Although the North American megafaunal extinctions and the formation of novel plant communities are
well-known features of the last deglaciation, the causal relationships between these phenomena are
unclear. Using the dung fungus Sporormiella and other paleoecological proxies from Appleman Lake,
Indiana, and several New York sites, we established that the megafaunal decline closely preceded
enhanced fire regimes and the development of plant communities that have no modern analogs. The loss
of keystone megaherbivores may thus have altered ecosystem structure and function by the release of
palatable hardwoods from herbivory pressure and by fuel accumulation. Megafaunal populations
collapsed from 14,800 to 13,700 years ago, well before the final extinctions and during the BøllingAllerød
warm period. Human impacts remain plausible, but the decline predates Younger Dryas cooling
and the extraterrestrial impact event proposed to have occurred 12,900 years ago.
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