Understanding how yesterday's biodiversity responded to “natural experiments” in climate change and extinction can help prepare us for tomorrow’s conservation challenges. During the Quaternary terrestrial species experienced repeated and often abrupt climate change, yet climate-driven extinctions are thought to have been rare. Are species more resilient than we think? Are we overestimating future extinction risk? Or have we just underestimated the prevalence of climate-driven extinctions in the recent fossil record? In this talk, I'll discuss the conservation lessons stemming from the global Quaternary extinction record, and then focus on a case study of megafaunal extinction impacts on Eastern North American forests.