Abstract: Environmental change has always impacted the Earth's biota. Extracting the responses of populations, species and communities to perturbations of the past is one of the best ways of unraveling how they will respond to perturbations of the future. Historic data from large environmental events such as the Pleistocene-Holocene transition and the Medieval Warm Period (MWP) provide a unique opportunity for insights into resilience of mammals in communities. The transition from the cold, arid Late Pleistocene (LP) glacial period to the warm, mesic Holocene interglacial witnessed extinction of many mammals in North America: 70 of ~220 of the largest species (32%) disappeared due to climatic and human stressors. The smaller mammalian survivors of the extinction (e.g., voles, gophers, ground squirrels, etc.) persisted but showed range changes, species turnover, diversity decline and significant alteration of population structure. I propose that study of historic responses to past climatic change fosters a richer understanding of the future. I demonstrate how populations and species interacted with their prehistoric environments to persist: by reshuffling individuals, increasing or decreasing population size, and favoring particular genotypes, all of which leave a mark on communities. Empirical evidence of this dynamic remains difficult to obtain, but a phylochronologic approach makes it possible.