215-2 Extinction of the Shasta Ground Sloth: A Revised History

Session: Coprolite Happens: Insights into Geobiology

Presenting Author:

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Abstract:

More than half a century ago, research on the extinction of the Shasta ground sloth, Nothrotheriops shastensis, was pivotal in applying radiocarbon dating to investigate the demise of the North American megafauna, and framing the debate surrounding the causal hypotheses of humans vs climate in driving these extinctions. A recent analysis of published radiocarbon dates from extinct megafauna, including these sloths, showed that while many taxa died out prior to the Younger Dryas, sloths and proboscideans may have persisted throughout the Younger Dryas, and even into the Holocene. However, conventional dating methods and inadequate pre-treatment protocols can yield imprecise and inaccurate radiocarbon chronologies that prevent a robust and reliable determination of extinction timing, and hence an accurate understanding of the causes of the extinction. Here, we revisit Paul Martin’s pivotal work on the extinction of the Shasta Ground sloth by directly dating >60 new and previously-dated Nothrotheriops coprolite and tissue specimens using accelerator mass spectrometry and, in the case of bone collagen, XAD preparation techniques, which can remove contaminants from exogenous plant acids. We test the hypotheses (1) that Shasta ground sloths disappeared synchronously across their sampled range, (2), that they persisted in the Desert southwest later than megafauna in neighboring Southern California, (3) that their extinction coincided with the peak of the Younger Dryas cooling, and (4), that their extinction coincided with the period of Clovis occupation. Our results show that Shasta Ground sloths last appear in the record by 12,829 cal BP, with a CRIWM projected extinction date of 12,757 cal BP. The youngest records all come from the Grand Canyon and southern New Mexico, and are several hundred years younger than those from the Guadalupe Mountains and over a thousand years younger than Great Basin sloths. These new data demonstrate that Nothrotheriops went extinct almost 600 years earlier than previous estimates, coinciding with the megafauna-specialized Clovis culture, but did in fact persist in the desert southwest two centuries beyond the disappearance of megafauna from Southern California.

Geological Society of America Abstracts with Program. Vol. 57, No. 6, 2025

doi: 10.1130/abs/2025AM-9535

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