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Furthermore, evidence exists that hunting may have been one of the multiple environmental factors leading to extinctions of the holocene megafauna and their replacement by smaller herbivores. North American megafauna extinction was coincidental with the Younger Dryas impact event, possibly making hunting a less critical factor in prehistoric species loss than had been previously thought. However, in other locations such as Australia, humans are thought to have played a very significant role in the extinction of the Australian megafauna that was widespread prior to human occupation.

What event was coincidental with the North American megafauna extinction?
Younger Dryas impact event