Pre-Younger Dryas megafaunal extirpation at Rancho La Brea linked to fire-driven state shift

The cause, or causes, of the Pleistocene megafaunal extinctions have been difficult to establish, in part because poor spatiotemporal resolution in the fossil record prevents alignment of species disappearances with archeological and environmental datasets. We obtained 172 new radiocarbon dates on megafauna from Rancho La Brea, USA, spanning 15.6 to 10 thousand calendar years before present (ka). Seven species of extinct megafauna disappeared by 13 ka, before the onset of the Younger Dryas. Comparison with high-resolution regional datasets reveals these disappearances coincided with an ecological state shift that followed aridification and vegetation changes during the Bølling-Allerød. Time series modeling implicates large-scale fires caused by humans as the primary cause of the extirpations; the catalyst of this state shift appears to have been mounting human impacts in a drying, warming, and increasingly fire-prone ecosystem.