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Herbivory exerts a profound influence on ecosystem function and physiognomy.� How a plant community responds to grazing by domestic herbivores is to a large degree dependent on its evolutionary history of herbivory.� Plants evolving in communities with a long evolutionary history generally possess adaptations that make them resilient to grazing, whereas plants evolving in communities without such history often do not.� The evolutionary history of herbivory therefore can serve as an indicator of a system�s resiliency to grazing.� However, determining a system�s evolutionary history of herbivory is problematic because quantitative measures are needed of native herbivores over an evolutionary time period, as is knowledge of plant origin and evolution.� Paleoecology provides a useful framework for assessing the co-evolution of plants and herbivores.� The Patagonian steppe of South America is a biotic province with an evolutionary history of herbivory whose resilience to grazing is uncertain.� Herbivory on the steppe transitioned from a diverse assemblage of megaherbivores during much of the Tertiary to an impoverished community consisting of a single, large herbivore�the guanaco (Lama guanicoe)�from the late Pleistocene extinction onward.� Here we present a paleoecological approach to reconstruct the evolutionary history of herbivory in Patagonian steppe and examine the role of megaherbivores and guanaco in shaping its vegetation.� We discuss how present management is misaligned with the steppe�s evolutionary history of herbivory and offer suggestions for steppe conservation under contemporary land use.