Abstract

A nearly complete and relatively well-preserved skeleton of the giant ground sloth Megatherium sp. in the hyperarid core of the Atacama Desert reveals how climate related taphonomic processes drastically transformed these remains over time. The individual, semi-exposed in situ by wind erosion, was found in late Pleistocene palaeowetland sediments that formed during the Central Andean Pluvial Event. Several radiocarbon dates on bone bioapatite and carbonate tufas date the specimen to c. 16 500 cal yr BP. Physical, organic, and inorganic traces were identified using histotaphonomic, mineralogical, and microscopic analyses (optical, scanning electron and petrographic microscopy, x-ray diffraction and FTIR-ATR). Surficial bones with rounded, polished surfaces due to wind erosion are well preserved, while buried bones are poorly preserved and structurally weak due to an early phase of bioerosion, which was followed by desiccation revealed by micro-cracks. Iron and manganese were deposited under anoxic conditions, followed by carbonates such as sparite and micrites, which formed due to a drier context, resulting in the encrustation of these bones by halite and calcium sulfates in hyperarid conditions that continue to this day. These observations imply that the ground sloth lived in a much wetter environment compared to today and its remains were subsequently affected by anaerobic wet cycles, an oxidizing sedimentary environment, and later an oxidizing hyperarid climate. In summary, the unravelled histotaphonomy is written in small fractions of bones which emerge as new proxies for understanding the complex palaeoclimatic history of the Atacama Desert.