Extinctions, scenarios, and assumptions: Changes in latest Pleistocene large herbivore abundance and distribution in western North America

Proposed explanations for the terminal Pleistocene large mammal extinction event in North America include climate warming and/or cooling, overhunting by early humans, disease, and bolide detonation or impact. A key assumption common to all these scenarios is that large mammals present in North America near the end of the Pleistocene were also present in similar abundance, with similar geographic distributions, during earlier, equally severe periods of climate change (e.g., ∼130 ka BP). This assumption is challenged here. An important difference in the latest Pleistocene was the profusion and geographic extent of the genus Bison, particularly in the American West. During the late Pleistocene, south of the glacial ice, the species Bison antiquus was more widely distributed and present in greater profusion than earlier species such as the larger B. latifrons. The increased abundance of these large, aggressive, herd-dwelling ruminants in the late Pleistocene constitutes a critical difference between this time period and earlier, similarly intense interglacials. Extinction scenarios for Pleistocene North America should avoid assuming a relatively static long-term faunal component, and account for the impacts of non-human immigrant species on natives, particularly when immigration events are close in time and space with climate changes.