Radiocarbon dates of fossil record assigned to mylodontids (Xenarthra - Folivora) found in Cueva del Milodón, Chile

Abstract

The Cueva del Milodón (CdM, southern Chile), has been explored repeatedly since the end of the 19th century. Many institutions in the world house specimens from CdM, standing out the mylodontid sloths. Until now, 36 14C measurements were performed on these remains using equivalent methodologies, Gas Proportional Counter (GPC), Liquid Scintillation Counting (LSC) and Accelerator Mass Spectrometry (AMS). The goals of this work are to review published dates, report two new radiocarbon dates made by us, and discuss the occurrence of the mylodonts in southernmost South America in a glacial context and its possible coexistence with humans. Among the published 16 direct (hair, skin, bone) and 20 indirect (excrement) 14C dates, 13 and 18 are considered here as reliable, respectively. Dates considered unreliable presented several issues (transcription errors, duplicate dates, misidentified samples, etc.), being excluded from the analysis to avoid further misunderstandings. Two new 14C dates performed by us on pieces housed in the Museo de La Plata (skin - AMS) and (bone - LSC) were added, making a total of 33 valid dates. A remarkable amplitude in the radiocarbon ages of the mylodont remains in CdM is evidenced, showing a range of values from ∼14,000 BP to ∼9800 BP, since upper Pleistocene (“Tarantian”) to early Holocene (Greenlandian). However, the direct dates of maximum confidence available show a strong modal representation in the Upper Pleistocene. Climate evidence available for this period indicates a complex interplay of deglaciation and brief cold reversals, but suggests that mylodonts could take advantage of their dense fur and thick skin, large body mass and suitability to live in caves to prosper in such cold and humid environments. Finally, evidence supporting coexistence of mylodonts and humans is briefly discussed.