Evidence of the earliest humans in the Southern Deseado Massif (Patagonia, Argentina), Mylodontidae, and changes in water availability

Abstract

Mylodontidae bones from La Gruta 3 rockshelter, which date to 11,077-10,571calBP (9560 ± 30-9470 ± 3014CBP) and 9539-9466calBP (8540 ± 3014CBP), indicate that the extinct giant ground sloth was in the area after it was first occupied by humans during the late Pleistocene at 12,799-12,049calBP (10,845 ± 61-10,477 ± 5614CBP). Sediment characteristics at La Gruta 1 and 3 rockshelters (LG1 and LG3) suggest that conditions were wetter during major periods of human occupation and this is supported by pollen data. Lacustrine silts and clays in La Barda, and La Gruta Lagoons 1 and 3, provide evidence of an arid interval prior to about 6500calBP (5690 ± 3514CBP) followed by wetter conditions. This may explain why there is no evidence of humans between ca. 7760 and 5583calBP (7500 ± 250 and 4770 ± 2514CBP) either at La Gruta or at La Martita and Viuda Quenzana, which are ca. 25km away. There is considerable evidence for occupation at Viuda Quenzana after 5581calBP and scanty evidence for occupation at La Gruta around 3800calBP with more abundant evidence after 1880calBP. In the last 1500 years, six radiocarbon ages show that humans occupied LG1 and LG3 before (1372-1271calBP) and after (539-156calBP), but not during, the Medieval Climate Anomaly, which may have been a time of increased aridity in the area. The findings at La Gruta show that Mylodontidae was probably present in the southern Deseado Massif after the first humans arrived but data from southern Patagonia show that it became extinct soon afterwards.