Recognition of Two Potential Warming Events in the Paleocene Terrestrial Record of North America and Associated Mammalian Responses

Authors

• Ross Secord, University of Nebraska-LincolnFollow
• Daniel J. Peppe, Baylor UniversityFollow
• Thomas E. Williamson, New Mexico Museum of Natural History and ScienceFollow
• Caitlin E. Leslie, Baylor University
• Stephen L. Brusatte, University of Edinburgh
• Andrew G. Flynn, New Mexico State UniversityFollow

ORCID IDs

Secord https://orcid.org/0000-0003-4400-9608

Peppe https://orcid.org/0000-0003-4263-133X

Williamson https://orcid.org/0000-0002-2856-9632

Brusatte https://orcid.org/0000-0001-7525-7319

Flynn https://orcid.org/0000-0002-1371-1878

Document Type

Article

Date of this Version

8-27-2026

Citation

PNAS Nexus (2026) 5: pgag289

doi: 0.1093/pnasnexus/pgag289

Includes supplemental material

Comments

Copyright 2026, the authors. Open access

License: Creative Commons Attribution-NonCommercial 4.0 International (CC BY-NC 4.0)

Published by Oxford University Press on behalf of National Academy of Sciences

Abstract

Numerous early Cenozoic transient warming events (“hyperthermals”) have been recognized in the marine record, but few have been located in fossiliferous terrestrial strata. Locating warming events is critical for understanding how terrestrial animals and plants responded to past climate change. We recognize two carbon isotope excursions (CIEs) in lower Paleocene (Danian) strata of the San Juan Basin, New Mexico, United States, based on sustained decreases in carbon isotope values in bulk organic carbon. The upper excursion correlates closely with the Latest Danian Event (LDE) hyperthermal, previously known with confidence only from the marine record. We correlate the lower excursion to a smaller CIE in the marine record tied to a 405,000-year eccentricity cycle, and modest warming. Both excursions in the San Juan Basin occur in red bed intervals bounded by drab-colored rocks, suggesting transient seasonal drying. Both are also associated with marked decreases in percent total organic carbon, possibly representing decreased primary productivity. The lower excursion is associated with a strong pulse of mammalian faunal turnover. Strata above the LDE are unfossiliferous, precluding local turnover analysis, but a strong, regional pulse of turnover occurs at or near the LDE. Our results suggest warming and/or drying during these events resulted in ecological perturbations, accelerating mammalian origination and extinction rates. Additionally, the first representatives of two North American mammalian families (Arctocyonidae, Plesiadapidae) reached Europe around the time of the LDE. We hypothesize that this was in response to short-term warming, which opened a previously impassable high-latitude dispersal route connecting the continents.