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Two dramatic shifts in upstate New York`s microfossil record may explain the fate of the region`s prehistoric megafauna. First, fossil spores of Sporormiella, a fungus common in most Pleistocene era sediments that grows only on the dung of large herbivores, vanish from the sedimentary record about 14,000 years ago. Soon after, levels of microscopic charcoal from landscape fires increase more than tenfold. Paleontologist Guy Robinson sees a connection: he suggests that local populations of mastodons and other big herbivores crashed when the first humans arrived and found the animals, previously unexposed to humans, easy prey. With most of the huge herbivores wiped out, fire-fueling vegetation accumulated on the landscape. So fires lit by the human newcomers burned hotter and spread farther than ever before.