and grassy habitats; just like herbivory of mammals through coevolutionary grass-grazer mechanisms. The results indicate that soils, vegetation, insects and mammal herbivores begun synchronously to record diverse traits related to grasslands showing mosaic vegetation since middle Eocene (∼44 Ma). These traits include mollic paleosols, abundant and persistent dung beetle trace fossils (Coprinisphaera ichnofacies), phytolith assemblages attributable to savannas and medium to large-size hypsodont mammals. We also track the evolutionary history after the reduction of closed forests, recognizing alternating subhumid savannas with riparian forests, where the relative frequency between grasses, palms, trees and shrubs fluctuated in time and space; and desert vegetation (shrublands) dominated by palms and shrubs during dryer periods. The advent and expansion of grasslands can be linked to the cooling and drying period subsequent to the Early Eocene Climate Optimum.

草原生长和扩张的时间和生态步骤不仅在地理位置上不同，而且根据可用信息的类型也不同。巴塔哥尼亚（阿根廷）被广泛认为是始新世草原和放牧者早期演化的地区，主要是基于哺乳动物的功能形态。但是，最近的古植物学研究对这种传统观点提出了质疑，并认为这种情况发生在中新世早期。为解决这一差异，我们使用从中始新世-巴塔哥尼亚中北部的中新世-中新世中凝性沉积物获得的多种证据，采取了多学科和综合的方法。收集的数据对应于沉积相，古土壤，昆虫痕迹化石，蛋白石植物石和哺乳动物化石（牙齿形态，体型）。持久而频繁的火山灰沉降在物理场景，生物系统和草丛生境中造成了永久性干扰；就像哺乳动物通过共同进化的放牧机制吃草一样。结果表明，土壤，植被，昆虫和哺乳动物食草动物同步开始记录自中始新世（〜44 Ma）以来与显示马赛克植被的草原有关的多种性状。这些特征包括软体动物古土壤，丰富而持久的虫痕迹化石（Coprinisphaera ichnofacies），可归因于热带稀树草原和中型至大尺寸七倍体哺乳动物的植石体组合。我们还追踪了封闭森林减少后的演化历史，认识到半湿润稀树草原与河岸森林交替出现，其中草，棕榈，树木和灌木之间的相对频率随时间和空间波动；干旱时期，以棕榈树和灌木为主的沙漠植被（灌木丛）。草原的来临和扩张可能与始新世早期气候最佳之后的冷却和干燥时期有关。