The abrupt extinction of approximately thirty-five genera of large mammalian megafauna across North America at the terminal Pleistocene (approximately 12,800 calendar years before present)—including mammoths, mastodons, saber-toothed cats, and giant ground sloths—remains one of the most vigorously contested debates in quaternary paleoecology. For decades, the dominant theoretical model was Paul Martin's "Blitzkrieg" or Overkill Hypothesis, which asserted that the arrival of Clovis paleo-hunters, armed with advanced fluted projectile points, decimated naive megafaunal populations that had evolved in the absence of hominin predation pressure and were biologically ill-equipped to sustain high anthropogenic mortality rates due to their prolonged gestational periods.
Over the past two decades, high-resolution stratigraphy, radiocarbon calibration, and fossil spatial mapping have mounted formidable empirical challenges to the Overkill model. Archaeological excavations across hundreds of terminal Pleistocene sites have yielded remarkably scant evidence of kill sites: Clovis hunting implements have been conclusively associated with only two genera—mammoths and mastodons—leaving the rapid disappearance of the remaining thirty-three genera entirely uncorroborated by direct taphonomic or hunting evidence. Moreover, paleogenomic ancient DNA analyses indicate that populations of several megafaunal species, such as the steppe bison and horse, had initiated precipitous demographic declines thousands of years prior to the appearance of Clovis material culture.
In place of single-cause human overkill, contemporary paleoecologists emphasize the catastrophic climatic instability of the Younger Dryas: a sudden, century-scale reversal to near-glacial temperatures triggered by the catastrophic drainage of glacial Lake Agassiz into the North Atlantic, which disrupted the Atlantic Meridional Overturning Circulation (AMOC). This abrupt climatic shock shattered established floral biomes, transforming homogeneous productive steppe-tundra into fragmented, nutrient-poor boreal forests and arid scrublands. Incapable of migrating rapidly across disrupted ecological corridors, specialized megafaunal herbivores suffered nutritional starvation and population collapse, which subsequently cascading into the extinction of apex carnivores. While human hunting undoubtedly exerted localized terminal pressures on dwindling relic populations, the primary macroscopic driver was ecological uncoupling driven by rapid planetary climate oscillation.