A HORSE, AN OTTER, AND A BEAR WALK INTO A BAR AND GET CARDED: REFINING AGES FOR IMPORTANT FOSSIL LOCALITIES AT HAGERMAN FOSSIL BEDS NATIONAL MONUMENT, IDAHO, USA
The Hagerman Horse Quarry is HAFO's youngest fossil locality. It preserves hundreds of single-toed horses (Equus simplicidens). At a similar elevation to the south, a paratype locality for the peccary Platygonus pearcei was long thought contemporaneous to the quarry; it is now known to be older. Our current work suggests that most HAFO localities are older than the quarry, leaving its context mostly unresolved.
Several older localities can be temporally linked however, including some valuable for understanding carnivoran evolution. Agriotherium, a bear otherwise restricted to the Hemphillian, is confirmed to extend into the Blancan at approximately 3.9-3.8 Ma. We also confirm that the holotype and paratype localities for the oldest New World river otter (Lontra weiri), while stratigraphically 10 m apart, are separated by a fault and contemporaneous. We refine their age to ca. 3.9 Ma which better aligns with molecular phylogenetic data for Lontra. Ferinestrix vorax is restricted to HAFO, but a 2020 discovery shows it persisted for several hundred thousand years. With an age range of 4.1-3.8 Ma, our oldest specimen predates Siberia’s Ferinestrix rapax, supporting an earlier branching event for this giant meline badger lineage.
Continuing tephrochronologic research will further refine the ages for these and other fossil localities at HAFO.