New mammal assemblage from last interglacial in Argentine Pampas: Debating biostratigraphic and biochronological reliability

This study analyzes one of the most complete mammalian fossil records from the Middle to the end of the Pleistocene in the Pampean Region, recovered from the Salto de Piedra Paleontological Locality along Tapalqué Creek. The site preserves a fluvial-palustrine sequence with six depositional units (U1–U6), separated by erosive unconformities or pedogenetic horizons. Radiometric dating (OSL and AMS ¹⁴C), integrated with sedimentological and faunal data, allows correlation with Marine Isotope Stages: Unit 1 (MIS 6–5; >127 ka), Unit 2 (MIS 3; ∼40.5 ka), Units 3–4 (MIS 2; 38–11.2 ka), and Units 5–6 (MIS 1; 12.6–7.8 ka). Three fossil assemblages were identified (U1, U3–4, U5–6), primarily linked to fluvial channels. The record provides critical biochronological information, with fossils showing minimal weathering and abrasion, and no evidence of reworking. The occurrence of Equus neogeus in U1 (>127 ka) expands the lower limit of its biozone back to ∼300 ka. Index taxa in Unit 1—Glyptodon munizi, Megatherium americanum, Equus neogeus—highlight biozone overlap, challenging the stratigraphic resolution of traditional schemes. Due to the lack of exclusive taxa and overlapping ages, we propose merging the Bonaerean with the Lujanian Stage/Age (∼300–11.6 ka). These findings call for a revision of Quaternary biozone frameworks in South America and improve biostratigraphic resolution for the Pampean fossil record.